The correlation of microstructure features, dry sliding wear behavior, hardness and tensile properties of Al-2wt%Mg-Zn alloys

Abstract

The effect of Zn addition on the as-cast microstructures, mechanical properties and dry sliding wear behavior of Al-2wt%Mg-Zn alloys is investigated in this study. Two Al-Zn-Mg ternary alloys, with 5% and 8% Zn contents and 2 wt% Mg, were developed: 752 alloy (Al-5wt%Zn - 2 wt%Mg) and 782 alloy (Al-8wt%Zn-2wt%Mg). Unidirectional vertical upward solidification experiments were performed using a metallic water-cooled mold instrumented by thermocouples. Samples extracted along the length of the resultant ingots were characterized by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), and mechanical properties were analyzed by hardness, microhardness, tensile and dry sliding wear tests. The results showed that the microstructures for both alloys are composed of an α-Al dendritic matrix and MgZn2 and Al2Mg3Zn3 interdendritic precipitates. An experimental equation is derived relating the secondary dendrite arm spacing (λ2) to the solidification cooling rate (Ṫ). Experimental relationships show that both Brinell Hardness (HB) and ultimate tensile strength (UTS) increased with the decrease in λ2. The wear resistance is shown to increase with the increase in the alloy Zn content and with the decrease in λ2. A correlation between wear, hardness and ultimate tensile strength was proposed, in which wear decreases with the increase in both HB and UTS. The observed wear mechanism is shown to be abrasive for all examined alloys and experimental conditions.