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ELSEVIER Journal of Materials Processing Technology 180 (2006) 216-220 Journal of Materials Processing Technology w vv vv. e ] se v i er. c om/l ocaie-^i uri alpro lec Studies on softening of heat-affected zone of pulsed-currentGMA welded A1 -Zn—Mg alloy Gaofeng Fu Corresponding author. Tel.: +86 24 fax: +86 24 E-mail address: 126.com (G. Fu). , Fuquan Tian, Hong Wang School of Materials and Metallurgy, Northeastern University, Shenyang 110004, ChinaReceived 15 December 2005; received in revised form 9 June 2006; accepted 12 June 2006 Abstract 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 °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 °C. The overageing zone is characterised by growth of precipitates and covers the peak temperature range between 230 and 380 °C. The hardness in the heat-affected zone can be recovered by post-weld heal treatment, especially in the dissolution zone. Artificial ageing is more effective than natural ageing considering the recovery of the hardness. ? 2006 Elsevier B.V. All rights reserved. Keywords: Aluminum alloys; Heat-affected zone: Softening; Welding: Thermal simulation Introduction The Al-Zn-Mg alloy has wide acceptance in fabrication of lightweight structures requiring a high strength-to-weight ratio, such as storage tanks of space rockets, transportable bridge girders and railway transport systems [1-3]. Within the Al-Zn-Mg alloy system the 7005 alloy is a medium-strength and weldable alloy which contains mainly 4.5% Zn, 1.4% Mg and some amounts of manganes