Effect of current polarity on thermal distribution, microstructural evolution and mechanical properties of AA8011 aluminum alloy TIG welded joints

Abstract

The impact of welding polarity on thermal distribution, micro-structure development and mechanical performance of AA8011 aluminum alloy joints that were prepared using Gas Tungsten Arc Welding (GTAW) was carefully researched. Direct current electrode negative (DCEN-TIG) and variable polarity TIG (VP-TIG) were used to do the welding with the same process conditions. The DCEN-TIG joints presented more penetrative dendritic microstructures, refined, and smaller pores, which lead to high ultimate tensile strength (135 MPa) and hardness (81 VHN). Conversely, VP-TIG welding had larger weld beads with concentrated porosity and coarsened grain because of increased heat input, resulting into lower strengths (112 MPa) and higher ductile (7.1 %) one. Analysis of fractographic showed that DCEN-TIG joints mostly exhibited ductile fracture, whereas VP-TIG joints exhibited mixed-mode fracture. The findings prove that the welding current polarity is a major determinant of heat input, solidification characteristics, and mechanical behavior of AA8011 weldments and offer useful information to the use of polarity in strength or ductility-critical conditions.