| Today, With Increasing scarcity of the metal resources, accelerating the scientific and technological research related to the magnesium alloy material is one of the important measures to achieve sustainable development. However, the main phase Mg17Al12 which has a relatively low melting point and is easy to soften under high temperature conditions can not effectively pin the grain boundaries and inhibit the high-temperature grain boundaries rotation in magnesium alloy.Therefore, improving the high temperature properties of magnesium alloy has become a critical issue at home and abroad.In this paper, the efforts of Ca and Ca,Nd addition on the as-cast microstructure and mechanical properties of Mg-Al alloys were investigated by the method of Ca and Ca,Nd compound modification.Experimental alloy were prepared by using as-cast forming technique.The efforts of Ca and Ca, Nd addition on the as-cast microstructure and mechanical properties of Mg-Al alloys were investigated and analyzed by scanning electron microscope(SEM),energy dispersive spectroscopy (EDS),X-ray diffraction (XRD),Brinell testing machines, electronic universal testing machine, et cetera.Results show that: The great effects of Ca addition on the microstructure and mechanical properties of Mg-Al alloy are produced. The experiments in this group, when the Al/Ca ratio is only less than 6, The addition of Ca result in refined matrix microstructure greatly. It was significantly smaller of the dendrite size of thickβ-Mg17Al12 phase and secondary dendrite spacing.The amount of them significantly reduced. Furthermore, a small amount ofβ-Mg17Al12 was refined to short strip or granules. The new phase Al2Ca appears when the Ca has been added. The morphology of Al2Ca phase is changed from bone-shaped into grid-like. Meanwhile,β-Mg17Al12 phase continued to decline. Al2Ca phase have continuous net-like along the grain boundaries when the Al/Ca ratio is more than 3.β-Mg17Al12 phase have disappeared completely at the time.(2) Effects of Ca addition on the hardness of the test alloys have been investigated. Results show that:with the increase of calcium content, the hardness of the alloy increased accordingly. The highest hardness values of the alloys are 54.7HB,56.4HB,61.8HB. When Al2Ca phase is changed to the main second phase, brinell hardness of the alloy obvious increases. Due to structure of alloy refined and the second phase which is high hardness separated. When the Al has been added, the effect of Ca is less to hardness of the alloy(3) Amount of Ca can improve the tensile properties of alloys in high temperature.With the increase of Ca content the tensile properties of alloys in high temperature of the test alloy first increases and then decreases. Results show that:the addition of Ca is useful to the tensile properties of alloys in high temperature. Due to heat separation of brittle phases Al2Ca, the properties of alloys in high temperature of both A and B group alloys reaches the maximum value when Ca addition up to 1 wt%.With the further increase of Ca content, high tensile strength began to decline, but still higher than the matrix alloy.With the increase of Ca content the yield strength of alloys in high temperature of the test alloy increases, which indicated that Ca can improve the deformation resistance of alloys in high temperature. The plastic of the alloy increased and the brittleness of the alloy increases with the addition of Ca increased both in room temperature and high temperature.(4) The addition of Nd results in refined matrix micro structure greatly and the second phase morphology changing greatly. When Nd addition up to 0.3 wt%, The compounds with Nd do not appears. However, compared to the matrix alloy, semi-continuous net-like Al2Ca phase has disappeared and the microstructure of alloy is refined. When Nd addition up to 0.6 wt%, a fine needle Al11Nd3 phase appears, and Al2Ca exists in form of bone-like.β-Mg17Al12 phase morphology is refined more than before, Which exists mainly in the form of particles and a small amount of Ca have been dissolve in the alloy. At this point the second phases are mainly Al11Nd3, Al2Ca andβ-Mg17Al12 phase. When Nd addition is up to 0.9 wt%, Al11Nd3 phase of matrix alloy is changed from a fine needle into a short stick. However, the morphology ofβ-Mg17Al12 phase and Al2Ca phase is coarsed. (5) The tensile strength of matrix alloy increases at room temperature and high temperature when Ca addition up is appropriate. The tensile strength and elongation of the test alloy first increases and then decreases. When Nd addition up to 0.6 wt%, tensile strength of alloy were both at the optimal at room temperature and high temperature and the valves are 191Mpa 173Mpa,respectively.They are increased by 17.1% and 19.3% more than the matrix alloy, respectively. Following that the tensile strength started to decline, but still higher than the matrix Alloy. The ductility of alloys have been improved at room temperature and high temperature.The elongation rates were 6.6% and 9.6%, respectively.They increased by 34.6% and 23.0% compared to the matrix alloy, respectively. With the addition of Ca, Al2Ca phase continuous precipitation has been inhibited and the brittle effect of Ca to magnesium alloy is reduced.
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