This work aimed to fabricate B4C reinforced aluminum matrix composites via blended powder semisolid forming that is an implementation of the benefits of semisolid forming to the powder metallurgy. Al7075 elements were...This work aimed to fabricate B4C reinforced aluminum matrix composites via blended powder semisolid forming that is an implementation of the benefits of semisolid forming to the powder metallurgy. Al7075 elements were incrementally added to ethanol solution under mechanical mixing. Al7075 constituents and B4C particles were blended in a high energy ball mill. Cold compacted Al7075/B4C blends were pressed at semisolid state. The effects of the size of the matrix(20, 45 and 63 μm), reinforcing volume fraction(5%, 10% and 20%) and semisolid compaction pressure(50 and 100 MPa) on the morphology, microstructure, density, hardness, compression and bending strength were thoroughly analyzed. Experimental results revealed that the highest microstructural uniformity was achieved when large B4C particles(45 μm) were distributed within the small particles(20 μm) of the matrix phase. Composites with matrix particles larger than reinforcing phase indicated agglomerations in loadings more than 10%(volume fraction). Agglomerated regions resisted against penetration of the liquid phase to the pores and lowered the density and strength of these composites. Composites with 20 μm Al7075 and 20%(volume fraction) 45 μm B4C powder pressed under 100 MPa exhibited the highest values of hardness(HV 190) and compressive strength(336 MPa).展开更多
Subjecting a normal mechanical vibration to a cooling slope plate,is a proposed method for preparing semisolid nondendritic slurry,named shear-vibration coupling sub-rapid solidification(SCS).Taking Al-8Si alloy as mo...Subjecting a normal mechanical vibration to a cooling slope plate,is a proposed method for preparing semisolid nondendritic slurry,named shear-vibration coupling sub-rapid solidification(SCS).Taking Al-8Si alloy as model material,the temperature field and distribution field of solid or liquid phase during SCS were simulated using COMSOL Multiphysics software to primarily choose the optimal processing parameters.Subsequently,the slurries were prepared with the parameters selected according to the simulation results and the microstructures of the slurries were experimentally investigated.Results indicate that the simulation results could provide a basis for roughly choosing the processing parameters,although the calculated solid fractions are always higher than the experimental ones.The processing parameters affect the primary grain size,shape factor and solid fraction mainly through altering the contact duration of melt on the plate,and thus affecting the cooling effect on the melt,nucleation rate,and grain dissociation and proliferation.Experiments with optimized processing parameters show that the primary grains in the slurry have an average size of about 32μm and shape factor of 1.38,and are quite uniform,even at the highest pouring rate of 2.81 kg·s^(-1),the size and shape factor are about 46μm and 1.7,respectively,which implies that the proposed SCS is a promising technology for efficient fabrication of high-quality Al slurry available for engineering applications.展开更多
A series of reheating-isothermal holding experiments and compression tests were conducted on pristine magnesium alloy AZ91 extruded by equal channel angular extrusion (ECAE) and SiC particles (a volume fraction of ...A series of reheating-isothermal holding experiments and compression tests were conducted on pristine magnesium alloy AZ91 extruded by equal channel angular extrusion (ECAE) and SiC particles (a volume fraction of 15%) reinforced AZ91 composite (AZ91-SiCp) by regular extrusion. Dissolution of eutectic com- pounds and partial melting of the ct-Mg matrix occurred during the reheating of these materials. Spherical semisolid slurries of these materials were obtained when the reheating temperature and isothermal hold- ing time were 550℃ and 20 s, respectively. The presence of SiCp in AZ91-SiCp not only caused lower liquid fractions of semisolid slurries but also resulted in higher values of flow stress during semisolid compression tests. Both AZgl alloy and AZ91-SiCp composite exhibited better thixoforming properties at high temperatures. Segregation of SiCp did not occur during thixoforming of AZ91-SiCp composite after an isothermal holding at semisolid temperatures for 20 s.2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.展开更多
基金Tabriz Branch,Islamic Azad University for the financial support of this research,which is based on a research project contract
文摘This work aimed to fabricate B4C reinforced aluminum matrix composites via blended powder semisolid forming that is an implementation of the benefits of semisolid forming to the powder metallurgy. Al7075 elements were incrementally added to ethanol solution under mechanical mixing. Al7075 constituents and B4C particles were blended in a high energy ball mill. Cold compacted Al7075/B4C blends were pressed at semisolid state. The effects of the size of the matrix(20, 45 and 63 μm), reinforcing volume fraction(5%, 10% and 20%) and semisolid compaction pressure(50 and 100 MPa) on the morphology, microstructure, density, hardness, compression and bending strength were thoroughly analyzed. Experimental results revealed that the highest microstructural uniformity was achieved when large B4C particles(45 μm) were distributed within the small particles(20 μm) of the matrix phase. Composites with matrix particles larger than reinforcing phase indicated agglomerations in loadings more than 10%(volume fraction). Agglomerated regions resisted against penetration of the liquid phase to the pores and lowered the density and strength of these composites. Composites with 20 μm Al7075 and 20%(volume fraction) 45 μm B4C powder pressed under 100 MPa exhibited the highest values of hardness(HV 190) and compressive strength(336 MPa).
基金financially supported by the National Key Research and Development Program of China (Grant No. 2018YFB2001800)
文摘Subjecting a normal mechanical vibration to a cooling slope plate,is a proposed method for preparing semisolid nondendritic slurry,named shear-vibration coupling sub-rapid solidification(SCS).Taking Al-8Si alloy as model material,the temperature field and distribution field of solid or liquid phase during SCS were simulated using COMSOL Multiphysics software to primarily choose the optimal processing parameters.Subsequently,the slurries were prepared with the parameters selected according to the simulation results and the microstructures of the slurries were experimentally investigated.Results indicate that the simulation results could provide a basis for roughly choosing the processing parameters,although the calculated solid fractions are always higher than the experimental ones.The processing parameters affect the primary grain size,shape factor and solid fraction mainly through altering the contact duration of melt on the plate,and thus affecting the cooling effect on the melt,nucleation rate,and grain dissociation and proliferation.Experiments with optimized processing parameters show that the primary grains in the slurry have an average size of about 32μm and shape factor of 1.38,and are quite uniform,even at the highest pouring rate of 2.81 kg·s^(-1),the size and shape factor are about 46μm and 1.7,respectively,which implies that the proposed SCS is a promising technology for efficient fabrication of high-quality Al slurry available for engineering applications.
基金financially supported by the National Natural Science Foundation of China (No. 51605055)Chongqing Natural Science Foundation (No. cstc2016jcyj A1027)Fundamental Research Funds for the Central Universities (No. 0903005203307)
文摘A series of reheating-isothermal holding experiments and compression tests were conducted on pristine magnesium alloy AZ91 extruded by equal channel angular extrusion (ECAE) and SiC particles (a volume fraction of 15%) reinforced AZ91 composite (AZ91-SiCp) by regular extrusion. Dissolution of eutectic com- pounds and partial melting of the ct-Mg matrix occurred during the reheating of these materials. Spherical semisolid slurries of these materials were obtained when the reheating temperature and isothermal hold- ing time were 550℃ and 20 s, respectively. The presence of SiCp in AZ91-SiCp not only caused lower liquid fractions of semisolid slurries but also resulted in higher values of flow stress during semisolid compression tests. Both AZgl alloy and AZ91-SiCp composite exhibited better thixoforming properties at high temperatures. Segregation of SiCp did not occur during thixoforming of AZ91-SiCp composite after an isothermal holding at semisolid temperatures for 20 s.2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.