Effect of Heat Treatment on Microstructure and Micro-Wear Resistance of Selective Laser Melted Mg-Al-Zn Alloy with La2O3 Addition

Abstract

In this study, the microstructure, intermetallic phase, microhardness and wear resistance of unheated and heat-treated Mg-6Al-1Zn-xLa (x = 0.5, 1, 2) alloy that fabricated by selective laser melting was studied. In this paper, La was added by adding La2O3. The grain size was reduced with the La addition which reached smallest with 1% La addition (1.58 μm). The scanning electron microscopy, energy-dispersive x-ray spectroscopy and x-ray diffraction results showed that the secondary phase of Al11La3 was formed during the eutectic reaction. Al11La3 phase still remains after solution treatment at 400 °C for 4h, short rod-shaped discontinuous Mg17Al12 is formed at the grain boundary during aging treatment. The mechanical properties of samples are further improved by aging treatment, microhardness increases with the increase in La content and its value reaches 140 HV for aging-treated Mg-6Al-1Zn-2La. The micro-scratch results show that the wear resistance is related to the La percent and heat treatment method. The residual depth of samples indicates that the addition of La can reduce the micro-wear and short rod-like precipitation of β phase which generates in aging treatment can decrease residual depth as well.