Fatigue property of semisolid A357 aluminum alloy under different heat treatment conditions

Effect of heat treatment conditions on fatigue property of a semisolid A357 aluminum alloy under cyclic tensile loading was investigated. Comparison of the fatigue property of the semisolid A357 under T5 and T6 heat treatment conditions with other aluminum alloys including conventional casting A357-T6 alloy and four wrought aluminum alloys: 2024-T4, 7075-T6, 5052-T6 and 6061-T6 was made. It is found that the fatigue strength of the semisolid A357 under both heat treatment conditions is much higher than that of the casting A357-T6 alloy, comparable to that of the 6061-T6, but lower than that of the 2024-T4 and 7075-T6. Two-parameter Weibull distribution of fatigue data for the semisolid A357 under the two heat treatment conditions was constructed to show the statistical significance in fatigue lifetime. Fatigue fracture surface of the semisolid A357 under T5 and T6 heat treatment conditions was examined using scanning electron microscope (SEM). In the stable crack propagation region, the semisolid A357-T5 shows fatigue damage species of severely deformed grains, void coalescence, striations and ridgelines, while the A357-T6 displays less plastic deformation as revealed by the fatigue damage features of intergranular cracks, and transgranular cleavage patterns.