The Microstructure, and Mechanical and Corrosion Properties of As-Cast and As-Extruded Mg-2%Zn-x%Cu Alloys After Solution and Aging Heat Treatments

Abstract

The effects of different Cu concentrations and heat treatment on the microstructure, mechanical and corrosion properties of the as-cast and hot-extruded Mg-2%Zn alloys were studied. The results showed that T6 heat treatment led to the dissolution of intermetallics and breaking the continuous networks of intermetallics. Also, the grain size of the base alloy decreased with further Cu additions after solution and aging heat treatments. Microstructural characterization indicated that Mg(Zn,Cu) and Mg(Zn,Cu)2 intermetallics were formed which their volume fractions increased with exceeding Cu additions. Moreover, the addition of 3 wt.% Cu and T6 heat treatment increased the Brinell hardness of both as-cast and hot-extruded specimens reached to 94 HBN and 116 HBN, respectively. The optimum amounts of the ultimate tensile strength and elongation values obtained from 0.1 wt.% Cu addition for both conditions after T6 treatment which were 253 MPa, 11.5% and 263 MPa, 14.7%, respectively. However, more Cu addition (> 0.5 wt.%) deteriorated the tensile properties of the alloy due to the high volume fraction of intermetallics. The yield tensile strength increased continuously with different Cu additions for the cast and extruded alloys after solution and aging heat treatments. After T6 heat treatment, extruded alloys showed better anti-corrosion properties than those of the cast alloys, while the extruded Mg-2%Zn-0.1%Cu alloy exhibited the best anti-corrosion property. Further Cu addition increased the volume fraction of intermetallics and enhanced the corrosion rate which was due to the galvanic couple effect.