Effects of plasma electrolytic oxidation on fatigue strength of thixomolded AZ91D magnesium alloy

Abstract

For the application of thixomolded AZ91D magnesium alloy to structural parts, the effects of carbon nanoparticle addition and phosphate anodization on fatigue properties were evaluated by rotary bending fatigue tests. Mechanical properties such as the tensile and fatigue strengths were improved by only 0.1 mass% of the carbon nanoparticle addition because of the refinement of crystal grains. Compared to the fatigue strength of un-treated specimens, the fatigue strength was reduced by phosphate anodization with and without carbon nanoparticle addition. In this case, pre-treatment before anodization reduced the fatigue strength by about 20 MPa. In phosphate anodization, there is concern that the plasma generated during electrolysis may heat the specimen surface and affect the microstructure. However, in this experiment, the effect of heating was negligible. It was expected that pores of a few microns in the anodic oxide film would adversely affect fatigue properties.