JPS6338560A - Al and al alloy sheet as fin material for aluminum heat exchanger having superior zn solderability - Google Patents

Abstract

PURPOSE:To manufacture an Al sheet as a fin material for an Al heat exchanger having superior Zn solderability by finally cold rolling an Al sheet at a low draft so that the rolled sheet as yield strength specified times the yield strength in a full annealed state. CONSTITUTION:An Al or Al alloy sheet is finally cold rolled at such a relatively low draft as about 15-30% so that the rolled sheet has yield strength 2-3.5 times the yield strength in a full annealed state. When the resulting fin material is soldered to a tube material with Zn, annealing proceeds slowly at about 400 deg.C Zn soldering temp., the working strain is not well relieved and the diffusion of the Zn solder in the fin material is accelerated to form an Al-Zn alloy phase. The fin material is firmly joined to the tube material with the Al-Zn alloy phase in-between.

Description

Detailed Description of the Invention [Industrial Application Field] This invention provides aluminum and aluminum that exhibit superior Zn solderability when used as a fin material when manufacturing an aluminum heat exchanger by Zn soldering. This relates to alloy thin plates.

[Conventional technology]

In general, aluminum heat exchangers are manufactured by vacuum brazing fin materials and tube materials made of Al and Al alloy thin plates using an Al1-8i alloy brazing filler metal in the form of a plating sheet without flux. It is well known that it is manufactured.

In addition, among these Al and Al alloy thin plates, those for fin materials are hot-tempered by applying homogenization treatment to Al and Al alloy ingots having a predetermined composition or without homogenization treatment. The hot-rolled plate is rolled to form a hot-rolled plate, and then this hot-rolled plate is subjected to cold rolling and intermediate annealing, and finally cold-rolled at a predetermined reduction rate that takes into account the thickness and hardness t of the fin material. It is also well known that they are manufactured by the same method and are used for brazing in that state.

[Problem that the invention seeks to solve]

On the other hand, in recent years, brazing using the above-mentioned M-8i alloy brazing filler metal has been replaced.

(1) Low bonding temperature.

(2) There is no need to use a praising sheet.

(3) Excellent corrosion resistance of joints.

Attempts have also been made to manufacture aluminum heat exchangers by Zn soldering, which has the following advantages.

In aluminum heat exchangers manufactured by Zn soldering, Zn is electrochemically less base than Al and Al alloys that make up the fins, so in practical use, Zn solder preferentially melts. .

In addition, since there is almost no diffusion of Zn solder especially into the fin material of the soldered part, there is a problem that the bond between the fin material and the tube material is almost lost, and the Zn solder does not function as a heat exchanger. At present, assembly of aluminum heat exchangers using this method has not been put into practical use.

[Means for solving problems]

Therefore, the inventors of the present invention, etc., from the above-mentioned viewpoint.

The fin material and tube material are joined using Zn solder 2.

The result of research to develop Zn soldering technology that maintains a strong bond even after Zn solder melts.

In the Al and Al alloy thin sheets for fin materials manufactured by the above conventional method, the final cold rolling is 70 to 809
Because the rolling reduction was performed at a rolling reduction ratio of 6, the thin plate had residual machining strain, that is, the cuff resistance a' was 4.0 to 4.5 times higher than the yield strength in the fully annealed state. If you perform Zn soldering in such a state, a
' Since a rapid annealing phenomenon occurs at the Zn soldering temperature (usually around 400°C) and high processing strain almost disappears, there is almost no diffusion of Zn solder into the fin material, but the final A state in which relatively low working strain remains due to a relatively low reduction ratio of 15 to 30% in cold rolling.

That is, Zn soldering is performed in a state with a proof stress 2 to 3.5 times that of a fully annealed state.

Annealing at Zn soldering temperature is slow and processing strain does not disappear, and this relatively low processing strain acts to promote the diffusion of Zn solder into the fin material, forming an M-Zn alloy phase. , the fin material and the tube material are firmly bonded via the M-Zn alloy phase.

Moreover, since this M-Zn alloy phase is electrochemically more sensitive than Zn, corrosion resistance also improves.

Therefore, even after the Zn solder melts, the M - Zn
They found that the alloy phase maintains a strong bond between the fin material and the tube material.

