Fabrication And Properties Of Aluminum Matrix Composites With A Quasi-continuous Network Distribution

Conventional aluminum matrix composites possess superior strength and stiffness, but own poor ductility and toughness. In the present work, network structure Al matrix composites with quasi continuous reinforcement distribution were designed by the idea of "microstructural toughening". Large size6061powders and fine ZrO2were employed as raw material. The composites were in-situ fabricated by low energy ball milling and vacuum hot pressing sintering technique. Microstructure of as-sintered composites was studied and reaction mechanism was discussed by SEM and XRD techniques.Room temperature and high temperature mechanical properties of network composites were measured, compared with data from the control group from homogeneous composites with same volume fraction of reinforcement. Effects of hot extrusion on microstructure and mechanical properties of network structure composites were studied.The optimum ball milling parameters are proved to be2hours and200rpm after studying influence of various milling time and speed on morphology of milled powders. Hot pressing sintering parameters have been optimized to be850℃and90min after studying effects of time and temperature on distribution and morphology of reinforcement. On basis of proper assumptions, kinetic model of network composites have been established to evaluate effects on growth velocity.Al3Zr and nano Al2O3were obtained from in situ reaction between6061Al alloys powders and ZrO2powders. Al3Zr, scattered along the boundary of6061particles to form3-D network structure. Matrix particles are not yet completely separated by reinforcement, which contributes to well strengthening effect. The nano-scale Al2O3, distributed uniformly along the matrix particle boundary. This benefits the strength of composites.Mechanical properties of composites have been tested under different conditions. The result shows that mechanical properties of network structure composites are far better than that of homogeneous composites. Room temperature tensile strength of network composites is200MPa, whereas homogeneous composites’ is120MPa. After extrusion, tensile strength of network composites is improved to230MPa and elongation is16%, much higher than that of as-sintered network composites1.5%. The fracture toughness of three kinds (network composite as-sintered, extruded network one and homogenous one)of materials has been tested and the distinctive crack expansion mechanism within network composites has been discussed. The results of high temperature mechanical properties indicates that high temperature mechanical properties testing result indicates that strength of extruded network composites is slightly less than as-sintered one, but presenting greatly better plasticity than the latter.