ES2980376T3 - Aluminum alloy for heat exchanger fins - Google Patents

Abstract

An aluminum alloy fin material comprising about 0.9-1.4 wt% Si, 0.3-0.6 wt% Fe, 0.20-0.60 wt% Cu, 1.0-1.7 wt% Mn, 0.01-0.25 wt% Mg, 0.01-3.0 wt% Zn, up to 0.10 wt% Ti, with the balance Al and impurities at <0.15 wt%. Aluminum alloy fin material is produced by a process that includes the steps of direct cold casting of an ingot, hot rolling of the ingot after direct cold casting, cold rolling of the aluminum alloy to an intermediate thickness, intermediate annealing of the cold-rolled aluminum alloy to an intermediate thickness at a temperature between 200 and 400 °C, and cold rolling of the material after intermediate annealing to achieve a % cold work (%CW) of 20 to 40%. Aluminum alloy fin material possesses an improved combination of pre- and post-weld strength, thermal conductivity, buckling resistance, and/or corrosion potential. (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Aluminum alloy for heat exchanger fins

Claim of priority

This Application claims priority from U.S. Provisional Application No. 62/727,806, filed Sep. 6, 2018.

Field

The present invention relates to the fields of materials science, materials chemistry, metallurgy, aluminum alloys, aluminum manufacturing and related fields. The present invention provides novel aluminum alloys for use in the production of heat exchanger fins, which are in turn used in various heat exchanger devices, for example, motor vehicle radiators, condensers, evaporators and related devices.

Background

The automotive heat exchanger industry places a number of demands on the aluminium materials used for the production of heat exchanger fins (“fin feedstocks”). These demands can be difficult to balance. There is a need for aluminium alloy fins with high strength in both pre- and post-brazing conditions, improved buckling resistance meaning good brazing behaviour, and reduced fin erosion. To make automobiles lighter, it is desirable to reduce the size and weight of automotive heat exchangers to save resources and energy. Various methods have been studied to achieve this goal and one of the desirable solutions is to reduce the material thickness of the aluminium fins. To reduce the material thickness of the fins, it is important to achieve higher strength after brazing and ensure adequate weldability. At the same time, the heat exchanger fins must have high conductivity and improved corrosion behaviour compared to the other components of the heat exchanger. For example, heat exchanger fins may be more anodic than the heat exchanger tube material such that the fins act sacrificially. A desirable aluminium fin starting material would possess properties and parameters that balance the above requirements. WO 2016/022457 A1 refers to an aluminium alloy fin starting material comprising about 0.9 to 1.2 wt % Si, 0.3 to 0.5 wt % Fe, 0.20 to 0.40 wt % Cu, 1.0 to 1.5 wt % Mn, 0 to 0.1 wt % Mg and 0.0 to 3.0 wt % Zn, with the balance being Al and impurities <0.15 wt %. In μm a EP 1323839 A1 reference is made to an aluminium brazing alloy, ideally suitable as a starting material for fins having the composition in weight percent: Si 0.7-1.2, Mn 0.7-1.2, Mg <0.2, Fe up to 0.8, Zn up to 3.0, Ni up to 1.5, Cu up to 0.5, optionally one or more selected from the group comprising Ti up to 0.20, In up to 0.20, Zr up to 0.25, V up to 0.25, Sn up to 0.25, Cr up to 0.25, impurities up to 0.05 each, up to 0.15 in total, the balance Al.

Compendium

The encompassed embodiments of the invention are defined by the claims, not by this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are described in more detail below in the Detailed Description section. This summary does not identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to the appropriate portions of the entire specification, any or all of the drawings, and each claim.

It is desirable to produce aluminum fin stock having a required combination of thickness (gauge), that can withstand brazing and exhibit appropriate mechanical characteristics before, during, and after brazing, strength and conductivity characteristics suitable for high performance heat exchanger applications, and suitable corrosion potential. Furthermore, it is desirable to produce aluminum fin stock from an input metal incorporating aluminum scrap to produce fin stock in a cost effective and environmentally friendly manner. An improved aluminum alloy fin stock is disclosed that possesses a combination of characteristics and properties that make it suitable for the production of heat exchanger fins, for use, for example, in heat exchangers such as those employed in the automotive industry. In one example, the improved aluminum alloy fin stock can be produced in sheet form with the desired thickness (gauge) that is suitable for the production of lightweight heat exchanger units. The aluminum alloy fin stock can be brazed and exhibits strength characteristics before, during, and after brazing that make it attractive for automotive heat exchanger applications. More specifically, the aluminum alloy fin stock better possesses pre-brazing strength characteristics that reduce fin crushing problems during brazing. The explained aluminum alloy fin stock also possesses sufficiently high thermal conductivity suitable for heat exchanger applications, and has a corrosion potential that is sufficiently negative for the fins to act sacrificially during heat exchanger corrosion. In summary, the aluminum alloy fin stock better has one or more of the following properties: high strength, desirable post-brazing mechanical properties, desirable buckling resistance, desirable corrosion resistance, and desirable conductivity. At the same time, the aluminum alloy fin stock can be produced from input aluminum that is, at least in part, suitable for recycling. More specifically, the starting material for aluminum alloy fins best contains concentrations of non-aluminum constituents, e.g., Cu, Fe, Mn, and Zn, that are compatible with the concentrations of these elements found in certain aluminum scrap as input metal.

The aluminum alloy fin stock discussed herein is produced in sheet form, plate form, or slab form. Also discussed are processes for producing better aluminum alloy fin stock that incorporate one or more casting, rolling, and annealing steps. In some cases, the process steps employed during production of the better aluminum alloy fin stock impart beneficial properties and characteristics to the material. In an exemplary process, the better aluminum alloy fin stock is produced using one or more cold rolling steps. Each of the cold rolling steps may, in turn, involve multiple cold rolling passes. A cold rolling step may be characterized by “percent cold work” or “%TF” achieved. It may be desirable to achieve a specific range or value of %TF to achieve the required strength range of the aluminum alloy fin stock. In one example, the aluminum alloy fin stock may be produced by a process involving direct cold casting and cold working (cold rolling) to produce a desirable pre-brazing temper, for example, an H14 temper. In some examples, the aluminum alloy fin stock may best be produced in a variety of different strain-hardened pre-brazing tempers, such as H16, H18, or other H1X tempers. The process for producing the aluminum alloy fin stock may also involve hot rolling after direct cold casting, and intermediate annealing prior to the final cold rolling stages (e.g., between the intermediate and final cold rolling stages). The term “intermediate annealing (IR)” refers to a heat treatment applied between the cold rolling stages. The IR temperature may affect the properties of the aluminum fin stock. For example, reducing the RI temperature from 400°C to 350°C results in a coarser grain size after brazing. A combination of % TF and RI temperature employed in production, along with other factors such as the composition of the aluminum alloy, results in desirable properties.

