Study On Microstructure And Mechanical Properties Of Mg-Y-Ca-Zr Magnesium Alloy Plate

Energy crisis and environmental problems have become more and more serious,the car lightweight, energy conservation has become a hot spot of public concern, the social is pressing need lightweight magnesium alloy to replace the existing heavy metal. Wrought magnesium alloy is easily oxidized, it is difficult to become an important issue restrict deformation of magnesium alloy plate has been widely used, the thesis by refining the alloy grain and improve the alloy rolling temperature, the development of a high oxidation-resistant material formability of magnesium alloy, and to study its microstructure and mechanical properties.This thesis presents the methods of casting, processing and testing of a magnesium alloy plate with high formability in the experimental environment. Neophot-21 optical microscope, JEM-200 CX and JSM-6460 scanning electron microscope were used to observe the microstructure of Mg-3.5Y-0.9Ca-0.6Zr magnesium alloy. Tensile tests were applied to materials for six different processing conditions: as cast, natural aging for three months after casting, as rolled, solution treatment at 420℃ for 5h, solution treatment at 450℃ for 5h and solution treatment at 470℃ for 5h.As cast Mg-3.5Y-0.9Ca-0.6Zr magnesium alloy shows a uniform equiaxed grain with a larger size.After natural aging, grains become fine, but there are many fine second phase precipitates of Mg24Y5 and Mg2 Ca, and a compound composed by α-Mg solid solution, Mg24Y5 and Mg2 Ca compound and dissociative Zr ion scattered along the grain boundaries, which forming elements segregation. The tensile properties were improved after natural aging with a tensile strength of 172.7MPa, yield strength of 57 MPa and elongation of 17.6%, which shows better plasticity than untreated one.After a solution treatment, the grain size of Mg-3.5Y-0.9Ca-0.6Zr magnesium alloy plate is larger than as rolled one, but finer than as cast one or as cast + natural aging. Similar to natural aging condition, there are relatively few second phase precipitates at grain boundaries.There still exists the phenomenon of segregation in the microstructure of the alloy after solution treatment. The segregation of various elements caused by Y element is not promptly dispersed into the grain matrix during the rolling process and it is distributed as elongated strip or circular strip along the grain boundaries.Mg-3.5Y-0.9Ca-0.6Zr-rolled magnesium alloy plates had been solution treatment respectively at 420℃, 450℃, 470℃ for 5 hours. CoMPared to the mechanical properties of the alloy plate after solution treatment at different temperatures, the plate at 450℃ has the best properties for tensile strength of 208.4MPa, yield strength of 102.2MPa, elongation of 25.9%.