Study On The Preparation Of Sub-micron Particle Reinforced Aluminum Matrix Composites

In recent years, aluminum matrix composites reinforced by sub-micon reinforcements have become the focus of studies on metal matrix composites. Because of their excellent mechanical properties and price which could compete with traditional metallic materials, they are prone to be applied in the fields of optics, electronic packaging, space navigation and weapons. The preparation technique is always the precursor and the key for manufacturing and using these aluminum matrix composites cosmically.In this paper, sub-micon particle reinforced aluminum matrix composites have been prepared directly by isothermally treating an Al-Si-Cu alloy system and rapid solidifying Al-Ni-Y alloys, respectively. The effects of the process condition and the alloy composition on the microstructure of these alloys have been studied and hardness tests of different composites have been made. For Al-Si-Cu matrix composites, the tensile tests have also been carried out and the fracture morphology has been observed under scanning electron microscope (SEM).It can been seen that the growth rate of silicon crystals can be decreased by adding a little amount of strontium into the Al-Si-Cu alloy as the nucleation ability of the silicon crystals can be influenced effectively. The silicon structure of Al-Si-Cu alloy has been changed from needle shape into grainy shape after isothermally treating under liquid-solid two-phase temperature. Both the microstructure and the mechanical properties of the Al-Si-Cu alloy have been improved by adjusting the holding time and the temperature. Spheric and fine silicon crystals can be obtained by increasing the holding time and the temperature in certain range. Because the alloy have separated out tiny strengthening phases when the holding time is 5min and the holding temperature is 580℃and 590℃, the hardness and the tensile strength of these samples are improved for solution strengthening and grain refining strengthening. The elongation value of the sample whose holding time is 10min is larger because of the improvement of the shape and distribution of silicon phase. In the experiment of Al-Ni-Y alloys, zirconium has substituted for nickel. The structure of alloy has been changed from long stick shape into short stick shape as the zirconium increases gradually. The stick structures will disappear entirely and be replaced by grainy shape as the zirconium content is 5 % .The hardness of Al-Ni-Y alloy increases gradually due to the solution strengthening and grain refining strengthening as the zirconium content increases.