The aluminum alloy fin stock discussed above can be used in a variety of applications, for example, to manufacture fins for heat exchangers. In some cases, the aluminum alloy fin stock is useful for lightweight, high-performance automotive heat exchangers. As non-limiting examples, the aluminum alloy fin stock can be used in automotive heat exchangers, such as radiators, condensers, and evaporators. However, the uses and applications of the aluminum alloy fin stock are not limited to automotive heat exchangers and other uses are anticipated, as the characteristics and properties of the aluminum alloy fin stock may also be beneficial for uses and applications other than the production of automotive heat exchanger fins. For example, aluminum alloy fin stock can best be used to manufacture various devices where heat exchangers are used and produced by brazing, such as devices used in heating, ventilation, air conditioning and refrigeration (HVAC&R).

As discussed above, the compositions and processes for producing aluminum alloy fin stock best result in a material that possesses a combination of beneficial characteristics and properties that make it suitable for manufacturing heat exchanger fins. For example, aluminum alloy fin stock exhibits beneficial combinations of one or more of the following characteristics: pre- and post-brazing mechanical properties, such as tensile strength and resistance to post-brazing buckling, thermal conductivity, and corrosion potential. Claim 1 of the present invention relates to an aluminum alloy comprising 0.9% to 1.4% by weight of Si, 0.3% to 0.6% by weight of Fe, 0.40% to 0.55% by weight of Cu, 1.0% to 1.7% by weight of Mn, 0.10% to 0.25% of Mg and 1.9% to 2.6% by weight of Zn, up to 0.10% by weight of Ti, with the balance of Al and impurities each in an amount of 0% to 0.05% by weight and in total <0.15% by weight, wherein optionally the impurities include Ga, V, Ni, Sc, Ag, B, Bi, Zr, Li, Pb, Sn, Ca, Hf, Sr, or combinations thereof. In the aluminum alloys discussed, one or more of Zr, V, Cr, or Ni may be present in an amount below 0.05% by weight, below 0.04% by weight, below 0.03% by weight, below 0.02% by weight, or below 0.01% by weight. In some cases, one or more of Zr, V, Cr, or Ni is absent (i.e., 0% by weight).

In some examples, the aluminum alloys discussed may have an ultimate tensile strength of one or both of the following: at least 200 MPa, measured in the pre-brazing condition, or at least 150 MPa, measured post-brazing. In one example, the aluminum alloy has an ultimate tensile strength of one or both of the following: from 200 MPa to 230 MPa, measured in the pre-brazing condition, or greater than 170 MPa measured post-brazing. The aluminum alloy may have a corrosion potential of -760 mV or less, measured post-brazing. The aluminum alloy may have a thermal conductivity greater than 40% IACS (International Annealed Copper Standard) which assumes the conductivity of 100% pure copper, measured post-brazing.

The aluminum alloys explained may be produced by a process comprising: direct cold casting of the aluminum alloy into an ingot; hot rolling of the ingot after direct cold casting; after hot rolling, cold rolling the aluminum alloy to an intermediate thickness; after cold rolling, intermediate annealing of the rolled aluminum alloy to the intermediate thickness at a temperature between 200 °C and 400 °C (200 °C to 400 °C); and, after intermediate annealing, cold rolling the aluminum alloy to achieve a cold work reduction percentage (%TF) in thickness of 20% to 40%, resulting in a sheet with a thickness of 45 μm to 100 μm, 45 μm to 90 μm, 47 μm to 85 μm, or 50 μm to 83 μm. In other processes, continuous casting may be used. The % TF achieved in the processes described above may be 30% to 40%. Intermediate annealing may be performed at a temperature between 320°C and 370°C (320°C to 370°C), between 290°C and 360°C (290°C to 360°C), or between 340°C and 360°C (340°C to 360°C). The intermediate annealing time may be 30 to 60 minutes. A heat exchanger comprising improved aluminum alloys is also discussed. The heat exchanger may be a heat exchanger of a motor vehicle. The heat exchanger may be a radiator, a condenser, or an evaporator. Processes for making objects and apparatus comprising the improved alloys are also discussed. An example of such a method is a method for making a heat exchanger, comprising brazing together at least a first aluminum alloy form made from the aluminum alloy with a second aluminum alloy form, comprising: assembling and securing the two or more aluminum forms together; and heating the two or more aluminum forms to a brazing temperature until seals are created between the two or more aluminum forms by capillary action. Uses of the improved aluminum alloys for the manufacture of heat exchanger fins and other objects and apparatus are also included within the scope of the present disclosure. Other objects and advantages of the invention will become apparent from the following detailed description.

Brief description of the drawings

Figures 1A-I show photographs of the particle structure for aluminum alloy samples prepared according to the present disclosure prior to brazing.

Figures 2A-I show photographs of the particle structure for aluminum alloy samples prepared according to the present disclosure after standard brazing.

Figures 3A-I show photographs of the particle structure for aluminum alloy samples prepared according to the present disclosure after rapid brazing.

Figures 4A-I show photographs of the grain size of aluminum alloy samples prepared according to the present disclosure after brazing.

Figures 5A-I show photographs of the grain size of aluminum alloy samples prepared according to the present disclosure after rapid brazing.

Figures 6A-I show photographs of the grain structure for aluminum alloy samples prepared according to the present disclosure prior to brazing.

Figures 7A-I show photographs of the grain structure of aluminum alloy samples prepared according to the present disclosure after standard brazing.

Figures 8A-I show photographs of the grain structure of aluminum alloy samples prepared according to the present disclosure after rapid brazing.

Figures 9A-D show the effect of cold working percentage and intermediate annealing on different properties of aluminum alloy samples prepared according to the present discussion.

Figures 10A-D show photographs of the grain structure of aluminum alloy samples prepared according to the present disclosure and subjected to standard brazing.

Figures 11A-D show photographs of the grain structure of aluminum alloy samples prepared according to the present disclosure and subjected to standard brazing.

Figures 12A-D show photographs of the grain structure of aluminum alloy samples prepared according to the present disclosure and subjected to rapid brazing.

