Incipient melting in partially melted zone during arc welding of AZ91D magnesium alloy

Welding and simulation experiments were conducted to study the melting behaviour in the partially melted zone during welding of AZ91D magnesium alloy. A relatively sharp transition from partially melted zone to the zone of no melting was observed in the welded samples. This has been explained by the observations of a fast α + β eutectic melting rate and a low rate of dissolution of β-phase before melting using simulation experiments. Examination of the heating rates during welding and simulation experiments, together with the metallography observation, suggested that there is practically no “critical heating rate” and partial melting may always take place during welding.