STRESS CORROSION CRACKING BEHAVIOR OF FRICTION STIR WELDED HIGH-STRENGTH ALUMINUM ALLOYS

摘要

Friction stir welding (FSW) was utilized to join three high-strength aluminum alloys, namely Al 7075, 2219 and 2195. In the present investigation, the stress corrosion cracking (SCC) behavior of these FSW alloys was studied by conducting two types of experiments: (ⅰ) four-point bending at three loading levels (50%, 65% and 85% of the ultimate tensile strength) under alternate immersion (AI) conditions in 3.5% NaCl solution for 90 days and (ⅱ) slow extension rate testing (SERT) at 3.3xl0~(-5) s~(-1) of specimens that were pre-exposed (PE) under AI in 3.5% NaCl solution. The latter set of experiments also involved testing of all specimens that survived the 90-day exposure under four-point bending. The results showed that all FSW alloys exhibited significantly lower strength compared to their parent alloy counterparts. Also, with respect to the corresponding parent alloys, FSW Al 7075 and 2195 exhibited lower ductility (～50% reduction), whereas FSW Al 2219 exhibited comparable ductility. The four-point bending results revealed no SCC susceptibility for any of the FSW alloys for the given exposure period and loading levels. Significant ductility reductions were observed only for Al 7075 in the more severe SERT experiments. In this case susceptibility increased with increasing PE time. The present evidence suggests that the observed environmental susceptibility in FSW Al 7075 is due to hydrogen embrittlement.