Figures 13A-D show photographs of the grain structure of aluminum alloy samples prepared according to the present disclosure and subjected to rapid brazing.

Figures 14A-E show photographs of corrosion test results for specimens comprising aluminum alloy samples prepared according to the present disclosure.

Detailed description

This document describes high strength, corrosion resistant aluminum alloys and methods for making and processing them. The aluminum alloys described herein exhibit improved mechanical strength, corrosion resistance, and/or formability. The alloys provided herein include more silicon (Si), copper (Cu), manganese (Mn), and magnesium (Mg) compared to existing alloys. The alloys provided herein may have improved post-braze strength compared to existing alloys. The alloy material can be formed as a fin stock and can be used in automotive heat exchangers such as radiators, condensers, and evaporators. The aluminum fin stock can be used for other brazed applications including, but not limited to, HVAC&R applications. Additionally, the aluminum alloy fin stock is useful for high performance, lightweight automotive heat exchangers. Fin material is designed to be less noble than tube, so that the former corrodes faster than the latter. Heat exchangers are designed based on this sacrificial corrosion prevention by fin stock on tubes. Accordingly, the fin stock described in this document provides this sacrificial protection to the tube.

Definitions and descriptions

The terms “invention” and “the invention”, “this invention” and “the present invention” used herein refer broadly to the entire subject matter of this Patent Application and the claims set forth below.

Throughout this discussion, alloys identified by aluminum industry designations such as “series” or “1xxx” are referred to. For an understanding of the numerical designation system most commonly used to name and identify aluminum and its alloys, see “International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys” or “Registration Record of Aluminum Association Alloy Designations and Chemical Compositions Limits for Aluminum Alloys in the Form of Castings and Ingot,” both published by The Aluminum Association.

As used herein, the meaning of “a,” “an,” or “the” includes both singular and plural references, unless the context clearly indicates otherwise.

As used herein, a plate generally has a thickness greater than about 15 mm. For example, a plate may refer to an aluminum product having a thickness greater than about 15 mm, greater than about 20 mm, greater than about 25 mm, greater than about 30 mm, greater than about 35 mm, greater than about 40 mm, greater than about 45 mm, greater than about 50 mm, or greater than about 100 mm.

As used herein, a plank (also known as a slab) generally has a thickness of about 4 mm to about 15 mm. For example, a plank may have a thickness of about 4 mm, about 5 mm, about 6 mm, about 7 mm, about 8 mm, about 9 mm, about 10 mm, about 11 mm, about 12 mm, about 13 mm, about 14 mm, or about 15 mm.

As used herein, a sheet generally refers to an aluminum product having a thickness of less than about 4 mm. For example, a sheet may have a thickness of less than about 4 mm, less than about 3 mm, less than about 2 mm, less than about 1 mm, less than about 0.5 mm, less than about 0.3 mm, less than about 0.1 mm, or less than about 0.05 mm.

This application refers to the temper or condition of the alloy. For descriptions of the most commonly used alloy tempers, see American National Standards (ANSI) H35 on Alloy and Temper Designation Systems. An F condition or temper refers to an aluminum alloy as manufactured. An O condition or temper refers to an aluminum alloy after annealing. An Hxx condition or temper, also referred to herein as an Hxx temper, refers to an aluminum alloy with or without heat treatment (e.g., annealing) after cold rolling. Suitable H tempers include HX1, HX2, HX3, HX4, HX5, X6, HX7, HX8, or HX9 tempers. For example, the aluminum alloy may be cold rolled to result in a possible H19 temper. In a further example, the aluminum alloy may be cold rolled and annealed to result in a possible H23 temper.

The following aluminium alloys are described in terms of their elemental composition in weight percent (wt%) based on the total weight of the alloy. The remainder is aluminium, with a maximum weight percent of 0.15% for the sum of all impurities.

As used herein, “electrochemical potential” refers to a material’s capacity for a redox reaction. Electrochemical potential can be used to assess the corrosion resistance of the aluminum alloys described herein. A negative value may describe a material that is easier to oxidize (e.g., lose electrons or increase oxidation state) compared to a material with a positive electrochemical potential. A positive value may describe a material that is easier to reduce (e.g., gain electrons or decrease oxidation state) compared to a material with a negative electrochemical potential. Electrochemical potential, as used herein, is a vector quantity that expresses magnitude and direction.

As used herein, the meaning of “ambient temperature” may include a temperature of from about 15°C to about 30°C, for example, from about 15°C, about 16°C, about 17°C, about 18°C, about 19°C, about 20°C, about 21°C, about 22°C, about 23°C, about 24°C, about 25°C, about 26°C, about 27°C, about 28°C, about 29°C, or about 30°C.

All intervals explained in this document should be understood to encompass any and all subintervals within them. For example, a stated interval of “1 to 10” should be considered to include any and all subintervals between (and including) the minimum value of 1 and the maximum value of 10; that is, all subintervals that begin with a minimum value of 1 or more, for example, 1 to 6.1, and end with a maximum value of 10 or less, for example, 5.5 to 10.

Alloy compositions

The new aluminum alloys are described below. The properties of the aluminum alloy fin stock vary depending on their composition. The aluminum alloy fin stock discussed in this document possesses several advantageous properties. The aluminum alloy fin stock can be produced in the form of sheets, plates, or sheets and possesses desirable strength before, during, and after brazing, even at gauges less than 200 |jm or 100 |jm, making it suitable for the manufacture of fins for heat exchanger applications. The aluminum alloy material also possesses thermal conductivity and corrosion potential suitable for the production of fin stock.

The aluminum alloy fin feedstock as explained herein may contain a higher content of one or more of Cu, Si and Mg, compared to known fin feedstock alloys. The composition of the aluminum alloy fin feedstock and/or its production process lead to improved material properties, such as reduced fin crushing during brazing, increased post-brazing strength, improved thermal conductivity, improved buckling resistance and increased anodic corrosion potential. The aluminum alloy fin feedstock possesses one or more of strength, thermal conductivity and corrosion potential that is improved compared to known alloys used for fin feedstock production. The relatively high concentrations of non-aluminum constituents in the aluminum alloy fin feedstock allow it to be produced from input metal that incorporates recyclable aluminum, allowing for different metal inputs.

