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The microstructures and mechanical properties of 2219 aluminium alloy joints welded by variable polarity TIG welding in four kinds of different heat treatment conditions, namely, with/without pre-/ post-weld heat treatment, were analysed and compared. The post-weld artificial aging treatment rendered fine dispersed precipitates (metastable h9 phase) separate out of weld metal, which made the hardness of weld metal increase by ,20%. Meanwhile, the fracture location of joints during tensile test changed from weld zone to heat affected zone (HAZ). The pre-weld solution treatment reduced the overaging degree of HAZ and a large number of h9 phase reprecipitated in HAZ after post-weld artificial aging treatment. Intermediate state welding, with pre-weld solution treatment and post-weld artificial aging treatment together, could increase 20% of the hardness of weld zone, increase 11.5% of the hardness of HAZ and increase 20.3% of the tensile strength of joint.

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