Aluminum alloy sheet for structural material

Abstract

Disclosed is a 7xxx-series aluminum alloy sheet having a specific chemical composition and produced by a common procedure. The aluminum alloy sheet has a good balance between a Zn content and a Mg content while having a lower Zn content so as to have a strength retained at high level. The aluminum alloy sheet has a microstructure having a specific endothermic peak temperature and a specific maximum height of exothermic peak(s) in a differential scanning calorimetric curve, where the curve is plotted after natural aging of the produced sheet. The aluminum alloy sheet can thereby have a high strength, satisfactory formability, and good corrosion resistance which are required for structural components.

Description

TECHNICAL FIELD[0001]The present invention relates to an aluminum alloy sheet for structural components (structural materials), which aluminum alloy sheet has better workability, excellent corrosion resistance, and a high strength. As used herein the term “aluminum alloy sheet” refers to a rolled sheet that is prepared by producing a rolled sheet by rolling, subjecting the rolled sheet sequentially to solution treatment and quenching, thereafter subjecting the rolled sheet to natural aging for two weeks or longer and is before forming into a structural component and before artificial aging treatment.BACKGROUND ART[0002]A social demand for weight reduction of automobile bodies has been increasingly made in consideration typically of the global environment. To meet the demand, aluminum alloy materials are applied to some of automobile body parts so as to replace part of iron / steel materials such as steel sheets. The target automobile body parts are exemplified by panels such as outer ...

AI Technical Summary

Benefits of technology

[0023]As used herein the term “aluminum alloy sheet” refers to a 7xxx-series aluminum alloy sheet that is a sheet produced by rolling and is produced by a common procedure including soaking an ingot, subjecting the soaked ingot sequentially to hot rolling and cold rolling to give a cold-rolled sheet, and further subjecting the cold-rolled sheet to a temper refining treatment (T4 in a temper designation) such as solution treatment and quenching. In other words, the term “aluminum alloy sheet” does not include sheets produced by such a special rolling method as to subjecting an ingot to forging and to repeat warm rolling operations many times, as in the techniques disclosed in PTL 5 and PTL 6.

[0024]As the aluminum alloy sheet according to the present invention, a 7xxx-series aluminum alloy sheet produced in the above manner and undergoing natural aging is controlled to have a specific microstructure. In addition, the aluminum alloy sheet is, as a material aluminum alloy sheet, processed or formed into an intended structural component. Accordingly, the term “aluminum alloy sheet” as used herein refers to a sheet that is produced in the above manner and undergoes natural aging (standing at room temperature) after production, but is before being formed into an intended structural component and before being subjected to artificial aging treatment.

[0025]The present inventors prepared a 7xxx-series aluminum alloy sheet having a chemical composition with a lower Zn content for better corrosion resistance and a higher Mg content for a certain strength and analyzed the microstructure of the 7xxx-series aluminum alloy sheet after natural aging based on a differential scanning calorimetric curve. As a result, the present inventors have found that dusters formed by natural aging in the 7xxx-series aluminum alloy sheet having the chemical composition have a different chemical composition and act in a different manner from a 7xxx-series aluminum alloy sheet having a high Zn content.

[0026]Specifically, the present inve...

Problems solved by technology

However, these automobile structural components require higher strength as compared with the automobile panels.

The 6xxx-series aluminum alloy sheets, however, are not anywhere near the high strength even when their chemical compositions are controlled and even when they are produced under controlled temper refining (e.g., solution treatment and quenching, and further artificial aging treatment) conditions.

However, the material 7xxx-series aluminum alloys as being Al—Zn—Mg alloys, have inferior general corrosion resistance.

In addition, these alloys achieve a high strength by allowing Zn—Mg precipitates MgZn2 to be distributed in a high density and may thereby cause stress corrosion cracking (hereinafter also simply referre...