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As a kind of green materials, magnesium (Mg) alloys have been widely applied to bicycles, cars, electronics, aviation, aerospace, defense and other fields because of low density, high specific strength and specific stiffness, excellent damping capacity and processing performance. AZ61are a kind of mature Mg alloys in Mg-Al series, which were used in bicycles and other industries in recent years. However, the low mechanical properties limit their application. The strengthening and toughening of AZ61by addition of rare earth(RE) is a effective method to expand the scope of application due to its purification to alloy melt, improvement to alloy microstructure, castability and mechanical properties.In this study, the effect of the addition of Pr and combined addition of Pr and Ti on the microstructure and mechanical properties of AZ61Mg alloy were analyzed by Optical microscope(OM), X-ray diffraction(XRD), scanning electron microscope(SEM), hardness testing, tensile properties testing and impact toughness testing. Two parts of conclusion can be drawn that:(1) Study of effect of single addition of RE element Pr on the microstructure and mechanical properties of AZ61alloys. when Pr was added into AZ61alloys,besides α-Mg and divorced eutectic β phases, new kinds of short-rod shaped or rodlike rare earth phases Al11Pr3and AlPr were observed in the as-cast microstructure. The original network structure spread out, transformed to blocks or island shape, the microstructure became berrer, and the grains were refined. In addition, the tensile strength was improved to202MPa from155MPa,the elongation was improved to9.98%from6.55%, the hardness was not obviously improved.(2) Study of effect of combined addition of Pr and Ti on the microstructure and mechanical properties of AZ61alloys. Single addition of0.6wt.%Ti is the most effective way to improve the microstructure. The structure transformed from the original coarse network to fine uniform-distribution island or granular shape, no new phases were observed. However, the SEM, EDS and XRD proved the existence of Al3Ti phases. Besides, the alloys showed best mechanical properties then.The tensile strength increased from the original155MPa to195MPa and the elongation increased from6.55%to9.12%. The most obvious improve is the impact toughness which transformed from original14.2J/cm2to21.2J/cm2. But the hardness was not improved obviously. After combined addition of0.6wt.%Ti and1.2wt.%Pr, the microstructure of the alloys was finer, and lots of short rod-shaped or needle-like phases appeared which were detected as Al11Pr3phase, AlPr phase and Al3Ti phase, they played a role of strengthening phases in the alloys. At this time, the mechanical properties had a little improvement,the tensile strength, elongation, impact toughness and hardness of alloy were improved from the original155MPa,6.55%,14.2J/cm2and53.5HB to210MPa,10.12%,22.1J/cm2and57.2HB.
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