Mechanical performance and failure modes of self-piercing riveted joints between AA6061 and solution-treated TC4 alloy

Abstract TC4 titanium alloy and AA6061 aluminum alloy are widely used in the transportation industry because of their excellent mechanical properties and lightweight. In this work, the TC4 titanium alloy was solution heat treated between 800 °C and 990 °C for 1 h, and water cooled to room temperature. The riveting and tensile tests at room temperature were conducted to evaluate the joint performance. The tensile strength and failure morphology were used to discuss the mechanical performance of joints. Solution heat treatment significantly improves the elongation, mechanical performance, and hardness of TC4 titanium alloy. Compared with the as-received material, the elongation of the treated TC4 titanium alloy is increased by 13% at the solution temperature of 900 °C, the tensile strength was added by 175 MPa at 930 °C, and the hardness was significantly increased. The optimal performance of the TC4 titanium alloy can be obtained at 930 °C. The tensile strength of the joint with the TC4 alloy solution heat treated at 930 °C is the highest of all joints. When the TC4 alloy was solution treated between 800 °C and 850 °C, the rivets were pulled from the AA6061. While at 900 °C and 930 °C, the AA6061 sheet was broken at the rivet. At 960 °C and 990 °C, the TC4 sheet was broken near the rivet. The crack size of TC4 titanium alloy gradually decreases from the rivet outward, and the crack spreads around the rivet. Severe friction can be found, which causes the peeling of the lower plate AA6061 alloy. The breaks of TC4 alloys were the plastic broken. The failure morphology of the TC4 alloy sheet is different under different solution heat treatment temperatures.