Exacerbated stress corrosion cracking in arc welds of 7xxx aluminum alloys

Abstract

Cu-lean, high-strength 7xxx series aluminum alloys (AAs) are increasingly utilized in welded structures for vehicle light-weighting. The complex stress corrosion cracking (SCC) phenomenon in the 7xxx AA base metals has been extensively studied in the literature. However, the SCC in a welded joint is further compounded by the existence of highly inhomogeneous microstructure formed during welding. The present investigation is focused on the exacerbated SCC observed in the joints made of AA 7003-T4 (Al–Zn–Mg) plates welded with AA 5356 (Al–Mg) filler metal. It studies the contribution to SCC by a variety of factors especially the precipitates in the weld toe and the heat-affected zone in the as-welded and post-weld heat-treated conditions. The stress intensity factor experienced at the crack tip is ranked using the peak strain measured using the digital image correlation technique. Based on the testing results, a theory for the exacerbated SCC in the weld joints is established. Finally, the feasibility of two different engineering solutions to SCC in these weldments is discussed.