Effect of overlapping direction in multipass friction stir processing

This paper aims to study the effect of overlapping direction in multipass friction stir processing (FSP). An AA 5083-H111 alloy 8 mm thick was tested. Structural and mechanical differences were observed when overlapping by the advancing side (AS) direction or by the retreating side (RS) one. The surface morphology was analysed and the processed zone was observed by optical microscopy, hardness measurements and bending tests were performed to evaluate surface ductility. Overlapping by the retreating side was found to generate smoother surfaces, while overlapping by the advancing side led to more uniform thickness layers. Hardness within the processed layer increased by 8.5% and was seen to be approximately constant between passes. The mechanical resistance and toughness under bending were improved by 18% and 19%, respectively.

► Overlap by RS generates smooth surface finishing and consolidates defects.
► Overlap by AS generates surfaces with more uniform thickness.
► Hardness increased 8.5% with the processed layer and do not vary between passes.
► Maximum bending load increase 18% in multipass FSP better overlapping by RS.