Preparation Of Grain-refiners And Their Effects On Microstructure And Mechanical Properties Of Magnesium And Magnesium Alloys

Several special master alloys such as Mg-Al-C, Mg-RE(Ce, La) and Mg-Zr were prepared to refine the corresponding magnesium alloys such as the pure Magnesium, AZ9l and Mg+4.5%Zn alloys. Their effects on microstructure and mechanical properties of magnesium alloys examined by SEM, X-ray, DTA, EDS, etc., are studied emphatically. The results show that Mg-Al-C, Mg-RE(Ce, La) and Mg-Zr master alloys are good refiners, the grain refining effect of Magnesium alloys is remarkable, and the tensile strength and hardness increases greatly. The refinement mechanisms are also discussed. The grain size of as-cast pure Magnesium changed from about 180～230μm to 30~50μm and the tensile strength increased from 115.2 MPa to 142.4~152 MPa after adding Mg-Al-C, Mg-Ce, Mg-La and Mg-Zr alloys respectively. These grain refiners also have a good effect on Magnesium alloys. The grain-refinement mechanism of Mg-Al-C for AZ91 alloy is the formation of nucleus particle A14C3, whose crystal lattice is the same asα-Mg and the lattice disregistry is small. As the addition amount of grain refiner in alloys increases, the grain size becomes smaller, meanwhile, the mechanical properties have been upgraded, the best addition for AZ91 Magnesium alloys is 0.6~0.9% and the grain refining effect is shown obviously. The mechanical properties with refined structures are tested. It proves that both plasticity and the strength are improved. Finally, the results show that grain refiner can keep active and have a long-life activity in the liquids of magnesium alloys. Adding Mg-RE(Ce, La) and Mg-Zr simultaneously into Mg+4.5%Zn alloy, the grain of the alloy was refined notably and its mechanical properties enhanced intensely, and the refinement mechanism also interpreted .