The aluminum alloy fin starting material is produced by a process that includes a heat treatment step (intermediate annealing) prior to a final cold rolling step. The intermediate annealing is carried out at a temperature of 200°C to 400°C for a period of about 30 minutes to 2 hours (e.g., for a time period of about 1 to 2 hours). The intermediate annealing is followed by cold rolling steps leading to a specified thickness reduction (“% cold work,” defined later in this document). In some examples, the above combination of process steps (intermediate annealing followed by cold rolling) results in an increase in pre-braze strength and a better post-braze coarse grain structure, which leads to better buckling resistance of the better aluminum fin starting materials, and also affects thermal conductivity and corrosion potential, thus leading to a material having a favorable combination of characteristics and properties. The alloys described herein may have the following elemental composition as given in Table 1 (not according to the invention).

Table 1

The alloys described herein may have the following elemental composition as given in Table 2 (not according to the invention).

Table 2

The alloys described herein may have the following elemental composition as given in Table 3 (not according to the invention).

Table 3

The alloys described herein may have the following elemental composition as given in Table 4 (not according to the invention).

Table 4

The alloys according to the invention have the following elemental composition as given in Table 5.

Table 5

The alloys may have the following elemental composition as given in Table 6 (not according to the invention).

Table 6

The alloys described herein may have the following elemental composition as given in Table 7 (not according to the invention).

Table 7

The alloys described herein may have the following elemental composition as given in Table 8 (not according to the invention).

Table 8

The alloys described herein may have the following elemental composition as given in Table 9 (not according to the invention).

Table 9

The alloys described herein may have the following elemental composition as given in Table 10 (not according to the invention).

Table 10

The alloy explained includes silicon (Si) in an amount of 0.9% to 1.4% (e.g., 0.95% to 0.35%, 1.0% to 1.30%, or 1.10% to 1.30%) based on the total weight of the alloy. For example, the alloy may include about 0.90%, about 0.91%, about 0.92%, about 0.93%, about 0.94%, about 0.95%, about 0.96%, about 0.97%, about 0.98%, about 0.99%, about 1.00%, about 1.01%, about 1.02%, about 1.03%, about 1.04%, about 1.05%, about 1.06%, about 1.07%, about 1.08%, about 1.09%, about 1.10%, about 1.11%, about 1.12%, about 1.13%, about 1.14%, about 1.15%, about 1.16%, about 1.17%, about 1.18%, 1.19%, about 1.20%, about 1.21%, about 1.22%, about 1.23%, about 1.24%, about 1.25%, about 1.26%, about 1.27%, about 1.28%, about 1.29%, about 1.30%, about 1.31%, about 1.32%, about 1.33%, about 1.34%, about 1.35%, about 1.36%, about 1.37%, about 1.38%, about 1.39%, or about 1.40% Si, All percentages are expressed in weight percent. Among other things, the Si content affects the melting temperature of an aluminum alloy. Increasing the Si content lowers the melting point of the aluminum alloy. Therefore, for the aluminum alloy fin stock to be weldable, the Si content of the alloy must be low enough so that the alloy does not melt during the brazing cycle. On the other hand, a relatively high Si content in the alloy leads to the formation of AlMnSi dispersoids which result in beneficial dispersoid strengthening of the matrix and improved strength characteristics of the alloy. The Si content used in the explained fin stock alloy balances the above factors.

In some examples, the alloy also includes iron (Fe) in an amount of 0.30% to 0.60% (e.g., 0.35% to 0.60%, 0.40% to 0.60%, or 0.41% to 0.47%) based on the total weight of the alloy. For example, the alloy may include about 0.30%, about 0.31%, about 0.32%, about 0.33%, about 0.34%, about 0.35%, about 0.36%, about 0.37%, about 0.38%, about 0.39%, about 0.40%, about 0.41%, about 0.42%, about 0.43%, about 0.44%, about 0.45%, about 0.46%, about 0.47%, about 0.48%, about 0.49%, about 0.50%, about 0.51%, about 0.52%, about 0.53%, about 0.54%, about 0.55%, about 0.56%, about 0.57%, about 0.58%, about 0.59%, about 0.60%, about 0.61%, about 0.62%, about 0.63%, about 0.64%, about 0.65%, about 0.66%, about 0.67%, about 0.68%, about 0.69%, about 0.70%, about 0.71%, about 0.72%, about 0.73%, about 0.74%, about 0.75%, about 0.76%, about 0.77%, about 0.78%, about 0.79%, about 0.80%, about 0.81%, about 0.82%, about 0.83%, about 0.84%, about 0.85%, about 0.86%, about 0.87%, about 0.88%, about 0.89%, about 0.90%, about 0.91%, about 0.92%, 0.59% or approximately 0.60% Fe. All percentages are expressed in weight percent. In an aluminum alloy, Fe may be part of intermetallic constituents that may contain Mn, Si, and other elements. It is often beneficial to control the Fe content in an aluminum alloy to influence the content of coarse intermetallic constituents.

The alloy explained includes copper (Cu) in an amount of 0.40% to 0.55% based on the total weight of the alloy. For example, the alloy may include about 0.40%, about 0.41%, about 0.42%, about 0.43%, about 0.44%, about 0.45%, about 0.46%, about 0.47%, about 0.48%, about 0.49%, about 0.50%, about 0.51%, about 0.52%, about 0.53%, about 0.54%, or about 0.55% Cu. All percentages are expressed in weight percent. Cu in solid solution increases the strength of an aluminum alloy. Increasing the Cu content can also lead to the formation of Cu-containing AlMnCu dispersoids, which store Mn and dissolve during brazing, thus leading to the release of Mn into a solid solution. This procedure results in improved post-brazing strength. The relatively high Cu content of the fin starting alloys enables cost reduction and increased recyclability.

