Effect of Ag interlayer on friction torque, mechanical properties and microstructure of large diameter aluminum/steel joints by continuous drive friction welding

Abstract

The large diameter aluminum/steel continuous driven friction welding component is prone to overload of the main motor due to high friction torque in the welding process. Therefore, multistage friction is used in industrial production to avoid overloading the main motors. However, multistage friction usually increases the heat input in the welding process and leads to the formation of thick and heterogeneous FeAl intermetallic compounds at the welding interface, which degrades the mechanical properties of the joints. Adding an Ag interlayer to the aluminum/steel interface can reduce the friction torque in the welding process, inhibit the interdiffusion of FeAl elements and reduce the thickness of FeAl intermetallic compounds. In this study, Q235 low-carbon steel rods (Diameter of weld end = 120 mm) with/without Ag interlayer and 1060 pure aluminum rods (Diameter of weld end = 90 mm) were welded by continuous drive friction welding. Voltage and Current of Major Motor (VCMM) in the welding process were processed and analyzed. The effects of the Ag interlayer on friction torque, mechanical properties of the post-weld joint and microstructure at the welding interface were analyzed. The research shows that the Ag interlayer can effectively reduce the initial peak torque and joint temperature in the welding process. The mechanical properties and intermetallic compound thickness of the post-weld joint still exhibit heterogeneity along the radial direction. The strength and toughness are significantly improved in the region of 0.5– 0.8R from the center, which is because the Ag2Al and Ag3Al phases with better toughness are formed in this region due to the change of the flow form of the interfacial viscoplastic metal by the Ag interlayer.