采用光学显微镜、扫描和透射电子显微镜研究了含Ca、Si镁合金的显微组织特征。铸态下,仅含Ca的镁合金主要由镁基体和晶界离异共晶组织(Mg+Mg2Ca)组成;加入约0.5%(质量分数)Si后,晶界离异共晶组织消失,在晶界附近及晶内形成弥散分布的细...采用光学显微镜、扫描和透射电子显微镜研究了含Ca、Si镁合金的显微组织特征。铸态下,仅含Ca的镁合金主要由镁基体和晶界离异共晶组织(Mg+Mg2Ca)组成;加入约0.5%(质量分数)Si后,晶界离异共晶组织消失,在晶界附近及晶内形成弥散分布的细小点状(球状)、针状和粗块状CaMgSi相;当含Si量较高(约1.0%)时,出现中国字形(针状)的Mg2Si相。固溶时效后,只含Ca的镁合金中晶界处离异共晶组织消失,代之以长大了的颗粒状Mg2Ca相;而Mg Ca Si合金的固溶时效组织较铸态无明显变化。对合金常温和高温短时拉伸性能也作了初步探讨。展开更多
Mg−Zn−Cu−Zr−Ca samples were solidified under high pressures of 2-6 GPa.Scanning electron microscopy and electron backscatter diffraction were used to study the distribution of Ca in the microstructure and its effect o...Mg−Zn−Cu−Zr−Ca samples were solidified under high pressures of 2-6 GPa.Scanning electron microscopy and electron backscatter diffraction were used to study the distribution of Ca in the microstructure and its effect on the solidification structure.The mechanical properties of the samples were investigated through compression tests.The results show that Ca is mostly dissolved in the matrix and the Mg_(2)Ca phase is formed under high pressure,but it is mainly segregated among dendrites under atmospheric pressure.The Mg_(2)Ca particles are effective heterogeneous nuclei ofα-Mg crystals,which significantly increases the number of crystal nuclei and refines the solidification structure of the alloy,with the grain size reduced to 22μm at 6 GPa.As no Ca segregating among the dendrites exists,more Zn is dissolved in the matrix.Consequently,the intergranular second phase changes from MgZn with a higher Zn/Mg ratio to Mg7Zn3 with a lower Zn/Mg ratio.The volume fraction of the intergranular second phase also increases to 22%.Owing to the combined strengthening of grain refinement,solid solution,and dispersion,the compression strength of the Mg-Zn-Cu-Zr-Ca alloy solidified under 6 GPa is up to 520 MPa.展开更多
In this work,two wrought Mg-3.66Al-4.25Ca-0.43 Mn(wt%)alloys with different morphology and distribution of Mg_(2)Ca particles were fabricated by hot extrusion and multi-pass(32)equal channel angular pressing(ECAP).The...In this work,two wrought Mg-3.66Al-4.25Ca-0.43 Mn(wt%)alloys with different morphology and distribution of Mg_(2)Ca particles were fabricated by hot extrusion and multi-pass(32)equal channel angular pressing(ECAP).The as-extruded alloy exhibits a banded microstructure with alternately arranged Mg_(2)Ca particle bands,fine α-Mg dynamically recrystallized(DRX)grain bands,and coarse α-Mg deformed grain bands.The Mg_(2)Ca bands are composed of broken Mg_(2)Ca particles which are aggregated and aligned along extrusion direction.The microstructure of ECAP alloy contains complete α-Mg DRX grains and refined Mg_(2)Ca particles which are dispersedly distributed at grain boundaries.Tensile test results show that the as-extruded alloy possesses high ultimate tensile strength(UTS)of 420 MPa and poor fracture elongation of 7%,while the ECAP alloy exhibits improved toughness with UTS of 347 MPa and fraction elongation of 16%.The higher strength of as-extruded alloy is mainly ascribed to the contribution of coarse deformed grains with strong texture,and its poor toughness is resulted from the formation of Mg_(2)Ca bands within which microcracks could form and extend rapidly.On the contrary,the refined and dispersedly distributed Mg_(2)Ca particles are effective to retard crack initiation and impede crack propagation,thereby enhancing the toughness of ECAP alloy significantly.展开更多
