查看更多>>摘要：Microstructure and mechanical properties of Mg-Zn-Y alloys with different Zn/Y atomic ratios with or without artificial cooling(AC)extrusion were systematically investigated in this work.The results show that bimodal microstructure consist-ing of submicron dynamic recrystallized(DRXed)grains with high fraction of low-angle grain boundaries(LAGBs)and elongated unDRXed grains was formed in Mg98.7Zn1Y0.3 alloy with AC extrusion.The AC process effectively limits the growth of precipitated phases,and large amount of nanoscale precipitates were dynamically precipitated during the extrusion process.AC extrusion could effectually refine the lamellar 14H LPSO phases and inhibit the transition from stacking faults to LSPO phases in Mg98Zn1Y1 alloy and the narrow LPSO phase in Mg98Zn1Y1-AC alloy which could promote the nuclea-tion of DRXed grains.The AC extrusion significantly improves the strength of Mg-Zn-Y alloys.Owing to AC extrusion,the strength improvement of Mg98.7Zn1Y0.3 alloy is mainly attributed to fine grain strengthening,dislocation strengthening,and nano-phases precipitation strengthening.After AC process,more fine grains and nano-phases jointly strengthen the Mg98Zn1Y1 alloy.The Mg98Zn1Y1 alloy obtains optimal mechanical properties after extrusion at 623 K,with ultimate tensile strength(UTS)of 406 MPa,yield strength(YS)of 388 MPa,and elongation(EL)of 5.6％.
查看更多>>摘要：The Mg-Zn-Gd alloy with quasicrystal icosahedral phase was processed by high-pressure torsion(HPT).The effect of bimodal I-phase on the dynamic recrystallization was analyzed by transmission electron microscopy.The results showed that the block I-phase can stimulate obvious particle-stimulated nucleation and dynamic recrystallization(DRX)grains were preferentially formed after HPT for 5 turns,while the granular I-phase only promoted the generation of sub-grains.The ori-entation relationship was determined as twofold//[1210]and fivefold//(0002)Mg.Moreover,after HPT for 9 turns,the DRX grains induced by block I-phase appeared to grow up and coarsened.Compared with block I-phase,the grains induced by granular I-phase presented much smaller size and distributed more homogeneous due to the strong pinning effect.
查看更多>>摘要：To investigate the potential of direct ultrasonic vibration on improving the performance of magnesium alloys,this study first employed the ultrasonic vibration compression(UVC)on the solid solution treated AZ91 alloy,and explored its microstruc-ture evolution and mechanical properties under UVC.Within only two seconds,the UVC alloys showed large deformation strains of 34.8-54.4％,and sudden increase of sample temperature to 243 ℃.Microstructure characterizations proved that UVC promoted the formation of abundant shear bands,fine grains,and the bimodal distribution of Mg17Al12 precipitates consisting of submicron particles located within the shear bands and nano-sized ones within the matrix.Owing to the unique microstructure,the micro-hardness(and nano-hardness)value of UVC alloy was increased by 37.7％(35％)when compared with the solution-treated alloy.Moreover,the nano-modulus of the developed AZ91 alloy was also significantly increased to 62 GPa by statistical nanoindentation tests,which could be ascribed to increased Mg17Al12 precipitates and decreased c/a value to some extent.In general,this work provides a new insight into the design and preparation of high-performance magnesium alloys by UVC at room temperature.
查看更多>>摘要：Magnesium and its alloys have attracting rising attention as one of biodegradable metallic materials.However,the rapid cor-rosion and severe localized corrosion still hinder their extensive applications in clinics.In this study,micro-alloying of Ca(≤ 0.1 wt％)into Mg0.5Zn0.2Ge alloy developed in our previous work was explored to further enhance the corrosion resist-ance and alleviate the localized corrosion of the alloy.The results reveal that the addition of Ca leads to the transformation of the cathodic Mg2Ge phase in Mg0.5Zn0.2Ca alloy into anodic MgCaGe phase in Ca-containing alloys,thereby changing the galvanic couples in alloys during immersion.The preferential dissolution of MgCaGe phase promotes the participation of Ca and Ge into the formation of corrosion products,resulting in the enrichment of Ca and Ge in the outmost of corrosion product layer,which stabilizes and passivates the corrosion product layer on Mg alloy surface.Additionally,the enrichment of Zn at the corrosion interface seems to further hinder the corrosion of Mg matrix.All of these factors confer a slower and more uniform corrosion on Mg0.5Zn0.2GexCa(x＜0.1 wt％)alloy,which provides favorable candidates for the further processing to gain suitable biodegradable Mg alloys.
查看更多>>摘要：The application of Mg alloys is always accompanied by various coating technology,but a reliable model predicting the service life of coatings on Mg alloys is lacking but urgent.In this work,a semi-mechanistic model was proposed to predict the service life of plasma electrolytic oxidation(PEO)coating/electrophoretic coatings on a VW63Z Mg alloy;the model was decomposed into three parts:a first part depicting the degradation time of organic coating(L1)and the diffusion time of electrolyte in the inorganic coating(L2),respectively;a second part interpreting the breakdown of coatings due to the cor-rosion process(L3);a final part establishing an algorithm converting the accelerated tests into the real service environment(α);the effect of structural stress and dissimilar metal joints on the service life of coatings was also considered.Based on the ongoing accelerated experiments,the semi-mechanistic model could be able to predict the service life of both PEO coatings and composite coatings on VW63Z Mg alloy with a satisfiable precision.