Therefore, the present invention was made based on the above knowledge, and it is found that when manufacturing an aluminum heat exchanger by Zn soldering, the yield strength after final cold rolling is 2 to 2 of the yield strength in the fully annealed state. It is characterized in that it is used as a v-fin material made of Al and Al alloy thin plates that have a yield strength equivalent to 3.5 times the yield strength.

Note that the yield strength ratio of the thin plate of this invention is determined empirically, and if the yield strength ratio is less than 2.

Because it is too soft, a slight external force during Zn soldering will cause deformation, causing product defects, and if the single force ratio exceeds 3.5, it will be completely annealed during Zn soldering and the processing distortion will disappear. , the Zn diffusion effect disappears, and M-Z
Since the n-alloy phase cannot be formed, the proof stress ratio is set to 2 to 3.
It was set as 5.

〔Example〕

Next, examples of Al and Al alloy thin plates of the invention will be explained.

By ordinary melting and casting methods, the composition of components 532 shown in Table 1 (both include Fe20.49 as an unavoidable impurity)
6 or less, Si: 0.2% or less, Cu: 0.0596 or less.

Zn m O, 03% or less, Cr: 0.01% or less -M
g: 0.02% or less, Zr: 0101% or less, Ti
: containing 0.05% or less), and 200 #
An ingot with dimensions of 300 tm x 40 layers was formed, and this ingot was homogenized at a predetermined temperature within the range of 450 to 585°C for 2 hours, and then hot rolled. A hot-rolled plate with a thickness of 5 mm was made, and then this hot-rolled plate was subjected to cold rolling and intermediate annealing to form fully annealed materials of different thicknesses, and the yield strength of this fully annealed material was measured. , followed by final cold rolling at the rolling reduction ratio shown in Table 1 to obtain thin sheets 1 to 15 of the present invention and comparative thin sheets 1 to 17, each having a thickness of O, 1, and 3M. : Each manufactured and its yield strength? It was measured.

Next, these various thin plates are formed into corrugated shapes by corrugating processing to form fin materials, which are then laminated with JISIO50 flat porous tube material formed separately by hot extrusion processing to form Zn solder.

Using a mixture of ZnCA2 powder, Zn powder, NaF, etc., and isopropyl alcohol, 1 atm Ar
Z in a gas atmosphere at a temperature of 430°C for 5 minutes.
An aluminum heat exchanger was manufactured by performing seven soldering steps, washing with water, and drying.

Regarding the resulting heat exchanger, the cross section of the Zn soldered portion of the fin material was observed using a microscope.

Long-term bonding? What is the formation width (Zn diffusion distance) of the AJ-Zn alloy phase guaranteed? In addition to measuring, we also conducted a CASS test to determine the time required for the fin material to separate from the pipe material. It was measured. What are the results of these measurements? It is shown in Table 1.

〔Effect of the invention〕

From the results shown in No. An AJ-Zn alloy phase is formed over the width of the AJ-7,n alloy phase, and even in the CASS test, the AJ-7,n alloy phase has excellent corrosion resistance. Comparative thin plate 1 with a yield strength ratio exceeding 3.5
When ~17 is used as the fin material, the high processing strain rapidly disappears during Zn soldering, so almost no Zn diffusion into the fin material occurs, and therefore CA
Even in the SS test, it is clear that when the Zn solder melts, separation occurs between the fin material and the tube material, so that the service life is only short.

As mentioned above, when the Al and Al alloy thin sheets of the present invention are used as fin materials in the production of aluminum heat exchangers, Zn diffuses into the fin materials during Zn soldering and forms an Al-Zn alloy phase. The formation of the Az-Zn alloy phase creates a strong bond between the fin material and the tube material, and this Al-Zn alloy phase also has excellent corrosion resistance, so it can demonstrate its performance as a heat exchanger for a long time. This brings about industrially useful effects such as the ability to

Claims (1)

[Claims] Al and Al alloy thin plates for aluminum heat exchanger fin materials with excellent Zn solderability, characterized in that the Al and Al alloy thin plates after final cold rolling have a yield strength 2 to 3.5 times the yield strength of the fully annealed state. Al alloy thin plate.