JPH07180009A - Production of high strength aluminum alloy sheet for forming - Google Patents

Abstract

PURPOSE:To produce an Al alloy sheet excellent in strength and press formability by subjecting the ingot of an Al-Mg alloy having a specified compsn. to homogenizing treatment, thereafter regulating the reduction of the sheet thickness per pass in rolling in a specified sheet thickness range and executing hot rolling. CONSTITUTION:The ingot of an Al-Mg alloy contg;, by weight, 4.5 to 8% Mg, 0.05 to 0.4% Cu, 0.005 to 0.10% Ti and 0.0001 to 0.01% Be or furthermore contg., for refining recrystallized grains and improving its strength, one or more kinds among 0.1 to 0.6% Zn, 0.05 to O.20% Mn, 0.05 to 0.15% Cr and 0.05 to 0.15% Zr, and the balance Al is subjected to homogenizing treatment by single or two stage heating at 420 to 510 deg.C for 2 to 24 hr to homogenize Mg, Cu or the like segregated in the ingot. Next, hot rolling is started at 450 to 510 deg.C, and a light draft of <=15mm reduction of the sheet thickness per pass is applied in the case of 50 to 150 mm thickness at the inlet of a milling roll of the Al allay ingot at the time of rolling. Thus, the Al alloy sheet with about 5mm thickness free from defects such as ear cracking and excellent in workability and strength can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-strength aluminum alloy sheet for forming, particularly a hot rolling method, which has high strength and excellent press formability and is suitable for automobile body panel materials and the like. is there.

[0002]

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been used as sheet materials for automobile body panels, but lightweight Al alloy sheets have been used as needed to reduce the weight of vehicle bodies to improve fuel efficiency. is there. This car body panel plate is
Generally, it is required to have high strength and excellent formability because it is obtained by hot rolling or cold rolling an ingot and press-molded into a desired shape. Therefore, even as an Al alloy used for the above plate material, an Al-high Mg-based alloy (for example, Mg: 4.0 to 5.0) that satisfies these characteristics.
5182 alloy containing wt% and also Mg: 5.8
AA-X5085 alloy containing ˜6.8 wt% has been put to practical use.

[0003]

[Problems to be Solved by the Invention] However, Al-M
When the amount of Mg in the g-based alloy increases, the hot workability deteriorates,
In particular, when it exceeds 4.5%, there is a problem that the yield becomes poor because the ear cracks, the surface cracks, the crocodile cracks, and the two plates are generated during the hot rolling. For this, a method of reducing the rolling reduction during hot working can be considered. For example, it is intended to prevent the occurrence of cracks by reducing the reduction which is usually performed by reducing the plate thickness by about 30 mm per pass by reducing the thickness by about 15 mm. However, if the rolling process, which was normally performed in 20 passes with a reduction in plate thickness of 30 mm, is performed with the above reduction in plate thickness, it takes 40 passes or more to reach the same final rolling thickness, and therefore work efficiency is improved. Is significantly reduced. The present invention has been made as a result of studying the above-mentioned problems. It does not cause fatal cracks during hot working, has a good yield, and minimizes the decrease in work efficiency as much as possible. The present invention provides a manufacturing method capable of obtaining

[0004]

[Means for Solving the Problem] Therefore, the present inventors have
From the above viewpoints, by repeatedly studying a method for producing a high-strength Al alloy sheet for forming, particularly a hot rolling method, and by regulating the reduction in sheet thickness per pass of rolling in a specific sheet thickness range, , Found that the occurrence of fatal cracks can be suppressed.

The method for producing a high-strength aluminum alloy sheet for forming according to the present invention is based on this finding. Specifically, in terms of weight%, Mg: 4.5-8%, C
u: 0.05 to 0.4%, Ti: 0.005% to 0.1
Al containing 0% and Be: 0.0001 to 0.01%
The alloy ingot is subjected to a one-step or two-step homogenization treatment at 420 to 510 ° C. for 2 to 24 hours, and then hot working is started at a temperature of 450 to 510 ° C. In this rolling, the inlet plate thickness is 1
When the thickness is 50 mm or less and 50 mm or more, the reduction in plate thickness per pass is 15 mm or less.

