Research On Light Weight Alloy Material Of Mg₂Si Intermetallic Compound

The intermetallic compound Mg2Si has such advantages as low density, high melting temperature and high special strength, so it has the potential to be used in aerospace and automobile industry as a kind of structural material at high temperatures. The Al based Mg2Si alloy was taken as the research object in this paper. Such methods as adding alloying elements into the melt during melting, electromagnetic stirring during solidification and heat treatment of samples were taken to modify the microstructures in order to improve the mechanical properties of Al-Mg2Si alloy.It is found from the experimental results that with appropriate alloying element additions, the microstructures of Al-Mg2Si hypereutectic alloy are effectively improved. The Mg3(P04)2 compound which was formed after adding P element into the alloy becomes the heterogeneous nucleus of the primary Mg2Si, and it not only makes Mg2Si refined but also improve the elongation and UTS of Al-20Mg2Si alloy. The AlnRE3 internetallic and other complex nonstoichiometric compounds which were synthesized after adding rare earth elements (RE or Ce) are mostly distributed around Mg2Si boundaries and change its size and morphology. The Ca2Si compound synthesized with high melting temperature and cubic structure becomes the heterogeneous nucleus of the primary Mg2Si and makes it refined. The Cr2Ti particle in Al7.2(Cr2Ti)3.3 refiner not only acts as heterogeneous nucleus of the primary Mg2Si but also distributes around Mg2Si boundaries to restrain the growth of Mg2Si, so that the morphology of Mg2Si changes into regular spherical or granular shapes.When the Al-Mg2Si melt was electromagnetic stirred during solidification, the polyhedral primary Mg2Si becomes rod like or granular and its boundaries become more smooth. When the magnetic density is in an appropriate range which is determined by the three phase voltages and is about 100-120V, not only the size of Mg2Si becomes the smallest, but also the morphology of itbecomes the most regular. It is found that the Mg2Si grains are segregated in radius direction when Al-20Mg2Si alloy is electromagnetic stirred. The segregation degree becomes larger with increases of magnetic densities.The grain shapes of the primary Mg2Si change from polyhedral to ellipsoidal or spherical after the Al-50Mg2Si alloy was treated under the circular up and down thermal heat treatment process. With increases of heat treatment temperatures, the size of the primary Mg2Si becomes larger. The boundaries of the primary Mg2Si become more smooth when alloying elements were added into the alloy before the Al-50Mg2Si alloy was heat treated.