JPH04210456A - Manufacture of aluminum alloy sheet excellent in strength and baking hardenability of paint - Google Patents

Abstract

PURPOSE:To obtain an Al alloy sheet high in the strength of stock and excellent in baking hardenability of paint even by heating treatment after painting the Al-alloy sheet with a low baking temp. paint by subjecting an Al-alloy sheet contg. prescribed amounts of Mg and Si to soln. treatment and thereafter executing specified low temp. heating treatment. CONSTITUTION:An ingot obtd. by subjecting an Al-Mg-Si series alloy contg., by weight, 0.3 to 1.5% Mg and 0.6 to 2.0% Si to melting and casting by the conventional method is subjected to homogenizing treatment and is then subjected to hot rolling and cold rolling into a desired sheet thickness. This sheet is subjected to soln. heating, is hardened to 50 to 130 deg.C at >=100 deg.C/min cooling rate, is held to 50 to 130 deg.C for 1 to 48hr as it is and is thereafter subjected to low temp. heating treatment at 140 to 180 deg.C for 3 to 10min.

Description

[Detailed description of the invention]

[00011

[Industrial Application Field] The present invention relates to a method for manufacturing an aluminum alloy plate with high strength and excellent bake hardenability. The present invention relates to a method for producing an aluminum alloy plate with excellent bake hardenability by heating. [0002] [Prior Art] Aluminum alloy sheets conventionally used for automobile parts, home appliance parts, machine parts, building materials, etc.
Forming processes such as pressing and bending are performed, and in the subsequent painting process, heating (baking) is performed after painting to maintain adhesion and strength of the painted film, and this heating is also used. Efforts have been made to improve the strength of aluminum alloy plates. [0003N or higher aluminum alloy plate should ideally be a material that has low strength and is easy to form during forming, and whose strength is significantly improved by heating the baking coating after forming. and mainly Al-Mg-
Si-based material is used. [0004]

[Problems to be Solved by the Invention] However, in the manufacturing method of Al-Mg-Si aluminum alloy sheets conventionally used for this type of application, emphasis is placed on formability, and if the strength is reduced, The strength of the material is also low, and it deforms even when a slight external force is applied, so the material is not strong enough. [0005] - On the other hand, further weight reduction of automobile parts is being promoted in accordance with regulations for low fuel consumption of automobiles. As a result, there is a tendency for aluminum alloy plates to be made thinner, but with conventional manufacturing methods, thinning has been difficult due to the low strength of the material. [00061Furthermore, the baking conditions for baking coatings have shifted to lower temperatures due to improvements in energy conservation and productivity, as well as the increased use of resin and other parts that do not want to be exposed to high temperatures, coupled with advances in paints. There is. However, the conventional Al-Mg-S
The method for producing i-series aluminum alloy sheets could hardly improve bake hardenability at low temperatures. [0007] The present invention was made in order to solve the problems of the above-mentioned conventional technology, and includes high strength and production of materials that can be made thinner, and bake hardening that is excellent even in post-painting heat treatment with low baking temperatures. The object of the present invention is to provide a method for manufacturing an aluminum alloy plate having properties. [0008]

