A Numerical Study on the Effect of Tool Speeds on Temperatures and Material Flow Behaviour in Refill Friction Stir Spot Welding of Thin AA7075-T6 Sheets

Abstract

A three-dimensional (3D) numerical model was created to simulate and analyze the effect of tool rotational speeds (RS) and plunge rate (PR) on refill friction stir spot welding (refill FSSW) of AA7075-T6 sheets. The numerical model was validated by comparing the temperatures recorded at a subset of locations with those recorded at the exact locations in prior experimental studies from the literature. The peak temperature at the weld center obtained from the numerical model differed by an error of 2.2%. The results showed that with the rise in RS, there was an increase in weld temperatures, effective strains, and time-averaged material flow velocities. With the rise in PR, the temperatures and effective strains were reduced. Material movement in the stir zone (SZ) was improved with the increment of RS. With the rise in PR, the top sheet’s material flow was improved, and the bottom sheet’s material flow was reduced. A deep understanding of the effect of tool RS and PR on refill FSSW joint strength were achieved by correlating the thermal cycles and material flow velocity results obtained from the numerical models to the lap shear strength (LSS) from the literature.

Microstructure and Mechanical Properties of Refill Friction Stir Spot-Welded Joints of 2A12Al and 7B04Al: Effects of Tool Size and Welding Parameters

“…Refill friction stir spot welding (RFSSW) is a green, energy-saving, environmentally friendly, and efficient spot-welding technology developed based on friction stir welding [3][4][5]. The technology is similar to friction stir welding, in which a solid joint is formed while the workpiece is kept below the melting temperature under the action of frictional heat and mechanical forces [6,7]. RFSSW has been identified as having better application potential for aluminum alloy joining with no exit hole after welding (and smooth surfaces), which overcomes the disadvantages encountered in resistance spot welding of aluminum alloy [8][9][10].…”

“…Welding parameters, such as tool rotation speed (RS), dwell time (DT), axial force, and plunge depth (PD), usually affect the flow and distribution of material grains [12][13][14]. The flow of the material and the resulting microstructure greatly influence the defects and pores, which often compromise the physical properties and performance characteristics of welded joints [6,[15][16][17].…”