Fabrication And Properties Of(Al₃Zr+Al₂O_3np)/6061 Composites With Reinforcement Network Distribution

Traditional aluminum matrix composites with high volume fraction and evenly distributed reinforcement own the high strength and toughness, but this kind of material always leads to the poor connection between matrixes, and the coordination of deformation between matrixes and reinforcement can be seriously influenced, so that the ductility of this kind of material is poor. In this paper,(Al3Zr+Al2O3)/6061 composites with soft matrix surrounded by quasi-continuous network reinforcement based on H-S theory was designed. By low energy ball milling technology and hot pressed vacuum sintered, aluminum matrix composites with 1%、3%、5%volume fraction were successfully fabricated. Scanning electron microscopy(SEM) and X-Ray Diffraction(XRD) were used to characterize microstructures of different composites. Mechanical properties at room temperature such as tensile strength,hardness, bending strength and fracture properties and density were analyzed.200rpm and 2h of low-energy milling process were chosen to mix the Zr O2 and6061 aluminum alloy powders. To determine the best process reaction between matrix and reinforcement powder, reaction temperature and holding time on the evolution of the composites microstructure needs to be studied. 850 o C and 90 min of holding time was considered to be the best process of the reaction.SEM and XRD show that the full reaction between Zr O2 raw materials and 6061 aluminum alloy matrix have happened to form the Al3 Zr and Al2O3 which are quasi-continuous distributed in the region of matrix. After hot extrusion deformation,the reticular structure unit, defection, the size of reinforcements and grain were decreased combining with the increasing density in the composites.The relative density of different volume fraction of materials after hot extrusion is about 99%. The relative density of composites diminishes by the increasing of volume fraction. Hardness test showed that the hardness of the material gradually increased from the matrix region to boundary of the reinforcement. Also, the hardness increased after extrusion and heat treatment. The increase of volume fraction has little effect on the hardness of the matrix region, but the hardness around the boundary between matrix and reinforcement increased.The tensile test at room temperature shows that the structure of the composite has excellent plasticity, and the strength increases with the increase of volume fraction,combining with the decreased elongation. After hot extrusion and heat treatment, the strength can be further enhanced, but the deformation of hot extrusion can increase the plasticity and the tensile strength of composite material at the same time. The strength of the hot extruded composite materials were increased to 179.9MPa,210.8MPa, 199.4MPa, and the plasticity was 20.1%, 17.8% and 16.9% respectively.The bending deformation of(Al3Zr+Al2O3)/6061 Al matrix composites is excellent.Macro cracks after bending cannot be found in the extruded materials, and the bending strength is pretty high. In the aspect of fracture toughness, low volume fraction reticular materials own the relatively low fracture toughness, but the load decreased more slowly after reaching the peak value, this phenomenon indicates the special network structure can effectively reduce the crack propagation rate.