The influence of welding polarity on mechanical properties, microstructure and residual stresses of gas tungsten arc welded AA5052

Abstract

The effect of welding current and polarity, i.e. AC and DCEN, on imposed thermal cycles, mechanical properties, microstructural events and residual stresses was investigated in GTA welding of AA5052. A three-dimensional thermo-mechanical model was utilized to evaluate thermal responses and residual stresses distribution in the weldments. Tensile testing and hardness measurements were also conducted to study the effect of welding polarity on the mechanical properties of components. Microstructural observations utilizing optical microscopy were carried out to assess the microstructural evolutions. The results show that wide varieties of microstructures are produced in DCEN sample from cells at the fusion boundary to equiaxed dendrites at the centre line. However, in the sample welded by AC current, the produced microstructure changes from columnar dendritic at the fusion line to equiaxed dendritic at the centre line. Although, these microstructural changes have no significant effects on the mechanical properties of weld metal. Furthermore, wider temperature contours in the AC sample resulted in a wider heat affected zone, i.e. 9.5 vs. 6.4 mm, and larger tensile residual stresses are produced in the longitudinal direction in the sample welded under DCEN polarity.