Effect of porosity on the high cycle fatigue behavior of casing AM60B magnesium alloy

The effect of casting defects on the high cycle fatigue property of magnesium alloy was investigated in this study. Two AM60B magnesium alloys were manufactured by high pressure die casting with different processing parameters such as die morphology, melt and die temperatures. One of AM60B alloys with relatively high porosity was called C1 (4.06%) and the other was called C2 (0.07%). Microstructures of both C1 and C2 were composed of primary dendrite α-Mg, Al rich α-Mg, AlMn particles and Mg₁₇Al ₁₂ phases. The tensile properties of both alloys were showed that C2 had superior strength and elongation. High cycle fatigue properties were also showed differently: fatigue limit of C1 exhibited 32 MPa at 10⁷ cycles beside that of C2 showed 82 MPa at same cycles. Thus, C1 had significantly lower fatigue life than that of C2. Fractographical observations performed to explain the differences of fatigue properties by using SEM. From the observation of the differences in porosities and fractography of two AM60B magnesium alloys, an attempt to explain the high cycle fatigue fracture behavior of casted magnesium alloys was made by using the amplitude of stress intensity factor, ΔK.