| Summary: | The objective of this research is to investigate the effect of welding parameters on the microstructure and mechanicalproperties of friction stir welded butt joints of dissimilar aluminum alloy sheets between Semi-Solid Metal (SSM) 356 and AA6061-T651 by a Computerized Numerical Control (CNC) machine. The base materials of SSM 356 and AA 6061-T651 werelocated on the advancing side (AS) and on the retreating side (RS), respectively. Friction Stir Welding (FSW) parameterssuch as tool pin profile, tool rotation speed, welding speed, and tool axial force influenced the mechanical properties of theFS welded joints significantly. For this experiment, the FS welded materials were joined under two different tool rotationspeeds (1,750 and 2,000 rpm) and six welding speeds (20, 50, 80, 120, 160, and 200 mm/min), which are the two prime joiningparameters in FSW. A cylindrical pin was adopted as the welding tip as its geometry had been proven to yield better weldstrengths. From the investigation, the higher tool rotation speed affected the weaker material’s (SSM) maximum tensilestrength less than that under the lower rotation speed. As for welding speed associated with various tool rotation speeds, anincrease in the welding speed affected lesser the base material’s tensile strength up to an optimum value; after which its effectincreased. Tensile elongation was generally greater at greater tool rotation speed. An averaged maximum tensile strength of197.1 MPa was derived for a welded specimen produced at the tool rotation speed of 2,000 rpm associated with the weldingspeed of 80 mm/min. In the weld nugget, higher hardness was observed in the stir zone and the thermo-mechanically affectedzone than that in the heat affected zone. Away from the weld nugget, hardness levels increased back to the levels of the basematerials. The microstructures of the welding zone in the FS welded dissimilar joint can be characterized both by the recrystallizationof SSM 356 grains and AA 6061-T651 grain layers.
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