通过向AZ91镁合金基体(采用镁合金铸锭)复合添加不同成分的碱土元素Ca、Sr,Ca和Sr元素是以Mg-30%Ca(质量分数)的镁钙中间合金和Mg-30%Sr(质量分数)的镁锶中间合金的形式添加,采用JVAM-1C型高真空电弧熔炼炉对添加后的合金在自制熔剂的...通过向AZ91镁合金基体(采用镁合金铸锭)复合添加不同成分的碱土元素Ca、Sr,Ca和Sr元素是以Mg-30%Ca(质量分数)的镁钙中间合金和Mg-30%Sr(质量分数)的镁锶中间合金的形式添加,采用JVAM-1C型高真空电弧熔炼炉对添加后的合金在自制熔剂的覆盖和氩气保护下熔炼,获得不同成分的AZ91镁合金试样。运用DM2700M型徕卡研究级材料显微镜、JSM-6360LV型扫描电镜(Scanning Electron Microscope,SEM)对合金铸态以及均匀化退火后固溶时效态的显微组织展开观察,利用XD98型X射线衍射仪开展合金相结构分析,同时对其抗拉强度、延伸率和断面收缩率进行测试分析。结果表明:在AZ91镁合金中复合添加碱土元素Ca、Sr后,铸态中晶粒细化机理、晶界高熔点化合物对力学性能作用;证实了AZ91镁合金通过碱土Ca、Sr的复合作用后在高温状态下的力学性能提高机理、强韧性改善机理。展开更多
The addition of ceramic reinforcements provides a promising approach to achieving high-performance magnesium matrix composites.In this work,AZ91D magnesium alloys and 2 wt.%TiC/AZ91D composites have been manufactured ...The addition of ceramic reinforcements provides a promising approach to achieving high-performance magnesium matrix composites.In this work,AZ91D magnesium alloys and 2 wt.%TiC/AZ91D composites have been manufactured by laser powder bed fusion(LPBF)with variations of laser processing parameters.The effect of TiC reinforcement addition on the laser absorption behaviors,forming quality,microstructure evolution and mechanical properties of the magnesium alloys is investigated.The TiC addition improves the interactions of laser with alloy powder and laser absorption rate of alloy powder,and decreases powder spatter of powder bed.The results show that high relative density of~99.4%and good surface roughness of~12μm are obtained for the LPBF-fabricated composites.The TiC addition promotes the precipitation of β-Mg_(17)Al_(12)in the alloys and the transformation of coarse columnar to fine equiaxed grains,where the grains are refined to~3.1μm.The TiC/AZ91D composites exhibit high microhardness of 114.6±2.5 HV_(0.2),high tensile strength of~345.0 MPa and a uniform elongation~4.1%.The improvement of tensile strength for the composites is ascribed to the combination of grain refinement strengthening and Orowan strengthening fromβ-Mg_(17)Al_(12)precipitates and Al_8Mn_5 nanoparticles.In the composites,the unmelted TiC particles can act as an anchor for the network structure of β-Mg_(17)Al_(12)precipitates,effectively impeding crack propagation and enhancing their performance.This work offers an insight to fabricating high-performance magnesium matrix composites by laser additive manufacturing.展开更多
Heat treatments play a crucial role in enhancing the mechanical properties of AZ91 Mg alloy by dissolving coarse phases during solution treatment and promoting precipitation during aging.However,non-uniform microstruc...Heat treatments play a crucial role in enhancing the mechanical properties of AZ91 Mg alloy by dissolving coarse phases during solution treatment and promoting precipitation during aging.However,non-uniform microstructures and coarse secondary phases in conventional casting methods hinder the effectiveness of these treatments,leading to reduced ductility,inconsistent properties,and prolonged durations.To overcome these challenges,this study introduces the Strain Integrated Gas-Infusion(SIGI)casting process that integrates strain and gas infusion in the semi-solid state.The impact of the SIGI process on the solution treatment and aging kinetics of AZ91 Mg alloy is explored.The SIGI process refinesα-Mg andβ-Mg_(17)Al_(12)phases,significantly enhancing mechanical properties.Experimental and quantitative analyses reveal that the SIGI process accelerates solute atom dissolution,reducing solution treatment times by half,and promotes faster nucleation and growth of precipitates during aging,shortening aging times by one-third.These improvements result in substantial gains in ultimate tensile strength(~40-50%)and ductility(~20-30%)after age hardening compared to conventional casting.The mechanisms driving these changes,including enhanced nucleation rates,reduced diffusion distances,and microstructural refinement,are discussed.These findings demonstrate the potential of the SIGI casting process to advance magnesium alloy performance for engineering applications.展开更多