文摘采用光学显微镜、扫描和透射电子显微镜研究了含Ca、Si镁合金的显微组织特征。铸态下,仅含Ca的镁合金主要由镁基体和晶界离异共晶组织(Mg+Mg2Ca)组成;加入约0.5%(质量分数)Si后,晶界离异共晶组织消失,在晶界附近及晶内形成弥散分布的细小点状(球状)、针状和粗块状CaMgSi相;当含Si量较高(约1.0%)时,出现中国字形(针状)的Mg2Si相。固溶时效后,只含Ca的镁合金中晶界处离异共晶组织消失,代之以长大了的颗粒状Mg2Ca相;而Mg Ca Si合金的固溶时效组织较铸态无明显变化。对合金常温和高温短时拉伸性能也作了初步探讨。
基金financial supports from the National Natural Science Foundation of China(Nos.51675092,51775099)the Natural Science Foundation of Hebei Province,China(Nos.E2018501032,E2018501033)。
文摘Mg−Zn−Cu−Zr−Ca samples were solidified under high pressures of 2-6 GPa.Scanning electron microscopy and electron backscatter diffraction were used to study the distribution of Ca in the microstructure and its effect on the solidification structure.The mechanical properties of the samples were investigated through compression tests.The results show that Ca is mostly dissolved in the matrix and the Mg_(2)Ca phase is formed under high pressure,but it is mainly segregated among dendrites under atmospheric pressure.The Mg_(2)Ca particles are effective heterogeneous nuclei ofα-Mg crystals,which significantly increases the number of crystal nuclei and refines the solidification structure of the alloy,with the grain size reduced to 22μm at 6 GPa.As no Ca segregating among the dendrites exists,more Zn is dissolved in the matrix.Consequently,the intergranular second phase changes from MgZn with a higher Zn/Mg ratio to Mg7Zn3 with a lower Zn/Mg ratio.The volume fraction of the intergranular second phase also increases to 22%.Owing to the combined strengthening of grain refinement,solid solution,and dispersion,the compression strength of the Mg-Zn-Cu-Zr-Ca alloy solidified under 6 GPa is up to 520 MPa.
基金Guangdong Province Key Field R&D Program Project (2020B010186002)National Natural Science Foundation of China (U2037601)Dongguan Key Technology Key Project (2019622134013)。
基金supported financially by the Fundamental Research Funds for the Central Universities(B200202131)the National Natural Science Foundation of China(Nos.51901068,51979099 and 51774109)+1 种基金the Nantong Science and Technology Project(No.JC2018109)the Key Research and Development Project of Jiangsu Province(No.BE2017148)。
文摘In this work,two wrought Mg-3.66Al-4.25Ca-0.43 Mn(wt%)alloys with different morphology and distribution of Mg_(2)Ca particles were fabricated by hot extrusion and multi-pass(32)equal channel angular pressing(ECAP).The as-extruded alloy exhibits a banded microstructure with alternately arranged Mg_(2)Ca particle bands,fine α-Mg dynamically recrystallized(DRX)grain bands,and coarse α-Mg deformed grain bands.The Mg_(2)Ca bands are composed of broken Mg_(2)Ca particles which are aggregated and aligned along extrusion direction.The microstructure of ECAP alloy contains complete α-Mg DRX grains and refined Mg_(2)Ca particles which are dispersedly distributed at grain boundaries.Tensile test results show that the as-extruded alloy possesses high ultimate tensile strength(UTS)of 420 MPa and poor fracture elongation of 7%,while the ECAP alloy exhibits improved toughness with UTS of 347 MPa and fraction elongation of 16%.The higher strength of as-extruded alloy is mainly ascribed to the contribution of coarse deformed grains with strong texture,and its poor toughness is resulted from the formation of Mg_(2)Ca bands within which microcracks could form and extend rapidly.On the contrary,the refined and dispersedly distributed Mg_(2)Ca particles are effective to retard crack initiation and impede crack propagation,thereby enhancing the toughness of ECAP alloy significantly.
