Strength, corrosion, and environmentally assisted cracking of a 7075-T6 friction stir weld

The microstructure and hardness of a friction stir welded (FSW) 7075-T6 alloy has been correlated with mechanical properties, corrosion and environmental cracking behavior for transverse and longitudinal orientations. The strength and ductility of the weld micro-zones are controlled by grain size, the presence and size of the coherent intragranular precipitates, along with the degree of sensitization achieved during the weld process. The corrosion behavior is influenced by the intermetallic phases as well as the grain boundary phases and/or precipitate-free zones, although a discrimination on the intergranular susceptibility between the micro-zones could not be clearly achieved with conventional polarization techniques. The heat affected zone in the trailing side of the weld is the highest susceptible micro-zone to corrosion as well as environmental assisted cracking which correlate with the sensitization level i. e. with the extent of Cu depletion at grain boundary.