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.

1 . An aluminum alloy sheet for structural components, the aluminum alloy sheet being an Al—Zn—Mg alloy sheet and comprising:
 in terms of a chemical composition in mass percent, 
 Zn in a content of 3.0% to 6.0%; 
 Mg in a content of 1.5% to 4.5%; and 
 Cu in a content of 0.05% to 0.5%, 
 the Zn content [Zn] and the Mg content [Mg] meet a condition as specified by: 
 [Zn]≧−0.3[Mg]+4.5, 
 with the remainder consisting of Al and inevitable impurities, 
 wherein, when the sheet is subjected sequentially to solution treatment, quenching, and natural aging, and a differential scanning calorimetric curve is plotted after the natural aging, a highest endothermic peak temperature is 130° C. or lower, and a maximum height of exothermic peak(s) in a temperature range of 200° C. to 300° C. is 50 μW/mg or more in the differential scanning calorimetric curve, and a work hardening coefficient n (10% to 20%) is 0.22 or more. 
 
     
     
         2 . The aluminum alloy sheet for structural components according to  claim 1 , wherein the aluminum alloy sheet further comprises at least one element selected from the group consisting of:
 in mass percent,   Zr in a content of 0.05% to 0.3%;   Mn in a content of 0.1% to 1.5%;   Cr in a content of 0.05% to 0.3%; and   Sc in a content of 0.05% to 0.3%.   
     
     
         3 . The aluminum alloy sheet for structural components according to  claim 1 ,
 wherein the aluminum alloy sheet further comprises in mass percent, Ag in a content of 0.01% to 0.2%.   
     
     
         4 . The aluminum alloy sheet for structural components according to  claim 1 ,
 wherein the Zn content [Zn] and the Mg content [Mg] in the aluminum alloy sheet meet a condition as specified by formula:   [Zn]≧−0.5[Mg]+5.75, and   wherein a 0.2% yield strength after artificial aging treatment is 400 MPa or more.