The tension-compression asymmetry presents notable challenges for the application of magnesium alloys in many fields.In this study,the solid-solution treated Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy's tension-compression a...The tension-compression asymmetry presents notable challenges for the application of magnesium alloys in many fields.In this study,the solid-solution treated Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy's tension-compression asymmetry was examined using optical microscope(OM),x-ray diffraction(XRD),viscoplastic self-consistent(VPSC)modeling,and electron backscatter diffraction(EBSD).The VPSC hardening parameters were significantly adjusted based on the Schmid factor of deformation modes in rare earth magnesium(Mg-RE)alloy,which came from the EBSD data.Excellent agreement was found between the modified VPSC model's calculation results,especially the stress-strain curves and pole figures.The alloy exhibited good strength with a negligible tension-compression asymmetry and an impressive 0.98 ratio of compressive yield strength to tensile yield strength(CYS/TYS).The main cause could be attributed to the unusual texture of(11-20)<0001>in alloy,which eliminated the imbalance in tension and compression deformation by having a negative effect on the activation of{10-12}twinning in tensile and a positive effect in compressive deformation.The activation level of{10-12}twinning was 0.37 and 0.40calculated by VPSC model,in the plastic deformation of tension and compression,respectively;in the tensile and compression samples,the EBSD data indicated that approximately 31.9%and 31.1%(area proportion)of the grains were deformed with twins,respectively.Both tension and compression deformation showed the{10-12}twinning in the early stage of deformation,which transformed to{11-22}twinning in the later stage.The considerable activation of pyramidal during the later stages of deformation endowed the alloy with good ductility.展开更多
This study systematically investigates the unusual tensile mechanical behavior of Mg-RE solid solution(SS)alloys,exhibiting anomalous tensile strengths(ATS)and an enhanced strain-hardening rate at high temperature.Bot...This study systematically investigates the unusual tensile mechanical behavior of Mg-RE solid solution(SS)alloys,exhibiting anomalous tensile strengths(ATS)and an enhanced strain-hardening rate at high temperature.Both the peak ultimate tensile strength(UTS)and tensile yield strength(TYS)values occur at 150-200℃,which are 12-50%higher compared to those at room temperature(RT).Meanwhile,the strain-hardening rate increases with the temperature rising from RT to 200℃ during the plastic deformation process.The results reveal that the formation of stacking faults(SFs)and the locking of dislocations,particularly immobile (c) partial dislocations,enhance resistance to plastic deformation,leading to higher strengths at high temperature.Furthermore,the interactivity between SFs and (c+a) dislocations intensify with rising of temperature.The presence of RE atoms in the SS plays a critical role in this unique mechanical behavior,as they preferentially occupy non-basal planes rather than basal planes,thereby reducing the stacking fault(SF)formation energy.This study provides new insights into the high-temperature strengthening mechanisms of Mg-RE based alloys,offering potential guidance for the design of advanced lightweight materials with superior mechanical properties.展开更多
To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced materi...To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced material characterization techniques.A suitable laser output mode fell into the transition mode,allowing for the fabrication of nearly full-density samples(porosity=0.85±0.021%)with favorable mechanical properties(yield strength=351 MPa,ultimate tensile strength=417 MPa,the elongation at break=6.5%and microhardness=137.9±6.15 HV_(0.1))using optimal processing parameters(P=80 W,v=250 mm/s and d=50μm).Viscoplastic self-consistent analysis and transmission electron microscopy observations reveal that the plastic deformation response of the SLM Mg-RE alloys is primarily driven by basal and prismatic slips.Starting from a random texture before deformation(maximum multiple of ultimate density,Max.MUD=3.95),plastic stretching led the grains to align with the Z-axis,finally resulting in a{0001}<1010>texture orientation after fracture(Max.MUD=8.755).Main phases of the SLM state are mainly composed ofα-Mg,Mg_(24)Y_(5) andβ'-Mg_(41)Nd_(5),with an average grain size of only 4.27μm(about a quarter of that in the extruded state),resulting in a favorable strength-toughness ratio.Except for the nano-β'phase and semi-coherent Mg_(24)Y_(5) phase(mismatch=16.12%)around the grain boundaries,a small amount of nano-ZrO_(2) and Y_(2)O_(3) particles also play a role in dispersion strengthening.The high mechanical properties of the SLM state are chiefly attributed to precipitation hardening(44.41%),solid solution strengthening(34.06%)and grain boundary strengthening(21.53%),with precipitation hardening being predominantly driven by dislocation strengthening(67.77%).High-performance SLM Mg-RE alloy components were manufactured and showcased at TCT Asia 2024,receiving favorable attention.This work underscores the significant application potential of SLM Mg-RE alloys and establishes a strong foundation for advancing their use in the biomedical fields.展开更多
