Effect of Heat Input on Heat-Affected Zone Softening of Cmt Welded 6082-T6 Aluminum Alloy Joints

Abstract

Mechanical properties degradation in the heat-affected zone (HAZ) is a prevalent issue during the welding of 6082-T6 aluminum alloy. Even for cold metal transfer (CMT) welded joints with low heat input, it is still challenging to avoid this problem. In this study, we investigated the impact of different heat input on HAZ softening of CMT welded 6082-T6 aluminum alloy joints, and the potential mechanism responsible for HAZ softening. The increase in heat input directly reduces the hardness of the welded joint at HAZ softening zone. Under the influence of thermal cycling with a maximum unit heat input of 224.8 J/mm, the softening of HAZ is the most serious, with a softening zone width of up to 5.5 mm and a minimum hardness of about 61 HV which reaches 58.65% of the base material (BM). The strength of HAZ softening zone is mainly affected by precipitation strengthening, solid solution strengthening, grain boundary strengthening, and dislocation strengthening. According to the strength model, precipitation strengthening and solid solution strengthening have the most obvious influence on the strength, accounting for 56.31% and 25.94% of the total strength, respectively. Compared with BM, the contribution of precipitation strengthening and solid solution strengthening in HAZ softening zone decreased by 85 MPa and 23 MPa, respectively. According to the microstructure analysis, the reduction of precipitation strengthening is primarily caused by the re-dissolution and transformation of the β′′ phase, as well as the growth and re-dissolution of the β′ phase.

Keywords: 6082-T6 alloy, CMT weld, heat input, HAZ softening mechanism