JPH10216806A - Method for hot-rolling al-mg base alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for hot-rolling an Al-Mg base alloy whose Mg content is high and which is suitable to automotive body panel scarcely generating cracks. SOLUTION: At the time of hot-rolling the Al-Mg base alloy consisting of 4.0-7.0wt.% Mg and the balance Al with inevitable impurities, by specifying the upper limit of draft of one pass in early stage of the hot rolling at 15/X% when the Mg content is X% or, moreover in the case of containing Y% Cu, at (15-5Y)/X% and, by executing hot rolling until the total draft becomes >=10% and, on and after that, executing ordinary hot rolling, the generation of cracks is remarkably suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hot rolling an Al-Mg alloy having a high Mg content.

[0002]

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been widely used as materials for forming body panels for automobiles and the like. However, in recent years, there has been an increasing demand for reducing the weight of a vehicle body in order to improve the fuel efficiency of an automobile, and aluminum alloy plates have been used for automobile body panels and the like as a means of reducing the weight. Aluminum alloys used for such applications require almost the same strength and formability as the cold rolled steel sheets used so far. As an aluminum alloy having such strength and formability, 4% or more Mg
And a 6000 series alloy capable of precipitation strengthening at the time of paint baking. At present, as the aluminum alloy used for such a body panel of an automobile, a 5000 series alloy, in particular, an alloy having a high Mg content is mainly used.

[0003]

The production of a 5000-series aluminum alloy sheet consists of many steps, but the hot rolling step destroys the solidified structure of the slab cast after the preparation of the components and reduces the desired sheet thickness. It is one of the important steps to get. A 5000-series alloy having a high Mg content is liable to generate cracks and crocodile cracks at the slab end and surface due to hot embrittlement during the hot rolling, thereby causing a problem of a significant decrease in yield. . In particular, when used for an outer panel, a high yield strength is required from the viewpoint of dent resistance. For this reason, 0.05 to 4% by weight of Cu may be added. It becomes more susceptible to cracking during cold rolling.

Conventionally, in order to avoid this problem, as disclosed in Japanese Patent Publication No. 53-6086, 426
In order to perform homogenizing annealing at a high temperature of not less than 4 ° C. for a long time of 4 to 48 hours and to remove a high-temperature brittle zone,
A method of performing hot rolling at ４０４404 ° C. has been performed. In an Al-Mg-based alloy having a high Mg content, generally, in such a temperature range, deformation resistance is large, and it is difficult not only to perform hot rolling with high productivity at a large rolling reduction, but also to generate cracks. It is difficult to say that it has been sufficiently reduced. The present invention solves the problem of exhibiting such brittleness during hot working, and solves the problem of Al having a high Mg content.
An object of the present invention is to provide a method of hot-rolling an Mg-based alloy with almost no cracks by defining the rolling reduction at the beginning of hot rolling.

[0005]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies on the hot workability of an Al-Mg alloy having a high Mg content. as a result,
In the early stage of hot rolling, if strain is introduced without generating cracks by light reduction and the solidification structure is changed to a recrystallized structure, hot brittleness can be suppressed, and therefore, during the subsequent hot rolling It has been found that the occurrence of cracks can be greatly reduced. And the amount of Mg added,
In the case where Cu is also added, rolling is performed until the total rolling reduction becomes 10% or more while defining the upper limit of the rolling reduction in one pass in the initial stage of hot rolling according to the amounts of Mg and Cu added.
It has been found that it is possible to hot-roll an Al-Mg-based alloy having a high g content with almost no cracks.

The present invention has been made based on the above-mentioned findings, and is intended to heat an aluminum alloy containing 4.0 to 7.0% of Mg by weight and the balance of Al and inevitable impurities. In the hot rolling, when the Mg content is X%, from the beginning of the hot rolling, hot rolling in which the rolling reduction in one pass is 15 / X% or less is performed until the total rolling reduction becomes 10% or more. Hot-rolling method of an Al-Mg-based alloy having a high Mg content, wherein Mg: 3.0-7.0%
In the case where 0.05 to 1.0% of Cu is simultaneously contained, when the Mg content is X% and the Cu content is Y%, the rolling reduction of one pass from the initial stage of the hot rolling is (15). -5Y) /
A hot rolling method for an Al-Mg-based alloy, wherein hot rolling of X% or less is performed until the total draft becomes 10% or more.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, the reasons for limiting the component composition in the present invention will be described. Mg: Mg is an alloy element that can increase strength without impairing formability as represented by elongation when added at a certain amount or more. % Or more is required. Also, if added in excess of 7.0%, cracks may occur even if hot rolling is performed under the conditions of the present invention. Therefore, the addition amount of Mg is specified within the range of 4.0 to 7.0%. However, when Cu is added at the same time, the hot workability is lower than when only Mg is contained. Therefore, the content is set to 3.0 to 7.0%.

Cu: Cu is an element that contributes to an increase in yield strength by forming fine precipitates at the time of coating baking after press forming, and 0.05% by weight in order to fully exert its effect. The above addition is required. 1.0%
If added in excess of the above, cracks may occur even if hot rolling is performed under the conditions of the present invention, and the corrosion resistance will decrease. Therefore, the addition amount of Cu is 0.05 to
It is specified within the range of 1.0%. The aluminum alloy of the present invention may contain, in addition to the above-mentioned alloying elements, F for the purpose of refining crystal grains or preventing oxidation, or as an unavoidable impurity.
e and Si are each 0.5% or less, and Mn is 0.5% or less at the maximum.
%, Each element of Cr, Zn, Ti, and B may be contained at 0.3% or less and Be may be contained at 0.1% or less. However, even if they are contained, the effect of the present invention is maintained.