Additive manufacturing (AM) of high-strength metallic alloys frequently encounters detrimental distortion and cracking, attributed to the accumulation of thermal stresses. These issues significantly impede the practic...Additive manufacturing (AM) of high-strength metallic alloys frequently encounters detrimental distortion and cracking, attributed to the accumulation of thermal stresses. These issues significantly impede the practical application of as-printed components. This study examines the Mg-15Gd-1Zn-0.4Zr (GZ151K, wt.%) alloy, a prototypical high-strength casting Mg-RE alloy, fabricated through laser powder bed fusion (LPBF). Despite achieving ultra-high strength, the GZ151K alloy concurrently exhibits a pronounced cold-cracking susceptibility. The as-printed GZ151K alloy consists of almost fully fine equiaxed grains with an average grain size of merely 2.87 µm. Subsequent direct aging (T5) heat treatment induces the formation of dense prismatic β' precipitates. Consequently, the LPBF-T5 GZ151K alloy manifests an ultra-high yield strength of 405 MPa, surpassing all previously reported yield strengths for Mg alloys fabricated via LPBF and even exceeding that of its extrusion-T5 counterpart. Interestingly, as-printed GZ151K samples with a build height of 2 mm exhibit no cracking, whereas samples with build heights ranging from 4 to 18 mm demonstrate severe cold cracking. Thermal stress simulation also suggests that the cold cracking susceptibility increases significantly with increasing build height. The combination of high thermal stress and low ductility in the as-printed GZ151K alloy culminates in a high cold cracking susceptibility. This study offers novel insights into the intricate issue of cold cracking in the LPBF process of high-strength Mg alloys, highlighting the critical balance between achieving high strength and mitigating cold cracking susceptibility.展开更多
The precipitation behavior of magnesium-rare earth(Mg-RE)alloys plays a crucial role for their properties.However,the precipitation happens at small-length and long-time scales,making it challenging to be analyzed by ...The precipitation behavior of magnesium-rare earth(Mg-RE)alloys plays a crucial role for their properties.However,the precipitation happens at small-length and long-time scales,making it challenging to be analyzed by state-of-the-art experimental techniques.Here,we combine the advantages of both molecular dynamic forcefields on describing atom interactions and Monte Carlo method on describing diffusive events to develop an embedded atom method(EAM)potential based kinetic Monte Carlo(KMC)model.Using the proposed model,we simulated the formation and evolution of Y clusters in Mg-Y alloy formed by the vacancy mechanism,and rationalize the simulation results using aberration-corrected scanning transmission electron microscopy characterize.We conducted a systematic analysis of the atomic structure,the evolution kinetics and path of the Y cluster by tracing Y atoms and comparing with density function theory(DFT)calculations.Our work reveals that,all solute columns in a same cluster trend to grow along the[0001]Mg direction synchronously.The method presented is not only used for the Mg-Y alloy but also other Mg-RE alloys such as Mg-Gd as illustrated in the last part of the paper.展开更多
基金financial support provided by Key Research and Development Program of Heilongjiang(Grant No.2022ZX01A01)Natural Science Found of Heilongjiang Province(LH2022E080)。
文摘The tension-compression asymmetry presents notable challenges for the application of magnesium alloys in many fields.In this study,the solid-solution treated Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy's tension-compression asymmetry was examined using optical microscope(OM),x-ray diffraction(XRD),viscoplastic self-consistent(VPSC)modeling,and electron backscatter diffraction(EBSD).The VPSC hardening parameters were significantly adjusted based on the Schmid factor of deformation modes in rare earth magnesium(Mg-RE)alloy,which came from the EBSD data.Excellent agreement was found between the modified VPSC model's calculation results,especially the stress-strain curves and pole figures.The alloy exhibited good strength with a negligible tension-compression asymmetry and an impressive 0.98 ratio of compressive yield strength to tensile yield strength(CYS/TYS).The main cause could be attributed to the unusual texture of(11-20)<0001>in alloy,which eliminated the imbalance in tension and compression deformation by having a negative effect on the activation of{10-12}twinning in tensile and a positive effect in compressive deformation.The activation level of{10-12}twinning was 0.37 and 0.40calculated by VPSC model,in the plastic deformation of tension and compression,respectively;in the tensile and compression samples,the EBSD data indicated that approximately 31.9%and 31.1%(area proportion)of the grains were deformed with twins,respectively.Both tension and compression deformation showed the{10-12}twinning in the early stage of deformation,which transformed to{11-22}twinning in the later stage.The considerable activation of pyramidal during the later stages of deformation endowed the alloy with good ductility.
