Fabrication and Damping Capacity of Short Alumina Fiber and VGCF Hybrid Reinforced Aluminum Alloy Composites
Topic(s) : Material science
Co-authors :
Kazunori ASANO (JAPAN), Yuki FUJIOKAAbstract :
Aluminum, which is used as a lightweight material for equipment, has problems such as low high-temperature strength and wear resistance. In addition, vibration and noise generation caused by weight reduction are also problems. The authors have shown that reinforcement with alumina short fibers improves the high-temperature strength of aluminum alloys, and that reinforcement with carbon fibers improves the wear properties, thermal expansion properties, and thermal conductivity of aluminum alloys. We expected that the reinforcement with VGCF (carbon nanofiber) , which are finer than carbon fibers, and alumina short fibers with aluminum alloys would provide the materials with high-temperature strength, wear resistance, and high vibration damping capacity. In this study, the hybrid aluminum alloy composites, in which alumina short fibers with superior high-temperature strength and VGCF with small diameter, high thermal conductivity, low thermal expansion, and wear resistance as the reinforcements, were fabricated, and the microstructure and damping capacity of the composites were investigated.
Reinforcement preforms with different volume fraction were prepared by mixing VGCFs with various volume fraction of 0, 3, 6, and 9 vol% and alumina short fibers with volume fraction of 5,10 and 15 vol%. Composites were fabricated by squeeze casting; the preforms were placed in a permanent mold, molten cast aluminum alloy was poured into the mold, and then the pressure was applied to accomplish the infiltration into the preforms.
Optical and electron micrographs of the composites showed that the VGCF existed among the alumina fibers in the composite. Although the VGCF was dispersed among the alumina fibers in the composite when the volume fraction of VGCF was small, the agglomeration of VGCF was clearly observed when the volume fraction of VGCF was great (especially 9 vol%). Electron microscopy revealed that the micro voids were observed near the agglomeration area. The voids would be microshrinkage or area where the melt infiltration was imperfect, which were formed during the melt infiltration process.
Damping capacity of the alloy was improved by the reinforcement at every temperature measured (RT-573 K). Damping capacity showed the highest when the volume fraction of VGCF and alumina fiber was 9 and 15 vol%, respectively. Improvement in the damping capacity would be due to the energy loss by shear at the reinforcement-matrix interface. The energy loss due to friction would be caused by the movement of VGCF at the micro voids near the agglomeration area, in addition to the energy loss due to the shear as mentioned above.
Reinforcement preforms with different volume fraction were prepared by mixing VGCFs with various volume fraction of 0, 3, 6, and 9 vol% and alumina short fibers with volume fraction of 5,10 and 15 vol%. Composites were fabricated by squeeze casting; the preforms were placed in a permanent mold, molten cast aluminum alloy was poured into the mold, and then the pressure was applied to accomplish the infiltration into the preforms.
Optical and electron micrographs of the composites showed that the VGCF existed among the alumina fibers in the composite. Although the VGCF was dispersed among the alumina fibers in the composite when the volume fraction of VGCF was small, the agglomeration of VGCF was clearly observed when the volume fraction of VGCF was great (especially 9 vol%). Electron microscopy revealed that the micro voids were observed near the agglomeration area. The voids would be microshrinkage or area where the melt infiltration was imperfect, which were formed during the melt infiltration process.
Damping capacity of the alloy was improved by the reinforcement at every temperature measured (RT-573 K). Damping capacity showed the highest when the volume fraction of VGCF and alumina fiber was 9 and 15 vol%, respectively. Improvement in the damping capacity would be due to the energy loss by shear at the reinforcement-matrix interface. The energy loss due to friction would be caused by the movement of VGCF at the micro voids near the agglomeration area, in addition to the energy loss due to the shear as mentioned above.