Partially melted zone in Al–Mg–Si alloy gas tungsten arc welds: effect of techniques and prior thermal temper

Abstract

Influence of prior thermal temper and welding techniques on microstructure changes in the partially melted zone (PMZ) of AA6061 alloy gas tungsten arc (GTA) welds was investigated. Welds of AA6061 in naturally aged (T4) and artificially aged (T6) thermal tempers were made by continuous current (CC) and pulsed current (PC) techniques of GTA welding. Optical, scanning electron microscopy and microhardness testing were carried out to study the PMZ in welds. Susceptibility to liquation was high in the T6 temper as compared to the T4 temper and was attributed to a greater amount of silicon rich eutectic at the grain boundaries of PMZ. The PC technique was found to improve the resistance to susceptibility to liquation in the PMZ of AA6061 alloy GTA welds and was due to the possible reduction in the peak temperature.