As known, mechanical properties of gas tungsten arc welded 7075 Al alloys are not desirable and some techniques should be utilized in order to refine the microstructure and hence to improve the mechanical properties of weld joints. In this research work, the microstructure of gas tungsten arc welded 7075 Al alloy was modified by friction stir processing. Evaluation of the tensile strength of the welded joints showed that the tensile strength of the welded joint (228 MPa) increases up to 320 MPa after friction stir processing. In addition, electron backscattered diffractometry (EBSD) was used in order to study the microstructure and grain boundary character evolutions during arc welding and friction stir processing. It was revealed that as-cast dendritic microstructure of gas tungsten arc welded joint completely disappears during friction stir processing and very fine equiaxed grains are formed in welded joints. Analysis of EBSD data showed that friction stir processing of gas tungsten arc welded joints leads to increase of specific boundaries from 0.7% up to 7.8%. In addition, fraction of high angle boundaries increases after friction stir processing which is resulted from dynamic recrystallization occurring during friction stir processing.
