Friction Stir Welding between Dissimilar Metalswith Circular Weld Line

Abstract

Hybrid metallic structure, which is composed of aluminum alloy as a representative of light metal and steel as that of high strength metal, has been paid attention remarkably in these days, especially in the transportation vehicle industry from the energy saving viewpoint. To perform the hybrid structure, friction stir welding FSW has been recognized to be an effective way for the welding between dissimilar metals, like between steel and Al alloy. Based on our previous findings on the butt welding between dissimilar metals with straight weld line, welding between dissimilar metals with circular weld line has been tried to open a new application field of FSW. The objective of this research is to get a fundamental finding on the welding between dissimilar metals with circular weld line and to clarify the effect of material character of Al alloy and tool design on the FSW between dissimilar metals. Typical results obtained in this study are summarized as follows: 1) Macroscopic defects often observed at the bottom part of the welding in case of ADC12 material. It indicates that insufficient stirring was given in the stirring zone due to the higher thermo-mechanical property of ADC12. 2) Tensile strength of the specimen welded with scroll shoulder tool was 266 MPa, while that with flat shoulder tool was 161 MPa. Tensile strength of the weld joint was improved by a factor of 1.65 by introducing the scroll onto the tool shoulder with normal thread probe. 3) High performance defect free ADC12/S45C weld structure with circular weld line could be fabricated by the tool with combination of scroll shoulder and thread probe.