基金supported by the National Natural Science Foundation of China(Grant No 52401209,52192603,52275308)Fundamental Research Funds for the Central Universities(2023JG007)。
文摘This study systematically investigates the unusual tensile mechanical behavior of Mg-RE solid solution(SS)alloys,exhibiting anomalous tensile strengths(ATS)and an enhanced strain-hardening rate at high temperature.Both the peak ultimate tensile strength(UTS)and tensile yield strength(TYS)values occur at 150-200℃,which are 12-50%higher compared to those at room temperature(RT).Meanwhile,the strain-hardening rate increases with the temperature rising from RT to 200℃ during the plastic deformation process.The results reveal that the formation of stacking faults(SFs)and the locking of dislocations,particularly immobile (c) partial dislocations,enhance resistance to plastic deformation,leading to higher strengths at high temperature.Furthermore,the interactivity between SFs and (c+a) dislocations intensify with rising of temperature.The presence of RE atoms in the SS plays a critical role in this unique mechanical behavior,as they preferentially occupy non-basal planes rather than basal planes,thereby reducing the stacking fault(SF)formation energy.This study provides new insights into the high-temperature strengthening mechanisms of Mg-RE based alloys,offering potential guidance for the design of advanced lightweight materials with superior mechanical properties.
基金supported by the National Key Research and Development Program of China(No.2022YFC2406000)the Guangdong Basic and Applied Basic Research Foundation(2024A1515011024)+5 种基金the Guangzhou Science and Technology Project(2024A04J4943)the Guangdong Academy of Sciences Development Special Fund Project(2022GDASZH-2022010107)the Guangdong province Science and Technology Plan Projects(2023B1212120008,2023B1212060045)the GDAS Projects of International cooperation platform of Science and Technology(2022GDASZH-2022010203-003)Special Support Foundation of Guangdong Province(2023TQ07Z559)Shenzhen Basic Research Project(JCYJ20210324120001003 and JCYJ20220531091802006)。
文摘To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced material characterization techniques.A suitable laser output mode fell into the transition mode,allowing for the fabrication of nearly full-density samples(porosity=0.85±0.021%)with favorable mechanical properties(yield strength=351 MPa,ultimate tensile strength=417 MPa,the elongation at break=6.5%and microhardness=137.9±6.15 HV_(0.1))using optimal processing parameters(P=80 W,v=250 mm/s and d=50μm).Viscoplastic self-consistent analysis and transmission electron microscopy observations reveal that the plastic deformation response of the SLM Mg-RE alloys is primarily driven by basal and prismatic slips.Starting from a random texture before deformation(maximum multiple of ultimate density,Max.MUD=3.95),plastic stretching led the grains to align with the Z-axis,finally resulting in a{0001}<1010>texture orientation after fracture(Max.MUD=8.755).Main phases of the SLM state are mainly composed ofα-Mg,Mg_(24)Y_(5) andβ'-Mg_(41)Nd_(5),with an average grain size of only 4.27μm(about a quarter of that in the extruded state),resulting in a favorable strength-toughness ratio.Except for the nano-β'phase and semi-coherent Mg_(24)Y_(5) phase(mismatch=16.12%)around the grain boundaries,a small amount of nano-ZrO_(2) and Y_(2)O_(3) particles also play a role in dispersion strengthening.The high mechanical properties of the SLM state are chiefly attributed to precipitation hardening(44.41%),solid solution strengthening(34.06%)and grain boundary strengthening(21.53%),with precipitation hardening being predominantly driven by dislocation strengthening(67.77%).High-performance SLM Mg-RE alloy components were manufactured and showcased at TCT Asia 2024,receiving favorable attention.This work underscores the significant application potential of SLM Mg-RE alloys and establishes a strong foundation for advancing their use in the biomedical fields.
