JP2786640B2 - Method of manufacturing aluminum alloy sheet for brazing with excellent droop resistance - Google Patents

Description

The present invention may be used as a fin material for an aluminum heat exchanger such as a radiator for an automobile, a condenser for a car cooler, an evaporator, or the like, or a core material of a brazing sheet. The present invention relates to a method for producing a thin aluminum alloy sheet for brazing, and more particularly to a method for producing a thin aluminum alloy sheet for brazing having excellent droop resistance during the application of brazing.

2. Description of the Related Art Conventionally, when a heat exchanger as described above is manufactured by brazing, an Al-Mn alloy thin plate as a fin material or an Al-Si alloy brazing material on one or both surfaces of the thin plate as a core material is formed by grading. The fin material and the tube material are brazed to each other.

By the way, with the demand for weight reduction and cost reduction of the heat exchanger, it is required to make the fin material as thin as possible. Deformation such as buckling is likely to occur at high temperatures under additional heat. Therefore, in order to reduce the thickness of the fin material, it is essential to improve the droop resistance of the fin material without deteriorating the formability and the like. Here, in order to improve the droop resistance, it is necessary to increase the high-temperature strength of the fin material and to increase the recrystallized grain size formed on the fin material thin plate when the brazing is applied. The reason for this is to increase the high-temperature strength by increasing the size of the recrystallized grains. Furthermore, during heating, the molten brazing material penetrates into the thin plate through the grain boundaries of the finned thin plate and erodes, so if the crystal grain size is small, the amount of erosion of the brazing material increases, resulting in droop resistance. On the contrary, when the recrystallized grain size is large, the erosion amount of the brazing material is reduced.

Problems to be Solved by the Invention However, Al-Mn conventionally used as a fin material
Alloy sheets have the disadvantage that the droop resistance is generally poor.

Therefore, in order to improve the droop resistance, Al-Mn alloy
One or two of Si, Sn, Zn, Mg and Zr may be contained (for example, JP-A-63-125635), Ta, Nb, Mo, W
Or one or more of the Group Va and Group VIa refractory metals such as those disclosed in Japanese Patent Application Laid-Open No. 63-125636 to improve the composition and final cold working after annealing. To improve the manufacturing process by specifying the rate (JP-A-63-125635)
And so on. However, none of the recent demands for thinner fin materials can provide sufficient satisfaction.

The present invention has been made in view of such technical background, and an object of the present invention is to provide a method for manufacturing an aluminum alloy thin plate having excellent droop resistance.

Means for Solving the Problems In order to achieve the above-mentioned object, the inventor repeated experiments and studies, and as a result, the recrystallized grain size of the thin plate at the time of the addition of brazing was coarsened to increase the high-temperature strength, and the brazing material erosion The present invention has been completed to find a method for producing an aluminum alloy thin plate for brazing, which achieves suppression and eventually has excellent droop resistance.

That is, the method for producing an aluminum alloy sheet having excellent droop resistance according to the present invention is as follows: Mn: 0.8 to 1.3 wt%, Si: 0.2 to 0.7
Using an aluminum alloy containing wt% and the balance of aluminum and unavoidable impurities, the aluminum alloy ingot was hot-rolled at a temperature of 350 to 450 ° C. without performing homogenization treatment, and then subjected to primary cold rolling. One intermediate annealing is performed at a temperature of 350 to 420 ° C. only between the rolling and the secondary cold rolling;
It is characterized in that the next cold rolling is performed at a rolling reduction of 20 to 40%.

First, the significance of addition of each element in a thin plate and the reason for limitation will be described.

Mn improves the room temperature strength, and Al and Si
To produce fine Al-Mn-Si-based precipitates, which delay recrystallization. As a result, the recrystallized grains are coarsened and, consequently, the droop resistance is improved. But 0.8wt%
If it is less than 1.3 wt%, the effect is small, and if it exceeds 1.3 wt%, coarse precipitates tend to be formed. The coarse precipitates not only deteriorate the formability but also serve as nuclei of the recrystallized grains to make the recrystallized grains finer, resulting in a decrease in high-temperature strength and erosion of the brazing filler metal, thereby deteriorating droop resistance.