查看更多>>摘要：AZ31B magnesium alloys are commonly used in lightweight structures of automobile and aerospace industry.In this work,the ultrasonic-induced transient liquid phase bonding technique is deployed to joint AZ31B magnesium alloys at 490 ℃ with Ag interlayer in the atmosphere.The effect of ultrasonic vibration on microstructure and mechanical properties of welding seam is investigated.As vibration duration increases,the width of the welding seam increases firstly and then decreases.When the ultrasound vibration sustained for one second,the eutectic reaction occurred in the contacting interface between Ag interlayer and the base metal AZ31B,resulting in formation of liquid phase and metallurgical bonding.When the ultra-sound vibration sustained for seven second,the width of the welding seam increased to a maximum of about 303.1 pm and the average shear bond strength of the welding joint attained the peak value of about 66.87 MPa.When the ultrasound vibra-tion sustained over seven seconds,the liquid phase is gradually squeezed out and the width of the welding seam decreases.α-Mg and AgMg3 can be observed in the welding seam.The analysis shows that α-Mg has a certain strengthening effect.The whole process of appearance,growth and integration of α-Mg is analyzed.
查看更多>>摘要：Here,the composition of TaMoNbZrTiAl refractory high entropy alloy(RHEA)is optimized by increasing Ti content to improve its mechanical property especially the ductility,through comparing two RHEAs with different Ti content.The RHEAs contain two body-centered-cubic(BCC)phases.The BCC phase in the dendritic region is rich in Ta,Mo and Nb,and the BCC phase in the interdendritic region is enriched in Zr,Ti and Al.The as-cast RHEA with a higher Ti content remains dendritic microstructures,and Ti is mainly enriched in the interdendritic region.After annealing treatment at 1300 ℃ for 48 h,the dendritic microstructures change into equiaxed-grain morphology,accompanied by needle-like micron precipitates at grain boundaries in the RHEA with higher Ti content.For the as-cast RHEAs,the fracture strain increases by～6.6％and the uniform plastic strain increases by～5.9％at the compression test due to the increase of Ti content.Our work offers a reference for the composition design of RHEAs and makes a preliminary exploration of the optimization of the microstruc-tures and mechanical properties.
查看更多>>摘要：Mg-based alloys must be dehydrogenated at high pressure and temperatures,limiting their practical application.In this paper,Nd5Mg41Ni alloy was prepared by vacuum melting,and the as-cast alloy was ball milled for 5 h,10 h,15 h,and 20 h.The effect of ball milling time on the microstructure and hydrogen storage properties of the alloy was systematically studied.The alloy comprises Nd5Mg41,NdMg12,NdMg3,and Mg2Ni phases.The Nd5Mg41Ni alloy milling for 10 h can reach 95％of the saturated hydrogen absorption at 553 K by 40 s,and the alloy can desorb hydrogen only by 20 min.The dehydrogenation acti-vation energy is only 99.9 kJ/mol H2.Ball milling makes the alloy produce many nanocrystalline and amorphous structures.The nano-grain boundary provides a channel for the diffusion of hydrogen atoms,and the high energy at the grain boundary provides energy for the phase deformation nucleus.Ball milling leads to the refinement of alloy particles and shortens the diffusion distance of hydrogen atoms to the interior of alloy particles.Defects such as twins and dislocations generated by milling provide energy for the phase deformation nucleus during the hydrogen absorption and desorption.
Ivana Cvijovi?-Alagi?Sla(d)ana Laketi?·Milo? Mom?ilovi?Jovan Ciganovi?...
1215-1230页
查看更多>>摘要：The Ti-45Nb(mass％)alloy's corrosive and biocompatible response in simulated physiological conditions was investigated before and after its additional high-pressure torsion(HPT)and laser irradiation processing.The grain size reduction from 2.76 pm to～200 nm and the appearance of laser-induced morphologically altered and highly oxidized surface led to the significant improvement of alloy corrosion resistance and cell-implant interaction.Moreover,an additional increase of the laser pulse energy from 5 to 15 mJ during the alloy irradiation in the air led to an increase in the surface oxygen content from 13.64 to 23.89％accompanied by an increase of excellent cell viability from 127.18 to 134.42％.As a result of the controlled alloy microstructural and surface modifications,the formation of protective bi-modal mixed Ti-and Nb-oxide external scale was enabled.The presence of this surface oxide scale enhanced the alloy's resistance to corrosion deterioration and simul-taneously boosted cell viability and proliferation.
查看更多>>摘要：For the evaluation of cavitation erosion resistance of metallic materials,it has always been a time-consuming technical prob-lem.This paper innovatively proposed a parameter named cavitation hardening rate to characterize the plastic deformation and work hardening behavior of metallic materials during the cavitation process and then found a positive correlation between cavitation hardening rate and strain hardening index.Finally,the relationship between cavitation volume loss and strain hardening index was obtained,and a simple and rapid evaluation method for cavitation erosion resistance was established.
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