Enhanced corrosion performance of ultrasonically shot peened and graphene nanoparticles reinforced squeeze-cast AZ91 magnesium alloy

Abstract

The current study examined the influence of ultrasonic shot peening (USP) for 10, 20, and 30 s on the corrosion behavior of AZ91 alloy integrated with graphene nanoplatelets (GNPs) (0.5, 1.0, 2.0 wt%) by squeeze casting. The Volta potential associated with Mg17Al12 phase in the AZ91 alloy decreased with the incorporation of GNPs. All of the nanocomposites illustrate less weight loss and hydrogen evolution, which further decreases after USP. With GNPs’ addition to the AZ91 alloy, the open circuit potential increases positively and became much nobler after USP. All the nanocomposites display lesser corrosion rates contrasting to AZ91 alloy, decreasing further after USP. The 20 s ultrasonically shot-peened (USPed) AZ91–2.0GNPs demonstrates the best corrosion resistance. Mg(OH)2, MgCO3, and Al-rich compounds were the predominant corrosion products generated on the alloys and nanocomposites, with the least in the 20 s USPed AZ91–2.0GNPs nanocomposite. The smaller grains, lower Mg17Al12 phase content, and lower Volta potential betwixt the α-Mg and Mg17Al12 phases improve the cast nanocomposites’ resistance to corrosion. On the contrary, the compressive residual stress and finer grains at the surface of the USPed alloy and nanocomposites ameliorated the corrosion resistance significantly.