Fabrication And Characteristics Of Porous Magnesium By GASAR Continuous Casting Process

Metal-gas eutectic solidification method (Gasar) is the research hotspot in the field of porous materials. Porous material with pores regular aligned in the direction parallel to the solidification direction can be fabricated by Gasar. At the moment, in the three Gasar preparation processes (Gasar directional solidification method Gasar zone melting method and Gasar continuous casting method), Gasar continuous casting method is the most promising preparation technology in the industrial applications. In this investigation, Gasarite magnesium bars were prepared by Gasar continuous casting method successful. The effete of process parameters (throwing rate and atmosphere pressure, etc.) on the porosity, number density of pores have been studied. The mechanical properties of different porosity of Gasarite magnesium have been analysis and studied.Pure magnesium bars and AZ31magnesium alloy bars were prepared by vacuum horizontal continuous casting with a multi-mold, which is composed of heated graphite mold and water cooling copper mold. Observation of microstructure of alloy and pure magnesium bars, the results showed that the microstructure of AZ31magnesium alloy consisted of quantities of fine equiaxed grains, therefore alloy has good comprehensive mechanical properties that the tensile strength and elongation increased obviously. The tensile fractures of the AZ31magnesium alloy apparently presented characteristics of quasi cleavage. The microstructure Continuous casting of pure magnesium bars are mainly consisted of columnar crystals by the axial parallel and continuous growth.Gasarite magnesium bars were prepared with Gasar continuous casting method by a multi-mold, which was composed of heated graphite mold and water cooling copper mold successful. Research finding indicate that due to overcome the additional pressure Δp, the pore nucleation was scanty in the front-end of initial solidification therefore the porosity of the front-end of continuous casting sample is low and in the presence of bars outer green layer exist a certain thickness without porosity zone. The change of casting rate in Gasar continuous casting experiment does not affect the porosity of the Gasarite magnesium bars. Atmosphere pressure is the main process parameters affect pore characteristics parameters, Under an atmosphere of pure hydrogen, the porosity of the Gasarite magnesium sample decreased with the hydrogen pressure increases, meanwhile maximum pore diameter and average pore diameter also decreases. In a mixed atmosphere, the hydrogen partial pressure is fixed at0.1MPa, with the argon partial pressure increasing, the porosity of the Gasarite magnesium specimens appeared a significant downward trend, the pore diameter, including the maximum, minimum aperture of the stomatal pore size, and the average pore diameter also showed a decreasing trend, the maximum pore size is most obvious.The test of the mechanical properties of the Gasarite magnesium showed that, for the imporous pure magnesium sample, the fewer porosity and more uniform distributed porous provide the Gasarite magnesium specimens a improvement to tensile strength and compression strength. With the porosity increased to20.31%, the tensile strength and compression strength are less than imporous pure magnesium sample. The pore in the Gasarite magnesium specimens reduces the initial elastic modulus of the material significantly.