Abstract
The segregation mechanism in nuggets of aluminium alloy spot welds was investigated. The nugget was grown under electrical currents during the period of weld cycles, and the formation of micro-structures in the nugget was highly dependent on the numbe of decay cycles during cooling process. The magnitude of the macro-segregation increased with increasing weld cycles and decreased with increasing decay cycles. The solution treatment of the weld decreased the segregation to a slight degree that was equal to the degree of the recovery of the micro-segregation formed at the solidification. These results indicated that this segregation was a type of the "macro-inverse-segregation" of the eutectic solute element owing to the rapid melting by the joule heat of a large electrical current and the rapid cooling under the high pressure through the loaded electrode.
