Study On The Al₂O₃Particles Reinforced Aluminum Matrix Composites

Particles reinforced aluminum matrix composite has a wide prospect of application because of its excellent performance, low price of the particles and the general method of processing. At present, the most widely used Al2O3/Al matrix composite are mostly prepared by particles plus method. Composites prepared by this method need large particles and the wettability between the particles and the matrix are not well which will influence the effect of particle enhancement. In this paper, we prepared Al2O3/Al composite by spark plasma sintering, and have studied the influence of different particle size, content, surface morphology (α-Al2O3and γ-Al2O3) on the microstructure and mechanical properties of the composite. The paper has also prepared Al2O3/Al composite by a new designed stir casting method. Using this method, α-Al2O3and γ-Al2O3particles are mixed separately with Al powder according to different volume fraction, and then they are pressed into blocks which are added to molten aluminum alloy in composite preparation. The dispersion degree of particles in aluminum matrix is studied.In spark plasma sintering method, the four component of Al2O3(5%、10%、15%and20%) are studied and the results show that the relative density of the composite increases when the particle content reduced, in the case of a sintering temperature of560℃, holding time5minutes, a pressure of20Mpa and a heating rate of100℃/min. In addition, for the15%volume fraction of Al2O3, the relative density of the composite decreases with particle size increasing from30nm,0.5μm,1μm to3.6μm. By the tests of three-point bending, hardness, friction and wear, the results show that the bending strength and hardness increase to the maximum with the increase of volume fraction of Al2O3from5%,10%to15%and fall while number increases to20%. However, wear resistance increase as the particle size decreases. According to SEM microstructure analysis, results show that the higher content of reinforcing particles, the better the degree of integration between the sintered particles, however, as the amounts exceed15%and reach20%it decreases. For the particle size, the smaller, the better the degree of integration.For the composite prepared by stir casting method, the SEM microstructure analysis found that there are a lot of pits in similar size on the surface of the sample. After analysis we believe that the pits are caused by the additional reinforcing particles agglomeration, because the number of pits increased with the increase of particle content. In addition, for the same content of α-Al2O3/Al, γ-Al2O3/Al composite, the pits in γ-Al2O3/Al composite is larger than in α-Al2O3/Al composite" s, this is due to the porous morphology of γ-Al2O3which lead to strong adsorption capacity and easier to agglutinate. When the A1powder mixed with α-Al2O3,γ-Al2O3particles was analyzed by transmission electron microscopy, we found that the oxidation A1powder was serious. We can conclude that the A1powder suppressed in the block did not fully melted in the molten aluminum alloy, combined with particle agglomeration which causes composites loose.