Investigating post-weld heat treatments to increase the corrosion and the environmental cracking behavior of 7075-T6 friction stir weld

Post weld heat treatments (5hours / 110 degreesC, 5 hours / 195 degreesC, 7 days / 100 degreesC, I hour / 480 degreesC, torch) have been investigated in order to increase the corrosion and the environmental cracking resistance of aluminum alloy 7075-T651 friction stir weld. The post weld heat treatments affected the microstructure and the corrosion behavior. A good compromise between hardness, corrosion and environmental cracking resistance was found with the torch treatment which slightly increased the corrosion resistance of the "soft" heat affected zones causing the main corrosion to occur in the nugget region resulting in a general increase in the weld corrosion resistance. The torch treatment also eliminated the grain boundary phases resulting in lower intergranular corrosion susceptibility and higher strain to failure.