The Impact Of The Rare Earth Elements On Microstructure And Mechanical Properties Of Az61 Magnesium Alloy

As the lightest structural metallic materials, magnesium alloys have high specific strength, high specific stiffness, excellent electro-magnetic shielding ability and heat dispersion, good processing properties and casting properties. Therefore, it is believed that magnesium alloy can be the most promising green material of the 21st century.magnesium alloys have been extensively applied in automotive, communication and aircraft industies. But because of its poor plastic deformation ability, low yield stress and fracture toughness, the use of magnesium alloys is limited for a long time.In this thesis, based on the AZ61 magnesium alloy ,the effects of different rare earth Ce, Y on the microstructure and mechanical properties of AZ61 magnesium alloy.The results show that, rare earth elements effectively refine grains of AZ61 magnesium alloy, increase room temperature mechanical properties and high temperature mechanical properties, and improve ductility of alloys.1.The appropriate amount of rare earth Ce can refine the microstructure of magnesium alloy significantly,βphases of AZ61 cast Alloy change less and thinner, the grains are refined remarkably. Most of Ce reacts with Al to produce AlCe3 compounds that with high melting point and elevated temperature stability; after the solid solution treatment,β-phase is completely dissolved and the rare-earth phase with needle-like or rod-shaped exist arround the grain boundaries; With Certain amount of Ce addition increasing, the strength and the hardness and the elongation of AZ61 magnesium alloy are raised at room-temperature and high-temperature, but as excess amount of Ce addition will make the performance down In this experiment, the mechanical tests indicate that AZ61 magnesium alloy has the best properties when the content of Ce is 1. 0 %.2.The microstructure and mechanical properties of AZ61 alloy are greatly improved affter adding the rare earth yttrium, the main mechanisms are: First, the lattice structure and atomic radiusof Y are similar to the ones of Mg so Y can be the heterogeneous core, thus and refine the grain and played the role of fine-grain strengthening; The second, the solubility of Y in magnesium is larger so it may played the role of solid solution strengthening; Third, Y reacts with Al to produce Al2Y3 compounds,they can improve the alloy's micro-hardness, rare-earth phase with high melting point can also enhance the high temperature mechanical properties of the alloys.3.The microstructure and mechanical properties at room temperature and high temperature of AZ61 magnesium alloy are improve by compound Rare Earth Y and Ce. Three types of strengthening mechanisms that the solid solution strengthening of Y and the fine grain strengthening of Y and Ce and second-phase precipitates strengthen of Y and Ce make the mechanical properties of alloy increased significantly, In this experimental, alloy the best properties when the content of Ce is 1. 0 %. and Y is 1. 0 %.4.Analysis the formation of rare-earth phase by Miedema model and explain the inevitability of its existence. The hot is -3.117 KJ ? mol-1 between Ce and Al by simplified calculation. and the hot is -0.0258 KJ ? mol-1 between Ce and Mg, the result show that: the affinity between Ce and Al is much greater than that between Ce and Mg, the formation of Al -Ce rare earth phase has its inevitability, combined with XRD test results known that the rare-earth phase is AlCe3.