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.