In the present work, Zn-（0-1）Mg（wt%） alloys were prepared by casting and indirect extrusion at 200 and300 ℃, respectively. With Mg addition, both the size and amount of second phase Mg2Zn（11） increased, and the...In the present work, Zn-（0-1）Mg（wt%） alloys were prepared by casting and indirect extrusion at 200 and300 ℃, respectively. With Mg addition, both the size and amount of second phase Mg2Zn（11） increased, and the equiaxed grains were significantly refined. The extrusion temperature had little influence on Mg2Zn（11）, but the grains were refined at low extrusion temperature. For the alloys extruded at 200 ℃, as Mg content increased, the tensile yield strength（TYS）increased from 64 MPa for pure Zn to 262 MPa for Zn-1Mg; the elongation increased from 14.3% for pure Zn to 25% for Zn-0.02Mg and then decreased to 5% for Zn-1Mg. For the alloys extruded at 300 ℃, as Mg content increased, the TYS increased from 67 MPa for pure Zn to 252 MPa for Zn-1Mg, while the elongation decreased from 11.7% to 2%. The alloy extruded at 200 ℃ exhibited higher TYS and elongation than the corresponding alloy extruded at 300 ℃. The combination of grain refinement and second phase Mg2Zn（11） contributed to the improvement in the TYS, and the grain refinement played a major role in strengthening alloy. Zn-0.02Mg and Zn-0.05Mg alloys extruded at 200 ℃ show a mixture of cleavage and ductile fracture corresponding to higher elongation, while the other alloys show cleavage fracture.展开更多
1.0wt.% carbon nanotube （CNT） reinforced 2024Al matrix composite was fabricated by cold isostatic press and subsequent hot extrusion techniques. The mechanical properties of the composite were measured by a tensile ...1.0wt.% carbon nanotube （CNT） reinforced 2024Al matrix composite was fabricated by cold isostatic press and subsequent hot extrusion techniques. The mechanical properties of the composite were measured by a tensile test. Mean-while,the fracture surfaces were examined using field emission scanning electron microscopy. The experimental results show that CNTs are dispersed homogeneously in the composite and that the interfaces of the Al matrix and the CNT bond well. Although the tensile strength and the Young’s modulus of the composite are enhanced markedly,the elongation does not decrease when compared with the matrix material fabricated under the same process. The reasons for the increments may be the extraordinary mechanical properties of CNTs,and the bridging and pulling-out role of CNTs in the Al matrix composite.展开更多
The incorporation of graphite particles into AA6016 aluminum alloy matrix to fabricate metal/ceramic composites is still a great challenge and various parameters should be considered. In this study, dense AA6016 alumi...The incorporation of graphite particles into AA6016 aluminum alloy matrix to fabricate metal/ceramic composites is still a great challenge and various parameters should be considered. In this study, dense AA6016 aluminum alloy/（0-20 wt%） graphite composites have successfully been fabricated by powder metallurgy process. At first, the mixed aluminum and graphite powders were cold compacted at 200 MPa and then sintered at 500 ℃ for 1 h followed by hot extrusion at 450 ℃. The influence of ceramic phases（free graphite and in-situ formed carbides） on microstructure, physical and mechanical properties of the produced composites were finally investigated. The results show that the fabricated composites have a relative density of over 98%. SEM observations indicate that the graphite has a good dispersion in the alloy matrix even at high graphite content. Hardness of all the produced composites was higher than that of aluminum alloy matrix. No cracks were observed at strain less than 23% for all hot extruded materials.Compressive strength, reduction in height, ultimate tensile stress, fracture stress, yield stress, and fracture strain of all Al/graphite composites were determined by high precision second order equations. Both compressive and ultimate tensile strengths have been correlated to microstructure constituents with focusing on the in-situ formed ceramic phases, silicon carbide（SiC） and aluminum carbide（Al4 C3）. The ductile fracture mode of the produced composites became less dominant with increasing free graphite content and in-situ formed carbides. Wear resistance of Al/graphite composites was increased with increasing graphite content. Aluminum/20 wt% graphite composite exhibited superior wear resistance over that of AA6016 aluminum alloy.展开更多
