| Mg?10wt.%Gd?3wt.%Y?0.5wt.%Zr (GW103K) magnesium alloy shows large promise for the automotive, aviation, military and communication industry due to its high strength?to?weight ratio, high specific strength at both room and elevated temperature. Unfortunatlly, the nonmetallic inclusions in the alloy impair the mechanical and corrosion properties of the alloy and then limit the usage of this alloy. Therefore, it is important to remove nonmetallic inclusions from the alloy melts. Currently, the traditional flux purification method is still considered as the main purifying method due to its high purifying effectiveness, low cost and convenience. However, ascribed to the reaction between rare earth and MgCl2, the traditional flux containing MgCl2 is not suitable for purifying GW103K alloy. Although the fluxes without MgCl2 were employed to refine Mg?RE alloys,the purifying effectiveness is not satisfied. Consquently, it is urgent to explore new fluxes for Mg?RE alloys. The ceramic foam filter (CFF) has been widely used in the foundry industry currently due to its excellent adsorption ability to the fine inclusions and liquid flux?inclusions. However, there are no reports of the use of the CFF for refining Mg?RE magnesium alloys. Therefore, it is meaningful to find new methods to refine GW103K alloy.GdCl3 and YCl3 were introduced into common commercial JDMJ and RJ6 flux in this study, and the effects of these fluxes on the nonmetallic inclusion contents, microstructures, phases, mechanical properties and corrosion resistance of GW103K alloy were investigated. It is found that JDMJ+5% GdCl3 showed greatest purifying efficiency among these fluxes. The quantitative analysis of the nonmetallic inclusions demonstrated that, compared with RJ6 purification, the statistical volume fractions of inclusions decreased from 0.869% to 0.389%.The process of the flux combined with CFF multistage purification method were conducted and has been proved to be an effective purifying method. The influence of the rare earth chlorides on the physicochemical properties of the fluxes has been tested. The mechanism of the flux adsorbing nonmetallic inclusions was discussed via thermodynamic analysis.The results indicated that the loss of Gd/Y in the alloy could be limited to a certain degree when introducing GdCl3/YCl3 into commercial JDMJ flux which contains MgCl2. The rate of Gd loss could reduce 13.5% when the melts were refined by JDMJ+5%GdCl3; the rate of Y loss reduced 37.8% when refined by JDMJ+5%YCl3. Based on the thermodynamic calculation, the reason of this suppressing effect lies on the reduction of Gibbs free energy of the reaction MgCl 2 + RE→RECl2+Mg. The decrease of Gibbs free energy means the rate of the reaction was slowed down and then suppressed the burn loss of the rare earth elements.The statistical volume fractions of the nonmetallic inclusions indicated that the contents of the nonmetallic inclusions in the alloy decreased to a certain degree after purified by JDMJ and RJ6 fluxes which containing proper contents of GdCl3 and YCl3. The mechanical properties of the alloy could benefit from the decrease of the nonmetallic inclusion contents. Theσb,σs andδof the alloy (the as?cast condition), which purified by JDMJ+5%GdCl3 combined with 10 ppi MgO foam filtratration, increased from 198.57MPa,145.25MPa and 1.64% (before purified) to 248MPa, 154.74MP and 3.12% (after purified), respectively. Due to the disadvantages of cutting continious of the base, caursing stress concentration and supplying crack resourse, the nonmetallic inclusions in the alloy do great harm to the mechanical properties. TEM investigation also revealed that these nonmetallic inclusions could block the moving of the dislocation. Hence, the blocking dislocation before the inclusions results in the stress concentration.The fluidity and hot?cracking were also improved while the melts were purified by JDMJ+5%GdCl3. The flowing length could reach 820mm and the hot?cracking factors (HCS) were nearly zero. At the same time, the flowing length of the unrefined specimen was only 780mm, and the HCS attains 8. Based on the Einstein equationμc =μ0 [1 +2.5φ+10.25φ2], the nonmetallic inclusions in the alloy melts could affect the solidification course and enhance the viscosities of the melts. The improvement of the viscosity decreases the fluidities of the alloy melts directly. The online measurements of the solidification of the alloy indicated that the"impact stress"caused by solidification and the inadequate feeding are considered as the two main reasons of the hot?cracking.Compared with the unrefined specimen (1.68mg cm?2 d?1), the corrosion rates of the specimens refined by JDMJ+5%GdCl3 and JDMJ+5%YCl3 decreased from 1.68mg cm?2 d?1 to 1.1 mg cm?2 d?1 and 0.98 mg cm?2 d?1, respectively. This was also verified by electrochemical tests. Moreover, the research results indicated that the nonmetallic inclusion and the Mg base could form couple corrosion and then accelerate the corrosion process. Therefore, the decrease of the inclusion contents results in the reduction of the cathode area, and then slowed down the corrosion rate.The effects of different temperature on the density, viscosity and surface tension of the fluxes were tested. The thermodynamic analysis about the spreadability, separation and refining properties of the flux revealed that the surface tension was an important parameter of the flux. Although the lowerσflux?inclusionis helpful for flux to adsorb nonmetallic inclusions, the low σflux-metal also makes it difficult for flux to separate from the Mg melts.The concept of adsorption potential was introduced to explain the dynamic course about the sinking of the nonmetallic inclusions. Then, a dynamic model that the flux adsorbs and dissolvs the nonmetallic inclusions was put forword. The Reynolds number of the inclusions during the course of sinking was calculated. Re < 2 indicates that sinking pattern of the inclusion clusters follows Stocks model: The model illustrated that the sizes of the inclusion clusters and the density of the flux were the main factors which affected the sinking velocities of the inclusions.A purifying efficiency equation to ceramic foam filtratoin was established as. The result indicats that the Purifyingefficiency of the CFF could be enhanced with the increase of the porosity. By means of analysing the startup conditions, the Mills model was modified as . This is helpful to guarantee the cast process goes well.Based on the laboratory experiments, a missile cabin was fabricated using GW103K alloy successfully. This will be helpful for extending the industrial application of GW103K alloy.
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