Joining of Q235 Low-Carbon Steel Plates by Friction Stir Welding With AA2A12 Strip As an Auxiliary Solder

Abstract This article proposed a novel friction stir welding process to weld high melting point alloy plates with low melting point alloy strip as auxiliary solder to reduce the wear of the friction stir welding tool and extend its service life, and feasibility of this process was evaluated. An AA2A12 strip was clamped to the gap between two Q235 low-carbon steel plates as an auxiliary solder before welding, then a joint with excellent surface quality and smooth weld edge transition was obtained by friction stir welding process in which the tool was made of low-cost material tungsten-carbide. Macrostructure, microstructure and fracture surface of the joints were investigated by optical microscope and scanning electron microscope. The tensile tests were conducted to evaluate the mechanical properties of the joint at rotational speed of 800 r/min, traverse speed of 50 mm/min, with plunge depth and probe offset of 0.1 mm. The tensile strength of the joint was 108.9 MPa at room temperature what proved the feasibility of the novel way we proposed. The micro-hardness value of the cross section of the welded joint is M-shaped from the AS to the RS, and gradually decrease from the top plane to the bottom plane. There is a certain relationship between the welding process parameters and the macroscopic morphology, micro-hardness and mechanical properties of the welded joint. Hence, the method we proposed has high innovation, and economy, high value of scientific research and industrial application, and provides a new idea about friction stir welding of high melting point alloys.