Analysis of the Influence of Friction Stir Processing on Gas Tungsten Arc Welding of 2024 Aluminum Alloy Weld Zone

Gas tungsten arc welding is the most commonly used process for joining of AA 2024 alloys, which are highly demanded in aircraft structural applications. The quality of the welds and strength of the welded joints achieved using this process, the weld fusion zone of this alloys usually exhibit the columnar grains, which are coarser than the substrate, due to the persisting thermal conditions when the fusion zone starts to solidify. This kind thermal attribution often causes to degrade the strength of the weld metal and lead to impair its resistance to sustain the hot cracking issues. In addition, there are some unavoidable micro structural defects formations such as porosity and micro cracks in the fusion zone. The formation of these defects at the top of the fusion zone will result in the reduction of weld strength about to half of the base metal strength. The present study will focus on the improvement of micro structural and mechanical properties of the gas tungsten arc welded 2024 aluminium alloys using a novel approach of friction stir processing procedures. In order to overcome these issues, the top surfaces of the gas tungsten arc welds are processed using friction stir processing up to certain depth from the top of the welds. The weld metal micro structural characterization studies revealed that the friction stir processing was controlled or decreased the amount of porosities and micro cracks formation. In addition, it destroyed the coarse grains dendritic structure in the weld zone and helped to dissolves the precipitates of secondary particles, which exists along the grain boundaries. The changes in the weld microstructures and grain refinement significantly improved the hardness of the friction stir processed welds over the base metal and gas tungsten arc welds. The mechanical properties also significantly changed along with the quality of the weldments. In addition, the formation of very fine precipitates is observed in stir zone due to the effect of intense plastic deformation and temperatures during friction stir processing.