Study On The Preparation And Microstructure Of Aluminum Matrix Composites Reinforced By In-Situ Aluminum Oxide Particle Composites

Aluminum alloy and its composite materials are widely used in aerospace,transportation and other fields due to their low density,excellent thermal conductivity,electrical conductivity,corrosion resistance,corrosion resistance and other characteristics.Among them,the hypereutectic Al-Si alloy is a cast aluminum alloy material with high strength and volume stability,and the further improvement of its performance has attracted much attention.In this paper,Al₂O₃@Al-20Si composites were prepared by in-situ reaction with Al-20Si alloy as matrix.The effects of Al₂O₃ fine grain strengthening and particle strengthening on the microstructure and properties of hypereutectic Al-20Si alloy were investigated.The effect of heat treatment on microstructure and properties of Al₂O₃@Al-20Si composites was also studied.（1）The preparation technology of Al-20Si@Al₂O₃ powder and the effect of Al-20Si@Al₂O₃ powder with different dosage（0-20 wt.%）on microstructure and properties of Al-20Si alloy were studied.The results show that Al-20Si@Al₂O₃ powder with ideal nano structure can be prepared by water bath method.γ-Al₂O₃ particles can be prepared by in-situ reaction by adding Al-20Si@Al₂O₃ powder into Al-20Si alloy melt.γ-Al₂O₃ particles not only significantly refine the primary silicon in the alloy,but also strengthen the alloy matrix as reinforcement phase.When the addition amount is 15 wt.%,the refining effect and mechanical properties of primary silicon are the best.At this time,the hardness and tensile strength of Al-20Si alloy composites reach 107.2 HB and 185.9 MPa,respectively.Compared with unmodified Al-20Si alloy,its hardness and tensile strength are increased by 42%and 55%,respectively.（2）The effects of different CuO addition levels and heat treatment processes on the microstructure of hypereutectic Al-20Si alloy were studied.The results show thatγ-Al₂O₃particles and Al₂Cu phase can be formed by in-situ reaction of Cu O.With the increase of Cu O addition amount,the average size of primary silicon decreases first and then increases.The average grain size decreased to 35.8 um when Cu O content was 0.5 wt.%.The eutectic silicon in the alloy is spheroidized obviously by heat treatment,and the size of eutectic silicon decreases obviously.The hardness of the alloy can reach 87.1 HV at 520℃solution for 8 h and 150℃aging for 8h,increasing by 14.5%.（3）The effect of Fe₁₂O₁₉Sr powder on the microstructure and properties of hypereutectic Al-20Si alloy was innovatively studied.The results show thatγ-Al₂O₃,Sr and Fe-rich phases are formed in situ.The microstructure of primary and eutectic Silicon in hypereutectic Al-20Si alloy is refined by the interaction ofγ-Al₂O₃ and Sr.At the same time,the mechanical properties of the alloy are enhanced by the combination ofγ-Al₂O₃ and Fe-rich phase.When the addition amount of Fe₁₂O₁₉Sr powder is 0.3wt.%,the comprehensive refinement effect of Si in Al-20Si alloy is the best,the average size of primary silicon reaches 55.9μm,and the average size of eutectic silicon reaches 9.7μm.At this time,the hardness of Al-20Si alloy reaches 91.3 HB and the tensile strength reaches 177.8 MPa.Compared with the unmodified Al-20Si alloy,the improvement rate is as high as 21.4%and 47.8%.