Effect of Ultrasonic Peening on the Fatigue Performance of Stir Welded Aluminum Alloy AA7075-T73
The friction stir welding (FSW) was carried out using a milling machine and a cylindrical tool with tapered pin to improve the mechanical properties and fatigue strength of the friction stir welded identical joints of aluminum alloy AA7075-T73. For rotational and travel speed, the welding parameters were 710 rpm and 35 mm min, respectively. Two types of ultrasonic peening treatment (UP) at the surface of the welded specimens were performed, i.e., one line (1UP) and two lines (2UP). Tensile tests results manifested that the welding efficiency was about 60% for the welded samples, and this value increased by using one and two lines ultrasonic peening treatment to 74%, and 71%, respectively. This improvement is due to the generating compressive stresses along the surface of welded joints. Fatigues tests were conducted at a constant amplitude at the room temperature (RT) and stress ratio R= -1. The results of the fatigue strength tests at 107 cycles were 73.1%, 84.1% and 80.2% for unpeened, one line and two lines peened specimens, respectively, compared to the base material. Due to the induced compressive stresses, one-line peened specimens (1UP) showed the greatest improvement in fatigue strength.
Keywords: Friction stir welding, Aluminum alloy, Fatigue strength, Ultrasonic peening.