Studies on softening of heat-affectedzone of pulsed-current GMA welded Al-Zn-Mg alloy

摘要

Studies on the softening behavior of the 7005 alloy by means of real welding experiments and heat-affected zone (HAZ) simulation have been conducted. Softening in the HAZ is found to occur above a peak temperature of about 200℃. It was found that the heat-affected zone of the alloys can be divided in two sub-zones according to their different mechanism of softening: the dissolution zone and the overageing zone. The dissolution zone is characterised by dissolution of precipitates and covers the peak temperature range above 380℃. The overageing zone is characterised by growth of precipitates and covers the peak temperature range between 230 and 380℃. The hardness in the heat-affected zone can be recovered by post-weld heat treatment, especially in the dissolution zone. As far as the recovery of the hardness is concerned, artificial ageing is more effective than natural ageing.