基金supported by the National Key Research and Development Program of China(No.2021YFB3701000)the National Natural Science Foundation of China(Nos.51971130,52201129,U21A2047,51821001,U2037601)+2 种基金support by the China Postdoctoral Science Foun-dation(2023M742219)the Postdoctoral Fellowship Program of CPSF under Grant Number GZB20240419support by the Ministry of Education,Singapore,under its Academic Research Fund Tier 2(MOE-T2EP50221-0013).
文摘Additive manufacturing (AM) of high-strength metallic alloys frequently encounters detrimental distortion and cracking, attributed to the accumulation of thermal stresses. These issues significantly impede the practical application of as-printed components. This study examines the Mg-15Gd-1Zn-0.4Zr (GZ151K, wt.%) alloy, a prototypical high-strength casting Mg-RE alloy, fabricated through laser powder bed fusion (LPBF). Despite achieving ultra-high strength, the GZ151K alloy concurrently exhibits a pronounced cold-cracking susceptibility. The as-printed GZ151K alloy consists of almost fully fine equiaxed grains with an average grain size of merely 2.87 µm. Subsequent direct aging (T5) heat treatment induces the formation of dense prismatic β' precipitates. Consequently, the LPBF-T5 GZ151K alloy manifests an ultra-high yield strength of 405 MPa, surpassing all previously reported yield strengths for Mg alloys fabricated via LPBF and even exceeding that of its extrusion-T5 counterpart. Interestingly, as-printed GZ151K samples with a build height of 2 mm exhibit no cracking, whereas samples with build heights ranging from 4 to 18 mm demonstrate severe cold cracking. Thermal stress simulation also suggests that the cold cracking susceptibility increases significantly with increasing build height. The combination of high thermal stress and low ductility in the as-printed GZ151K alloy culminates in a high cold cracking susceptibility. This study offers novel insights into the intricate issue of cold cracking in the LPBF process of high-strength Mg alloys, highlighting the critical balance between achieving high strength and mitigating cold cracking susceptibility.
基金supported by National Natu-ral Science Foundation of China(No.U1737208)SAST Foundation.
文摘The precipitation behavior of magnesium-rare earth(Mg-RE)alloys plays a crucial role for their properties.However,the precipitation happens at small-length and long-time scales,making it challenging to be analyzed by state-of-the-art experimental techniques.Here,we combine the advantages of both molecular dynamic forcefields on describing atom interactions and Monte Carlo method on describing diffusive events to develop an embedded atom method(EAM)potential based kinetic Monte Carlo(KMC)model.Using the proposed model,we simulated the formation and evolution of Y clusters in Mg-Y alloy formed by the vacancy mechanism,and rationalize the simulation results using aberration-corrected scanning transmission electron microscopy characterize.We conducted a systematic analysis of the atomic structure,the evolution kinetics and path of the Y cluster by tracing Y atoms and comparing with density function theory(DFT)calculations.Our work reveals that,all solute columns in a same cluster trend to grow along the[0001]Mg direction synchronously.The method presented is not only used for the Mg-Y alloy but also other Mg-RE alloys such as Mg-Gd as illustrated in the last part of the paper.