A comprehensive analysis of the microstructure and defects of a thixomolded AZ91D alloy was conducted to elucidate their influences on mechanical properties.Samples were made at injection temperatures ranging from 580...A comprehensive analysis of the microstructure and defects of a thixomolded AZ91D alloy was conducted to elucidate their influences on mechanical properties.Samples were made at injection temperatures ranging from 580 to 640℃.X-ray computed tomography was used to visualize pores,and crystal plasticity finite element simulation was adopted for deformation analysis.The microstructure characterizations reveal a hierarchical cell feature composed of α-Mg and eutectic phases.With the increase of injection temperature,large cell content in the material decreases,while the strength of the alloy increases.The underlying mechanism about strength change is that coarse-grained solids experience smaller stress even in hard orientations.The sample fabricated at a moderate temperature of 620℃ exhibits the highest elongation,least quantity and lower local concentration of pores.The detachment and tearing cracks formed at lower injection temperature and defect bands formed at higher injection temperature add additional crack sources and deteriorate the ductility of the materials.展开更多
Thin walls of an AZ91 magnesium alloy with fine equiaxed grains were fabricated via cold arc-based wire arc additive manufacturing(CA-WAAM),and the droplet transfer behaviours,microstructures,and mechanical properties...Thin walls of an AZ91 magnesium alloy with fine equiaxed grains were fabricated via cold arc-based wire arc additive manufacturing(CA-WAAM),and the droplet transfer behaviours,microstructures,and mechanical properties were investigated.The results showed that the cold arc process reduced splashing at the moment of liquid bridge breakage and effectively shortened the droplet transfer period.The microstructures of the deposited samples exhibited layered characteristics with alternating distributions of coarse and fine grains.During layer-by-layer deposition,the β-phase precipitated and grew preferentially along grain boundaries,while the fineη-Al_(8)Mn_(5)phase was dispersed in the α-Mg matrix.The mechanical properties of the CA-WAAM deposited sample showed isotropic characteristics.The ultimate tensile strength and elongation in the building direction(BD)were 282.7 MPa and 14.2%,respectively.The microhardness values of the deposited parts were relatively uniform,with an average value of HV 69.6.展开更多
文摘通过向AZ91镁合金基体(采用镁合金铸锭)复合添加不同成分的碱土元素Ca、Sr,Ca和Sr元素是以Mg-30%Ca(质量分数)的镁钙中间合金和Mg-30%Sr(质量分数)的镁锶中间合金的形式添加,采用JVAM-1C型高真空电弧熔炼炉对添加后的合金在自制熔剂的覆盖和氩气保护下熔炼,获得不同成分的AZ91镁合金试样。运用DM2700M型徕卡研究级材料显微镜、JSM-6360LV型扫描电镜(Scanning Electron Microscope,SEM)对合金铸态以及均匀化退火后固溶时效态的显微组织展开观察,利用XD98型X射线衍射仪开展合金相结构分析,同时对其抗拉强度、延伸率和断面收缩率进行测试分析。结果表明:在AZ91镁合金中复合添加碱土元素Ca、Sr后,铸态中晶粒细化机理、晶界高熔点化合物对力学性能作用;证实了AZ91镁合金通过碱土Ca、Sr的复合作用后在高温状态下的力学性能提高机理、强韧性改善机理。
基金supported by the National Natural Science Foundation of China(52205382,52225503)National Key Research and Development Program(2023YFB4603300)+1 种基金Key Research and Development Program of Jiangsu Province(BZ2024019,BE2022069)International Joint Laboratory of Sustainable Manufacturing,Ministry of Education and the Fundamental Research Funds for the Central Universities(NG2024014,XCA2300501)。
文摘The addition of ceramic reinforcements provides a promising approach to achieving high-performance magnesium matrix composites.In this work,AZ91D magnesium alloys and 2 wt.%TiC/AZ91D composites have been manufactured by laser powder bed fusion(LPBF)with variations of laser processing parameters.The effect of TiC reinforcement addition on the laser absorption behaviors,forming quality,microstructure evolution and mechanical properties of the magnesium alloys is investigated.The TiC addition improves the interactions of laser with alloy powder and laser absorption rate of alloy powder,and decreases powder spatter of powder bed.The results show that high relative density of~99.4%and good surface roughness of~12μm are obtained for the LPBF-fabricated composites.The TiC addition promotes the precipitation of β-Mg_(17)Al_(12)in the alloys and the transformation of coarse columnar to fine equiaxed grains,where the grains are refined to~3.1μm.The TiC/AZ91D composites exhibit high microhardness of 114.6±2.5 HV_(0.2),high tensile strength of~345.0 MPa and a uniform elongation~4.1%.The improvement of tensile strength for the composites is ascribed to the combination of grain refinement strengthening and Orowan strengthening fromβ-Mg_(17)Al_(12)precipitates and Al_8Mn_5 nanoparticles.In the composites,the unmelted TiC particles can act as an anchor for the network structure of β-Mg_(17)Al_(12)precipitates,effectively impeding crack propagation and enhancing their performance.This work offers an insight to fabricating high-performance magnesium matrix composites by laser additive manufacturing.
