Microstructure and Mechanical Properties of 6005A-T5 Aluminum Alloy Welded Joints by Friction Stir Welding and Metal Inert Gas Welding

Abstract

The 6005A-T5 aluminum alloy welded joints were prepared by use of friction stir welding (FSW) and metal inert gas welding (MIG). The difference in microstructure and mechanical properties of the two types of welded joints were investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscope (TEM), Vickers hardness, and tensile tests. The results showed that both two methods could be used to weld this alloy successfully. The nugget zone (NZ) of FSW joint experienced a mass of heat input, hence the fine equiaxed grains appeared and the β″ phases dissolved completely. The grown and elongated grains have been preserved in the thermo-mechanically affected zone (TMAZ). The grains in heat-affected zone (HAZ) grew significantly. The microstructure in weld metal of MIG joint shows an evident feature of dendrites. The fusion zone (FZ) is composed of large columnar crystals formed along the direction of heat dissipation. The upgrowth of grains in the HAZ region was more significant than that of FSW. Both the HAZ of the FSW and MIG joints consist of β′ phase and Q′ phase. The minimum hardness of FSW joints is located in the HAZ region, while that of MIG joints is located in the weld zone. The tensile strengths of the FSW and MIG joints reach 80.3 and 72.8% of the BM, respectively. Both of FSW and MIG joints show the ductile fracture.