On the Effect of Quenching on Postweld Heat Treatment of Friction-Stir-Welded Aluminum 7075 Alloy

This work focuses on the effect of postweld heat treatment (PWHT) on the mechanical properties and microstructural evolution of aluminum 7075 alloy processed via friction stir welding (FSW). FSW is known to be capable of grain refinement in the nugget zone (NZ). Two different quench media (water and air) were employed for PWHT. Regardless of the quench media, the PWHT led to the occurrence of grain growth in the NZ of the FSWed aluminum 7075 alloy. Abnormal grain growth occurred in the water quenched specimen. It is shown that ductility and strength of FSWed aluminum 7075 alloy are strongly dependent on the quenching rate. Changes in the mechanical properties and microstructure reveal that only at lower cooling rate this alloy is prone to the formation of precipitate-free zones (PFZs) in the vicinity of grain boundaries. Eventually, the PFZs deteriorate mechanical properties of this alloy.