Backing plate effect on temperature controlled FSW process

Abstract

Friction stir welding (FSW) has become an important application in modern industries. Friction stir welding is a widely used solid state joining process for soft materials such as aluminum alloys as it avoids/minimizes common problems of fusion welding processes, i.e. distortion, porosity, solidification and liquation cracking etc. Improper selection of parameters such as welding speed, rotational speed, forge force, back plate material etc. affects the weld quality. Thermal boundary condition at the bottom of the work pieces to be joined is important in determining the result of weld quality and its properties, for a given alloy type, tool geometry and selected process parameters (welding speed, rotational speed etc), These thermal boundary conditions are governed by the back plate material used. By using backing plates made out of materials with widely varying thermal diffusivity this work seeks to elucidate the effects of the root side thermal boundary condition on weld process variables and resulting joint properties. Welds were made in 5-mm-thick AMг5 (AA 5056) using siliceous coating, stainless steel, mild steel, and aluminum as backing plate (BP) material. Effects of backing plate material on the tensile strength and elongation were obtained for a particular case.