Effect of Zr modification on solidification behavior and mechanical properties of Mg–Y–RE (WE54) alloy

Magnesium alloys containing rare earth elements (RE) have received considerable attention in recent years due to their high mechanical strength and good heat-resisting performance. Among them, Mg–5%Y–4%RE (WE54) magnesium alloy is a high strength sand casting magnesium alloy for use at temperatures up to 300 ℃, which is of great interest to engineers in the aerospace industry. In the present work, the solidification behavior of Zr-containing WE54 alloy and Zr-free alloy was investigated by computer-aided cooling curve analysis (CA-CCA) technique. And the solidification microstructure and mechanical properties of them were also investigated comparatively. It is found from the cooling curves and as-cast microstructure of WE54 alloy that the nucleation temperature of α-Mg in WE54 alloy increases after Zr addition, and the as-cast microstructure of the alloy is significantly refined by Zr. While the phase constitution of WE54 alloy is not changed after Zr addition. These phenomena indicate that Zr acts as heterogeneous nuclei during the solidification of WE54 alloy. Due to refined microstructure, the mechanical properties of Zr-containing WE54 alloy is much higher than Zr-free WE54 alloy.

Characterization and Prediction of Microporosity Defect in Sand Cast WE54 Alloy Castings

In order to study the effect of Zr modification and riser size on microporosity defect distributions in WE54 alloy sand castings,the microporosity volume percentage in Zr-free and Zr-containing WE54 alloy plate castings was determined by density measurement based on Archimedes' principle,and the microstructure of the microporosity defects was observed by optical microscopy and scanning electron microscopy.Then by using Procast software,the Niyama criterion was calculated in order to investigate the validity of Niyama criterion on prediction of microporosity defects in WE54 alloy sand castings.It is found from the density measurement results that Zr addition does not affect the microporosity distributions in WE54 alloy castings.While the distribution area of microporosity defect in the plate castings decreases significantly as the riser size increases.Based on the experimental results,a riser selection principle for production of compact WE54 alloy castings is proposed that the solidification modulus of the riser should be greater than that of the casting by 30%,simply m_r > 1.3m_c.By comparing the experimental and simulating results,it is found that the predicted microporosity regions by Niyama criterion agrees well with experimental results,and a critical Niyama value of0.4 ℃^(0.5) s^(0.5) mm^(-1) is suggested for prediction of microporosity formation in WE54 alloy sand castings.

Hot Tearing of Sand Cast Mg-5 wt.% Y-4 wt.% RE (WE54) Alloy

Hot tearing is a common and severe defect occurring during solidification of castings.The rational understanding of hot tearing formation mechanism is beneficial to the foundry process design.In the present research,a new developed instrumented"CRC"equipment was applied in characterization of hot tearing in sand cast Mg-5 wt.%Y-4 wt.%RE(WE54)alloy with and without Zr addition.Microstructure observation and thermal analysis were carried out to help analyzing the results.The results showed that hot tearing onset occurs at a relatively low solid fraction(fs)in WE54 alloy sand castings,which indicates the participation of remaining liquid during hot tearing formation.Microstructure observation of the hot tearing surface also proves the liquid film existence between solidifying dendrites.The contraction strain caused by casting solidification induces the flowing of remaining liquid between solidifying dendrites and results in formation of interdendritic liquid films.These liquid films are separated by sufcient contraction stress and form hot cracks.The addition of Zr in WE54 alloy significantly refines the alloy microstructure and increases the solid fraction at hot tearing onset,both of which result in increasing of the fracture stress of interdendritic liquid film.Thus the hot tearing susceptibility of WE54 alloy is weakened by Zr addition.

Pivotal roles of tumor-draining lymph nodes in the abscopal effects from combined immunotherapy and radiotherapy

Background:Currently,due to synergy enhancement of anti-tumor effects and potent stimulation of abscopal effects,combination therapy with irradiation and programmed cell death protein 1/programmed death-ligand 1(PD-1/PD-L1)immune checkpoint inhibition(immuno-radiotherapy,iRT)has revolutionized the therapeutic guidelines.It has been demonstrated that tumor-draining lymph nodes(TDLN)are essential for effective antitumor immunity induced by radiotherapy,immunotherapy,or iRT.Given that the function of TDLN in iRT remains unclear,this study aimed to investigate the function and mechanism of TDLN in iRT-induced abscopal effects.Methods:The function of TDLN was evaluated using unilateral or bilateral MC38 and B16F10 subcutaneous tumor models with or without indicated TDLN.The flow cytometry,multiple immunofluorescence analysis,and NanoString analysis were utilized to detect the composition and function of the immune cells in the primary and abscopal tumor microenvironment.Additionally,we tempted to interrogate the possible mechanisms via RNA-sequencing of tumor-infiltrating lymphocytes and TDLN.Results:TDLN deficiency impaired the control of tumor growth by monotherapy.Bilateral TDLN removal rather than unilateral TDLN removal substantially curtailed iRT-stimulated anti-tumor and abscopal effects.Furthermore,in the absence of TDLN,the infiltration of CD45+and CD8+T cells was substantially reduced in both primary and abscopal tumors,and the anti-tumor function of CD8+T cells was attenuated as well.Additionally,the polarization of tumor-associated macrophages in primary and abscopal tumors were found to be dependent on intact bilateral TDLN.RNA-sequencing data indicated that impaired infiltration and anti-tumor effects of immune cells partially attributed to the altered secretion of components from the tumor microenvironment.Conclusions:TDLN play a critical role in iRT by promoting the infiltration of CD8+T cells and maintaining the M1/M2 macrophage ratio.