Cu donor material assisted friction stir welding of AA2024 and AA6061 dissimilar alloys: Effect on downward force, temperature profile, and mechanical properties

This research investigation focuses on copper (Cu) donor material assisted friction stir welding (FSW) of AA2024-T4 and AA6061-T6 plates of 6.35 mm thickness. FSW joints were prepared at optimized process parameters of 1400 rpm and welding speeds of 1, 2, or 3 mm/s. The Cu donor material of 25% and 50% thickness with respect to the workpiece thickness were selected to assist the FSW joining during the plunge stage. The downward force generated in the FSW process was gradually decreased after introducing the Cu donor material because more heat was produced in the donor material and conducted to the base plate. The temperature profiles that the inclusion of the Cu donor material increased the temperature at the beginning of the welding process. The welded joints were characterized in terms of the micro-hardness and tensile properties. Defect-free joints could be obtained when placing high strength AA2024 alloy at the advancing side of the weld with 25% thick donor material. From the hardness profiles, it is observed that the hardness decreases from the base metal of AA 2024 to the center of the weld followed by thermomechanical affected zone (TMAZ) and the heat affected zone (HAZ). The hardness measurements are lower in the TMAZ and HAZ where tensile failure occurs. The maximum tensile strength improved by 130% with 25% Cu donor material as compared to the as welded samples. SEM Fractography images confirmed mixed modes of brittle and ductile fracture surfaces with tearing ridges and finer dimples after the inclusion of donor material in FSW.