In addition, in the second invention, in addition to the components of the Al alloy ingot, Zn: 0.1 to 0.6%, Mn:
0.05 to 0.20%, Cr: 0.05 to 0.15%,
Zr: 0.05 to 0.15% at least one kind is contained.

In the hot rolling of the present invention, when the inlet plate thickness exceeds 150 mm or less than 50 mm, the above regulation is not necessary and the rolling can be efficiently performed with a large reduction rate. For example, the entrance plate thickness is 150
At the stage of exceeding mm, it is desirable to reduce the plate thickness by 20 mm or more excluding the initial rolling. If it is less than 50 mm, it is desirable to carry out rolling at a rolling reduction of 30% or more.
By these rolling, a hot rolled plate of about 3 to 10 mm is finally obtained. After that, cold rolling and forming are performed by a conventional method.

[0008]

In other words, according to the present invention, an Al alloy sheet material having high strength and excellent formability can be satisfactorily hot-rolled without causing cracking, and the work efficiency at that time is reduced. Can be kept to a minimum. Next, the reasons for limiting each condition in the present invention will be described. First, the reasons for limiting the alloy components of the Al alloy ingot used in the present invention will be described.

Mg: 4.5-8% Mg is a basic component of the present alloy, and the higher the amount added, the higher the strength and ductility. In order to obtain the effect sufficiently, it is necessary to add 4.5% or more. But 8
If it exceeds%, the hot workability is remarkably deteriorated, and the rolling process becomes impossible even by the method of the present invention. So M
The g content was set to 4.5-8%. Cu: 0.05 to 0.4% Cu is an element that improves the strength, and particularly suppresses the decrease in strength when coating baking is performed after the molding process. However, if less than 0.05%, the effect is small, while 0.4
If it exceeds 0%, the cold workability is deteriorated and the corrosion resistance is also deteriorated. Therefore, the Cu content is set to 0.05 to 0.4%.

Ti: 0.005% to 0.10% Ti is effective in preventing casting cracks and refining the crystal grains of the ingot, but if it is less than 0.005%, the effect is insufficient. , 0.10%, a huge intermetallic compound is formed, and the ductility decreases. Therefore, the Ti content is 0.005
% To 0.10%. Be: 0.0001 to 0.01% Be has an effect of improving castability in an alloy having a high Mg content, but if it is less than 0.0001%, the effect is insufficient and exceeds 0.01%. Since its toxicity becomes a problem, its content was set to 0.0001 to 0.01%.

Zn: 0.1 to 0.6% Mn; 0.05 to 0.20% Cr: 0.05 to 0.15% Zr: 0.05 to 0.15% These elements are 1 if necessary. Including more than one species,
Although it is effective in making the recrystallized grains finer and improving the strength, if both are less than the lower limit, the effect is small, while if it exceeds the upper limit, the ductility decreases, so the respective ranges were set to the above.

Next, the reasons for limiting the manufacturing conditions will be described. Homogenization treatment: 420 to 510 ° C. for 2 to 24 hours This treatment has an effect of homogenizing Mg and Cu segregated during casting. For this purpose, 2 ~ 24 at 420 ~ 510 ℃
Heat and hold for a time, preferably 2 to 16 hours. If the heating temperature is less than 420 ° C, the effect of homogenization is small, and 510
If the temperature exceeds ℃, there is a possibility of coarsening of crystal grains or eutectic melting of the segregated phase. If the heating time is less than 2 hours, the homogenizing effect is small, and if it exceeds 24 hours, the effect is saturated. Therefore, the heating temperature and time were limited to the above. When the amount of Mg is high, the β phase (Mg5Al
Since the eutectic compound containing 8) has a melting point of about 450 ° C., the first-stage homogenization treatment is preferably performed at 420 to less than 450 ° C., and subsequently the temperature is raised to 450 ° C. or higher to obtain a second-stage homogenization treatment. Process.

