变形温度对塑性变形新方法加工的AZ31镁合金显微组织和织构的影响

提出一种新的反复镦挤变形(RUE)方法。采用光学显微镜(OM)、X射线衍射(XRD)、电子背散射衍射(EBSD)和维氏硬度计分析不同变形温度对RUE变形AZ31镁合金显微组织和织构的影响。结果表明:经RUE变形后,AZ31镁合金组织局部细化至0.8μm,细化机制主要为连续动态再结晶(CDRX);随着温度的升高,首先形成平行于剪切面的基面织构,随后形成强度减弱的{11■0}<10■0>织构,最后形成{0001}<10■0>和{0001}<11■0>织构。基面和锥面位错滑移导致织构分裂。经RUE变形后AZ31镁合金的最大硬度较初始状态提高42.4%,主要原因是细晶强化和位错强化。

添加VN颗粒的铸态AZ91镁合金在NaCl溶液中的腐蚀行为

采用光学显微镜(OM)、X射线衍射(XRD)、扫描电子显微镜(SEM)技术和电化学实验研究铸态AZ91−xVN(x=0,0.25,0.5,1,质量分数,%)合金的显微组织和腐蚀行为。结果表明,VN对AZ91合金显微组织具有明显的细化和改性作用。随着VN颗粒的加入,AZ91合金的耐腐蚀性能先提高后降低。铸态AZ91−0.25VN合金具有最佳的耐腐蚀性能,其腐蚀速率最低(PW=(1.47±0.06)mm/a),这主要归因于其具有更多可作为腐蚀屏障的晶界。随着VN含量的进一步增加,合金中片状β-Mg17Al12析出相的量增加,由于β相与α-Mg基体易发生电偶腐蚀,合金的耐蚀性能逐渐降低。

预压缩对热挤压AZ91−2Y镁合金动态析出相形成及蠕变各向异性的影响

研究经预压缩(PC)和未经预压缩(NPC)的热挤压AZ91−2Y镁合金在180℃不同应力下的蠕变各向异性行为。采用扫描电子显微镜(SEM)、电子背散射衍射(EBSD)、透射电子显微镜(TEM)和拉伸蠕变试验对合金的显微组织、织构和力学性能进行分析。结果表明,抗蠕变性能与球形Mg_(17)Al_(12)析出相的体积分数成正比。NPC试样中动态析出高体积分数层片状Mg_(17)Al_(12),使其以基面áañ滑移为主导蠕变机制,且NPC试样具有明显的各向异性。PC试样动态析出高体积分数的球形Mg_(17)Al_(12),对基面áañ滑移有抑制作用。锥面ác+añ滑移和孪晶显著提高蠕变各向异性抗力。

Effect of Vanadium Nitride(VN)Particles on Microstructure and Mechanical Properties of Extruded AZ31 Mg Alloy

The effect of vanadium nitride(VN)particles additives on microstructure and mechanical properties of the extruded AZ31 Mg alloy was systematically investigated.The experimental results revealed that the addition of 0.5 wt%VN decreased the average grain size of AZ31 Mg alloy from 6.4 to 4.9µm.With the increase in VN content,the refining effect would weaken because excessive VN particles would negatively affect the dynamic recrystallization process of the alloys.The scanning electron microscopy and energy-dispersive spectroscopy indicated that AlN,VN and Al-V-N particles with different morphologies were distributed in the streamline along the extrusion direction during the extrusion process.The mechanical properties of AZ31 Mg alloy vary with the addition of VN.The extruded AZ31+0.5 wt%VN Mg alloy possesses an excellent combination of high strength and ductility.The yield strength and ultimate tensile strength of the extruded AZ31+0.5 wt%VN Mg alloy were increased without sacrificing ductility.This is mainly due to the grain refinement caused by double-heterogeneous nucleation particles.With a further increase in VN content,the presence of excessive VN particles increases the stress concentration,and the initiation source of microcracks in the alloy during alloy deformation makes the cracks more easily propagated and results in a decrease in the ductility of the extruded alloy.

In-situ Micro-CT analysis of deformation behavior in sandwich-structured meta-stable beta Ti−35Nb alloy

Beta Ti−35Nb sandwich-structured composites with various reinforcing layers were designed and produced using additive manufacturing(AM)to achieve a balance between light weight and high strength.The impact of reinforcing layers on the compressive deformation behavior of porous composites was investigated through micro-computed tomography(Micro-CT)and finite element method(FEM)analyses.The results indicate that the addition of reinforcement layers to sandwich structures can significantly enhance the compressive yield strength and energy absorption capacity of porous metal structures;Micro-CT in-situ observation shows that the strain of the porous structure without the reinforcing layer is concentrated in the middle region,while the strain of the porous structure with the reinforcing layer is uniformly distributed;FEM analysis reveals that the reinforcing layers can alter stress distribution and reduce stress concentration,thereby promoting uniform deformation of the porous structure.The addition of reinforcing layer increases the compressive yield strength of sandwich-structured composite materials by 124%under the condition of limited reduction of porosity,and the yield strength increases from 4.6 to 10.3 MPa.