文摘Heat treatments play a crucial role in enhancing the mechanical properties of AZ91 Mg alloy by dissolving coarse phases during solution treatment and promoting precipitation during aging.However,non-uniform microstructures and coarse secondary phases in conventional casting methods hinder the effectiveness of these treatments,leading to reduced ductility,inconsistent properties,and prolonged durations.To overcome these challenges,this study introduces the Strain Integrated Gas-Infusion(SIGI)casting process that integrates strain and gas infusion in the semi-solid state.The impact of the SIGI process on the solution treatment and aging kinetics of AZ91 Mg alloy is explored.The SIGI process refinesα-Mg andβ-Mg_(17)Al_(12)phases,significantly enhancing mechanical properties.Experimental and quantitative analyses reveal that the SIGI process accelerates solute atom dissolution,reducing solution treatment times by half,and promotes faster nucleation and growth of precipitates during aging,shortening aging times by one-third.These improvements result in substantial gains in ultimate tensile strength(~40-50%)and ductility(~20-30%)after age hardening compared to conventional casting.The mechanisms driving these changes,including enhanced nucleation rates,reduced diffusion distances,and microstructural refinement,are discussed.These findings demonstrate the potential of the SIGI casting process to advance magnesium alloy performance for engineering applications.
基金supported by the National Natural Science Foundation of China(Nos.51825101,52001202)the National Key Research and Development Program of China(No.2021YFA1600900)。
文摘A comprehensive analysis of the microstructure and defects of a thixomolded AZ91D alloy was conducted to elucidate their influences on mechanical properties.Samples were made at injection temperatures ranging from 580 to 640℃.X-ray computed tomography was used to visualize pores,and crystal plasticity finite element simulation was adopted for deformation analysis.The microstructure characterizations reveal a hierarchical cell feature composed of α-Mg and eutectic phases.With the increase of injection temperature,large cell content in the material decreases,while the strength of the alloy increases.The underlying mechanism about strength change is that coarse-grained solids experience smaller stress even in hard orientations.The sample fabricated at a moderate temperature of 620℃ exhibits the highest elongation,least quantity and lower local concentration of pores.The detachment and tearing cracks formed at lower injection temperature and defect bands formed at higher injection temperature add additional crack sources and deteriorate the ductility of the materials.
基金supported by the National Natural Science Foundation of China(No.51805265)the Fundamental Research Funds for the Central Universities,China(No.30922010921).
文摘Thin walls of an AZ91 magnesium alloy with fine equiaxed grains were fabricated via cold arc-based wire arc additive manufacturing(CA-WAAM),and the droplet transfer behaviours,microstructures,and mechanical properties were investigated.The results showed that the cold arc process reduced splashing at the moment of liquid bridge breakage and effectively shortened the droplet transfer period.The microstructures of the deposited samples exhibited layered characteristics with alternating distributions of coarse and fine grains.During layer-by-layer deposition,the β-phase precipitated and grew preferentially along grain boundaries,while the fineη-Al_(8)Mn_(5)phase was dispersed in the α-Mg matrix.The mechanical properties of the CA-WAAM deposited sample showed isotropic characteristics.The ultimate tensile strength and elongation in the building direction(BD)were 282.7 MPa and 14.2%,respectively.The microhardness values of the deposited parts were relatively uniform,with an average value of HV 69.6.
