Effect of Extrusion Ratio on Fatigue Behaviour in Mg2Si-Particulate Reinforced Magnesium Alloy Composites

Abstract

This paper describes the effect of extrusion ratio on the fatigue behaviour of Mg2Si-particulate reinforced magnesium alloy composites produced with 2 mass% Mg2Si particles by powder metallurgy. The matrix magnesium alloy powders used were AZ61 and AZ80. Rotating bending fatigue tests have been performed using smooth specimens of materials extruded at three different extrusion ratios of 36, 67 and 133 at a low extrusion temperature. It was found that the extrusion ratio dependence of fatigue strength was different between two composites, Mg2Si/AZ61 and Mg2Si/AZ80. In the former composite, extrusion ratio exerted no significant influence on fatigue strength, while in the latter composite, there existed no discernible difference in fatigue strength between the materials extruded at the extrusion ratios of 36 and 67, but the material extruded at the extrusion ratio of 133 exhibited higher fatigue strength than those materials. Different crack initiation mechanisms operated depending on matrix alloy, extrusion ratio and applied stress level. In Mg2Si/AZ61, cracks initiated at Mg2Si particles regardless of extrusion ratio and applied stress level, while in Mg2Si/AZ 80, the same crack initiation mechanism as in Mg2Si/AZ61 operated at the materials extruded at the extrusion ratios of 36 and 67, but cracks generated due to cyclic slip deformation of the matrix at low applied stresses in the material extruded at the extrusion ratio of 133. It was indicated that such crack initiation behaviour was the primary cause of the observed fatigue strength in the present composites.