Abstract:Dissimilar joining of Al alloy and steel is a key issue in the lightweight manufacture of the automotive industry, however achieving good weld is very difficult for the traditional fusion welding methods. In this study, 5182 Al alloy and DP1180 high strength steel plates with 1.2 mm in thickness are friction stir lap welded using different tool sizes. Microstructure analysis indicates that defect-free joints are obtained with both tool sizes under a rotation rate of 800 r/min and a

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... ing speed of 50 mm/min. Obvious "Hook" defect forms in the joint with small tool, however it is significantly inhibited while using the big tool, and the stacking layered structure is more obvious due to the sufficient reaction between Al and steel in this case. Hardness values sharply fluctuates near the interface, due to the formation of the intermetallic compounds in the stacking layered structure, and the highest hardness value is 641 HV which is higher than that of the steel base metal. When using the small tool, weak tensile shear properties are obtained with the joints failed along the interface due to the small lap area; however, sound tensile shear properties are obtained with the joints failed at the Al side using the big tool when the Al alloy plate is located at the advancing side, and the shear force is as high as 3.42 kN. This indicates that high quality Al-steel dissimilar lap joint can be successfully obtained by friction stir lap welding.