Study On Purification Flux For Mg-Gd-Y-Zr Alloys

Rare earth compounds are able to purify alloy melt, refine alloy structure, improve casting ability, mechanical properties, corrosion resistance and so on. A series of RE magnesium alloys with the high performance have been developed, such as GW series and NZK series, which is greatly helpful to expand magnesium application field.However, RE magnesium alloy can not be purified by present fluxes, because rare earth can react with MgCl2 in the fluxes which lead to mass loss of rare earth compound, and the effect of the flux without MgCl2 can not reach the expected level. Therefore, new kinds of fluxes suitable for RE magnesium alloy refining need to be developed as soon as possible.According to the purifying problems of the Mg-Gd-Y alloy, the present study researched on developing new fluxes JDY and JDGd. Also, the study has investigated the effects of the new fluxes JDY and JDGd on the impurity content, microstructure, phase, loss of RE compound, mechanical properties, corrosion resistance and casting fluidity of RE magnesium alloy GW103K by experimental methods such as inductively coupled plasma analyzer(ICP), optical microscopy(OM), image analysis apparatus with a Leco image analysis software, scanning electron microscopy(SEM) with energy dispersive X-ray analyses (EDAX), X-ray diffractometer (XRD), electrochemical measuring system.The main research results are as followed:1) The new fluxes containing some chloridize rare earth can greatly remove the impurities, and reduce the content of impurities larger than 10μm from 26.49% to 14.42%. However, when the chloridize rare earth is excessive, the flux will be inclined to become conglomeration, which will lead to flux impurities in the alloy melt.2) The Y losses of alloys which are purified by the new fluxes JDY decrease as the YCl3 content increases, when the addition of YCl3 is 7.5wt%, the loss of Y will keep steady in some 11.2wt%; The Gd losses of alloys which are purified by the new fluxes JDGd decreas as the GdCl3 content increases, when the addition of GdCl3 is 7.5wt%, the loss of Y will keep steady in some 4.4wt%.3) After refined by the fluxes JDY和JDGd,mechanical properties, corrosion resistance and casting fluidity of RE magnesium alloy are improved greatly. When the addition of YCl3 is 2.5%, the alloy examples'mechanical propertiesσb andδreach to the highest 228.25MPa and 5.26%, and the corrosion rate decreases to the lowest 0.452mg·cm-2·d-1 , and the casting fluidity longth is the longest 121cm; When the addition of GdCl3 is 2.5%, the alloy examples'mechanical propertiesσb andδreach to the highest 225.63MPa and 5.12%, and the corrosion rate decreases to the lowest 0.513mg·cm-2·d-1 , and the casting fluidity longth is the longest 122cm.4) According to the experiments of flux composition optimization, physical and chemical properties testing and refining draft optimization, the research results show that the new complex fluxes JDRJ+2.5%YCl3/GdCl3 can not only greatly reduce the loss of Y and Gd, but also purify the alloy melt effectively, which is better than the present fluxes RJ-6 and JDMJ.