JPH0196356A - Manufacture of sagging-resistant fin material for protection - Google Patents

Abstract

PURPOSE:To improve the sagging resistance of the title material at the time of brazing it to a tube of a heat exchanger by using the cold rolled plate of an Al alloy having specific compsn. as the fin material of a heat exchanger and simultaneously subjecting the material to intermediate annealing and final cold rolled working under specific conditions. CONSTITUTION:The Al alloy contg., by weight, 0.2-1.5% Mn, 0.2-2.0% Zn, 0.05-0.5% Ca, 0.05-0.6% Si, <0.6% Fe and either or both 0.05-0.5% Cu and 0.05-0.3% Zr is used as the corrosion-resistant fin of a heat exchanger. The Al alloy ingot having the above compsn. is subjected to a homogenizing treatment, is thereafter worked into a plate material by hot rolling and cold rolling, is successively heated at 400 deg.C/hr warming rate into the temp. range of 350-450 deg.C, is subjected to intermediate annealing in said temp. range and is thereafter subjected to final cold working, by which the fin material for cathodic protection having the desired thickness is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a cathodic protection fin material having excellent droop resistance.

(Prior art) Heat exchangers such as automobile radiators, condensers for heaters and coolers, and evaporators, which are generally made of aluminum or aluminum alloy, are assembled with a cooling tube whose surface is coated with aluminum and aluminum fins for heat radiation. In addition, it is manufactured by brazing and joining using the vacuum brazing method.

Heat exchangers made in this way have a cathodic protection effect obtained by adding an element to the fin material that lowers its potential appropriately compared to the tube, in consideration of use in severe corrosive environments. It can be used to improve the corrosion resistance of tubes.
A method is being used to make the situation worse. For example, an An-Mn alloy containing Zn as an additive element in cathodic protection materials has been put into practical use, and cathodic protection due to Zn evaporation during vacuum brazing, which is a drawback of such Zn-containing fin materials, has been put into practical use. Fin materials to which Ca is added in addition to Zn have also been developed to prevent deterioration of effectiveness.

(Problem to be solved by the invention) However, when cathodic protection fin materials containing Zn and Ca are made thinner in response to the recent trend toward thinner walls, their strength decreases at high temperatures (around 600°C) during brazing. As a result, sagging resistance deteriorates and deformation occurs due to so-called buckling, which often causes problems such as inability to ensure good brazing properties. Therefore, there is a need for materials that do not deform at such high temperatures.

An object of the present invention is to provide a method for manufacturing a cathodic protection fin material that does not undergo high-temperature deformation during brazing and has excellent sagging resistance.

(Means for Solving the Problems) The present inventors have conducted various studies in view of the shortcomings of the conventional techniques, and have obtained the following findings.

That is, buckling of the aluminum alloy fin material at high temperatures is due in part to the low melting point of the material. This is a problem of high-temperature strength. For example, materials with high melting points such as iron and copper have high high-temperature strength, so no matter what the structure of the material is, buckling at high temperatures will cause a decrease in load resistance. do not have. Therefore, even if various alloying elements are added to aluminum to improve its strength, if the melting point of the material is lowered as a result, the high temperature during brazing (approximately 600'
In the condition (around C), the strength decreases significantly and sagging is unavoidable. If the melting point (solidus temperature) is lower than about 620°C, significant sagging occurs, making it unsuitable as a fin material.

Next, even if the melting point is about 620° C. or higher, it alone cannot completely prevent drooping. The present inventors have found that in addition to the above melting point conditions, when the amount of strain on the brazing heating surface increases, it becomes easier to sag.

In general, highly strained materials have a high dislocation density, so even at low temperatures, vacancy diffusion through dislocations is likely to occur, and grain boundaries are likely to move when changing from a processed structure to a recrystallized structure. As the grain boundaries move, deformation is more likely to occur as the grain boundary area increases. This phenomenon is significant when the recrystallization temperature is lower than 350°C. The present inventors further discovered that in addition to this drooping mechanism in a relatively low temperature range (250 to 450°C), there is another drooping mechanism in a high temperature range. This is a high temperature range (550℃~600℃)
This is a phenomenon that occurs even after recrystallization has already been completed, and the amount of drooping at this time is due to the recrystallized grain size being 3001L during the brazing heat.
When the recrystallized grain size is smaller than m, it is remarkable that the recrystallized grain size is 3001Lm.
If it is above, the amount of drooping was quite small. This is thought to be due to a type of diffusion creep since it occurs at very high temperatures and in a state where there are not many dislocations. Diffusion creep is a phenomenon in which deformation itself occurs due to the movement of substances by diffusion between the planes of crystal grains, regardless of dislocations. Therefore, the smaller the grain size is, and the more sub-grain boundaries remain. The smaller the grain size of the subcrystal, the easier it is to deform, which closely matches the actual phenomenon.

