| On the basis of reading a large amount of literatures and reports, this dissertation investigated the properties of Mg-6Al alloy in order to development novel heat-resistant magnesium alloy with excellent mechanical properties, castability, high cost effective at normal and high temperature through alloying of yttrium, neodymium, gadolinium. The influence of the rare earth elements Y, Nd, Gd to the Mg-6Al alloy of the microstructure and the tensile mechanical properties at high temperature were studied systemically by optical microscope, scanning electron microscope, X-ray diffraction, and precious universal electronic tensile test system.The following results are attained through adding elements yttrium in Mg-6Al alloy. Rare earth elements yttrium is capable of refining grains, and improving the morphology, changing distribution ofβ-Mg17Al12 phase, and producing Al2Y point-like phase with high melting point at grain boundary and intracrystalline, moreover, theβ-Mg17Al12 decreases with the increasing of yttrium content and till disappears as the content of yttrium is 1.2wt%. The performances of the Mg-6Al alloy at room temperature and high temperature are enhanced obviously by adding elements yttrium. And the strength of the AY alloy at room temperature and high temperature reaches highest point as the content of yttrium is 1.2wt%, and the tensile strength is 224MPa, tensile strength at high temperature 150℃, 175℃, 200℃is 221MPa, 192MPa, 162MPa, respectively. The specific elongation increases as the temperature increases, at the same temperature, the alloy with yttrium content of 1.2wt% has the best plasticity and highest specific elongation.The following results are attained through adding elements neodymium in Mg-6Al-1.2Y alloy. Rare earth elements neodymium is capable of refining structure of Mg-6Al-1.2Y, and changing the distribution and the shape of the second phase, and producing Al2Y, Al2Nd point-like phase with high melting point at grain boundary and intracrystalline, moreover, the second phase increases with the increasing of neodymium content, and the distribution and shape are also changing along with it. When the neodymium content of the alloy is 0.3wt%, the larger second phases are distributed at grain boundary, and this kind thicker, larger second phase cannot prevent the boundary to slip, cause the stress concentration in the vicinity, so the mechanical properties of AYN6103 alloy is lower than AY612 alloy. When the neodymium content of the alloy is 0.9wt%, the second phase well distribut in the alloy, further increase will result in the segregation and growth of the second phase. The AYN alloy strength at room temperature and high temperature reaches highest point as the content of neodymium is 0.9wt%, and the tensile strength is 253MPa, tensile strength at high temperature 150℃, 175℃, 200℃is 253MPa, 223MPa, 173MPa, respectively. Importantly, the tensile properties meet the application requirements at 175℃. The specific elongation increases as the temperature increases, at the same temperature, the AYN alloy with neodymium content of 0.9wt% has the best plasticity and highest specific elongation.The following results are attained through adding elements gadolinium in Mg-6Al-1.2Y-0.9Nd alloy. Rare earth elements gadolinium is capable of producing Al2Y, Al2Nd, Al2Gd dispersing second-phase with high melting point, moreover, the phase morphology and distribution correlated with the gadolinium content: when the gadolinium content is 1.2wt%, 2.4wt%, the Al2Gd is strip like, and appears discontinuous distribution along the grain boundary, when the gadolinium content is 3.6wt%, 4.2wt%, Al2Gd turns to sphere like, and well distributed along the grain boundary and intracrystalline. The alloy strength at room temperature and high temperature reaches highest point as the content of gadolinium is 3.6wt%, and the tensile strength is 257MPa, tensile strength at high temperature 150℃, 175℃, 200℃is 256MPa, 226MPa, 184MPa, respectively. The specific elongation increases as the temperature increases, at the same temperature, the alloy with gadolinium content of 0.9wt% has the best plasticity and highest specific elongation.For alloy Mg-6Al-(x)Y, the solid solubility of Al in Mg increases with the increasing of yttrium content, however, the solid solubility of Y in Mg decreases. For Mg-6Al-1.2Y-(x)Nd, the solid solubility of Al in Mg increases with the increasing of neodymium content, howerer, the solid solubility of Nd and Y in Mg decreases. For Mg-6Al-1.2Y-0.9Nd-(x)Gd, the solid solubility of Al, Y, Nd, Gd in Mg increases with the increasing of Gd content. When the Gd content is 3.6wt%, the solid solubility of all elements in Mg reaches the highest point, and result in the best solid solution intensification effect.
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