The alloy includes manganese (Mn) in an amount of 1.0% to 1.7% (e.g., 1.10% to 1.65%, 1.15% to 1.35%, or 1.2% to 1.35%) based on the total weight of the alloy. For example, the alloy may include about 1.0%, about 1.01%, about 1.02%, about 1.03%, about 1.04%, about 1.05%, about 1.06%, about 1.07%, about 1.08%, about 1.09%, about 1.1%, about 1.11%, about 1.12%, about 1.13%, about 1.14%, about 1.15%, about 1.16%, about 1.17%, about 1.18%, about 1.19%, about 1.2%, about 1.21%, about 1.22%, about 1.23%, about 1.24%, about 1.25%, about 1.26%, about 1.27%, about 1.28%, about 1.29%, %, about 1.3%, about 1.31%, about 1.32%, about 1.33%, about 1.34%, about 1.35%, about 1.36%, about 1.37%, about 1.38%, about 1.39%, about 1.4%, about 1.41%, about 1.42%, about 1.43%, about 1.44%, about 1.45%, about 1.46%, about 1.47%, about 1.48%, about 1.49%, about 1.50%, about 1.51%, about 1.52%, about 1.53%, about 1.54%, about 1.55%, about 1.56%, about 1.57%, about 1.58%, about 1.59%, about 1.60% %, about 1.61 %, about 1.62 %, about 1.63 %, about 1.64 %, about 1.65 %, about 1.66 %, about 1.67 %, about 1.68 %, about 1.69 %, or about 1.7 % Mn. All percentages are in weight percent. Mn in solid solution increases the strength of an aluminum alloy, but also moves the corrosion potential toward a more cathodic state. The dispersoid (FeMn)-Al<6> or Al<15>Mn<3>Si<2> increases the strength of an aluminum alloy by particle strengthening, when present in a fine, dense dispersion. Depending on the composition and solidification rate, Fe, Mn, Al and Si combine during solidification to form various intermetallic constituents, i.e. particles within the microstructure, such as Al<15>(FeMn)<3>Si<2>, AbFeSi, or Al<s>FeMg<3>Si<6>, to name a few. Higher Mn content, particularly in combination with higher Fe content, can lead to the formation of coarse Mn-Fe intermetallic constituents.

The alloy includes zinc (Zn) in an amount of 1.9% to 2.6% based on the total weight of the alloy. For example, the alloy may include about 1.9%, about 1.91%, about 1.92%, about 1.93%, about 1.94%, about 1.95%, about 1.96%, about 1.97%, about 1.98%, about 1.99%, about 2.0%, about 2.01%, about 2.02%, about 2.03%, about 2.04%, about 2.05%, about 2.06%, about 2.07%, about 2.08%, about 2.09%, about 2.1%, about 2.11%, about 2.12%, about 2.13%, about 2.14%, about 2.15%, about 2.16%, about 2.17%, about 2.18%, about 2.19%, %, about 2.2%, about 2.21%, about 2.22%, about 2.23%, about 2.24%, about 2.25%, about 2.26%, about 2.27%, about 2.28%, about 2.29%, about 2.3%, about 2.31%, about 2.32%, about 2.33%, about 2.34%, about 2.35%, about 2.36%, about 2.37%, about 2.38%, about 2.39%, about 2.4%, about 2.41%, about 2.42%, about 2.43%, about 2.44%, about 2.45%, about 2.46%, about 2.47%, about 2.48%, about 2.49%, about 2.5%, about 2.51%, about 2.52%, about 2.53%, about 2.54%, about 2.55%, about 2.56%, about 2.57%, about 2.58%, about 2.59%, or about 2.6% Zn. All percentages are expressed in weight percent. Zn is typically added to aluminum alloys to move the corrosion potential toward the anodic end of the scale. In the starting aluminum alloy for fins, a relatively high Zn content of up to 3% by weight compensates for the change in corrosion potential due to increased Si and Cu contents, thus resulting in a higher anodic corrosion potential, allowing fins manufactured from the alloy to act sacrificially and protect the heat exchanger tubes, thereby improving the overall corrosion resistance of the heat exchanger.

The alloy includes Mg in an amount of 0.10% to 0.25% (e.g., 0.10% to 0.20%) based on the total weight of the alloy. For example, the alloy may include about 0.1%, about 0.11%, about 0.12%, about 0.13%, about 0.14%, about 0.15%, about 0.16%, about 0.17%, about 0.18%, about 0.19%, about 0.2%, about 0.21%, about 0.22%, about 0.23%, about 0.24%, or about 0.25% Mg. All percentages are expressed in weight percent. Mg contributes to the strength of the aluminum alloys described herein by solid solution strengthening.

In some examples, the ratio of Cu to Zn is from 2:1 to 1:15, for example, from 1:1 to 1:10, or from 1:5 to 1:10. The ratio of Cu to Zn may be 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, or 1:15.

Aluminum alloys as described herein may include titanium (Ti) in an amount up to 0.10% (e.g., 0 to 0.05%, 0.001 to 0.04%, or 0.01 to 0.03%) based on the total weight of the alloy. For example, the alloy may include about 0.001%, about 0.002%, about 0.003%, about 0.004%, about 0.005%, about 0.006%, about 0.007%, about 0.008%, about 0.009%, about 0.01%, about 0.02%, about 0.03%, about 0.04%, about 0.05%, about 0.06%, about 0.07%, about 0.08%, about 0.09%, or about 0.1% Ti. In some cases, Ti is not present in the alloy (i.e., 0% by weight). All percentages are expressed as weight percent.

Alloy compositions may further include other minor elements, sometimes referred to as impurities, each in amounts of about 0.05% or less, 0.04% or less, 0.03% or less, 0.02% or less, or 0.01% or less. These impurities may include, but are not limited to, Ga, V, Ni, Sc, Ag, B, Bi, Zr, Li, Pb, Sn, Ca, Hf, Sr, or combinations thereof. Accordingly, the elements Ga, V, Ni, Sc, Ag, B, Bi, Zr, Li, Pb, Sn, Ca, Hf, or Sr may be present in the alloys in amounts of 0.05% or less, 0.04% or less, 0.03% or less, 0.02% or less, or 0.01% or less. The sum of all impurities does not exceed 0.15% (e.g. 0.1%). All percentages are expressed as weight percent. The remaining percentage of each alloy is aluminum.

Procedures for making raw material for aluminum alloy fins

In certain aspects, the alloy compositions discussed are a product of a discussed method. Without intending to limit the discussion, the properties of the aluminum alloy are partially determined by the formation of microstructures during the preparation of the alloy. In certain aspects, the method of preparing an alloy composition can influence or even determine whether the alloy will have suitable properties for a desired application.

A process for producing aluminum alloy fin stock employs direct cold casting (DC) of an aluminum alloy into an ingot. Following DC casting, the process includes hot rolling of the ingot. The preheating temperature and duration of hot rolling are precisely controlled to preserve a large grain size and high strength after welding the finished fin stock. In some examples, for hot rolling, the ingots may be preheated to a temperature of up to about 500°C, e.g., at a temperature of 450°C to 480°C, in a furnace for up to about 12 hours at a suitable heating rate, e.g., 50°C/h, followed by holding the temperature (“soaking” or “dipping”) at a temperature of about 450°C to 500°C, e.g., at a temperature of about 470°C to 480°C, for 5-7 hours. After preheating and soaking, the ingots are hot rolled to a thickness of 2 mm to 10 mm, e.g. 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm, which may be referred to as “out gauge” after hot rolling.

