Preparation Of Copper Matrix Composites With Al-CuO-La₂O₃ System

In order to reduce the larger size of Al₂O₃particles which were easily formed in Al-CuO system during the in-situ reaction,the rare earth La₂O₃was introduced to form the Al-CuO-La₂O₃system.Using La₂O₃powder,Al powder,CuO powder,Cu powder as raw materials to make precast blocks,and pure copper as matrix,Cu-based composites were prepared by in-situ reaction near melting point casting method.Use optical microscope,X-ray diffractometer,differential thermal-thermogravimetric analyzer,scanning electron microscope,energy spectrometer,and transmission electron microscope to observe and analyze the type,size,morphology,and distribution of products in each in-situ reaction system and its interface structure with Cu matrix.Comparing the in-situ reaction process and in-situ reaction products of Al-CuO system and Al-CuO-La₂O₃system,the thermodynamic of the Al-CuO-La₂O₃system was calculated and the in-situ reaction process model was constructed.The effects of La₂O₃addition,Al₂O₃production on the size,morphology,quantity,and distribution of in-situ reaction products in the Al-CuO-La₂O₃system were investigated,as well as the properties of the Cu-based composites,and concluded the optimal process parameters for preparing Cu-based composites.The interface formation mechanism,orientation relationship between the in-situ reaction product Al₂O₃and Cu matrix was studied.The specific results are as follows:After adding La₂O₃into the Al-CuO system,the in-situ reaction process,in-situ reaction products,morphology,size and distribution changed significantly.During the in-situ reaction,La₂O₃improved the wettability between CuO and Al,and accelerated the reaction between CuO and Al,so that nano-Al₂O₃particles are generated at a relatively low temperature,and the Al₂O₃particle morphology changed from the original spherical to irregular polygons,the added La₂O₃reacts with the generated Al₂O₃at high temperature to produce a rare-earth phase La Al₁₁O₁₈with a smaller size.The interface structure between the nano-Al₂O₃particles and the copper matrix was analyzed using transmission electron microscopy and high resolution.The results showed that there was a coherent or semi-coherent interface structure between the nano-Al₂O₃particles and the Cu matrix.When the melt preheating temperature was 1180℃,the reactant powder mixing time was 60min,the preform molding pressure was 12MPa,and the molar ratio of the reactants in the preform was Al:CuO:Cu:La₂O₃=2.2:3:6.5:0.21（the content of La₂O₃was 0.6%wt of the matrix,and the amount of Al₂O₃particles generated was 0.9%wt of the matrix）,during the solidification process,nano-Al₂O₃particles acted as nucleation cores to promote nucleation,the small amount of micro-Al₂O₃particles pinned at the grain boundaries and hindered the growth of the grains.Both of them worked together to refine the grains,uniform and fine structure was obtaied finally.The prepared Cu-based composite material has the highest conductivity and hardness,and the lowest wear.