Si becomes Al-Mn-Si-based fine precipitates and has an effect of coarsening recrystallized grains. However, when the content is less than 0.2% by weight, the effect is small. When the content exceeds 0.7% by weight, the precipitate becomes coarse, and the coarsening of recrystallized grains cannot be expected.

In addition to the above-mentioned essential addition elements, if necessary, the inclusion of Zr and Cr as optional addition elements is allowed. Zr and Cr have the effect of improving fin formability and droop resistance. In view of such effects, the two elements are equivalent, and it is sufficient if any one of them is contained. However, if the total content is less than 0.04% by weight, the above effect is poor. If the content exceeds 0.12% by weight, coarse precipitates are formed and the recrystallized grains become fine.

In addition to the above elements, impurities such as Fe, Cu, Mg, Cr, Zn,
The inclusion of elements such as Ti is allowed. Of these, Fe is Al-Fe
, And Al-Mn-Fe-based coarse precipitates are formed, and serve as nuclei for recrystallization. For this reason, not only the recrystallized grains are refined and the high-temperature strength is reduced, but also the brazing material erodes into the thin plate when the brazing heat is applied. Therefore, it is preferable to reduce the content of the brazing material as much as possible, preferably 0.3 wt%. It is better to regulate to the following content. In addition, when using a thin plate as a heat exchanger fin material, Cu has a function of deteriorating the corrosion resistance of the heat exchanger by making the potential of the fin material noble with respect to the tube material. Good, preferably 0.05wt%
It is better to regulate to the following content.

Next, a manufacturing method according to the present invention will be described as a most preferable method for manufacturing an aluminum alloy sheet having the above composition. The basic idea of this manufacturing method is to suppress the formation of coarse precipitates of Mn, which is the core of recrystallization, without applying heat as much as possible to the thin plate until brazing, and to set the final draft in an appropriate range. The purpose is to regulate and control the driving force of recrystallization. The details are as follows.

That is, a manufacturing method according to a conventional method is to melt and cast an aluminum alloy having the above composition, perform a homogenization treatment on the obtained ingot, and then perform hot rolling, intermediate annealing, and cold rolling. However, in the present invention, hot rolling is performed without performing homogenization after melting and casting. The reason for omitting the homogenization process in this way is that when the homogenization process is performed, Mn becomes an Al-Mn-based
This is because it is formed as a coarse precipitate of -Mn-Fe system, becomes a nucleus of recrystallization, and refines recrystallized grains. Hot rolling must be performed at a temperature in the range of 350 to 450 ° C. in order to minimize the formation of coarse precipitates.

Next, cold rolling is performed by omitting intermediate annealing before hot rolling after hot rolling. In addition, only during the cold rolling, that is, only between the primary cold rolling and the secondary cold rolling, the only intermediate annealing is performed at a temperature of 350 to 420 ° C. The reason why the intermediate annealing before hot rolling and before cold rolling is omitted is to suppress the formation of coarse precipitates as described above. The intermediate annealing performed between the primary cold rolling and the secondary cold rolling is performed for the purpose of releasing the strain and facilitating the rolling and controlling the rolling reduction of the secondary rolling. However, the reason why the temperature of the intermediate annealing is specified to be 350 to 420 ° C. is that the above effect is poor at a temperature lower than 350 ° C.
If the temperature exceeds 20 ° C., coarse precipitates are formed, the recrystallized grains are refined, and the droop resistance is deteriorated. And again
The secondary cold rolling is performed at a rolling reduction of 20 to 40%. When the rolling reduction is specified as above, if less than 20%, recrystallization does not occur and the crystal grains remain unstable during brazing,
This is because the brazing material erodes the inside of the thin plate along the substream. On the other hand, if the rolling reduction exceeds 40%, the driving force for recrystallization is too large, and the crystal grains become finer, so that the erosion amount of the brazing material also increases. The final thickness is obtained by this secondary cold rolling. The conditions for the primary cold rolling are not particularly limited, and ordinary cold rolling conditions may be adopted. When a thin plate is used as a core material of an aluminum brazing sheet, a brazing material layer may be clad on one or both surfaces of the thin plate in a hot rolling step.

