Friction plug-riveting spot welding process of steel/aluminum dissimilar materials and the joint formation mechanism.

The welding characteristics of 7075 aluminum alloy and DP980 dual-phase steel sheet were systematically studied by the friction plug-riveting spot welding technology. The effects of different welding parameters on the weld formation, tensile strength, and microstructure of welded joints were analyzed. The complete metallurgical joining interface was formed between the rivet and steel plate. A partial metallurgical joining interface was formed between the circumferential surface of the rivet shaft and the aluminum alloy close to the steel sheet. However, the position of the rivet head did not form a metallurgical joining with the aluminum alloy. During the welding process, the area of the rivet interface underwent severe plastic deformation by frictional heat and down pressure; thus, there was a violent interaction between the plastically deformed metal and the surrounding aluminum alloy. The molten aluminum infiltrated into the rivet at the most of sample joints. The penetration of aluminum had a negative effect on the shear load. The maximum shear load of the joint was 14.374 kN. There were two types of fractures: the internal fracture of the rivet and the fracture of the steel/steel friction interface. When the fracture mode was an internal fracture of the rivet, the shear load was generally greater than the steel/steel friction interface. [ABSTRACT FROM AUTHOR]