Study On Interfacial Microstructure And Properties Of Al(6061)/Cu(T2) Bimetal In Liquid-solid Compound Casting Process

With the development of science and technology and the progress of the society, then the energy crisis, environmental pollution, resource shortages appeared. It have put forward higher requirements on the material performance and application. A single material has been unable to meet the needs of today’s society. Preparation of the materials with different sets of physical, chemical, mechanical processing performance and the price difference in the integration of new composite materials has been the trend of The Times, and is of great significance and wide application prospect. Aluminum and aluminum alloy, copper and copper alloy with their excellent performance have become the most widely used non-ferrous metal materials. The performance of these two kinds of material in some ways can be complementary. The Al/Cu composite structure combined the comprehensive advantages of the two, and minimized their own shortcomings, so Al/Cu bimetal component has been becoming more and more widely used.This paper adopted a liquid-solid composite casting method for the preparation of Al/Cu bimetal. In the process, there existed a difficult problem that the thermal oxidation of Cu substrate. And the oxides prevented the solid copper from direct contacting with molten aluminium, which eventually leaded to limited metallurgical bonding interface. In this paper, a nickel layer of the thick of approximately 6μm was deposited on copper substrate by the process of chemical plating nickel. A comparative analysis of the interface microstructure and properties of Al/Cu composite sample with and without nickel plated was made. It can be concluded that the chemical plating nickel layer can effectively protect the copper substrate from the thermal oxide, which was beneficial to the formation of metallurgical combination. We carried out the process under different parameters. It suggested that the the nickel layer not only acted as a protective film preventing from oxidation of copper substrate, but also acted as as an intermediary inhibiting the atom diffusion of aluminum and copper, avoiding the formation of brittle intermetallic compound and improving the bonding strength of the joint. Heating temperature, and the preheating time had a great influence on the microstructure and properties of the composite, the higher the temperature and the longer the preheating time, the thicker and more kinds of intermetallic layers(Al2Cu3,Al3Cu4,Al2Cu,AlCu,Al4Cu9) appeared, and the mechanical properties and conductivity were decreased. At 780℃,150s, the Al/Cu joint exhibited the best comprehensive performance, which the intermetallic layers only had a thickness of 25μm, the shear strength was 49.8 MPa, the conductivity was 5.29 x 105 S/cm, respectively.The influence of rare earth element Ce on the microstructure and properties of Al/Cu was studied. The Al was mixed with suitable amount of rare earth element Ce, then combined with Cu on the basis of the chemical plating nickel. It can be concluded that the Ce can improve the interface microstructure, the mechanical properties and conductivity of Al/Cu joint. Small amount (less than 0.2wt.%) of Ce can refine the matrix and eliminate the adverse effects of harmful impurities. When Ce content was higher (0.4wt.%), it would occur eutectic reaction with aluminum liquid and form rare earth compounds, which would become the core of nucleation, increase the nucleation rate and refine the grains. Besides, the Ce can make the Al2Cu distribute dispersely, strengthen the Al/Cu interface. When Ce content was 0.6wt.%, the surplus of Ce would be integrated into the Al-Cu compounds or form complex rare earth compounds(Al6Cu7Ce,Al3CuCe), with the increasing of the content of Ce, the intermetallics gathered to grow up and distributed at the interface between Al/Cu, greatly reduced the mechanical properties of the interface. When Ce content was as high as 2wt.%, the side of aluminum substrate formed a large number of rare earth compounds, thickening the grain boundary. Although the amount of Al2Cu phases was least in the side of copper substrate, the intermetallics of Al-Cu-Ce significantly reduced the bonding strength of joint. The highest shear strength achieved 56.7MPa, and the best conductivity was 5.43×105S/cm when the Ce addition was 0.4wt.%.