Study On Preparation And Properties Of In Situ Al Alloy Matrix Composite

ZL109 (GB) is one of the most widely used alloys for pistons. The problem of ZL109 is high-temperature strength decreased obviously which can not meet the raising engine power at present. Aluminium-matrix composites have been considered as excellent engineering materials because of their high specific strength and modulus, improved wear resistance, and good processability. Among various processing technologies, in situ technology is particularly attractive due to its simplicity, economy and flexibility.Oxides including CuO, ZnO, SiO₂, MnO₂, TiO₂ and so on have been used to react with Al for synthesizing Al₂O₃/Al composites. But there are few reports about Fe₂O₃ used to produce Al₂O₃/Al composites. It has been studied that Fe can raise the tensile strength at high temperature and creep strength of Al alloys. This paper discussed the preparation technology of Al₂O₃/Al composite by adding CuO and Fe2O₃ into molten ZL109. Cu and Fe were replaced by Al and Al₂O₃ produced during in situ reaction process. Cu and Fe acts as alloying element and in situ Al₂O₃ act as reinforcement particles to strengthen the matrix.The feasibility analysis of the in situ reaction in the CuO/Al and Fe2O₃/Al system was studied by thermodynamics, DSC, XRD and SEM. And the result showed that the CuO/Al and Fe2O₃/Al system really reacted on the temperature of molten ZL109. The mass ratio of the two reaction system also played a key role to the reaction effect. The result showed that, when the mass ratios of the two reaction were m_Al:m_CuO=1:1 and m_Al:m_Fe2O3=1:1.3, the system reacted moderately, not too violent but apparent. Add 1% mass fraction of Mg to the reaction system could cut down the induction time evidently, and improve the operating efficiency.The microstructure and mechanical properties of the composites were analyzed in the paper. The OM micrograph in a low magnification indicated that blocky primary Si, needle-like eutectic Si and net-like alloy phases distributed in the matrix. It was hard to see the new-produced Al₂O₃ particles due to their small size. To investigate the feature of Al₂O₃ particles, SEM and TEM was conducted in a bigger magnification. The result showed white Al₂O₃ particles distributed in the alloy matrix. The scale of these reinforcements was in the range from 0.1μm to about 1μm.As a kind of impurity of the Al-Si alloy, needle-like Fe usually appears on the matrix and reduces the room temperature mechanical properties but enhance the high temperature mechanical properties. Add MnO₂ into the reaction to raise the Mn mass could cut down the mass of needle-like Fe and enhance the high temperature mechanical properties.The tensile strength at room temperature of the composites had a small increase compared with the matrix. However, the tensile strength at 300℃could reach 146.07MPa, which was 21.23 MPa higher than that of the matrix. The hardness of the composites had a small raise.