[Means for Solving the Problems] In order to achieve the above object, the present inventor first discovered that in the conventional manufacturing method of Al-Mg-Si aluminum alloy plates, the strength of the material was insufficient, and furthermore, We investigated the cause of low hardenability. [0009] The conventional manufacturing method involves cooling to room temperature and quenching after solution treatment as a final heat treatment. However, the bake hardenability of the Al-Mg-8i alloy plate manufactured by this method deteriorates several hours after quenching, and although the strength becomes slightly higher than immediately after quenching, it is difficult to thin the material. Hardly enough. [00101 Therefore, the inventor of the present invention conducted extensive research to find a manufacturing method that would allow the material strength to be sufficiently high even when the wall thickness was made thinner, and also provide sufficient bake hardenability at a low baking temperature.As a result, the inventors adjusted the chemical composition. At the same time, we have discovered a method that can significantly improve the strength and bake hardenability of the material by controlling the heat treatment conditions after solution heating and then performing low-temperature heat treatment. [0011] That is, the present invention provides Mg: 0.3 to 1.
AI-Mg- containing 5% and Si:O06~2.0%
For the 8i alloy, after homogenization treatment, hot rolling is performed, and then cold rolling is performed to obtain the desired thickness, and after solution heating, the cooling rate is 100 ° C / min or more to 50 ~
After being heat treated to a temperature of 130℃, it is left as is for 5 minutes.
Aluminum with high strength and excellent bake hardenability, characterized by holding at a temperature of 0 to 130°C for 1 to 48 hours, and then performing low-temperature heat treatment in a temperature range of 140 to 180°C for 3 to 10 minutes. The gist is the manufacturing method of alloy plates. The present invention will be explained in more detail below. [0012]

[Operation] First, the reasons for limiting the chemical components in the present invention will be explained. Mg: Mg is an element that imparts strength in cooperation with Si, but if the Mg content is less than 0.3%, the strength after heat treatment after painting will be low;
If it exceeds 0%, elongation will be low and toughness will be poor. Therefore, the Mg content is in the range of 0.3 to 1.0%. [0013] Si: Si is an element that works together with Mg to impart strength. However, if the Si content is less than 0.6%, the strength after the post-coating heat treatment will decrease, while if it exceeds 2.0%, the elongation will be low and the toughness will be poor. Therefore, the Si content is in the range of 0.6 to 2.0%. It goes without saying that other alloying elements and impurities are permissible as long as they do not impair the effects of the present invention. [00141 Next, the conditions of the manufacturing method of the present invention will be explained. The Al-Mg-5i-based aluminum alloy having the above chemical components is melted and cast by a conventional method, subjected to a homogenization treatment, and subjected to hot rolling and cold rolling (including intermediate annealing in some cases). After cold rolling, solution treatment is applied. The conditions up to this solution treatment are not particularly limited. [0015] The present invention controls the heat treatment conditions after solution heating, that is, the cooling rate during quenching, the quenching temperature, and the holding time at that temperature. and control time. [0016] First, regarding the quenching temperature (that is, the quenching end temperature) and the temperature maintained after quenching, if it is less than 50°C, there is little effect on improving the strength after baking the paint, and if it exceeds 130°C, the forming It is undesirable because it reduces the
The quenching temperature is in the range of 50 to 130°C. Furthermore, the cooling rate when quenching to this quenching temperature is 100°C/mi.
If it is less than n, the strength after quenching will be extremely low and the bake hardenability will also be extremely poor, which is not preferred. Therefore, 100
The cooling rate is set to be less than ℃/min. [00171] If the holding time after firing is less than 1 hour, the effect of improving the strength will be small, and if it exceeds 48 hours, the moldability will deteriorate, which is not preferable. Therefore, the quenching temperature is 5
The temperature is maintained at a temperature of 50 to 130°C for up to 48 hours. [0018] After quenching, a low temperature heat treatment is subsequently performed. There is no limitation on the period from after quenching to when heat treatment is performed. However, when the heating temperature is less than 140°C, no improvement in material strength is observed even if heated for 10 minutes or more, and when the heating temperature exceeds 180°C, the formability decreases significantly even when heated for less than 3 minutes, and bake hardening occurs. Sexuality does not improve. Therefore, the low temperature heat treatment is performed at a temperature of 140 to 180°C for 3 to 10 minutes. Incidentally, the coating baking process can be carried out at a low temperature such as 170° C. or lower. Next, examples of the present invention will be shown. [0019]

