Effect of Spark Types on Anodic Oxidation Coatings and Tensile Property of AZ91D Magnesium Alloy

Abstract

Oxidation coatings have been prepared on AZ91D magnesium alloys. Effect of spark type on the thickness, morphology, chemical composition and structure of the coatings was studied. Tensile properties of the samples were also investigated. The surface morphologies, chemical composition and phase structure of the coatings have been characterized by scanning electron microscopy (SEM), energy dispersion spectrometry (EDS) and X-ray diffraction (XRD) respectively. The results show that the oxidation coatings under three types of spark were porous and had the same phase structure. Under spark II, the thickness of the coating was 17~27μm and the coating was uniform and compact. Compared with AZ91D substrate, the tensile strength of the spark I and III coatings decreased and that of the spark II increased. The fracture mode of untreated/anodized magnesium alloys was quasi-cleavage fracture.