JPH0387328A - Aluminum alloy sheet for forming having excellent corrosion resistance and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture the Al alloy sheet having excellent corrosion resistance and formability by subjecting a continuously cast slab of an Al-Mg-Si series alloy contg. specified small amounts of Zn, Mn, Ti and B and in which the content of Cu as impurities is reduced to homogenizing treatment, to rolling and thereafter to soln. treatment. CONSTITUTION:The molten metal of an Al-Mg-Si series alloy having the compsn. contg., by weight, 0.3 to 0.8% Mg, 1.0 to 1.8% Si, 0.15 to 1.0% Zn, 0.05 to 0.3% Mn, 0.01 to 0.05% Ti and 0.002 to 0.01% B, in which Cu as impurities is regulated to <=0.04% and the balance Al is subjected to continuous casting. The surface of the continuously cast ingot is scarfed to remove oxides or the like, is thereafter heated at 520 to 580 deg.C for 4 to 24hr and is subjected to homogenizing treatment. Next, the ingot is hot-rolled and cold-rolled to work into a sheet material, which is thereafter subjected to soln. treatment at 520 to 580 deg.C. In this way, the Al alloy sheet material having excellent strength, corrosion resistance and formability can be obtd.

Description

[Detailed Description of the Invention] The present invention is suitable for use in automobile parts, mechanical parts, home appliance parts, etc. that are molded by press molding, bending, etc. This invention relates to an aluminum alloy plate with excellent corrosion resistance and formability, and a method for manufacturing the same.

Jakuraitan's pincer strained aluminum alloy sheets have good formability, so they are used for car bodies, machinery, casings for home appliances, etc.

Such automobile bodies, casings, etc. are assembled by processing aluminum alloy plates by press bottom shaping, bending, etc., and then applying paint baking treatment, or by welding, etc. after forming.

By the way, if the strength of aluminum plywood is high, it can be made thinner and lighter, and it will have better punt resistance (bending resistance) and will be less likely to get scratched. however,
High strength generally reduces formability, so it is not a good idea to increase the strength before forming. It is hoped that there will be no decline. Furthermore, since most of the forming processes involve stretch forming and bending, it is required that these properties be excellent. Furthermore, we use resistance spot welding and TIG for parts assembly.

Since fusion welding such as MIG is used, these properties are also required to be good. In addition, since it is used in harsh natural environments, it is used in a coated state for boat fishing, but the coating film may be damaged, so It is necessary to have good corrosion resistance.

Therefore, these applications require materials with good overall strength, formability, bondability, and corrosion resistance.

Today, Al-Mg-Si alloys, such as 6009
Alloys such as 6010 alloy and 6111 alloy have been put into practical use.

Problems 11 and 14 However, these alloys have the advantage of high dent resistance, but they have some disadvantages in formability, as the paint hardens during the baking process (a phenomenon in which strength improves due to heating for baking). In addition, it has the disadvantage of being sensitive to corrosion resistance, especially intergranular corrosion.

Although Al-Cu alloys, such as 2036 alloy, have high strength, their corrosion resistance and formability are inferior to other alloy systems, and therefore their use tends to decrease.

Although Al-Mg alloys, such as 5182 alloy, have good formability and corrosion resistance, their strength is somewhat low, and because they are solid solution strengthened alloys, no significant improvement can be expected. Furthermore, there is a disadvantage that stretcher strain marks are generated during pressing, spoiling the appearance of the outer inkstone.

That is, an object of the present invention is to provide an aluminum alloy plate having excellent corrosion resistance such as string rust resistance and intergranular corrosion resistance, and excellent formability such as stretch formability and bendability, and a method for manufacturing the same. That is.

In order to solve the above drawbacks, the inventors used Al-Mg
-As a result of studying St-based alloys, Mg, St.

The present invention was completed by discovering the optimum content of each element of Zn, Mn+ Tl and B, the upper limit of the elements to be restricted, and the most preferable manufacturing method.

