Aluminum alloy sheet for structural components

Abstract

Disclosed is a 7xxx-series aluminum alloy sheet that has a specific chemical composition and is produced by a common procedure. The sheet maintains high strength via a good balance between Zn and Mg, while the Zn content is controlled. The average compositional ratio of Zn to Mg in grain-boundary precipitates is controlled in the sheet that is naturally aged after production; and the average compositional ratio of Zn to Mg in intragranular precipitates is controlled in the sheet that is further artificially aged after the natural aging. Thus, the aluminum alloy sheet is allowed to have formability, corrosion resistance, and such high strength as to be demanded of structural components.

Description

TECHNICAL FIELD[0001]The present invention relates to a high-strength aluminum alloy sheet for structural components, where the aluminum alloy sheet offers better workability and still has excellent corrosion resistance. As used herein the term “aluminum alloy sheet” refers to a rolled sheet that is obtained after subjecting a sheet produced via rolling to solution treatment and quenching and subsequently to natural aging at room temperature for 2 weeks or longer and is one before forming into a structural component and before artificial aging. Also as used herein the term “microstructure” of the sheet after natural aging at room temperature refers to the microstructure of the sheet after subjected to natural aging at room temperature for 2 weeks or longer subsequent to solution treatment and quenching.BACKGROUND ART[0002]Social requirements for reduction in automobile body weight have increased more and more in consideration typically of global environment. To meet these requiremen...

AI Technical Summary

Benefits of technology

The present invention is about a process for improving the corrosion resistance, strength, and formability of a 7xxx-series aluminum sheet. By controlling the chemical compositions of grain-boundary precipitates and intragranular precipitates in the microstructure of the sheet, the amount of Zn and Mg in the sheet is reduced while still maintaining good corrosion resistance. The reduction in Zn content in the grain-boundary precipitates allows for a higher amount of Zn solute in the matrix, which leads to better strength and formability even at lower Zn content. The reduction of Zn content in the intragranular precipitates prevents the formation of aging precipitates and maximizes the formation of natural aging precipitates, resulting in better strength and formability. The resulting aluminum sheet has good BH response and balance between strength and formability, making it suitable for structural components.

Problems solved by technology

The 6xxx-series aluminum alloy sheets, however, are far from the high strength as mentioned above, even when the chemical composition and temper (heat treatments) are controlled.

However, the 7xxx-series aluminum alloys, which are Al—Zn—Mg alloys, have poor general corrosion resistance.

These alloys may therefore possibly cause stress corrosion cracking (the stress corrosion cracking is hereinafter also referred to as “SCC”).

This reduces the features of the alloys as high-strength alloys.

However, the repeated warm rolling is performed because hot rolling and / or cold rolling according to a common procedure fails to give such a metallic texture including small angle grain boundaries in an amount of 25% or more.

Accordingly, the technique is significantly different in process (steps) from the common procedure and is not considered as a practical technique for producing a target sheet.