| With the entrance of 21st century the environment protecting and sustainable development have become the common concerns of the world. In order to realize the conversion of traditional high consuming pattern to sustainable developing pattern, reasonable using, saving and protecting of the resource have received the recognition. Magnesium and magnesium alloys are kinds of the lightest structural metal alloys without pollution. The exploitation and application of them are very important to the development of the materials science field and society.Magnesium alloys have many excellent properties, such as low weight, high specific strength and stiffness, high heat and electrical conductivity, good damping and shock absorption, excellent electromagnetic shielding capability and easy processing, as well as a good recovery capability. In recent years, the application of magnesium alloys has become the important research item for the countries with the developing automobile industry.Magnesium resource is abundant in our country. The production of original magnesium is sencond in the word, which is only lower than that of the America. However, the total amounts of excellent magnesium alloys products are very small. It is mainly because that the magnesium alloys processing technology of our country is far drop behind the developing countries. It is urgent affairs for our country to exert the resource predominance and tranform the original to the excellent products under the condition of resource absence. So the study andextending applization of the magnesium alloy processing techonology have extensive foreground and high significance.In present, more than 90% magnesium alloy components are produced by die-casting. However, the die-casting processing has many problems which cannot be overcame. Semisolid casting can solve the problems above and decrease macrosegregations, porosity and forming efforts. The non-dendritic microstructure is the key of the semisolid casting.Several processes can generate the non-dendritic globular microstructure. Among which, Magnetohydrodynamic Stirring and Strain-induced Melt Activation ( SIMA) are the better processes applied in the industry. However, the electricity energy consumption of the former is too large, and the equipment and processing of which are too complex, and the stirring efficiency of which is also low. SIMA has been the subject of many studies. Comparing with other starting semisolid material producing methods SIMA has several advantages. It omits the procedure of molten metal treatment, cleans the metals, increases the production and is applicable for both low and high melting alloys. Moreover, oxidation and burning can be avoided for the magnesium alloy produced by SIMA process. However, for the last few decades, most attention has been focused on the investigation into thixotropic properties and forming of aluminum alloys and Pb-Sn alloys. However, The attention to evolution mechanism of magnesium alloy is very limited, which retards the development and application of the magnesium alloy semisolid technology.The AZ91D magnesium alloy semisolid billets are fabricated by SIMA processing in this paper. The main researches are following.(1) The effect of RE oxide on the casting and semi-solid microstructure of AZ91D magnesium alloy produced by SIMA process. The microstructures of AZ91D magnesium alloys with 1% RE oxide were investigated. The RE oxide includes Ce2O^ Sm2O3> Pr2O3> La2O3> Nd2O3> Y2O3> Dy2O3> Er2O3.The results indicate that the RE oxide affect the microstructure of casting AZ91D alloys, especially the Mgi7Ali2 phase. The RE oxide Sm2O3> Pr2O3, La2O3 obviously affect the microstructure of semi-solidAZ91D magnesium alloys, the others effect were inconspicuous.(2) The effect's characters and principles of RE oxide on the semi-solid microstmcture of AZ91D magnesium alloy produced by SIMA process. The experiments analyzed the configuration, size of RE oxide in AZ91D magnesium alloys. The RE oxide namiparticules discretely distributed in the AZ91D magnesium alloys, so as to enhance the propagation of dislocations, to resist the climb and slip of dislocations and ultimately restrain the combination and growth and combination of the recrystallization grains. For this reason, we could obtain the smaller grains.(3) The effect of RE oxide Pr2O3 on the semi-solid microstmcture of AZ91D magnesium alloy produced by SIMA process. The addition of Pr2C>3 to the AZ91D alloy can obtain the smaller grains, because the recrystallization grains were prevented by the dispersive distribution of AlnPr3 from growing. If the overabundant P^Cb (over 2%) was added to the AZ91D, the "claviform" AluPrs would be founded. The effect of claviform AlnPr3 particle on growth of recrystallized grains is smaller than that of the dispersive distribution of AlnPr3 particle. Therefore, as to appropriate P^Cb addition (2%), the effect of get fine grains is not obvious.(4) The effect of RE oxide Pr2O3 on the semi-solid properties of AZ91D magnesium alloy produced by SIMA process. The addition of Pr2C>3 to the AZ91D alloy can improve the rigidity, but the effect wasn't obvious. Under the same load, the loss of mass on the AZ91D magnesium alloys with 1% and 2% Pr2O3 were lower than the AZ91D alloys. But the loss of mass improve when the overabundant Pr2O3 (3%) was added to the AZ91D. These phenomenons indicate the RE oxide Pr2O3 addition can improve the resistance of wear at stated range.
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