| Bimetal clad materials is a new type of material which is prepared by some advanced composite technology, achieving a good combination of two different alloys with different physical, chemical, and mechanical properties. By bringing out one’s strengths to make up for one’s weaknesses, this materials can meet the need in special conditions. These materials are conventionally fabricated by roll bonding, explosive welding, diffusion bonding, extrusion clad, and spray deposition technique. Recently, a new fabrication technology of continuous casting has been developed and drawn great attention by many researchers. Focusing on the key science problem of formation mechansim of clad materials’interface during casting, in this paper, the congener metals having approach melting point, the dissimilar metals having large different melting point, the dissimilar metals having major interface reaction were choosed to study the formation mechansim. Based on these studies, two new continuous casting methods to prepare bimetal clad round ingot were developed. One is DC continuous casting of Al/Al clad round billet. This method achieved continuous casting of Al/Al clad round billet by pouring one kind of aluminum melt (Melt2) into solid or semisolid supporting layer forming by the other aluminum melt (Melt1). The inner mold was installed in the outer mold, and the solid or semisolid supporting layer was formed when the melt1contacted with the outer part of inner mold. The other method is short process horizontal continuous casting of copper clad aluminum. In this method, copper tube was first formed by cooling the high-melting-point copper melt, and the the low-melting-point aluminum melt would contact with the copper tube. The strong metallurgical bonding near the interface of two metals came true by remelt bonding and element diffusion.In order to determine the parameters of continuous casting process for3003/4004aluminum alloy clad composite materials, the influence of cooling water intensity of the inner mold, pouring temperature of3003,4004alloy and drawing speed on temperature field, distribution of liquid fraction and velocity field in continuous casting process of clad cast ingot are numerically analysed using FluentTM software. The simulation results show that the selection for cooling water intensity of inner mold must be reasonable. If the cooling water intensity is too small, the intensity of solid or semisolid supporting layer is not enough resulting in the mixture of two metals, and if the intensity of cooling water is too large, the solidification of alloy will bind the inner mold leading to the stuck phenomenon. In these experimental conditions, the better parameter of cooling water is700Lh". The pouring temperature of two alloys should be controlled as low as possible, however, if the pouring temperature is too low, the ingot-drawing can not go well. When drawing speed is more than70mm/min, the mixture phenomenon of two metals already appears. By using the same software of FluentTM, the effect of pouring temperature of aluminum and casting speed on the distribution of temperature field, liquid fraction and velocity field for copper clad aluminum during continuous casting process. The simulation results show that when the pouring temperature of aluminum melt is reasonable, the effect on the distribution of temperature field, velocity field and liquid fraction is not obvious. However, the pouring temperature of Al melt is high resulting in the temperature contacted with copper tube is high, the reaction between copper and aluminum is easier. When the casting speed is faster, the depth of liquid cave of aluminum melt is deeper and the contact time of liquid aluminum and copper tube is shorter. In addition, che temperature of the wall of copper tube near the end of graphite core will be much higher. The high-temperature aluminum melt contacts with copper wall, the reaction between copper and aluminum is easy to happen. In this experimental conditions, the better casting parameter i.e., casting speed200mm/min.After optimizating design of inner mold, outer mold, pouring box, dummy bar and other related equipments, we prepared bimetal clad round ingot successfully. The macro structure of clad ingot, the solidification structure and element distribution at the interface of3003/4004aluminum clad composite ingot were systemicially-studied. The experimental results indicate that3003alloy served as a substrate of heterogeneous nucleation of4004alloy at the interface of two alloys. Because of diffusions of Si and Mn elements, the interfacial bonding between4004alloy and3003alloy could be realized. The thicknesses of diffusion layers were about40μm on average, and the tensile strength of the interface was more than106.8MPa. The graphite mold, pouring system, drawing system were self-designed during developing the technology of copper clad aluminum horizontal continuous casting, and the copper clad aluminum ingot of88mm in diameter was prepared successfully. The solidification structure, element distribution and conditions of interface-bonding intensity were studied. The results indicate that during the stabilization stage of continuous casting i.e. the casting temperature of copper is1150±5℃, casting speed is200mm·min-1, pouring temperature of aluminum is710±10℃, the first cooling water is1.7m3·h-1, the second cooling water is2.5m3·h-1, for the copper clad aluminum ingot prepared in this conditions, the first phase is Cu9Al4in the copper side, and the width of Cu9Al4phase layer is about1μn. And then, there are a lot of CuAl2phases. The IMCs layer of Cu/Al is about200μm. The shear strength of interface is about45MPa。... |
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