Effect of Tool Rotational Speed and Dwell Time on the Joint Strength of Friction Stir Spot Welded AA6061-T6 Sheets

Abstract

Friction stir spot welding (FSSW) is a technique employed to join materials in the solid state. It was first employed by the companies Mazda and Kawasaki as a novel sub-technique of friction stir welding to alternate the spot resistance welding. FSSW successively joined both similar and dissimilar metals. Tool rotational speed and dwell time are the most effective FSSW process parameters. This study investigated the role of the rotational speed of the tool and the dwell time in determining the FSSW joints’ strength using AA6061-T6 aluminum alloy sheets with a thickness of 1.8 mm as a work piece material. A classic milling machine was employed to carry out the welding process. Four different values of the rotational speed of tools with two dwell time values were taken to fabricate the FSSW joints. Four joints were made for each FSSW process condition. Three joints were averaged to determine the tensile–shear fracture load. The other specimen was employed to examine the micro-Vickers hardness and the microstructure. The investigation reported an increase in the joint strength within a certain range of tool rotational speeds and dwell time values corresponding to grain refinement in the weld zone. The variation in mechanical properties was attributed to the corresponding frictional heat generation and material flow during the welding process. Strain hardening and dynamic recrystallization determined the weld nugget hardness. Lower mechanical properties were observed with the excessive heat generation and flow of material with very high speeds and dwell time values.

Keywords

• FSSW
• rotational speed
• dwell time