That is, the first invention has Mg0.3 to 0.8%, Si1
, 0 to 1.8 wt%, Zn 0.15 to 1.0 wt%,
Mn 0°05~0.3wt%, Ti0.01~0.0
5 wt%, B 0.002 to 0.01 wt%,
The remainder consists of A1 and impurities, with Cu as an impurity being 0.
．． This is an aluminum alloy plate for forming process with excellent corrosion resistance, characterized by having a content of 0.04 wt% or less. Further, the second invention continuously casts a molten aluminum alloy having the composition described in the claims, heats the obtained ingot at a temperature of 520 to 580°C for 4 to 24 hours to homogenize it, and then rolls it. After that, the final rolled plate is subjected to solution heat treatment at a temperature of 520 to 580°C.

First, the ingredients contained in the He1 alloy plate of the first invention and the reason for limiting the content will be explained.

Mg is an element that imparts reinforcement together with Si. If the content is less than 0.3 imt%, the strength is low and 0.7i+t%
If the content exceeds the above, moldability will deteriorate. Therefore, from the viewpoint of strength and moldability, the content is set at 0.3 to 0.8 wt%.

Si, together with Mg, is an element that imparts strength.

If the content is less than 1.0 wt%, sufficient strength cannot be obtained and ductility is low. If it exceeds 1.8 wt%, moldability deteriorates. Therefore, from the viewpoint of strength and formability, 1.0 1.
It is set to 8wt%.

Zn is an element that prevents intergranular corrosion and pitting corrosion.

If the content is less than 0.15 wt%, the effect will not be sufficient, while if the content exceeds 1.0 wt%, thread rust resistance will deteriorate. Therefore, from the viewpoint of intergranular corrosion resistance, pitting corrosion resistance, and thread rust resistance, the content is set at 0.15 to 1.0 wt%.

Cu is an effective element for increasing strength, but 0.04
If the content exceeds wt%, intergranular corrosion resistance will be significantly deteriorated, so the content is regulated to 0.04wt% or less.

Mn is an element that improves formability because it makes the crystal grain size finer and makes deformation more uniform.

If it is less than 0.05 t%, the effect is small and 0.3w
If it exceeds t%, large crystallized particles will increase and the moldability will deteriorate, so it is set at 0.05-0.3wt%.

Ti is an element that works together with B to refine the crystal grain size of the ingot and is effective in preventing casting cracks, as well as uniformly distributing crystallized particles and improving formability. 0.01wt
%, the effect is not sufficient; on the other hand, Q, 05wt
Even if the content exceeds %, the effect is saturated, and rather
B2 particles increase and formability deteriorates, so 0.01 0
．． The range is 0.05 wt%.

B works with Ti to refine the crystal grain size of the ingot and is effective in preventing casting cracks, and is an element that uniformly distributes crystallized particles and improves formability. 0.002w
If it is less than t%, the effect is not sufficient; on the other hand, 0.01wt
Even if the content exceeds %, the effect is saturated, and rather
Bz, ^lBz particles increase and formability deteriorates, so 0
．． The range is 0.002-0.01 wt%.

Fe, which is an unavoidable impurity, is allowed as long as it is 0.25 wt% or less because it does not impede the purpose of the present invention.

Next, a method for manufacturing an A1 alloy plate according to the second invention will be explained.

Regarding the homogenization treatment of the ingot, heating below 520°C is insufficient for solid solution and uniform distribution of crystallized substances generated during casting, and heating above 580°C may cause local melting. . Therefore, the temperature should be in the range of 520-580°C. If the homogenization treatment time is less than 4 hours, a sufficient effect will not be obtained, and even if the homogenization treatment is heated for more than 24 hours, the effect will be saturated. Therefore, the range is 4-24 hours.

Regarding solution treatment, if the temperature is lower than 520°C, re-dissolution of precipitates such as MgS i z generated in the rolling process will be insufficient, and if heated above 580°C, the crystal grains will become coarse and formability will deteriorate. . Therefore, the temperature should be in the range of 520-580°C.

