查看更多>>摘要：The repair and regeneration of bone defects are highly challenging orthopedic problems.Recently,Mg-based implants have gained popularity due to their unique biodegradation and elastic modulus similar to that of human bone.The aim of our study is to develop a magnesium alloy with a controllable degradation that can closely match bone tissue to help injuries heal in vivo and avoid cytotoxicity caused by a sudden in-crease in ion concentration.In this study,we prepared and modified Mg-3Zn,Mg-3Zn-1Y,and Mg-2Zn-1Mn by hot extrusion,and used Mg-2.5Y-2.5Nd was as a control.We then investigated the effect of additions of Y and Mn on alloys'properties.Our results show that Mn and Y can improve not only compression strength but also corrosion resistance.The alloy Mg-2Zn-lMn demonstrated good cytocompatibility in vitro,and for this reason we selected it for implantation in vivo.The degraded Mg-2Zn-1Mn implanted a bone defect area did not cause obvious rejection and inflammatory reaction,and the degradation products left no signs of damage to the heart,liver,kidney,or brain.Furthermore,we find that Mg-2Zn-1Mn can promote an osteoinductive response in vivo and the formation of bone regeneration.
查看更多>>摘要：The deformation mechanisms and dynamic recrystallization(DRX)behavior of specifically grown bicrystals with a symmetric 90°＜10(1)0＞and 90°＜(11(2)0)＞tilt grain boundary,respectively,were investigated under deformation in plane strain compression at 200 ℃ and 400 ℃.The microstructures were analyzed by panoramic optical microscopy and large-area electron backscatter diffraction(EBSD)orientation mapping.The analysis employed a meticulous approach utilizing hundreds of individual,small EBSD maps with a small step size that were stitched together to provide comprehensive access to orientation and misorientation data on a macroscopic scale.Basal slip primarily governed the early stages of deformation at the two temperatures,and the resulting shear induced lattice rotation around the transverse direction(TD)of the sample.The ex-istence of the grain boundary gave rise to dislocation pile-up in its vicinity,leading to much larger TD-lattice rotations within the boundary re-gion compared to the bulk.With increasing temperature,the deformation was generally more uniform towards the bulk due to enhanced disloca-tion mobility and more uniform stress distribution.Dynamic recrystallization at 200 ℃ was initiated in {10(1)1}-compression twins at strains of 40％and higher.At 400 ℃,DRX consumed the entire grain boundary region and gradually replaced the deformed microstructure with progress-ing deformation.The recrystallized grains displayed characteristic orientations,such that their c-axes were perpendicular to the TD and addition-ally scattered between 0° and 60° from the loading axis.These recrystallized grains displayed mutual rotations of up to 30° around the c-axes of the initial grains,forming a discernible basal fiber texture component,prominently visible in the {11(2)0} pole figure.It is noteworthy that the de-formation and DRX behaviors of the two analyzed bicrystals exhibited marginal variations in response to strain and deformation temperature.
查看更多>>摘要：The extruded AZ80+0.4％Ce magnesium alloy was twisted in the temperature range of 300-380 ℃ by using a Gleeble 3500 thermal simula-tion test machine with a torsion unit.The deformed cylindrical specimens were cooled at a cooling rate of 10 ℃/s or 0.1 ℃/s,respectively,and aged at 170 ℃.The microstructure analysis results showed that the grain size decreased with increasing specimen radial position from center(SRPC),and that the strong initial basal texture of the extruded magnesium alloy was weakened.Both continuous and discontinuous dynamic re-crystallization mechanisms were involved in contributing to the grain refinement for all specimens investigated.And a novel extension twinning induced dynamic recrystallization mechanism was proposed for specimen deformed at 300 ℃.For the specimens deformed at 300 ℃ and 340 ℃ followed by a slow cooling rate(0.1 ℃/s),precipitates of various shapes(β-Mg17Al12),with the dominant precipitates being on the grains boundaries,appeared on the surface section.For specimen deformed at 380 ℃,lamellar precipitates(LPS)in the interiors of the grains were pre-dominant.After aging,the LPS still dominated for specimens twisted at 380 ℃;however,the LPS gradually decreased with decreasing deforma-tion temperatures from 380 ℃ to 300 ℃.Dynamically precipitated β,especially those decorating the grain boundaries,changed the competition pictures for the LPS and precipitates of other shapes after aging.Interestingly,LPS dominated the areas for the center section of the specimens after aging regardless of deformation temperatures.Low temperature deformation with high SRPC followed by rapid cooling rate increased the micro hardness of the alloy after aging due to refined grain,reduced precipitates size,decreased lamellar spacing as well as strain hardening.