A process for producing aluminum alloy fin starting materials then includes cold rolling steps to produce the desired thickness (gauge) and other material properties. For example, after a hot rolling step, the hot rolled aluminum alloy is cold rolled to reduce the material thickness to a value of 1 mm to 2 mm, for example, 1 mm, thickness or gauge (initial cold rolling gauge) during an initial cold rolling step, which may include multiple cold rolling passes, followed by further cold rolling to a thickness or gauge of 100 µm to 200 µm (intermediate cold rolling gauge) during an intermediate cold rolling step, which may also involve multiple passes. Depending on the hot rolling gauge, the desirable final thickness, and other properties discussed below, an aluminum alloy may require more or fewer cold rolling passes to achieve the desired gauge. The number of cold rolling passes is not limited and can be adjusted appropriately, for example, depending on the desirable thickness of the final sheet and other material properties.

Following intermediate cold rolling, the process for producing aluminum alloy fin starting materials includes an intermediate annealing step to produce the desired properties of the aluminum alloy fin starting material. The term “intermediate annealing” refers to a heat treatment applied between cold rolling stages. As described herein, intermediate annealing is applied between the intermediate and final cold rolling stages. Intermediate annealing involves heating the aluminium alloy to a temperature of 200°C to 400°C, for example, 225°C to 400°C, 225°C to 375°C, 225°C to 350°C, 225°C to 325°C, 300°C to 375°C, 325°C to 350°C, 340°C to 360°C, 290°C to 360°C or 345°C to 350°C (“intermediate annealing temperature”), and holding the intermediate annealing temperature for 3-5 hours, for example, for 4 hours, followed by cooling. The holding period at 200°C to 400°C may also be referred to as “soaking” or “soaking”. For heating and cooling the material before and after soaking, a constant rate of 40 °C/h to 50 °C/h, e.g. 50 °C/h, may be applied. Intermediate annealing conditions affect the structure and properties of the aluminum alloy fin starting material in a number of ways. For example, higher intermediate annealing temperatures may lead to lower post-brazing strength. Accordingly, intermediate annealing conditions are selected within the ranges specified herein to result in desirable properties of the aluminum alloy fin starting material.

After intermediate annealing, final cold rolling is performed to achieve the percentage of cold work (%TF) during the final stage of cold rolling (which may comprise multiple cold rolling passes) of 20% to 45%, 25% to 40%, 20% to 40%, 20% to 35%, 25% to 35%, or 5% to 45%, where:

In some embodiments, the % TF is less than or equal to 35% while in some other embodiments, the % TF is greater than 35%. After the final cold rolling steps, the aluminum alloy fin stock of the present invention has a thickness (gauge) of 45 μm to 100 μm, 45 μm to 90 μm, 47 μm to 85 μm, or 50 μm to 83 μm.

The final stage of cold rolling affects the structure and properties of the aluminum alloy fin starting material. For example, as %TF increases, the pre-braze strength (ultimate tensile strength (UTS), yield strength (Ys), or both, measured under pre-brazed conditions) of the aluminum material increases. Accordingly, the %TF employed is adjusted within the ranges specified in this document to achieve desirable properties of the aluminum alloy fin starting material.

The processes for producing aluminum alloy fin starting materials as explained herein can be performed in a manner that leads to an aluminum material having the desired temper. For example, the processes can be performed to provide an aluminum material that can be described as “strain hardened,” “cold worked,” and/or having or being in “H1X” temper (e.g., H14 temper). In some examples, the aluminum alloy fin starting material best described herein can be produced in H14, H16, or H18 tempers. It should be understood that a particular range of properties is associated with the temper designation. It should also be understood that the temper designation refers to the pre-brazing properties of the material.

Properties

The aluminum alloy fin starting material discussed herein possesses a number of advantageous properties, characteristics, or parameters. These properties, singly or in various combinations, allow the aluminum alloy materials described herein to be used in the production of heat exchanger fins. However, it should be understood that the scope of the present invention is not limited to specific uses or applications, and the properties of the aluminum alloy fin starting materials may be advantageous for a variety of different applications. Some of these properties are discussed below. Some other properties may not be specifically described, but may result from the composition and/or production processes employed to manufacture the aluminum alloy fin starting material described herein.

Some embodiments of the aluminum alloy materials described herein are manufactured as sheets, for example, as sheets less than 4 mm thick, for example, 45 µm to 100 µm thick. The aluminum alloy sheets can be produced in H1X temper (e.g., H14, H16, or H18 temper). The aluminum alloy materials described herein may possess one or more of the following properties, in any combination: UTS of 210 MPa or more (in other words, at least 210 MPa) or 210 MPa to 230 MPa, measured in the as-brazed condition; UTS of 150 MPa or more (in other words, at least 150 MPa) or 150 MPa to 170 MPa, measured post-brazing; buckling resistance of 25 mm to 33 mm measured post-brazing; Thermal conductivity of 40-48, 43-47, or 44-45 IACS measured post-brazing; Open circuit potential corrosion value (compared to standard calomel electrode (SCE), also referred to as “corrosion potential”) of -740 mV or less (e.g., -750 mV); and/or Post-brazing coarse-grained microstructure of 80 μm to 400 μm. Parameters measured “post-brazing” or “after brazing” also referred to as “post-brazing” are measured after a simulated brazing cycle, during which aluminum alloy samples are heated to 595 °C to 610 °C and cooled to room temperature over a period of approximately 20 minutes. Parameters measured before brazing (“pre-braze” or “pre-braze” condition), also called “pre-braze” parameters, are measured before or without subjecting the material to any brazing cycle.

The aluminum alloy fin stock explained has better strength and conductivity and exhibits lower corrosion potential values. The aluminum alloy fin stock explained can also withstand at least 20 days of copper accelerated salt spray (CASS) testing according to ASTM B368 (2014) without separating from a welded joint. The CASS test is generally carried out by forming a fin and tube specimen, welding to form a joint, and subjecting the welded specimen to the test. The above properties and advantages allow the aluminum alloy fin stock of the present invention to be advantageously employed in various uses and applications, which are discussed in more detail below.

