Microstructure and Mechanical Properties of AZ81 Magnesium Alloy

Abstract

The microstructure and mechanical properties of AZ81 magnesium alloy have been studied by micro-analysis and tensile tests. The results showed that the alloy mainly consists of α-Mg matrix, Mg17Al12. The tensile strength of AZ81 magnesium alloy is measured, The best tensile strength is 258MPa at 20°C. Introduction In today's world, the energy crisis and environmental pollution are increasingly serious, which makes people pursuit of lightweight material. As the lightest metal structure material, magnesium alloy has become a research focus. Moreover due to the small density, good thermal conductivity and the characteristics of the electromagnetic interference resistance, magnesium alloy is more widely application in 3C products[1-5]. The biggest application is casting of magnesium alloy. In addition to the necessary strength at room temperature, a considerable part requires enough high temperature strength. And the most widely used is Mg-Al alloys that are die casting magnesium alloys. AZ81 magnesium alloy is one of the most widely used in industrial application of magnesium alloy[6-10]. The experiment is on the basis of previous studies, the microstructure and mechanical properties of AZ81 magnesium alloy have been further studied. Experimental The raw materials for experiment are pure magnesium(99.95%), industrial pure Al (99.9%), Zn. Magnesium alloy is smelt in an induction furnace, using 1vol.% SF6+99vol.% CO2 gas mixture for smelting protection. solid solution process is cared out at 420°C for 12h, and then quenched in warm water. Aging process is perfored at 200°C for 16h, and then cooled in air. Mechanics performance test is made on AG-I 250KN precision universal experimental machine, stretching rate is 1 mm/min. At 20 °C, 150°C and 150 °C, the tensile strength and elongation of the AZ81 magnesium alloy is measured, the tensile sample is shown in Fig. 1. Use D8ADVANCE type X-ray diffractometer to analyze the phases on the alloy, The microstructure of the alloy is analyzed by optical microscopy .Use JMS-5610LV scanning electron microscope to observe the tensile fracture morphology. Fig.1 Tensile sample International Conference on Materials, Environmental and Biological Engineering (MEBE 2015) © 2015. The authors Published by Atlantis Press 981 Results and analysis The phases of as-cast AZ81 magnesium alloy are analyzed, and the X-ray diffraction patterns of the AZ81 magnesium alloy is shown in Fig. 2. It can be seen that the alloy consists of α-Mg matrix, Mg17Al12. In addition, some peaks of Zn contented phase are not observed since the addition of Zn is little. Fig.2 X-ray diffraction patterns of the as-cast AZ81 alloy Fig. 3 shows the microstructure of AZ81 magnesium alloy. The microstructure of as-cast AZ81 alloy is shown in Fig. 3(a), It can been seen from Fig. 3(a) that the alloy is mainly composed of dendritic shaped α-Mg matrix and gray divorced eutectic β-Mg17Al12[11] phase which distributed in the grain boundary. Fig. 3(b) shows the microstructure solid solution and aging AZ81 alloy, it can be seen that block-shaped β-Mg17Al12 phase distributes on the grain boundary. Fig.3 The microstructure of AZ81 magnesium alloy. (a) as-cast AZ81 ; (b) solid solution and aging AZ81 It can be seen from table 1, that from room temperature (20 °C) and high temperatu 150°C and 175°C), the tensile strength of the alloy decreases, and the peak appears at 20°C. Mechanical properties of the alloy are the best at room temperature. The mechanical properties of the alloy under the high temperature remain to be improved.