Effect of post weld heat treatment on the microstructure and corrosion behavior of AA2219 aluminum alloy joints welded by variable polarity tungsten inert gas welding

Abstract

AA2219 aluminum alloy was successfully welded by variable polarity tungsten inert gas (TIG) welding, and the effect of post weld heat treatment (PWHT) process on the microstructure, mechanical properties, and corrosion behavior of the welded joints was investigated. The PWHT process being used for the welded joints was consisted of solution treatment at 535°C for 30min, water quenching, and artificial aging at 175°C for a soaking time of 12h. The microstructure and precipitated phase of the as-welded joints and PWHT joints were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X ray diffraction (XRD) and transmission electron microscopy (TEM), while the corrosion behavior was evaluated by intergranular corrosion and stress corrosion cracking. The results showed that, by implementing PWHT, the microstructure of the joint was more homogeneous than the welded joint. Meanwhile, the tensile strength was increased by 44% and the joint efficiency reached 76%. Moreover, the corrosion resistance of the PWHT joint was superior to that of the welded joint. The heat affected zone (HAZ) was observed to be the most critical corroded zone, the susceptibility to corrosion behavior of the HAZ was attributed to the dissolution and segregation of Al2Cu phase along the grain boundaries.