Study Of Preparation Of Ignition-Proof Magnesium Alloy Controlled By Pulsed Magnetic Fields

Magnesium alloys, as a kind of environmental materials, have been widely used in aeronautic, automotive, electronic industries in recent years. Refining solidification structure of the alloys could enhance their mechanical properties,A lot of studies showed that using the magnetic field during so1idification of alloys is an effective way to refine the microstructure of the alloys.This thesis tests a low-voltage pulse magnetic field(LVPMF) device designed and made by ourselves with Al and reports the preparation process, microstructure and mechanical properties of Ignition-Proof magnesium alloy ZM5-3%Ca under LVPMF, as well as the related mechanism.The experimental results show that solidified structures of aluminum and magnesium alloy ZM5-3%Ca can be improved apparently by LVPMF. With the increase of pulse voltage, pulse frequency or preheating temperature of mold, Solidification Structure of pure Al are refined, the depth of cavitations reduces, the proportion of equiaxed grains of aluminum increases gradually. solidified structure of the alloy can be refined greatly by low-voltage pulsed magnetic field. With the increase of pulse voltage , pulse frequency, casting temperature or preheating temperature of mold, grain size of the alloy decreases, dendrites degrades gradually and primary phase changes from well-developed dendrite to equiaxed grain or rose-shaped crystal. Without LVPMF,With the increase of casting temperature or preheating temperature of mold, Solidification Structure of pure Al and ZM5-3%Ca alloy are coarsened, morphology of Solidification Structure always is developed columnar crystal and dendrite respectively. Compared with influence of direct current pulsation magnetic field(DCPMF), the effect of LVPMF on solidified structure of the alloy is more obvious.LVPMF treatment influences the preferred orientation of magnesium alloy ZM5-3%Ca. Under the the magnetic field, the originally preferred orientation is changed. Furthermore, with long time treatment, new preferred orientation of magnesium alloy ZM5-3%Ca takes place instead of the originally preferred orientation.Non-dendritic semi-solid magnesium alloy which primary phase is globular or nearly spherical particles can also be produced by reheating the magnesium alloy with LVPMF treatment. Discharging voltage, heating temperature and holding time affect the microstructure evolution during partial remelting.With LVPMF treatment, the strength of magnesium alloy ZM5-3%Ca can be increased, and the maximal extent of the increase of ultimate tensile strength is about 15.7%, but the plasticity is not changed. The yield strength and ultimate tensile strength increase with the increment of discharging voltage and frequency.The compression stress of semi-solid specimen prepared by LVPMF is much lower than that of the semi-solid specimen solidified conventionally and it decreases with the decrease of strain rate or the increase of deformation temperature. Strain rate, deformation temperature and compressed amount all affect microstructure of semi-solid compression.