Akira Oarashi (Example 1) A molten aluminum alloy having the alloy composition shown in Table 1 is treated by a normal degassing method, and then passed through a filtration device to remove inclusions, and a continuous cast ingot with a thickness of 400mm is produced. After casting and facing 5
It was homogenized at 60° C. for 8 hours, then hot rolled to a thickness of 6 strips, further cold rolled to 0.9 w, and finally solution treated at 565° C. for 30 seconds and cooled in water. Fifteen days after water cooling, the properties of the plates, such as strength, formability, and corrosion resistance, were evaluated.

The results are shown in Table 2.

Margin below The overall evaluation in Table 2 was based on the following criteria.

Judgment criteria Tensile strength: 25kg/2 or more Erichsen value: 9.3 mm or more Flexibility R/lio, 5 or less Yarn end occurrence: None Intergranular corrosion: None Measuring method Tensile test: JIS No. 13 B test piece was used.

Erichsen test, according to JIS Z2247A method.

Bending test: The minimum bending radius R/l without causing cracks on the surface when rolled up at a bending angle of 1456 was determined.

Intergranular corrosion susceptibility test; acetic acid saline solution (5% N
Add 1 sample to the test solution of aC1+ 6 ml/1 acetic acid).
After soaking for 0 minutes, dry for 50 minutes. A 168-cycle alternating immersion test was carried out with this as one cycle, and the cross section near the surface of the sample after the test was observed with an optical microscope to evaluate the presence or absence of intergranular corrosion.

Residual corrosion test: After pre-treatment with alodine, apply cationic electrodeposition, bake at 170°C for 30 minutes, cross-cut the coated sample surface with a cutter knife to reach the base material, and then apply 3.5% salt. Sprayed with water for 24 hours, then heated to 40°C.
After being kept in a constant temperature and humidity chamber with a humidity of 85% for 2000 hours, the occurrence of residual symptoms was observed. The average length of the five strands is 2mm.
In the following cases, it was determined that there was no remorse. When the average length of the five strands exceeded 2 mm, it was determined that lingering was present.

As is clear from Table 2, the alloy plate of the present invention is excellent in strength, formability, and corrosion resistance, and satisfies the criteria. On the other hand, it can be seen that the comparative examples are insufficient in terms of strength, moldability, and corrosion resistance.

(Example 2) The molten metal having the composition of sample number 1 shown in Table 1 was subjected to normal degassing treatment and filtration treatment to remove inclusions, and then
It was cast into a 50u semi-continuous cast ingot, and after face cutting, it was homogenized under the homogenization treatment conditions shown in Table 3, hot rolled to a thickness of 7fi, and further cold rolled to a thickness of 1.0w, Finally, it was solution treated under the conditions shown in Table 3 and cooled with water. After water quenching 1
Strength and moldability were evaluated on the 5th day. The results are shown in Table 3.

As is clear from the results shown in Table 3 below, it can be seen that the method of manufacturing the alloy plate of the present invention allows the production of alloy plates with excellent strength and formability that satisfy the criteria.

In addition, as explained above, the aluminum alloy sheet and the method for manufacturing the same according to the present invention have excellent corrosion resistance and formability, and are therefore suitable for use in automobile parts, especially automobile body sheets, machinery,
It has such effects that it can be used for casings of home appliances, etc.

Claims (2)

[Claims] (1) Mg0.3-0.8wt%, Si1.0-1.8
wt%, Zn0.15~1.0wt%, Mn0.05~
0.3wt%, Ti0.01-0.05wt%, B0.
002 to 0.01 wt%, the remainder being Al and impurities, and having Cu as an impurity of 0.04 wt% or less. (2) A molten aluminum alloy having the composition according to claim 1 is continuously cast, the resulting ingot is heated at a temperature of 520 to 580°C for 4 to 24 hours to homogenize it, and then after rolling, A method for producing an aluminum alloy plate for forming with excellent corrosion resistance, which comprises subjecting the final rolled plate to solution heat treatment at a temperature of 520 to 580°C.