Preparation Of Magnesium Matrix Composites By In-situ Reaction Method With Oxides

Magnesium matrix composites （Mg-MMCs） are a kind of composites that contain highstrength and high modulus as their reinforcements being added into matrix of magnesiumor magnesium alloy. Compared with magnesium and magnesium alloy, Mg-MMCspossess better mechanical and physical properties, as well as lower density and gooddamping capacity. As a result, Mg-MMCs are more promising material than traditionalmetals and Aluminum matrix composite and have being research focus in the area ofcomposites since1970’s.In this research, Mg-MMCs have being prepared by the method of in-situ reactionbelow the melting point of magnesium （649℃）, with kinds of oxides, including SiO₂,Al₂O₃, ZnO and TiO₂. The reaction mechanism and process of each system has beenresearched. Also the microstructures, mechanical properties and wear resistance of eachkind of Mg-MMCs have been researched and discussed.First of all, thermodynamically calculations were conducted on each oxide system andthe results proved that all oxides were able to react with magnesium below the meltingpoint of magnesium and produced MgO or other intermetallic compounds with highhardness as the reinforcements of composites. Based on the results of XRD and DTAanalysis, the reaction process and products in all systems have been studied. With the helpof analysis of microstructures, the reaction mechanism in each system was carefullyresearched. The results turned out that diffusion controlled the process of in-situ reaction.Furthermore, hardness, tensile strength and wear resistance of composites with differentoxide system or with different contents of oxide were examined and compared.This research also focused on the influence of preparation process, including blendingmanner, compacting pressure, sintering process, on the microstructures and properties ofdifferent composites. Ultrasonic assisted stirring was a new kind of blending manner,which was able to disperse fine particle well and thoroughly, while ball milling methodwas capable of producing crystal defects and internal stress that were advantageous forraise internal energy of the system. When the compacting pressure reached500MPa, sintered composites would get best properties and microstructures. For different oxidessystem, the influence of sintering process was different as well.At last, the growth mechanism of MgO nanorods growing in Mg-SiO₂and Mg-Al₂O₃systems was studies and it’s found that the growth of MgO nanorods produced by in-situreaction method followed the VS mechanism.