查看更多>>摘要：The sessile drop method was applied to the experimental investigation of the wetting and spreading behaviors of liquid Mg drops on pure Ni substrates.For comparison,the experiments were performed in two variants: (1)using the capillary purification(CP)procedure,which allows the non-contact heating and squeezing of a pure oxide-free Mg drop;(2)by classical contact heating(CH)procedure.The high-temperature tests were performed under isothermal conditions(CP: 760 ℃ for 30 s;CH: 715 ℃ for 300 s)using Ar+5％(mass fraction)H2 atmosphere.During the sessile drop tests,images of the Mg/Ni couples were recorded by CCD cameras(57 fps),which were then applied to calculate the contact an-gles of metal/substrate couples.Scanning and transmission electron microscopy analyses,both coupled with energy-dispersive X-ray spectrosco-py,were used for detailed structural characterization of the solidified couples.It was found that an oxide-free Mg drop obtained by the CP procedure showed a wetting phenomenon on the Ni substrate(an average contact angle θ＜90°in＜1 s),followed by fast spreading and good wetting over the Ni substrate(θ(CP)about 20° in 5 s)to form a final contact angle of θf(CP)about 18°.In contrast,a different wetting behavior was observed for the CH procedure,where the unavoidable primary oxide film on the Mg surface blocked the spreading of liquid Mg showing apparently non-wetting behavior after 300 s contact at the test temperature.However,in both cases,the deep craters formed in the Ni substrates under the Mg drops and significant change in the structure of initially pure Mg drops to Mg-Ni alloys suggest a strong dissolution of Ni in liquid Mg and apparent values of the final contact angles measured for the Mg/Ni system.
查看更多>>摘要：To study the formation and transformation mechanism of long-period stacked ordered(LPSO)structures,a systematic atomic scale analysis was conducted for the structural evolution of long-period stacked ordered(LPSO)structures in the Mg-Gd-Y-Zn-Zr alloy annealed at 300-500 ℃.Various types of metastable LPSO building block clusters were found to exist in alloy structures at different temperatures,which precipitate during the solidification and homogenization process.The stability of Zn/Y clusters is explained by the first principles of density functional theo-ry.The LPSO structure is distinguished by the arrangement of its different Zn/Y enriched LPSO structural units,which comprises local fcc stac-king sequences upon a tightly packed plane.The presence of solute atoms causes local lattice distortion,thereby enabling the rearrangement of Mg atoms in the different configurations in the local lattice,and local HCP-FCC transitions occur between Mg and Zn atoms occupying the nea-rest neighbor positions.This finding indicates that LPSO structures can generate necessary Shockley partial dislocations on specific slip surfaces,providing direct evidence of the transition from 18R to 14H.Growth of the LPSO,devoid of any defects and non-coherent interfaces,was ob-served separately from other precipitated phases.As a result,the precipitation sequence of LPSO in the solidification stage was as follows: Zn/Y cluster+Mg layers→various metastable LPSO building block clusters→18R/24R LPSO;whereas the precipitation sequence of LPSO during homogenization treatment was observed to be as follows: 18R LPSO→various metastable LPSO building block clusters→14H LPSO.Of these,14H LPSO was found to be the most thermodynamically stable structure.
查看更多>>摘要：This work reports an exceptional reversed yield strength asymmetry at room temperature for a rare-earth free magnesium alloy containing a mass of fine dispersed quasicrystal(Ⅰ-phase)precipitates.Although exhibiting traditional basal texture,it owns an exceptional CYS/TYS as high as about 1.17.Electron back-scattered diffraction(EBSD)and transmission electron microscopy(TEM)examinations indicate pyramidal＜c+a＞and prismatic＜c＞dislocations plus tensile twinning being activated after immediate yielding in compression while basal and non-basal＜a＞dislocations in tension.Ⅰ-phase particles transferred the concentrated stress by self-twinning to provide the driving force for tensile twin ini-tiating in neighboring grains,thereby significantly increasing the critical resolved shear stress of tensile twinning to possibly the level of pyrami-dal＜c+a＞slip,finally leading to the dominance of pyramidal＜c+a＞slip plus tensile twinning in texture grains.This results in a higher con-tribution on yield strength by about 55 MPa in compression than in tension,which reasonably agrees with the experimental yield strength differ-ence(about 38 MPa).It can be concluded that I-phase particles influence deformation modes in tension and in compression,finally result in re-versed yield strength asymmetry.