The present invention has been made based on these findings.

That is, the present invention contains 0.2 to 1.5% by weight of Mn (hereinafter, % by weight in the alloy composition is simply translated as %) and 0.2 to 2% by weight of Zn.
．． 0%, Ca 0.05~0.5%, Si0.05~0
．． 6%, Fe 0.6% or less and Cu 0.05 ~
An aluminum alloy containing Zr 0.5% and one or two of Zr 0.05 to 0.3%, with the balance consisting of A and unavoidable impurities, is subjected to homogenization treatment, hot rolling and cold rolling. After rolling, increase the temperature at a rate of 400°C/hr or less to 35
The present invention provides a method for producing a sagging-resistant cathodic protection fin material, which comprises performing intermediate annealing at a temperature of 0 to 450°C and then cold working at a final cold rolling reduction of 50% or less.

Next, the present invention will be explained in detail.

The reasons for selecting and limiting the components and composition of the aluminum alloy used in the present invention are as follows.

The Mn content is 0.2 to 1.5%. Mn is An-M
In addition to forming n-based and A-Mn-Si-based and other fine intermetallic compounds, it has the effect of increasing the ILT crystal temperature on the brazing heating surface and increasing the recrystallized grain size after intermediate annealing. It has the effect of improving high temperature strength. However, M
If the n content is less than 0.2%, sufficient effects cannot be obtained,
If the content exceeds 1.5%, further improvement cannot be expected.

Zn content shall be 0.2-2.0%. Zn has the effect of lowering the potential of aluminum alloy by its addition,
Suitable as a sacrificial anode material used in cathodic protection. However, if the Zn content is less than 0.2%, the effect is small;
．． Even if the content exceeds 0%, no further improvement effect can be expected.

Ca content shall be 0.05-0.5%. When Ca alloys aluminum, it lowers its potential like Zn,
It is effective as a sacrificial anode material, does not evaporate during vacuum brazing and contaminates the furnace, and when coexisting with Zn, creates an oxide layer of Ca on the surface layer and has the effect of suppressing the evaporation of Zn. However, if the Ca content is less than 0.05%, the potential will not be low enough to exert a cathodic protection effect.
On the other hand, even if the content exceeds 0.5%, no further improvement can be expected.

The Si content is 0.05 to 0.6%. Si is AIL
-M It has the effect of promoting the precipitation of n-based and Al-Zr-based fine compounds, and increases the recrystallized grain size.

It has the effect of increasing high temperature strength. However, the Si content is 0.
If the content is less than 0.05%, no effect will be obtained, while if the content exceeds 0.6%, the melting point will decrease and the sagging resistance will deteriorate.

The Fe content is set to 0.6% or less. Fe is Al-M n
-Fe Facilitates the formation of coarse e-based crystals. However, if Fe content exceeds 0.6, the recrystallization temperature will be lowered due to coarse products, and the recrystallized grain size will also be reduced.
1 Degrades droop resistance.

Cu content shall be 0.05-0.5%. Cu has the effect of improving strength. However, the Cu content is 0.05%
If the content is less than 0.5%, the effect will not be maintained, and if the content exceeds 0.5%, the effect of assimilating the electric potential will increase and cathodic protection will be impaired.

Zr content shall be 0.05-0.3%. Like Mn, Zr has the effect of increasing the recrystallization temperature and increasing the recrystallized grain size on the brazing heating surface. However, Z "content is 0.0
If the content is less than 5%, no effect will be obtained, and on the other hand, if the content exceeds 0.3%, further improvement cannot be expected.

In the present invention, Cu and Zr are effective in improving sagging resistance whether they are added alone or in combination.

The purpose of the present invention will not be impaired if the impurities contained in the aluminum alloy used in the present invention are at the level of impurities contained in aluminum ingots that are usually reprinted. For example, Ni0005% or less, Mg0.0
There is no particular problem as long as the content is 5% or less, Cr 0.05% or less, and the total of other trace impurities 0.05% or less.

The aluminum alloy used in the present invention can have a melting point of 620° C. or higher due to the above-mentioned alloy composition. The reason why the melting point is set to 620'C or higher is that since the material is heated to around 600°C during vacuum brazing, the strength of a material with a low melting point at high temperatures decreases significantly, and the sagging resistance significantly deteriorates. The melting point of aluminum gold is 6209C
The above can be achieved by appropriate selection of the composition and blend according to conventional methods.

Next, the processing steps for aluminum alloy material in the present invention will be explained.

First, an aluminum alloy having the above composition and melting point is melted and cast into an ingot using a conventional method. Next, this ingot is subjected to homogenization treatment and hot rolling, but these conditions are not particularly limited and may be set according to conventional methods. After hot rolling, cold rolling may be performed, or if there is a concern about variations in precipitated structures among materials during hot rolling, annealing may be performed after hot rolling.Normally, this is not necessary. Conditions for cold rolling following hot rolling may be set according to conventional methods.