Uses and applications

The aluminum alloy fin starting materials described herein can be used in a variety of applications, for example, but not limited to, heat exchangers. In one example, but not limited to, the aluminum alloy fin starting material can be used in automotive heat exchangers, such as radiators, condensers, and evaporators. For example, the aluminum alloy fin starting material can best be used to manufacture a variety of devices where heat exchangers are employed and produced by brazing, such as devices used in heating, ventilation, air conditioning, and refrigeration (HVAC&R). The uses and applications of the aluminum alloy fin starting materials described herein are included within the scope of the present invention, as are objects, shapes, apparatus, and the like made from or comprising the aluminum alloys described herein. Methods for making, producing, or manufacturing such objects, shapes, apparatus, and the like are also included within the scope of the present invention.

The aluminum alloys described herein are suitable for fabrication or manufacturing processes that require joining metal surfaces by brazing. Brazing is a metal joining process in which the filler metal is heated above a melting point and is distributed between two or more closely fitting parts by capillary action. The uses of aluminum alloys in brazing and the related processes and results, such as objects manufactured by the manufacturing process involving brazing, are generally referred to as “brazing applications.” The heat exchanger parts described herein are joined by brazing during the manufacturing process. During brazing, the filler metal melts and is converted to a filler metal that is available to flow to the contact points between the components being brazed by capillary action.

An exemplary object that can be manufactured using aluminum alloy fin starting materials described herein is a heat exchanger. Heat exchangers are produced by assembling parts comprising tubes, plates, fins, headers, and side supports, to name a few. For example, a radiator is constructed of tubes, fins, headers, and side supports. Except for the fins, which are typically bare, meaning they are not clad with an Al-Si alloy, all other parts of a heat exchanger are typically clad with a braze coating on one or two sides. Once assembled, a heat exchanger unit is secured by bands or a similar device to hold the unit together via flux and brazing. Brazing is commonly effected by passing the unit through a tunnel furnace. Brazing can also be performed by dipping in molten salt or in a batch or semi-continuous process. The unit is heated to a brazing temperature between 590°C and 610°C, soaked at a suitable temperature until capillary action joints are created, and then cooled below the solidus of the filler metal. The heating rate depends on the type of furnace and the size of the heat exchanger produced. Other examples of objects that can be manufactured using aluminum alloy fin starting materials described in this document are an evaporator, radiator, heater, or condenser.

The following examples will serve to illustrate the present invention in greater detail without, however, constituting any limitation thereof.

Example 1

Nine samples of aluminum alloy were prepared with the compositions shown in Table 11 below. Each sample comprised up to 0.15% by weight of impurities, the balance being Al. Each sample was prepared by direct cold casting of the aluminum alloy into an ingot and then hot rolling. The ingots produced by DC casting were preheated for hot rolling. The ingots were then hot rolled to an exit gauge and then cold rolled to an initial cold rolling gauge. The ingots were then cold rolled to an intermediate cold rolling gauge. The ingots were then subjected to intermediate annealing. After intermediate annealing, final cold rolling was performed to achieve a %TF of 20% to 40%, resulting in each sample having a thickness of 45 μm to 100 μm.

Table 11

The mechanical properties, conductivity, corrosion potential, and solidus temperature were then tested for each of the samples in Table 11 under pre-brazing, after standard brazing, and after flash brazing conditions. During standard brazing, the samples were heated to a temperature of 605 °C and cooled to room temperature over a period of approximately 45 minutes, to simulate the temperature and time profile of a commercial brazing procedure. Flash brazing was performed at a much faster heating and cooling rate compared to a standard brazing cycle. The material was heated to a temperature between 600 °C and 605 °C and cooled to room temperature over a period of approximately 20 minutes. All samples were tested for yield strength, ultimate tensile strength, and uniform elongation. Testing was performed in accordance with ASTM B557. Three samples of each alloy variant were tested and average values were reported under both pre- and post-brazing conditions. Electrical conductivity was reported as %IACS (International Annealed Copper Standard, which assumes pure copper conductivity for 100%). The results for yield strength, ultimate tensile strength and elongation are shown below in Table 12. The solidus temperature is also reported in Table 12. Thermal conductivity and corrosion potential measured after brazing are reported in Table 13. The experimental alloys had a minimum yield strength after brazing of 55 MPa and a higher ultimate tensile strength than Comp. 1 alloy.

The open circuit corrosion potential value compared to standard calomel electrode (SCE) of 764 mV for Comp 1 - 735 mV for Alloy H indicated that the finned variants will perform sacrificially to either tube alloy if the difference in corrosion potential is kept at approximately 30 mV to 150 mV between the tube and fin alloy.

Table 12

Table 13

Each of the Comp. 1 and A-H samples were photographed using an optical microscope. Microstructure characterization was carried out to investigate the dispersoids and intermetallic sizes and distribution as well as the grain structure before and after brazing. The microstructure was examined by etching the samples in 2.5% HBF<4> for 60 seconds followed by cleaning in HNO<3>. Figures 1A-I show the pre-brazing microstructure, Figures 2A-I show the microstructure after standard brazing, and Figures 3A-I show the microstructure after rapid cycle brazing. Barker etching was used to reveal the grain structure. Figures 4A-I show the grain structure in plain view after standard brazing, and Figures 5A-I show the grain structure in plain view after rapid cycle brazing. Each of the Comp. 1 and A-H samples was imaged using an optical microscope. 1 and A-H were also photographed to show the cross-sectional grain structure before brazing (Figures 6A-I), after standard brazing (Figures 7A-I), and after rapid brazing (Figures 8A-I). For each set of photomicrographs, Figure A corresponds to Comp. 1, Figure B corresponds to Sample A, Figure C corresponds to Sample B, and so on.

Example 2

Alloy samples C, E, G, and H were prepared as in Example 1 except that the % TF was varied during the intermediate anneal at 350 °C (pre-weld). The results are shown below in Table 14 and Figure 9A. As shown below and in FIG. 9A, the yield strength was improved when more than 35% TF was made compared to when 35% or less TF was made. Except for Sample E, the ultimate tensile strength also increased when more than 35% TF was made compared to when less than 35% TF was made. Except for Sample H, the percent elongation decreased when more than 35% TF was made compared to when less than 35% TF was made.

