Optimization Of Matrix Component And Tribological Properties Of Al₂O₃·SiO_2sf/Al Composites

The Al₂O₃·SiO_2sf/Al composites were fabricated by squeeze casting method. The Al, Al-Cu, and Al-Cu-Mg alloys were selected as the matrix, respectively, which were adjusted so as to get composites with excellent property and low cost. The research provided a theoretical base for finding a kind of short fiber reinforcement Al matrix composite material for civil use.The microstructure and interface of Al₂O₃·SiO_2sf/Al composites are investigated by SEM, TEM and DEX. The results showed that during the manufacturing process of Al₂O₃·SiO_2sf/Al composites, there was a chemical reaction between the liquid Al and the SiO2 amorphous layer on the fiber surface. Therefore, the silicon dissolved into matrix alloy or precipitated as single crystal silicon phase. The aggregation of Cu element which generated at the interface of the fiber could effectively prevent or inhibit the reaction. When the Cu content increased to 5%, the reaction at the interface basically did not occur, the solute atoms in the matrix changed from silicon to Cu. In addition, small amount of CuAl2 phase precipitated at the local area of interface. X-ray results showed that CuAl2O4 spinel and MgAl2O4 spinel were formed in the Al₂O₃·SiO_2sf/Al-Cu and Al₂O₃·SiO_2sf/(2024Al+Mg) composites. Gibbs energy calculation of possible reactions in Al₂O₃·SiO_2sf/Al-Cu and Al₂O₃·SiO_2sf/ (2024Al+Mg) composites shows that CuAl2O4 is obtained through oxidation of CuAl2, not the reaction product of the interface, and that MgAl2O4 was the reaction product between fiber and matrix alloy during extrusion cladding.The age hardening precipitation behavior of Al₂O₃·SiO_2sf/Al-Cu and Al₂O₃·SiO_2sf/(2024Al+Mg) composites was studied. Results showed that with the increasing of Cu content, the hardness was increased, and the peak aging time was shortened. The effect was the most obvious when aging at temperature 190oC. With the increasing of Mg content the peak aging time was postponed and the temperature range of peak aging was enlarged. The most obvious effect of aging treatment was at 185 oC. The results of hardness test and microstructure observation showed that the precipitation of Al₂O₃·SiO_2sf/(2024Al+1%Mg) was fine and acicular, which provided with the best effect of strengthening and plasticity. Some bulk precipitation, which the size was still small, was found in the Al₂O₃·SiO_2sf/(2024Al+2%Mg) composite and a slight decrease of hardness is obtained. For Al₂O₃·SiO_2sf/(2024Al+3%Mg), the precipitation grows larger which leads to further decrease of hardness.Addition of Cu and Mg elements were both benefit to decrease the thermal expansion coefficients (CTEs) of the Al₂O₃·SiO_2sf/Al composites. The CTEs value of composites decreased with the Cu or Mg increasing. With the addition of Mg in the 2024 matrix alloy, the CTE curve of the composite was flat and the thermal expansion property of the Al₂O₃·SiO₂/(2024Al+3%Mg) composite material was optimum. During the heating temperature of 100³00oC the CTE values of the Al₂O₃·SiO_2sf/(2024Al+Mg) composites increased linearly and slowly with the temperature increasing. When the temperature is above 300oC the CTE value of Al₂O₃·SiO_2sf/(2024Al+Mg) composites increased sharply with the temperature increasing. While the thermal expansion was coefficient of Al₂O₃·SiO_2sf/(2024Al+3%Mg) composite increased smoothly.Research work on the wear process showed that Al₂O₃·SiO₂ short fiber was firmly fixed in the matrix and formed the framework. The fiber in composites would be hardly pulled out during the wear processing. When the soft matrix material in the composite worn off, the bare area of Al₂O₃·SiO₂ fiber frictionated the opposite grinding material, The contact area was reduced and the fiber either took partial load or reduced local stress, protecting the comparatively soft matrix and improved the wear resistance of the composites. The wear mechanism of Al₂O₃·SiO_2sf/pure Al composite was mainly adherence abrasion. The wear mechanism of Al₂O₃·SiO_2sf/Al-Cu composite was mainly appeared to be adhesive wear, accompanied by abrasive wear. For the Al₂O₃·SiO_2sf/(2024Al+Mg) composite, the mechanism mainly was adhesive wear and grain wear mechanism.At the same time, the loss of the material on the surface of the matrix alloy appeared to be grinding debris, peeling-off type and flow slip.The result showed that the friction coefficient of the Al₂O₃·SiO_2sf/Al composites decreased with the load increasing under low spinning speed and same sliding distance, but the friction coefficient of the Al₂O₃·SiO_2sf/Al composites increased with the load increasing under high spinning speed. The addition of multi-components made it possible to obtain smaller friction coefficient under both high load and high speed. In addition, the stability of the friction coefficient showed the excellent wear resistance of the Al₂O₃·SiO_2sf/(2024Al+1%Mg) after design.