After the homogenization treatment, hot rolling and cold rolling treatment, in the present invention, the temperature is increased by heating at a temperature increase rate of 400°C/hr or less to 35°C.
After intermediate annealing at a temperature of 0-450'C, 50%
Cold working is performed at the following final cold rolling rate. The reasons for limiting these conditions are as follows.

The heating temperature for intermediate annealing is 400°C/hr or less. If the temperature increase rate exceeds 400℃/hr, precipitation will occur after recrystallization, and not only can we not expect coarsening of crystal grains due to fine precipitates, but also fine precipitates due to the absence of strain before precipitation. As the amount of steel decreases, the recrystallization completion temperature in the final cold-rolled sheet also becomes lower than 350°C, resulting in poor sag resistance.

The temperature of intermediate annealing is 350 to 450°C. If the annealing temperature is less than 350°C, the diffusion rate of alloying elements will be slow and sufficient precipitation cannot be expected, whereas if it exceeds 450°C, the amount of solid solution of alloying elements will increase and the amount of precipitation will decrease. The Φ annealing treatment time is not particularly limited, and is preferably about 4 hours. It is sufficient if this intermediate annealing is performed before the final cold rolling, but there is no harm in performing intermediate annealing two or more times as necessary.

stomach.

The rolling ratio in the final cold working following intermediate annealing is 50% or less. When the rolling ratio exceeds 50%, the recrystallization temperature of the brazing hot surface becomes lower than 350''C, and at the same time, the recrystallized grain size becomes less than 300 gm, resulting in a significant deterioration in sagging resistance.

(Example) The present invention will now be described in more detail based on examples.

Example 28 types of fin material samples were produced by casting aluminum alloys having the compositions shown in Table 1 using a conventional method, and processing each ingot according to the process conditions A to H shown in Table 2. did. In this experiment, the melting point of each alloy was determined by measuring the solidus temperature by thermal analysis and using that as the melting point. The results are shown in Table 1.

Next, the fin material obtained as described above was subjected to a droop test, and also tested for recrystallization temperature, recrystallized grain size, and Zn residual ratio after the droop test. The test results obtained are shown in Table 3.

(i) Droop test For the droop test, a sample (1) with a width of 22 mm and a length of 60 mm is prepared from the fin material, and this is placed on a stand (2) as shown in Figure 1 (a).
) using a fixture (3) to hold it in a cantilever with a length of 50 mm. The distance from the tip of the sample material was measured as the amount of droop as shown in FIG. 1 (b). The smaller the amount of droop, the better.

The Zn residual ratio after the sagging test is expressed as a percentage of the Zn amount (i.e., Zn component amount) before the sagging test, obtained by dissolving the entire test piece after the sagging test and measuring the Zn amount by chemical analysis. .

(ii) Recrystallization temperature and recrystallized grain size Recrystallization temperature refers to the recrystallization completion temperature, which means the temperature at which recrystallization is completely completed in the temperature raising process for brazing. The recrystallization temperature was determined from the softening curve when the sample was heated at each temperature for 10 minutes. In addition, the crystal grain size at this time is determined by comparing the crystal grains revealed by macroetching with aqua regia with a standard sample with an average grain size of 300 lm. is marked with an X.

As is clear from Table 3, aluminum alloy fin materials obtained by the method of the present invention (Experiment No. 1 to 15)
The amount of sagging under vacuum and high temperature is small, the Zn residual ratio is high, and the sagging resistance and cathodic corrosion resistance are excellent. On the other hand, the samples of comparative examples have a low recrystallization temperature, a small recrystallized grain size, a large amount of sagging, and poor sagging resistance, and some have a low Zn residual ratio.

(Effects of the Invention) According to the present invention, it is possible to manufacture a fin material for brazing having excellent sagging resistance and cathodic protection. Therefore, according to the method of the present invention, it is possible to further reduce the thickness of the fins of the heat exchanger manufactured by the vacuum brazing method, and it is possible to reduce the weight and cost of the heat exchanger.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a sagging test method for evaluating sagging resistance. Explanation of symbols

Claims (1)

[Claims] Mn0.2-1.5%, Zn0.2-2.0%, Ca0
．． 05-0.5%, Si0.05-0.6%, Fe0.
6% or less, Cu0.05~0.5% and Zr0.05~
An aluminum alloy containing one or two of 0.3% and the remainder consisting of Al and unavoidable impurities (wt%) is subjected to homogenization treatment, hot rolling and cold rolling, followed by temperature elevation. Raise the temperature at a rate of 400℃/hr or less to 350-450℃
1. A method for producing a sagging-resistant and anticorrosive fin material, which comprises performing intermediate annealing at a temperature of .degree. C. and then final cold working at a cold rolling rate of 50% or less.