Table 14

Example 3

Alloy samples C, E, G, and H were prepared as in Example 1 except that the % TF was varied during the intermediate anneal at 350 °C (post brazing). The results are shown below in Table 15 and Figure 9B. As shown below and in FIG. 9B, except for Sample G, the yield strength was improved when more than 35% TF was made compared to when 35% or less TF was made. Except for Sample H, the ultimate tensile strength decreased when more than 35% TF was made compared to when less than 35% TF was made. Overall, the percent elongation remained approximately the same or decreased when more than 35% TF was made compared to when 35% or less TF was made.

Table 15

Example 4

Alloy samples C, E, G, and H were prepared as in Example 1 except that the intermediate anneal temperature was varied to >35% TF (pre-braze). The results are shown below in Table 16 and Figure 9C. As shown below and in FIG. 9C, at higher inter-anneal temperature, yield strength, ultimate tensile strength, and percent elongation decreased. Table 16

Example 5

Alloy samples C, E, G, and H were prepared as in Example 1 except that the effect of the interanneal temperature was varied to >35% TF (post-brazing). The results are shown below in Table 17 and Figure 9D. As shown below and in FIG. 9D, at higher interanneal temperatures, the yield strength decreased, the elongation increased, and the ultimate tensile strength either remained the same (for Sample C) or decreased (Samples E, G, and H).

Table 17

Alloy samples C, E, G, and H were then subjected to either standard cycle or rapid cycle brazing and photographed as described above. For samples interannealed at 250 °C and subjected to a standard cycle brazing, the plain view grain size after brazing is shown in Figures 10A-D, with FIG. 10A corresponding to sample C, FIG. 10B corresponding to sample E, FIG. 10C corresponding to sample G, and FIG. 10D corresponding to sample H. Similarly, for samples interannealed at 350 °C and subjected to standard cycle brazing, the plain view grain size after brazing is shown in Figures 11A-D, with FIG. 11A corresponding to sample C, FIG. 11B corresponding to sample E, FIG. 11C corresponding to sample G, and FIG. 11D corresponding to sample H.

For samples interannealed together at 250 °C and subjected to rapid cycle brazing, the plain view grain size after welding is shown in Figures 12A-D, with FIG. 12A corresponding to sample C, FIG. 12B corresponding to sample E, FIG. 12C corresponding to sample G, and FIG. 12D corresponding to sample H. Similarly, for samples interannealed at 350 °C and subjected to rapid cycle brazing, the plain view grain size after welding is shown in FIGS. 13A-D, with FIG. 13A corresponding to sample C, FIG. 13B corresponding to sample E, FIG. 13C corresponding to sample G, and FIG. 13D for sample H. Based on the grain structure images, it is seen that increasing the %TF to >35 led to a finer post-brazing grain size due to an increase in the driving force for recrystallization, but this effect does not appear to have a negative impact on buckling opposition. Similarly, reducing the inter-anneal temperature from 350 °C to 250 °C in combination with a lower %TF resulted in a coarser post-brazing grain size. A combination of inter-anneal temperature and %TF was carefully selected based on the desirable properties required. For example, a different combination of AI and %TF may be required to achieve fin crushing opposition or a coarser grain size.

Example 6

The comparative sample and Samples C, E, G, and H were prepared as in Example 1 and brazed. A fin and tube specimen were joined for each sample and then each specimen was subjected to CASS testing per ASTM B368 (2014). CASS testing was performed for a period of 40 days. Corrosion activity was characterized by examining the welded joint and fin at 10 days, 20 days, and 40 days. At the end of the 40-day period, each fin acted sacrificially, thereby protecting the tube.

The results shown for Examples 2-5 confirmed that some elements, such as Mg and Cu, play a role in contributing to the yield strength and ultimate tensile strength of the alloys. However, an increase in Mg and Cu is typically expected to also lead to increased corrosion, compared to samples with lower amounts of Mg and Cu. The images shown in FIGS.

14A-E are metallographic cross sections taken at 100x magnification. Surprisingly and unexpectedly, as shown in FIGS. 14A-E, the samples with higher amounts of Mg and Cu did not have increased corrosion, compared to the samples with lower amounts of Mg and Cu. Consequently, each of samples C, E, G, and H behaved similarly to the comparative sample in terms of corrosion, but had other superior properties.

All of the above-mentioned Patents, Patent Applications and Publications are incorporated herein in their entirety by reference. Various embodiments of the invention have been described in furtherance of the various objectives of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the scope of the invention as defined in the following claims.

Claims (7)

1. An aluminium alloy, comprising from 0.9% to 1.4% by weight of Si, from 0.3% to 0.6% by weight of Fe, from 0.40% to 0.55% by weight of Cu, from 1.0% to 1.7% by weight of Mn, from 0.10% to 0.25% by weight of Mg, from 1.9% to 2.6% by weight of Zn, up to 0.10% by weight of Ti, with the balance being Al and impurities each in a percentage of from 0% to 0.05% by weight and in total <0.15% by weight, wherein optionally the impurities include Ga, V, Ni, Sc, Ag, B, Bi, Zr, Li, Pb, Sn, Ca, Hf, Sr, or combinations thereof. 2. A method for producing the aluminum alloy of claim 1, wherein the method comprises: direct cold casting of the aluminum alloy into an ingot; hot rolling of the ingot after direct cold casting; after hot rolling, cold rolling of the aluminum alloy to an intermediate thickness; after cold rolling, intermediate annealing of the aluminum sheet rolled to the intermediate thickness at a temperature of 200 °C to 400 °C; and, After intermediate annealing, cold rolling of the aluminum sheet to achieve a cold working percentage (%TF) of 20% to 40%, resulting in the sheet having a thickness of 45 μm to 100 μm, 45 μm to 90 μm, 47 μm to 85 μm, or 50 μm to 83 μm. 3. The method of claim 2, wherein the intermediate annealing is at a temperature of 250°C to 360°C or 290°C to 360°C; and/or where the intermediate annealing time is 30 to 60 minutes; and/or where the % TF is 30% to 40%. 4. A heat exchanger comprising the aluminum alloy of claim 1. 5. A method of making a heat exchanger comprising brazing together at least a first aluminum alloy shape made from the aluminum alloy of claim 1 to a second aluminum alloy shape, comprising: assembling and securing the two or more aluminum shapes together; and, heating the two or more aluminum shapes to a brazing temperature until seals are created between the two or more aluminum shapes by capillary action. 6. The method of claim 5, wherein the first aluminum alloy is capable of withstanding at least 20 days of CASS testing according to ASTM B368 (2014) without detaching from the joint. 7. Use of the aluminum alloy of claim 1 for the manufacture of heat exchanger fins.