Influence of Metal Transfer Modes and Postweld Heat Treatment on Tensile Properties of Gas Metal Arc–Welded AA6061-T6 Aluminum Alloy Joints

Abstract

The issues of dissolution or overaging of precipitates in the weld metal or heat-affected zone of aluminum alloy joints welded by conventional or constant-current gas metal arc welding (CC-GMAW) process are the key factors responsible for the formation of softening region, which leads to the degradation of the mechanical properties of the joint. In order to prevent the precipitate dissolution, a low heat input welding process is required. Further, to improve the mechanical properties of the welded joints, reprecipitation is necessary, and this can be achieved by postweld heat treatment (PWHT). The main aim of this investigation is to study the combined effect of metal transfer modes (i.e., CC-GMAW, pulsed-current gas metal arc welding [PC-GMAW], and cold metal transfer gas metal arc welding [CMT-GMAW]) and heat treatment on the tensile properties of gas metal arc–welded AA6061 aluminum alloy joints. This investigation effectively implements the low heat input GMAW variants like PC-GMAW and CMT-GMAW to control the dissolution of precipitates. Moreover, PWHT procedure (solutionizing at 530°C for 1 h, followed by quenching in water and then artificial aging at 170°C for 19 h, and finally cooling in air at an ambient temperature) was imposed on the specimens in order to recover the mechanical properties of the welded joints. It is observed from the tensile properties that PWHT joints exhibited improved mechanical properties compared with the as-welded joints. But the joint welded by CC-GMAW process has shown no improvement in the tensile properties because of the segregation of alloying elements that are observed along the grain boundary. The PWHT CMT-GMAW joint showed huge improvement in tensile properties (i.e., 13 % higher than the CC-GMAW joint and 9 % higher than the PC-GMAW joint) because of the controlled segregation of alloying elements with nucleation of β″ precipitates.