Effect of the Invention As described above, by using the method for manufacturing an aluminum alloy sheet according to claim 1, an aluminum alloy sheet having excellent droop resistance can be provided.
As a result, the thickness of the thin plate can be reduced, and an aluminum alloy thin plate suitable as a fin material of the heat exchanger alone or as a core material of the brazing sheet can be provided.

Examples (Example 1) A brazing sheet was manufactured using various aluminum alloy sheets having the compositions shown in Table 1 below as core materials. Manufacturing followed the following procedure. In other words, after melting and casting, each aluminum alloy ingot was subjected to beveling without performing homogenization treatment, and then a brazing filler metal made of an Al-Si alloy was clad on both sides at a rate of 15%, and hot-rolled at 400 ° C at 400 ° C. It was rolled to a thickness of 3.2 mm. Then
Wall thickness without intermediate annealing between hot rolling and cold rolling
After the first cold rolling to 0.2 mm, intermediate annealing of 370 × 1 hour was performed, and the second cold rolling was further performed to 0.13 mm to obtain the final thickness. Here, the rolling reduction of the core material in the second cold rolling was 35%.

For each aluminum brazing sheet obtained above, a droop resistance test was performed, and the fin height was 12 mm ×
Formability when processed into a corrugated louver fin having a width of 50 mm and a pitch of 10 mm was examined. For the droop resistance test, width 20 ×
Of the test piece cut out to a length of 80 mm, the portion from one end in the length direction to 35 mm is held horizontally, and the remaining 45 mm portion is protruded unsupported, and in this state 605 ° C. in vacuum
The measurement was performed by measuring the amount of droop of the free end in the protruding portion of the test piece when the test piece was held for 5 minutes. Good moldability was indicated by ○, and poor moldability was indicated by ×.

 The results are shown in Table 2 below.

(Example 2) An aluminum alloy ingot was manufactured by melting and casting an aluminum alloy having a composition indicated by alloy symbols A to F in Table 1 of Example 1 as a material. Then these ingots,
After the homogenization treatment was performed or without, the surface was cut. Next, a brazing material made of an Al-Si alloy was
%, And hot-rolled to a thickness of 3.2 mm. Next, after performing primary cold rolling to a wall thickness of 0.2 mm with or without intermediate annealing, various types of aluminum brazing sheets were manufactured by sequentially performing intermediate annealing and secondary cold rolling. Table 3 summarizes the presence / absence of each step and the processing conditions.

The aluminum brazing sheet obtained as described above was subjected to a sag resistance test and the formability was examined. Both the sag resistance test and the investigation of the moldability were performed under the same conditions as in Example 1. Table 3 also shows the results.

From the results of Examples 1 and 2 above, it was confirmed that the brazing aluminum alloy sheet manufactured by the method of the present invention can improve the droop resistance without deteriorating the formability.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI C22F 1/00 651 C22F 1/00 651A 683 683 685 685Z 686 686A 6961 691B 694 694B 694A 694A (58) Investigation field (Int.Cl. ⁶ , DB name) C22F 1/04-1/057 C22C 21/00-21/18

Claims (1)

(57) [Claims] 1. An aluminum alloy containing Mn: 0.8-1.3 wt% and Si: 0.2-0.7 wt%, the balance being aluminum and unavoidable impurities. After performing hot rolling at a temperature of ~ 450 ° C, one intermediate annealing is performed at a temperature of 350 to 420 ° C only between the first cold rolling and the second cold rolling, and the second cold rolling is performed. And producing the aluminum alloy sheet for brazing with excellent droop resistance.