Muhamad Tehyo, Prapas Muangjunburee, and Somchai Chuchom

pp. 441 - 448

Abstract

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