Hydrolysis properties, corrosion behavior and microhardness of AZ91 “model” alloys

Abstract

A model AZ91 alloy containing the same amount of Mg and Mg17Al12 than a commercial AZ91 alloy was reproduced using various strategies. These “model” materials consist of a “homemade AZ91” powder, Mg melted or milled with Mg17Al12. The properties of the various model materials were compared to the commercial alloy (used as reference). The weak bond between Mg and Mg17Al12 is highlighted by SEM observations. Milling Mg with Mg17Al12 enhances the formation of microstructural defects due to the brittleness of the intermetallic. Vickers microhardness of pure Mg17Al12 is 250 Hv while that of AZ91 is 72 Hv. The hardness of Mg17Al12 decreases gradually from the center of the particle to its border in contact with Mg while the hardness of Mg is higher at the interface Mg-Mg17Al12. The galvanic coupling between Mg and Mg17Al12 improves the hydrolysis performance of the materials. The best hydrolysis performance was 80% of the theoretical capacity of hydrogen production reached in 60 minutes by the milled Mg + Mg17Al12. The preparation method of the models strongly affects their corrosion behavior. The passivation layer formed during the corrosion of highly-reactive materials affects the electrochemical measurements results. The mechanical properties and the corrosion behavior of the model materials depends on their composition and their structure.