Influence of plasma spray WCCrCNi coating and shot peening on surface properties and corrosion behavior of AZ31 Mg alloy

In the present research work, an attempt has been made to improve the mechanical properties and corrosion resistance of AZ31 Mg alloy by shot peening and Plasma spray coating processes. Samples such as coated metal (CM), Post-shot peening coated (PSC), Pre-coated shot peening (PCS) were prepared. The following parameters were maintained to perform plasma spray coating: current density 30–4 A/dm2, deposition speed 25 μm/h and focus distance 40 mm. Double side Plasma spray coating and shot peening processes were implemented in the 5 mm thickness sheet of AZ31 Mg alloy. Results showed that Mg grain boundaries were converted into α-Mg grain boundaries and α′dynamic recrystallization growth were noted in AZ31 Mg alloy owing to the heat input. In case of PSC and PCS samples, 28% and 22% highest elongation was noted respectively, compared to coated metal. Plasma spray coating was implemented on the outer and inner surfaces; hence, high heat inputs directly affected the Mg crystallographic and MgO phase structures. Microstructure studies revealed that large Mg bulk structures were rehabilitated into the secondary phases and CrCo structures due to the high heat inputs of coating process. Further, MgCNi3-xCrC oxides were formed on the outer layers. Hardness results indicated that PSC and PCS samples showed 13% higher average hardness values compared to base materials. The surface roughness characteristics of all the samples were investigated using atomic force microscope. Corrosion resistance of all the samples was analyzed by electrochemical study using potential dynamic polarization. PSC and CM exhibited better corrosion resistance and surface properties.