Fatigue properties improvement of welded joints for LF21 aluminum alloy by ultrasonic peening method

The ultrasonic peening method was used to improve the fatigue strength of welded joints of aluminum. The S-N curves and fatigue limits of TIG cruciform and T-shape joints of LF21 aluminum were obtained at both as welded and peening conditions. The results show that it should be more careful to design according to high strength classic S-N curves, for the tests reveal little difference of the fatigue strength between TIG and other welding methods as in the same form of welded joints. The fatigue strength of cruciform joints of LF21 by ultrasonic peening treatment have been increased by 26 % (tension) under the stress ratio R = 0.5 and the fatigue life is 2-4 times longer than that of the as welded ones. When the stress ratio R = 0.1, the fatigue strength of T-shape joints have been improved by 37% and fatigue life is 4-8 times longer. When R = -1, the fatigue strength of T-shape joints have improved by 44% and fatigue life is 5-8 times longer.