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

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 degrees C. It was found that the heat-affected zone of the alloys can be divided into 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 degrees C. The overageing zone is characterised by growth of precipitates and covers the peak temperature range between 230 and 380 degrees C. The hardness in the heat-affected zone can be recovered by post-weld heat treatment, especially in the dissolution zone. Artificial ageing is more effective than natural ageing considering the recovery of the hardness. (c) 2006 Elsevier B.V. All rights reserved.