Mechanical and Microstructural Characterization of Al-5083/St-12 lap joints made by friction stir welding

Abstract Al-5083 and St-12 alloys sheets were friction stir lap welded at various traveland rotation speeds of the welding tool. Microscopic examinations indicate that the joint strength is due to the macroscopic and microscopic mechanical lockings and also atomic diffusion. The reaction zone of the welded joints consists of mixed layers of ultra-fine grains and the intermetallic compounds. The microhardnessand nano indentationresults prove that the intermetallic phase layer is more brittle in comparison to base metals and ultra-fine grain region. The fracture surfaces are a combination of brittle and ductile fractures. The fracture loads show that the joint strength improves significantly by decreasing the travel speed of the tool.