Cu Donor Material Assisted Friction Stir Welding of AA2024 and AA6061 Dissimilar Alloys: Effect on Downward Force, Temperature Profile, and Mechanical Properties

Abstract

Abstract In this research, the authors investigated copper (Cu) donor material assisted friction stir welding (FSW) of AA2024-T4 and AA6061-T6 aluminum plates of 6.35 mm thickness. FSW joints were prepared at optimized process parameters at a constant tool rotational rate of 1400 rpm and welding speeds at 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 at the plunge stage. During the welding processes, it was observed that the downward force generated in the FSW process was gradually decreased after introducing Cu donor material. Temperature profiles proved that the inclusion of copper donor material increased the temperature at the beginning of the welding process. Post-weld analysis was characterized in terms of micro-hardness and tensile properties of the welded joints. The experimental results revealed that defect-free joints could be obtained when placing high strength AA2024 alloy at the advancing side with 25% thick donor material. Micro-hardness test results indicated that the hardness decreased from the base metal (BM) to the stir zone across the heat affected zone (HAZ) and thermo-mechanically affected zone (TMAZ). The lowest hardness measurements occurred in the TMAZ and HAZ where tensile failure occurs. The maximum tensile strength improved by 130% with 25% Cu donor material as compared to as-welded condition. SEM Fractography images confirmed mixed modes of brittle and ductile fracture surface with tearing ridges and finer dimples after heat treatment.