Enhanced mechanical properties and corrosion resistance of a fine-grained Mg-9Al-1Zn alloy: the role of bimodal grain structure and β-Mg17Al12 precipitates

ABSTRACT A good combination of mechanical properties and corrosion performance is desired when employing Mg alloys in engineering applications. Therefore, it is essential to investigate both the mechanical properties and corrosion resistance of processed Mg alloys to determine the optimum combinations of materials properties. This study investigates the microstructure, mechanical properties, and corrosion resistance of AZ91 (Mg–9Al–1Zn, wt.%) alloys in chloride-containing environments under different processing conditions. The findings revealed that the AZ91 alloy exhibits good mechanical properties combined with high corrosion resistance after microstructure modification through equal channel angular pressing (ECAP). This microstructure was characterized by a bimodal grain structure with the formation of a high volume fraction of well dispersed β-Mg17Al12 precipitates. The superior mechanical properties of the AZ91 alloy after ECAP process were mainly attributed to the combined effect of significant grain refinement and high volume fraction of fine β-Mg17Al12 precipitates that provided grain boundary and precipitation strengthening and promoted a more uniform plastic deformation. The enhanced corrosion resistance of the fine-grained AZ91 alloy was related to the presence of a highly protective oxide layer, the formation of a highly adherent and compact layer of corrosion products, and the development of uniform corrosion with shallow corrosion pits. This simultaneous improvement in strength, ductility, and corrosion resistance of fine-grained AZ91 alloys can serve as a guide for future alloy design and represents a promising alternative for industrial applications.