7XXX SERIES ALUMINUM ALLOY MEMBER EXCELLENT IN STRESS CORROSION CRACKING RESISTANCE AND METHOD FOR MANUFACTURING THE SAME

摘要

An aluminum alloy member resistant to cracking and having high strengths and excellent stress corrosion cracking resistance is manufactured by crushing a 7xxx aluminum alloy extrudate. Specifically, a 7xxx aluminum alloy extrudate containing Zn of 3.0-8.0%, 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 crushing within 72 hours after the reversion treatment, and then to aging. The reversion treatment includes heating at a temperature use rate of 0.4° C./second or more, holding in a temperature range of 200-550° C. for longer than 0 second, and cooling at a rate of 0.5° C./second or more. The ratio of the tensile residual stress σrs to the 0.2% yield stress σ0.2 after aging and the total content X of Mg and Zn satisfy a condition specified by Expression (1):;Y≦−0.1 X+1.4   (1)

主权项

1. A method for manufacturing a 7xxx series aluminum alloy member by subjecting a region of a 7xxx series aluminum alloy extrudate to crushing to give a member, the region corresponding to at least a part of the extrudate and lying along a longitudinal direction of the extrudate, and the crushing performed perpendicularly to an extrusion direction of the extrudate, wherein:
the 7xxx series aluminum alloy extrudate has a chemical composition comprising:
Zn in a content of from 3.0 to 8.0 percent by mass;Mg in a content of from 0.4 to 2.5 percent by mass;Cu in a content of from 0.05 to 2.0 percent by mass;Ti in a content of from 0.005 to 0.2 percent by mass; andat least one element selected from the group consisting of:Mn in a content of from 0.01 to 0.3 percent by mass;Cr in a content of from 0.01 to 0.3 percent by mass; andZr in a content of from 0.01 to 0.3 percent by mass; the chemical composition further comprises Al and inevitable impurities; the extrudate comprises two or more sheets; the extrudate is manufactured through press quenching; the method comprises the steps of:
subjecting at least the region of the extrudate as a work to a reversion treatment before the crushing;performing the crushing within 72 hours after the reversion treatment under such a condition as to satisfy conditions as specified by expressions as follows:
5≦t≦4.03t/2≦R≦10t where t represents a thickness (in mm) of a sheet undergoing largest bending deformation among the two or more sheets; and R represents a minimum value of a bend inner radius (in mm); and
subjecting the entire member after the crushing to aging; and the reversion treatment comprises the substeps of:
heating the work at a rate of temperature rise of 0.4° C./second or more;holding the work in a temperature range of from 200° C. to 550° C. for a duration of longer than 0 second; andsubsequently cooling the work at a cooling rate of 0.5° C./second or more.