Microstructures and Properties of Copper to Stainless Steel Joints by Hybrid FSW

The present research article is focused to investigate the heating- and cooling-assisted friction stir welding (FSW) on dissimilar copper to stainless steel joints along with normal FSW. Gas tungsten arc welding torch was applied for heating-assisted source in front of the FSW tool, wherein preheating current was varied as 20, 40, and 60 A with rest of constant FSW parameters. Similarly, cooling-assisted FSW was performed by compressed air and water behind the FSW tool for constant FSW parameters, wherein the compressed air flow rate was varied as 15 and 30 PSI and water cooling was applied with 75 ml/min one after another. Weld properties of assisted approaches were compared with normal FSW on the scale of macrostructure and microstructure analysis, tensile testing, and microhardness properties. The obtained results reveal that the normal FSW of dissimilar copper to stainless steel joint was observed as superior relative to assisted approaches. Surface oxides were observed for the welds of heating-assisted FSW and cooling-assisted FSW of compressed air. Elimination of surface oxides was noted for FSW assisted by water cooling. Highest tensile strength was reported for normal FSW relative to heating-assisted FSW and cooling-assisted FSW. Tensile strength was deteriorated as cooling conditions increase. The microstructures of the stir zone were observed as metal matrix type with Cu matrix and SS particles, wherein SS particles were reported as in random distribution with its varying size. Major defects were reported around the largely dispersed SS particles inside Cu matrix.