7000 series aluminum alloy member excellent in stress corrosion cracking resistance and method for manufacturing the same

Abstract

An aluminum alloy member resistant to cracking and having high strengths and excellent stress corrosion cracking resistance is manufactured by expanding a 7000 series aluminum alloy hollow extrusion material at a rate of 5% or more. Specifically, a 7000 series aluminum alloy hollow extrusion material containing Zn of 3.0-9.5%, Mg of 0.4-2.5%, Cu of 0.05-2.0%, and Ti of 0.005-0.2%, in mass percent, and prepared through press quenching is subjected to a reversion treatment, to pipe expansion within 72 hours after the reversion treatment, and to temper aging. The reversion treatment includes heating at a temperature rise rate of 0.4 DEG C / second or more, holding in a temperature range of 200-550 DEG C for longer than 0 second, and cooling at a rate of 0.5 DEG C / second or more. The ratio Y ([sigma]rs / [sigma]0.2) of the tensile residual stress [sigma]rs to the 0.2% yield stress [sigma]0.2 after temper aging and the total content X of Mg and Zn satisfy Expression (1): Y<=-0.1X+1.4 (1).

Description

technical field [0001] The present invention relates to a 7000-series aluminum alloy member and a manufacturing method thereof, in which a high-strength 7000-series aluminum alloy extruded hollow section is expanded to form a member, and a method for manufacturing the same, particularly to a 7000-series aluminum alloy member excellent in stress corrosion cracking resistance and methods of manufacture thereof. Background technique [0002] Patent Documents 1 and 2 describe pipe expansion of a 6000-series aluminum alloy hollow extruded material by electromagnetic forming, and Patent Documents 3 and 4 describe a 6000-series aluminum alloy having excellent pipe expandability by electromagnetic forming As the hollow extruded material, Patent Document 5 describes a 6000-series aluminum alloy hollow extruded material excellent in pipe expandability by hydroforming. The 6000-series aluminum alloy hollow extruded materials described in Patent Documents 1 to 5 are all pipe-expanded i...

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Problems solved by technology

[0016] Indeed, if this regression treatment is applied to T1 quenched and tempered 7000 series aluminum alloy extruded materials, the strength of the extruded materials will decrease, and generally speaking, the formability will improve

However, when a 7000-series aluminum alloy hollow extruded material is expanded by electromagnetic forming, the effect of preventing cracks cannot be sufficiently obtained at a practical level of expansion rate.

In addition, even if cracks do not occur, high tensile residual stress is imparted to the processed part after pipe expansion, and there is still a problem that the stress corrosion cracking resistance decreases.

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