High-strength aluminum alloy sheet

Abstract

An Al—Mg—Si aluminum alloy sheet has a chemical composition which includes at least one element selected from the group consisting of Mn, Cr, and Zr and which meets the condition: 0.6≤([Mg]/[Si]-0.15[Mn]-0.3[Cr]-0.1[Zr]≤1.8. The aluminum alloy sheet is controlled to have a higher aspect ratio of grains, thereby has significantly higher strength after artificial aging such as paint bake (after bake hardening), and satisfactorily has strength necessary for automobile structural components, without deterioration in bendability.

Description

TECHNICAL FIELD[0001]The present invention relates to Al—Mg—Si aluminum alloy sheets. As used herein, the term “aluminum alloy sheet” refers to a rolled sheet such as a hot-rolled sheet or a cold-rolled sheet, after subjected to heat treatments such as solution treatment and quenching (temper; T4), but before forming into a structural component to be used. Hereinafter, “aluminum” is also simply referred to as “Al”.BACKGROUND ART[0002]Social demands for weight reduction of vehicles such as automobiles have become higher and higher in consideration typically of global environment. To meet these demands, aluminum alloy materials are increasingly applied as automobile materials instead of ferrous materials such as steel sheets, because the aluminum alloy materials have formability and bake hardening properties (bake hardenability) at excellent levels and have lighter weights. The “bake hardening” is hereinafter also referred to as “BH”.[0003]Representative examples of aluminum alloy she...

AI Technical Summary

Benefits of technology

[0017]In the present invention, the relationship between grain aspect ratio and bake hardenability of a 6xxx-series aluminum alloy sheet was reconsidered, on the precondition that the aluminum alloy chemical compositions and production conditions of conventional aluminum alloy sheets are not significantly changed. As a result, it was found that the 6xxx-series aluminum alloy sheet has better bake hardenability with an increasing grain aspect ratio; and that the resulting aluminum alloy sheet can have a higher 0.2% yield strength of 300 MPa or more without deterioration in bendability, even after natural aging at room temperature, where the 0.2% yield strength is determined alter 2% stretching and subsequent BH treatment at 185° C. for 20 minutes.

[0018]Control of the grain aspect ratio of such 6xxx-series aluminum alloy sheets is publicly known as described above, but the relationship between the grain aspect ratio and bake hardenability has not yet been known well.

[0019]With the present invention, a 6xxx-series aluminum alloy sheet can have significantly higher strength after artificial aging such as paint bake (alter BH) without deterioration in bendability, by a simple technique of controlling the 6xxx-series aluminum alloy sheet to have a higher grain aspect ratio. This configuration allows the 6xxx-series aluminum alloy sheet to satisfactorily have strength necessary for automobile structural components, which strength is higher as compared with the strength necessary for automotive body panels.

Problems solved by technology

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

However, it is not so easy to achieve such higher strength of conventional 6xxx-series aluminum alloy sheets without significantly changing chemical compositions and production conditions and without deterioration in properties such as bendability.