Study On Microstructure And Propertise Of Mg-Al-Sr-RE Magnesium Alloys

Magnesium alloy is one of the lightest metal structure materials in the practical application, which have many special advantages, such as low density, high specific strength, high specific rigidity, good machinability, good electromagnetie shielding performance and easy recycling etc. They have been successfully used in various structures such as navigation, space flight, 3C product, power tool and traffic etc. However, the commercial die casting magnesium alloys fail to meet the requirement of drive train and other systems in automobiles. This is mainly on account of their imperfect strength and toughness, especially the weak strength in high temperature.At present, Al is the main alloying elements in the major industrial magnesium alloys. Mg17Al12 is the most important strengthening phase for Mg-Al series alloys, but its low melting point, poor stability and reticular existing in magnesium alloys. Practice shows that alloying can effectively improve the mechanical properties. The sizes of crystalline grains affect the mechanics properties of the magnesium alloys. Research shows that rare earth and alkaline earth elements Sr have a better refinement on magnesium alloys grain organizations. Therefore, this paper adopt the Mg, Al, Sr and RE alloys to determine the existing way and strengthening mechanism of RE and Sr in Mg-Al based Alloys.In this paper, Mg-Sr master alloys, AJ62 magnesium alloy and various Y, Nd content of the AJ62 alloy were prepared by "mixture method". Then the microstructure of various Y, Nd content of the AJ62 alloy were analyzed by XRD and EDS, and also the mechanical properties were tested, Finally the fracture morphology were studied and determined the fracture mechanism by SEM.The results show that:â‘ Mg-4Sr master alloy is consist of a-Mg, Mg17Sr2, and Mg17Sr2 is distributed along the boundary of matrix grain. Mg-6Al-2Sr is consisted of a-Mg,Mg17Al12 and Al4Sr, and Al4Sr is distributed along grain boundaries.â‘¡Y ,rare earth elements, has refining effect on magnesium alloy structure. While adding 1.5wt% Y, the grain of AJ62+Y is finest. XRD and EDS show that new high-temperature and hard phases Al2Y and Al3Y are formed in the alloys, which are distributed in grain boundary and intragranular after adding Y. The mechanical property test shows that containing 1.5wt% Y, AJ62 alloy reached the best mechanical properties, which tensile strength, yielding strength and elongation respectively improves 20.6%,24.6% and 52.9%, and the fracture mechanism mainly are cleavage fracture and quasi-cleavage fracture.â‘¢Nd has refining effect on alloy grain structure too. When containing 0.5wt% Nd, the structure refinement effect of the alloy is best; XRD Analysis and EDS spectrum show that with adding Nd the alloy formed the high-temperature and hard new phases Al2Nd and Al3Nd, The mechanical property test shows that containing 0.5wt% Nd, the alloy reached the best mechanical properties, which tensile strength, yielding strength and elongation respectively improves 13.5%, 15.9% and 49.1%, and the fracture morphology mechanism mainly is quasi-cleavage fracture.