Hot rolling start temperature: 450 to 510 ° C. Normally, the ingot is once cooled to room temperature after the above homogenization treatment, and then reheated before hot rolling. At the time of cooling after this homogenization treatment, the Al-Cu-Mg-based compound precipitates at the grain boundaries, which causes hot rolling cracks. In order to re-dissolve this compound, it is reheated to 450 ° C. or higher and hot rolling is started. Further, if the rolling temperature exceeds 510 ° C., eutectic melting occurs and cracking occurs, so the range is limited to the above range.

Hot rolling light reduction When the ingot of the present alloy, which has a plate thickness of about several hundred mm, is rolled under a normal pressure to a plate thickness of 150 mm, the degree of deformation of crystal grains is larger at the plate surface portion than in the inside. A large amount of β-phase is precipitated, and the hardness is increased, resulting in remarkable non-uniformity. That is, the strength of the inside is relatively weakened as compared with the surface portion due to rolling, and when a strong reduction is applied in this state, due to the tensile stress in the plate thickness direction that acts on the rolling exit side,
Cracks (crocodile cracks) may occur inside the weak interior, and the cracks may propagate to form a double plate. On the other hand, when the plate thickness is less than 50 mm, the reduction is effective even inside the plate and the above-mentioned structure,
Since the non-uniformity of strength and the like is eliminated, cracking does not occur even if strong reduction is applied at a high reduction rate. From the above, in the present invention, rolling with a plate thickness of 150 mm or less and 50 mm or more is performed under a light pressure (a reduction in plate thickness per pass of 15 mm or less).

[0015]

EXAMPLES The present invention will be described below with reference to examples. No. shown in Table 1 1 to 3 (invention example) and No. 4,5
Alloy ingot having the composition of (Comparative Example) (thickness 508 mm, width 15
75 mm) by an ordinary method, the ingot is subjected to homogenization treatment and hot rolling under the conditions shown in Table 2, and finally 5 m
A hot rolled sheet having a thickness of m was obtained. The results are also shown in Table 2. As is clear from Table 2, the plate material according to the method of the present invention could be satisfactorily rolled without cracking during hot rolling. On the other hand, according to the comparative method, cracking occurred during hot rolling and it could not be used.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

As described above, according to the method for producing a high-strength aluminum alloy sheet for forming according to the present invention, Mg: 4.5-8%, Cu: 0.05-0. Four
%, Ti: 0.005% to 0.10%, Be: 0.00
01-0.01%, and optionally Z
n: 0.1 to 0.6%, Mn: 0.05 to 0.20%,
Cr: 0.05 to 0.15%, Zr: 0.05 to 0.1
The Al alloy ingot containing 5% of one or more of
After performing a one-step or two-step homogenization treatment at 10 ° C for 2 to 24 hours, start hot working at a temperature of 450 to 510 ° C,
In this rolling, the inlet plate thickness is 150 mm or less, and 5
When the thickness is 0 mm or more, the reduction in plate thickness per pass is set to 15 mm or less, so that the aluminum alloy ingot can be hot-rolled without causing cracking, and the aluminum alloy plate has high strength and excellent formability. Can be manufactured with good yield and efficiency.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Kawamata 85 Hiramatsu, Susono City, Shizuoka Prefecture Mitsubishi Aluminum Co., Ltd.

Claims (2)

[Claims] 1. By weight percent, Mg: 4.5-8%, Cu:
0.05 to 0.4%, Ti: 0.005% to 0.10.
%, Be: 0.0001-0.01% containing Al alloy ingot, after performing a one-step or two-step homogenization treatment at 420-510C for 2-24 hours, at a temperature of 450-510C. Hot working was started, and at the time of this rolling, the inlet plate thickness was 15
A method for manufacturing a high-strength aluminum alloy sheet for forming, characterized in that the thickness reduction per pass is 0 mm or less when the thickness is 0 mm or less and 50 mm or more. 2. In addition to the components of the Al alloy ingot according to claim 1, Zn: 0.1-0.6%, Mn: 0.05-
0.20%, Cr: 0.05 to 0.15%, Zr: 0.
A method for producing a high-strength aluminum alloy sheet for forming, characterized by containing at least one of 05 to 0.15%