Quality and properties of the friction stir welded AA2024-T4 aluminium alloy at different welding conditions

Abstract

effect of welding parameters on weld quality and joint properties of friction stir welds in the high strength aluminium alloy AA2024 in T4 temper state was investigated in the present work. The employed rotating speeds of the tool were 1520 and 2140 rpm, while the advancing selected speeds were 40, 56, 112, 160 and 224 mm/min. The microstructural evolution of the joints was analysed by optical and scanning electron microscopy (SEM) observations of the welds cross sections. The mechanical properties of the joints were evaluated by means of microhardness (HV(0.05)) and tensile tests at room temperature. Also, the fracture surfaces of the tensile tested specimens were characterised using SEM. In all cases, the minimum microhardness values were observed in the thermo-mechanically affected zone (TMAZ) / heat affected zone (HAZ) boundary. The microhardness values in the TMAZ and HAZ of the joints decreases with increasing the heat input. Some welding defects such as porosity in the stir zone of the joints fabricated with the advancing speeds of 112, 160, and 224 mm/min at 2140 rpm were observed, whilst defect free welds were obtained with the advancing speeds of 40 and 56 mm/min at 1520 and 2140 rpm. The stirring defects decreases with increasing the heat input. All joints obtained with different welding parameters exhibited reduced strength and ductility compared with the base metal. 2024-T4 aluminium alloy plates friction stir welded at a tool advancing speed of 40 and 56 mm/min at 2140 rpm exhibited higher tensile strength and ductility, whereas lowest tensile properties were observed for samples welded at a higher tool advancing speeds of 112, 160, and 224 mm/min at 2140 rpm.