Muhamad Tehyo, Prapas Muangjunburee, Abdul Binraheem, Somchai Chuchom, and Nisida Utamarat

pp. 415 - 421

Abstract

The objective of this research is to investigate the effect of welding parameters on the microstructure and mechanical
properties of friction stir (FS) welded butt joints of dissimilar aluminum alloy sheets between Semi-Solid Metal (SSM) 356-T6
and AA6061-T651 by a computerized numerical control (CNC) machine. The base materials of SSM356-T6 and AA6061-T651
were located on the advancing side (AS) and on the retreating side (RS), respectively. 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. 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 206.3 MPa was derived from 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 than that in the thermo-mechanically 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 SSM356-T6 grains and AA6061-T651 grain layers.