【Example]】

[Table 1] An aluminum alloy having the chemical composition shown in the table was melted and cast using a conventional method, and the resulting ingot was homogenized at 540°C for 4 hours, followed by hot rolling and cold rolling. A plate with a thickness of 1 mm was obtained. [00201 This plate was heated to a solution temperature of 530°C, held for 40 seconds, quenched to a temperature of 50-0°C, and kept at a temperature of 60°C for 24 hours. Thereafter, a low temperature heat treatment was performed at 170° C. for 5 minutes. [00211 Material properties and baking of the obtained material (17
Baking hardenability (yield strength) after 0°C x 20 minutes)

[Table 2] shows. As is clear from this, invention example No. 1=
No. 07 is compared to Comparative Examples No. 8 to No. 11,
It can be seen that this is an excellent material with significantly improved raw material strength (tensile strength and yield strength) and bake hardenability. on the other hand,
In the comparative examples, both material strength and bake hardenability were not improved. [0022]

[Example 2] Aluminum alloy with NO65 shown in Table 1 of Example 1 (within the scope of the present invention) was melted and cast by a conventional method, and the resulting ingot was homogenized at 540°C for 4 hours. After applying the coating, hot rolling and cold rolling were performed to obtain a plate having a thickness of 1.0 mm. [0023] The plate was heated to a solution temperature of 530°C and held for 40 seconds, then held at a temperature of 20 to 150°C for 0.5 to 6.0 hours at a cooling rate of 500°C/mjn, and then A low temperature heat treatment was performed at 170° C. for 5 minutes. [00241 Characteristics and baking (170℃) of the obtained material
x 20 minutes) after baking hardenability (post-baking yield strength)

It is shown in [Table 3]. From Table 3, invention examples No. 12 to No. 1
It can be seen that Sample No. 4 is a material with high strength and excellent bake hardenability compared to Comparative Examples No. 15 to No. 16. [0025]

[Example 3] Aluminum alloy No. 5 shown in Table 1 of Example 1 (within the scope of the present invention) was melted and cast by a conventional method, and the obtained ingot was homogenized at 540°C for 4 hours. After that, hot rolling and cold rolling were performed to obtain a 1N thick plate. [0026N] This plate was heated to a solution temperature of 530°C and held for 40 seconds, then quenched at a cooling rate of 500°C/min to a temperature of 50°C, held as it was for 6 hours, and then heated to a solution temperature of 130°C.
Low-temperature heat treatment was performed in a temperature range of ~190°C for 1 to 60 minutes. Material properties and baking (170℃) of the obtained material
x 20 minutes) after baking hardenability (post-baking yield strength)

[Table 4] shows. From the same table, invention examples No. 17 to No. 1
It can be seen that Sample No. 9 has higher material strength than Comparative Examples No. 20 to No. 21, and has excellent bake hardenability at a low baking temperature of 170°C. [0027]

[Effects of the Invention] As detailed above, according to the present invention,
Mg and Si of Al-Mg-Si aluminum alloy plate
By adjusting the content, controlling the solution treatment conditions, and performing low temperature heat treatment under specific conditions after the solution treatment,
It is possible to obtain an aluminum alloy plate which has extremely high material strength and also has excellent strength and improved bake hardenability even when baked at low temperatures. Therefore, it has extremely great practical effects as a method of reducing material costs by making the aluminum alloy thinner, and furthermore, as an industrial and economical manufacturing method.

Claims (1)

[Claims] Claim 1: Mg: 0.3 to 0.3% by weight (the same applies hereinafter)
Al-Mg containing 1.5% and Si: 0.6-2.0%
- After homogenizing the Si-based alloy, hot rolling is performed, and then cold rolling is performed to obtain the desired thickness,
After solution heating, the cooling rate is 50°C/min or more.
Heat treatment is performed to harden to a temperature of ~130°C, held at a temperature of 50 to 130°C for 1 to 48 hours, and then low-temperature heat treatment is performed in a temperature range of 140 to 180°C for 3 to 10 minutes. A manufacturing method for aluminum alloy sheets with high strength and excellent bake hardenability.