Next, the reason for defining the hot rolling method of the present invention will be described. In the present invention, when the Mg content is X%, until the total rolling reduction at the initial stage of hot rolling becomes 10% or more,
Hot rolling is performed in which the rolling reduction in one pass is 15 / X% or less, and thereafter normal hot rolling is performed. Further, when the Mg content is X
%, And the Cu content is Y%, the rolling reduction in one pass is (15) until the total rolling reduction at the beginning of hot rolling becomes 10% or more.
Hot rolling of -5Y) / X% or less is performed, and thereafter normal hot rolling is performed. This is because, in the early stage of hot rolling, when strain is introduced under light pressure to the extent that cracking does not occur, the solidification structure changes to a recrystallized structure, hot brittleness is suppressed, and cracking during subsequent hot rolling is performed. This can greatly reduce the occurrence of the problem.

The upper limit of the rolling reduction in one pass is defined by the Mg content and the Cu content. When the amount of these alloying elements increases, the alloy becomes more susceptible to hot embrittlement, and cracks occur when a large reduction is applied. This is because Although the lower limit of the rolling reduction in one pass is not particularly specified, the smaller the rolling reduction is, the more preferable from the viewpoint of preventing the occurrence of cracks.
An extremely small size not only greatly impairs productivity, but also results in insufficient introduction of a strain that is a driving force for recrystallization.

The reason that the above-mentioned light reduction is performed until the total reduction becomes 10% or more is to provide a driving force necessary for recrystallization to occur during hot rolling. , The effect is not sufficiently obtained. If this condition is satisfied, a hot-rolled sheet having a desired thickness can be obtained without significant cracking during hot rolling. In particular, for suppressing the occurrence of cracks at the end of the slab, it is effective to use an edger or the like to reduce the slab end face under the above-described conditions. The temperature and strain rate of hot rolling are within normal ranges.

Prior to hot rolling, homogenizing annealing is performed to reduce solidification segregation of the slab, and when Cu is contained, an Al-Mg-Cu intermetallic compound is dissolved again. Is preferred. However, the use of the hot rolling method of the present invention can substantially prevent the occurrence of cracks during hot rolling even with homogenization annealing for a shorter time than is generally performed. Aluminum alloy hot-rolled under the conditions of the present invention, as it is as a hot-rolled plate, or cold-rolled,
After a process such as recrystallization annealing, it is used as a coil or sheet for an automobile body panel.

[0013]

The present invention will be described below with reference to examples. A 500 mm-thick aluminum alloy slab having the composition shown in Table 1 was heated at 470 ° C. for 3 hours, and then hot-rolled to a total draft of about 10% by the pass schedule shown in Table 2, and thereafter the strain rate was calculated. Normal hot rolling was performed at about 1 to 100 / s to a thickness of 5 mm. The resulting hot-rolled sheet was visually observed to investigate the “situation of cracking”. ○ indicates that hot rolling could be performed to a thickness of 5 mm without cracking, and Δ indicates that hot rolling could be performed to a thickness of 5 mm despite the occurrence of small cracks that would not be a problem with some care. X indicates that significant cracking occurred such that rolling could not be continued during hot rolling.

[0014]

[Table 1]

[0015]

[Table 2]

If hot rolling is carried out by the method of the present invention, there is no problem at all as in Examples 2, 4, 7, 10, 12, and 15 of Table 2 or relatively good as in Example 5 of the present invention. Hot rolling can be performed in a suitable state. In the case of alloys with a low Mg content, as shown in Comparative Example 1, hot rolling can be easily performed even if the conditions of the present invention are deviated, but sufficient strength cannot be obtained. When the content of Mg is large and Cu is also contained, the conditions of the present invention are deviated from Comparative Examples 8, 9, 11,
As in 13 and 14, it is extremely difficult to perform hot rolling.

[0017]

According to the present invention, a high-strength, high-formability, high-Mg-content Al-Mg-based alloy is reduced in the early stage of hot rolling by reducing the Mg content or the relationship between the Mg content and the Cu content. By defining the ratio, hot rolling can be performed with almost no cracks.

Claims (2)

[Claims] 1. When hot rolling an aluminum alloy containing 4.0 to 7.0% of Mg by weight and the balance being Al and unavoidable impurities, when the Mg content is X%, the hot rolling is performed. The rolling reduction of one pass from the beginning of cold rolling is 15 / X%
A hot rolling method for an Al-Mg-based alloy, wherein the following hot rolling is performed until the total draft becomes 10% or more. 2. Mg: 3.0 to 7.0% by weight,
When hot rolling an aluminum alloy containing 0.05 to 1.0% of Cu and the balance of Al and unavoidable impurities, when the Mg content is X% and the Cu content is Y%, From the beginning of cold rolling, the rolling reduction of one pass is (15-5
A hot rolling method for an Al-Mg based alloy, wherein hot rolling of Y) / X% or less is performed until the total draft becomes 10% or more.