| Due to low density, high specific strength and stiffness and a series of advantages Magnesium alloy has been attracted much attention. At the same time there is also the disadvantage of Magnesium alloy, such as poor corrosion resistance. Fe is the main element as the deterioration of the corrosion resistance in magnesium alloys. How to remove Fe has become a hot topic in field of magnesium alloy. Vary-temperature Measurements of Melt was used to process pure magnesium, According to Mg-Fe phase diagram, solubility of Fe in magnesium was decreased though change temperature, meanwhile Fe was settled into the crucible after stewing reasonable time, by this way magnesium ingots with high properties can be obtained. First, use Magnesia porcelain crucible on 5Kw resistance furnace to melt pure magnesium by Vary-temperature Measurements of Melt, obtain a set of optimized process parameters. Then use the process parameters using Fe crucible on 20 Kw resistor furnace by Vary-temperature Measurements of Melt. The results are following:① Magnesium was processed by Vary-temperature Measurements of Melt in MgO ceramics crucible. The content of Fe in pure magnesium can be effectively reduced. when the standing temperature 650 ℃, the holding time 3h, The content of Fe in magnesium can be reduced from 110ppm(0.011%wt%) to 30ppm( 0.003%wt%). While At the temperature of 630℃, 670℃, 690℃, respectively, the holding time 3h, The content of Fe in magnesium can be reduced to 50ppm(0.005wt%), 40ppm(0.004wt%), 40ppm(0.004wt%). At the temperature of 650℃, the holding time is 1h, 2h respectively. The content of Fe can be reduced to 60ppm(0.006wt%), 50ppm(0.005wt%). The location of sample were from the bottom of the ingot 75 mm, 1/2 Radius.② The sample through Vary-temperature Measurements of Melt were investigated by OM, SEM and EDS analysis. We found that the size of grain is both big, but the grain size of the sample after Vary-temperature Measurements of Melt is much smaller. After treatment the second phase inclusions decreased significantly. After Vary-temperature Measurements of Melt, the hardness of pure magnesium increased from 25.2 up to 27.4, relative conductivity increased from 38.7 to 41. The room temperature mechanical properties of pure magnesium also significantly raise out, theyield strength increased from 26.3MPa to 31.8MPa, tensile strength increased from 65.6MPa to 91.6MPa, elongation increased from 5.844% to 11.711%.③ After Vary-temperature Measurements of Melt, standing temperature 650 ℃, the holding time 3h, corrosion resistance significantly improved. corrosion rate increased with the increase of time both with and without Vary-temperature Measurements of Melt, when corrosion time more than 96 h, both of the corrosion rate are stable. Whether the increase in the corrosion rate of the corrosion rate stabilized phase or stage, the corrosion rate of sample which through Vary-temperature Measurements of Melt is lower than the sample without Vary-temperature Measurements of Melt.④ Using large capacity and low carbon steel crucible melt temperature treatment of pure magnesium production. The study was divided into three groups. The first group test without the melt temperature treatment, a second set of experiments in 650℃, insulation 3h, pouring temperature is 690℃,. The third experiment in 650℃, insulation 3h, pouring temperature for 670℃,. ICP composition analysis show that the 90 ppm 0.009wt% and 70 ppm 0.007wt% not by the melt temperature treatment cast above the mouth position of the upper, middle and lower part of the three part melt of Fe content were 90 ppm 0.009wt%. After the melt temperature and pouring temperature is 690℃, poured above the mouth position of the upper, middle and lower part of the three part melt of Fe content were 30ppm(0.003wt%) and 20 ppm 0.002wt%, 40 ppm 0.004wt%. After the melt temperature and pouring temperature of 670℃, cast above the mouth position of the upper, middle and lower part of the three part melt of Fe content were 40 ppm(0.004wt%) and 40 ppm(0.004wt%) and 40 ppm 0.004wt%. Results show that the device of pure magnesium melt temperature treatment can effectively reduce the content of Fe in pure magnesium, and pouring temperature from 670℃, rise to 690℃, has no influence on the effect of purified.⑤ The Fe atom in magnesium melt as the research object, established the Fe atom of settling velocity and sediment mathematical model of distance in magnesium melt. Suffered gravity, buoyancy, movement, etc. according to the viscous resistance of Fe atoms in the molten magnesium to establish a balance equation, obtain Fe atom by magnesium melt temperature, melt viscosity coefficient, holding time and other factors control in magnesium melt Warming in the process of settling velocity and sedimentation distance model: 1)2exp(1)2exp(+-=Akt Akt k Aν andktg Sdf693.018)1(2--=γμργ. |
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