Partially Melted Zone in Aluminium Alloy Welds

Partially Melted Zone (PMZ) of aluminium alloy welds is an important region and requires careful attention. This is mainly because PMZ in these materials is weak link in the weldments and is significantly affected by welding parameters. Microstructure changes in PMZ are related not only to welding heat input and techniques, but also depend on the initial thermal history of alloy (for example, whether it is in T-4, T-6 or T-87 condition etc). Interestingly not many detailed studies are available in this respect. In the present work effect of prior thermal temper and welding techniques mainly continuous and pulsed current Gas Tungsten Arc Welding (GTAW) on the PMZ behaviour of AA2219 and AA6061 alloys were studied. Susceptibility to liquation was high in T-6 temper of 2219 alloy compared to that of T-87 temper. Susceptibility to liquation is high in T-6 temper of AA6061 alloy compared to that of T-4 temper and has been attributed to more amount of silicon rich eutectic at the grain boundaries of PMZ. Pulsed current technique was found to improve the resistance to the susceptibility to liquation in PMZ of AA2219 and AA6061 alloys and is due to the possible reduction in the peak temperature.