Microstructures And Mechanical Properties Of Mg-Si-X Magnesium Alloy Research

Magnesium alloys have been developed and used in industry for its low density, high strength, good shielding performance, excellent casting and cutting performance. As a green construction materials in 21st, magnesium alloy had significant advantages in environmental protection, while, the variety and application of magnesium alloy are very limited, and to this end, development for new alloys is still ongoing. It is expected to develop excellent performance alloys in business. To reduce costs is entrepreneurs’dream. It was considered that the magnesium alloys, which contain Si and Zn like commercial alloys AS41 and AZ91D, are lower in production costs than the other alloys. In this paper, the microstructures of cast Mg-Si binary alloys in different chemical compositions were observed and analyzed, the refinement and modification of Y, Sr, Zr upon the hypoeutectic alloy Mg-1.0Si were presented and concluded, the microstructures and mechanical properties of Mg-1.0Si-xZn alloys were studied. Besides microstructural observation, the density and hardness were measured, and tensile test was carried on for those alloys.The results are showed as followed:(1) The structure of Mg-Si binary cast alloy is mainly composed of α-Mg and Mg2Si. The content of Si changes in 0.5-1.5wt.%,α-Mg is dendritic in shape, Mg2Si is in eutectic structure. When the content of Si is more than 2.0%, Mg2Si is like polygons as primary phase or lamellar in eutectic Mg2Si. With the increase of Si content, dendritic α-Mg is significantly refined, in particular, when added 2.0Si,α-Mg likes small lumps, their size is approximately 1/20 of 0.5Si, and 1/40 of 1.0Si、1.34Si、1.5Si. Mg2Si in eutectics changes from mesh to lamellar to fibrous or rod shapes, and pre-eutectic Mg2Si likes polygons.(2) Y and Sr had a role of refinement or modification for cast Mg-1.0Si magnesium alloys, especially for the morphology of Mg2Si. Addition of 1.0Y changed Mg2Si into characters from lamellar shape,0.02Sr maked Mg2Si more dense, Zr had a good refinement role for Mg-1.0Si magnesium alloy, 1.0Zr had a good dendrite refinement for a-Mg,1.5Zr had a significant modification effect on eutectic Mg2Si, and it further improved the structure and mechanical property of Mg-1.0Si alloy.(3) Mg-l.OSi-xZn cast alloys consist of a-Mg matrix, Mg2Si and MgZn2 And the microstructures change significantly by an increase of Zn. When analyzed under a laser scanning confocal microscope (LSCM), the microstructure of Mg-1.0Si-2.5Zn alloys is the most uniform in phase distribution when compared with other alloys in change of Zn content. The density of cast Mg-1.0Si-xZn magnesium alloy, change in the interval of 1.74-1.82g·cm-3, is close to the experimental AZ91D alloy. The study shows that the average tensile strength of Mg-1.0Si-2.5Zn alloy is 127.6MPa with an improvement of 17.7% and the elongation is 12.92% with 166.9% in comparison with the AZ91D alloy.