Aluminum and steel composite structure is one of the effective ways to achieve lightweight carriers, in order to guide the industrial application of aluminum and steel friction stir welding technology, aluminum and steel dissimilar materials must be carried out friction stir welding process tests. The friction stir welding technology is used for the butt welding of 2.8 mm thick Q235 cold-rolled steel and 2.9 mm thick 5A06 aluminum alloy dissimilar metals, the study of the macroscopic morphology, microstructure, composition, microhardness and fracture appearance of the joint. The results show that the C shape interface concave depth and interface IMC layer thickness increase with the increase of rotational speed; a large number of Al3Ni particles diffusely distribute in the weld; at a rotational speed of 420 r/min, the interface IMC layer is 1.3μm thick FeAl phase, the joint is mainly fractured in the weld core zone and the fracture mode is ductile fracture, the average tensile strength of the joint is 240.3 MPa, the forward bending angle is 19.3° and back bending angle is 13.4°; the microhardness of the joint asymmetrically distributes and shows step characteristics.
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