| Rare earth can significantly improve the strength, heat and corrosion resistance of the conventional magnesium alloys, which makes the rare-earth magnesium alloys(Mg–RE) more and more attractive for aerospace and automotive applications. However, owing to the high chemical activity of both magnesium and rare earth elements, they tend to oxidize rapidly and to burn on air to bring a lot of inclusions into the Mg melt during the alloy melting process. Now the purification technology of Mg–RE alloy has become one of the key bottlenecks which restricting its application in industry. Because to get the expected effects, the amount of fluxes is at least 2%(wt. %) which results in severe environmental pollution and may increase the chance of additional flux inclusions and also lead to mass loss of rare earth compound. Recently, the gas bubbling as a non-flux refining method has attracted more and more attention due to its inclusion removing ability and excellent degassing capacity. Howe ver, up to now, there are no reports of the use of gas bubbling for refining Mg–RE alloys are reported. Therefore, the study on refining technologies for further improving the inherent quality of Mg–RE alloys has practical significance.In this study, the parameters of rotary injection Ar refining process on purifying effectiveness of Mg–10Gd–3Y–0.5Zr alloy were optimized. On this basis, the effect of complex melt-refining treatment(flux incorporating with rotating gas bubble stirring) on microstructure and mechanical behavior of the Mg–10Gd–3Y–0.5Zr alloy was studied systematically, and the optimal melt treatment process was obtained. In addition, the melt purifying mechanism of the complex melt-refining treatment for the Mg–10Gd–3Y–0.5Zr alloy was discussed systematically.Obtain the optimal parameters combination(Ar flow rate: 2L/min, time: 10 min, rotating speed: 150r/min). In this case, the volume fractions of nonmetallic inclusions in the unrefined alloy can be reduced from 0.47% to 0.32%, where clean melt can be achieved. Correspondingly, the UTS and the EL reached to 296.6 MPa, 1.4% respectively compared with 244.9 MPa, 0.7% of the unrefined one. In the process of gas bubbling treatment, high Ar flow rate will lead to the violently moving of melt, thus the surface oxidation will be raised; Enough Ar spraying time should be guaranteed to introduce the small, uniform and well distributed Ar bubbles, howe ver, the overtime rotating gas bubble stirring process will decrease the mechanical properties; High rotating speed could provides intensive melt shearing, resulting in the formation of fine Ar bubbles and also the inclusion particles, thus improve the chance of inclusions wetted by gas bubbles.Combined rotating gas bubble stirring with flux is an effective ne w method in refining Mg–10Gd–3Y–0.5Zr alloy. While 1% JDMJ flux incorporating with rotating gas bubbling refining method was employed, the volume fractions of nonmetallic inclusions in the unrefined alloy can be reduced significantly from 0.47% to 0.15%, where clean melt can be achieved. Correspondingly, the UTS and the EL reached to 312.3 MPa, 4.5% respectively compared with 244.9 MPa, 0.7% for the unrefined one. The use of melt flux decreased by 50% and significantly reduced environmental pollution. In addition, the melt purifying mechanism of the complex melt-refining treatment for the alloy was discussed systematically.The complex treatment would not change the phase composition but it does have a certain effect on the fracture pattern of the Mg–10Gd–3Y–0.5Zr alloy. In addition, the new melt treatment can decrease the loss of Zr.Based on the laboratory experiments, a missile cabin was fabricated usingGW103 K alloy successfully. This will be helpful for extending the industrial application of GW103 K alloy. |
PDF Full Text Request