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

The present invention relates to a method for producing a 7xxx-series aluminum alloy sheet with improved corrosion resistance and better balance between strength and ductility. The alloy sheet has a specific microstructure controlled through a natural aging process after production. The method involves soaking an ingot, rolling the ingot, and subjecting it to a temper refining treatment. The resulting aluminum alloy sheet has a unique microstructure and improved properties, including better corrosion resistance, strength, and formability. The invention also provides a control method to induce the formation of dusters in the alloy sheet, which contribute to its overall performance. The microstructure of the alloy sheet can be indirectly specified and controlled based on the analysis of a differential scanning calorimetric curve.

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 referred to as “SCC”).

The literature, however, does not disclose the SCC resistance performance at all and fails to describe corrosion resistance data in working examples.

This is because such large angle grain boundaries cause the potential difference between the grain boundary and the grain inside, where the potential difference in turn causes SCC resistance deterioration.

However, the repeated warm rolling operations are performed because hot rolling and cold rolling by a common procedure fail to give a metallic texture including small angle grain boundaries in an amount of 25% or more.

The techniques therefore significantly differ in process from the common procedure and are not considered to be practical techniques to produce sheets.