Effect of heat treatments on the tensile strength and SCC-resistance of AA7050 in an alkaline saline solution

Effect of heat treatments (namely T6, T73, RRA, OP1 and OP2) on the tensile strength (TS) and stress corrosion cracking (SCC) resistance of aluminum alloy 7050 in 3.5% NaCl solution at pH 12 has been investigated using constant extension rate tester (CERT). T6 increases the TS but decreases the SCC-resistance. To the opposite, T73 (i.e., T6 + 160 degrees C/30 h) increases the SCC-resistance but decreases the TS. Retrogression and re-aging (RRA, i.e., T6 + 200 degrees C/10 min + water quench + 120 degrees C/24 h) increases both TS and SCC-resistance but this treatment confines only to thin and small specimens. Step-quench aging (SQA, i.e., 470 degrees C/1 h + step-quench to 200 degrees C/1 min + water quench/or air cooling + natural aging at room temperature/1 week + 120 degrees C/24 h) provides a relatively practical treatment to enhance both the TS and SCC-resistance even the specimen either having quenched in water (OPI) or cooled in the air (OP2) in the process. Through electrochemical testing and micro-structural examination, we found that both the TS and SCG-resistance of AA7050 is governed by the microstructures that depend on heat treatments. (c) 2005 Elsevier Ltd. All rights reserved.