Characterization of Microstructure and Properties of Plasma Sprayed Ceramic Coatings on AZ91 Magnesium Alloy

Abstract

The paper presents the microstructure test results of carbide layers with bond coat obtained on the magnesium alloy with WC/Co – NiCr – AZ91D type thermal spraying method. Layers were sprayed with the APS method on the sandblasted surfaces of approx. 5 mm thick elements manufactured with high pressure die casting (HPDC). The standard process parameters were used for the powders sprayed. The scope of the tests included characteristics of the AZ91D alloy top surface after HPDC process and after sandblasting. The stereometric analysis of surface was performed by using the laser profilometer. The top surface geometric parameters were determined and presented in the form of numbers and topographic maps. Both surfaces were subject to SEM analysis by using the Hitachi S3400N microscope and chemical composition analysis in micro areas (EDX analysis by using the Noran System Six software) to determine presence of impurities and other type of artefacts on the alloy surface before plasma spraying. The alloy surfaces were also subject to detailed tests after spraying process (on lateral micro-sections) to determine the influence of the spraying process on the substrate quality and consequently layer adhesion. Phase composition assessment of the NiCr 80/20 type bond coat and carbide layers WC/10Co and WC/8Co was also performed. Further tests referred to top surface morphology of both carbide layers and chemical composition assessment in micro areas.