基金supported by the National Natural Science Foundation of China (Nos.51525101 and 51371046)the Program for New Century Excellent Talents in University (No.NECT-12-0109)the Fundamental Research Funds for the Central Universities (Nos.N130510002,N141008001)
文摘In the present work, Zn-（0-1）Mg（wt%） alloys were prepared by casting and indirect extrusion at 200 and300 ℃, respectively. With Mg addition, both the size and amount of second phase Mg2Zn（11） increased, and the equiaxed grains were significantly refined. The extrusion temperature had little influence on Mg2Zn（11）, but the grains were refined at low extrusion temperature. For the alloys extruded at 200 ℃, as Mg content increased, the tensile yield strength（TYS）increased from 64 MPa for pure Zn to 262 MPa for Zn-1Mg; the elongation increased from 14.3% for pure Zn to 25% for Zn-0.02Mg and then decreased to 5% for Zn-1Mg. For the alloys extruded at 300 ℃, as Mg content increased, the TYS increased from 67 MPa for pure Zn to 252 MPa for Zn-1Mg, while the elongation decreased from 11.7% to 2%. The alloy extruded at 200 ℃ exhibited higher TYS and elongation than the corresponding alloy extruded at 300 ℃. The combination of grain refinement and second phase Mg2Zn（11） contributed to the improvement in the TYS, and the grain refinement played a major role in strengthening alloy. Zn-0.02Mg and Zn-0.05Mg alloys extruded at 200 ℃ show a mixture of cleavage and ductile fracture corresponding to higher elongation, while the other alloys show cleavage fracture.
文摘1.0wt.% carbon nanotube （CNT） reinforced 2024Al matrix composite was fabricated by cold isostatic press and subsequent hot extrusion techniques. The mechanical properties of the composite were measured by a tensile test. Mean-while,the fracture surfaces were examined using field emission scanning electron microscopy. The experimental results show that CNTs are dispersed homogeneously in the composite and that the interfaces of the Al matrix and the CNT bond well. Although the tensile strength and the Young’s modulus of the composite are enhanced markedly,the elongation does not decrease when compared with the matrix material fabricated under the same process. The reasons for the increments may be the extraordinary mechanical properties of CNTs,and the bridging and pulling-out role of CNTs in the Al matrix composite.
文摘The incorporation of graphite particles into AA6016 aluminum alloy matrix to fabricate metal/ceramic composites is still a great challenge and various parameters should be considered. In this study, dense AA6016 aluminum alloy/（0-20 wt%） graphite composites have successfully been fabricated by powder metallurgy process. At first, the mixed aluminum and graphite powders were cold compacted at 200 MPa and then sintered at 500 ℃ for 1 h followed by hot extrusion at 450 ℃. The influence of ceramic phases（free graphite and in-situ formed carbides） on microstructure, physical and mechanical properties of the produced composites were finally investigated. The results show that the fabricated composites have a relative density of over 98%. SEM observations indicate that the graphite has a good dispersion in the alloy matrix even at high graphite content. Hardness of all the produced composites was higher than that of aluminum alloy matrix. No cracks were observed at strain less than 23% for all hot extruded materials.Compressive strength, reduction in height, ultimate tensile stress, fracture stress, yield stress, and fracture strain of all Al/graphite composites were determined by high precision second order equations. Both compressive and ultimate tensile strengths have been correlated to microstructure constituents with focusing on the in-situ formed ceramic phases, silicon carbide（SiC） and aluminum carbide（Al4 C3）. The ductile fracture mode of the produced composites became less dominant with increasing free graphite content and in-situ formed carbides. Wear resistance of Al/graphite composites was increased with increasing graphite content. Aluminum/20 wt% graphite composite exhibited superior wear resistance over that of AA6016 aluminum alloy.
