Corrosion fatigue of die-cast magnesium alloys

The fatigue properties of die-cast magnesium alloys AM50HP and AZ91HP were determined in ambient air and in 3.5% sodium chloride solution, respectively. It is found that fatigue cracks initiate from the casting pores within the specimen and near the surface in both environments depending on the relative pore size, and the S-N curves of both alloys are steeper in corrosive environment than in ambient air. Both die-cast magnesium alloys do not have endurance limits in 3.5% NaCl solution, whereas endurance limits could be detected in ambient air, which are about 90 MPa and 100 MPa for AZ91HP and AM50HP respectively. The die-cast magnesium alloy AM50HP shows a higher sensitivity to the action of 3.5% NaCl solution in comparison with AZ91HP, and the corrosion fatigue behaviour of both die-cast magnesium alloys correlates with their mechanochemical behaviour. The latter was studied by the polarization measurements of the dissolution rate of strained magnesium alloys.