查看更多>>摘要：The role of microstructural features on in-vitro degradation and surface film development of a thermomechanically processed Mg-4Zn-0.5Ca-0.8Mn alloy has been investigated employing electrochemical studies,scanning electron microscopy and X-ray photoelectron spectroscopy.The specimen forged at 523 K temperature developed a coarse unimodal microstructure consisting of basal oriented grains,whereas the specimens forged at 623 K and 723 K temperatures exhibited bimodal microstructures containing randomly oriented fine grains and basal oriented coarse grains.The bimodal microstructures exerted higher resistance to corrosion compared to the unimodal microstructure in presence of a protective surface film.The optimum size distribution of fine and coarse grains as well as the prevalence of basal oriented grains led to the lowest anodic current density in the specimen forged at 623 K.The morphology of Ca2Mg6Zn3 precipitates governed the cathodic kinetics by controlling the anode to cathode surface area ratio.Despite the specimen forged at 723 K comprised comparatively lower fraction of precipitates than at 623 K,the mesh-like precipitate morphology increased the effective cathodic surface area,leading to enhanced localised corrosion in the former speci-men.Optimal microstructural features developed at 623 K forging temperature formed a well-protective surface film with lower Mg(OH)2 to MgO ratio,exhibiting distinctly high polarization resistance and superior cytocompatibility in terms of cell-proliferation and cell-differentiation.
查看更多>>摘要：Magnesium and aluminum alloys are widely used in various industries because of their excellent properties,and their reliable connection may increase application of materials.Intermetallic compounds(IMCs)affect the joint performance of Mg/Al.In this study,AZ31 Mg alloy with/without a nickel(Ni)coating layer and 6061 Al alloy were joined by ultrasonic-assisted soldering with Sn-3.0Ag-0.5Cu(SAC)filler.The effects of the Ni coating layer on the microstructure and mechanical properties of Mg/Al joints were systematically investigated.The Ni coating layer had a significant effect on formation of the Mg2Sn IMC and the mechanical properties of Mg/Al joints.The blocky Mg2Sn IMC formed in the Mg/SAC/Al joints without a Ni coating layer.The content of the Mg2Sn IMC increased with increasing soldering temperature,but the joint strength decreased.The joint without a Ni coating layer fractured at the blocky Mg2Sn IMC in the solder,and the maximum shear strength was 322 MPa.By pre-plating Ni on the Mg substrate,formation of the blocky Mg2Sn IMC was inhibited in the soldering temperature range 240-280 ℃ and the joint strength increased.However,when the soldering temperature increased to 310 ℃,the blocky Mg2Sn IMC precipitated a-gain in the solder.Transmission electron microscopy showed that some nano-sized Mg2Sn IMC and the(Cu,Ni)6Sn5 phase formed in the Mg(Ni)/SAC/Al joint soldered at 280 ℃,indicating that the Ni coating layer could no longer prevent diffusion of Mg into the solder when the sold-ering temperature was higher than 280 ℃.The maximum shear strength of the Mg(Ni)/SAC/Al joint was 58.2 MPa for a soldering temperature of 280 ℃,which was 80.7％higher than that of the Mg/SAC/Al joint,and the joint was broken at the Mg(Ni)/SAC interface.Pre-plating Ni is a feasible way to inhibit formation of IMCs when joining dissimilar metals.
查看更多>>摘要：Mg97Zn1Y2 alloys with high ignition temperatures were developed by adding Sr.The addition of Sr resulted in the formation of a uniform and thin Y2O3 film.Mg-Zn-Y alloys containing at least 0.25％Sr exhibited ignition temperatures of 1270-1320 K.As a result of EDS measurement,Sr was found to be concentrated in the Y2O3 film.In addition,a mixed film of MgO and SrO formed on the outer layer in the 1.5％(atomic percent)Sr-containing Mg97Zn1Y2 alloy.These findings suggest that the uniform and thin Y2O3 film that maintains high soundness at high tem-peratures was formed owing to valence control and the formation of a protective outer oxide film.
查看更多>>摘要：Magnesium(Mg),being the lightest structural metal,holds immense potential for widespread applications in various fields.The development of high-performance and cost-effective Mg alloys is crucial to further advancing their commercial utilization.With the rapid advancement of ma-chine learning(ML)technology in recent years,the"data-driven"approach for alloy design has provided new perspectives and opportunities for enhancing the performance of Mg alloys.This paper introduces a novel regression-based Bayesian optimization active learning model(RBOALM)for the development of high-performance Mg-Mn-based wrought alloys.RBOALM employs active learning to automatically ex-plore optimal alloy compositions and process parameters within predefined ranges,facilitating the discovery of superior alloy combinations.This model further integrates pre-established regression models as surrogate functions in Bayesian optimization,significantly enhancing the precision of the design process.Leveraging RBOALM,several new high-performance alloys have been successfully designed and prepared.Notably,after mechanical property testing of the designed alloys,the Mg-2.1Zn-2.0Mn-0.5Sn-0.1Ca alloy demonstrates exceptional mechanical properties,in-cluding an ultimate tensile strength of 406 MPa,a yield strength of 287 MPa,and a 23％fracture elongation.Furthermore,the Mg-2.7Mn-0.5Al-0.1Ca alloy exhibits an ultimate tensile strength of 211 MPa,coupled with a remarkable 41％fracture elongation.
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