| Clad metal is conventionally manufactured by roll bonding, cast bonding, explosive welding, diffusion bonding, extrusion cladding and spray deposition technique. Among them, continuous casting is an ideal method for producing clad metal because it realizes liquid state contact between two metals directly and avoids the problem of low bonding strength attribute to oxide, inclusion and greasy dirt.The main purpose of this dissertation is to develop novel continuous casting processes for preparing the 3003/4004 aluminum alloy bimetal slab and reveal their basic rules, the structure, composition and properties of the bimetal slab are also studied. The main contents of this dissertation include:A new electromagnetic continuous casting process for preparing clad slab was studied. The software ANSYS and FLUENT are combined to study the effect of magnetic flux density of level direct current electromagnetic field on the flow of the alloy melts. The results indicate while the magnetic flux density (B) is 0.15T, the impact velocity and distance of the flow to the narrow face and underside of the dividing plate decreased remarkably. So the flow impact to the liquid pool was depressed. At the same time, the high temperature zone of the melt moved away from the narrow face and the dividing plate, and distributed more uniform. The wider semi-solid area next to the dividing plate helped to the bonding of 3003 and 4004 aluminum alloys. While the B is 0.25T, the best braking effect was reached. While the casting temperature of 3003 alloy was 680℃, the B was 0.25T and the casting speed was 100 mm·min-1, then the dividing plate would just be positioned in the semi-solid area, that would be helpful to the bonding of 3003 and 4004 aluminum alloys. However, the casting speed was increased to 140mm·min-1 or the casting temperature was increased to 720℃, the gap between the dividing and liquid pool would increase and lead to mixing of these two aluminum alloys.On the basis of numerical simulation results, the direct current electromagnetic field generator, mold, dividing plate and other additional equipments which suited to produce clad aluminum alloy slab were designed. In the experiments, while the casting temperature of 3003 alloy was 680℃, the B was 0.25T, the casting speed was 130 mm·min-1, and the cooling water flow rate of mold was 2.5m3·h-1, the clad slab which had metallurgical excellent bonding and without any discontinuities along the interface was obtained. It was proved that the mixing of 3003 and 4004 alloys were depressed effectively during the continuous casting of clad slab under direct electromagnetic field. The experiment results also supported the validity of the simulation results. The results of composition analysis showed that Si, Mg and Mn element contents gradiently distributed transverse to the clad interface direction. The diffusion distance of Si and Mg element were greater than that of the Mn elements.A new direct chilled continuous casting process for preparing clad slab was presented. A series of related devices including the water-cooled dividing plate, the flow rate control and distribution device and the draw block were developed. The influence of process parameters on the solidification of clad slab was numerically studied with the engineering software FLUENT. The simulation results showed that the cooling intensity of the dividing plate, casting speed and height of the cooling part of the dividing plate had more influence on the effective thickness, which is the thickness of 3003 alloy solidification shell formed on the water-cooled dividing plate, and the distribution uniformity of the solidification shell. In the experiments, well clad slab could be obtained while the cooling water flow rate of dividing plate chose 180,200,225 and 250 L·h-1, respectively, the casting speed chose 70 and 80 mm·min-1, the casting temperature of 3003 and 4004 alloys were 710 and 670℃, respectively. The prepared clad slabs had metallurgical excellent bonding and straight bonding interface without any discontinuities. The results of composition analysis under different casting conditions showed that Si, Mg and Mn element contents gradiently distributed transverse to the clad interface direction. The diffusion distance of Si and Mg elements were less than 20μm and that of the Mn element was less than 10μm. In addition, the influence of other process parameters including casting temperature of 4004 alloy, the insert depth of dividing plate into the mold, the draw force of block, the numbers and distribution of sprues as well as the cooling water flow rate of the mold on the interface bonding of the clad slab were also analyzed.A one-dimensional steady heat transfer model about solidification of 3003 alloy on the dividing plate was built. The quantitative relationship of influence of casting parameters, including cooling water flow rate of dividing plate, the casting speed, casting temperature of 3003 alloy and the height of the cooling part of the dividing plate, on the water temperature difference in and out of the dividing plate as well as the effective thickness of 3003 solidification shell were obtained. The computation results showed good agreement with the experimental results. The bonding of the clad interface was composed of two phases, called formation phase of core layer and metallurgical bonding phase. The formation phase of core layer was completed on the cooling part of the dividing plate. At the metallurgical bonding phase,4004 alloy attached on surface of the core layer, which had coherent interface with 4004 alloy, to nucleate and to grow. As the emergence and enlargement of constitutional super cooling zone on solidification front, the morphologies of the crystals of 4004 alloy changed according to following order:planar, cellular and dendritic. Among them, most growing directions of the dendrites were perpendicular to the interface.The results of homogenization treatment showed that the Brinell hardness and tensile strength of the 4004 alloy side of the clad slab was remarkably decreased. The distribution of Si and Mn element contents changed little while the heat treatment temperature was 490℃, the treatment time varied from 7h to 14h or the heat treatment time was 7h, the treatment temperature varied from 490℃to 510℃. However, more Mg element diffused into the 3003 alloy side. The clad slab with thickness of 29 mm was rolled to 3mm by hot rolling at 510℃and then continued to roll till 1mm in thickness by cold rolling. The microstructure observation and composition analysis indicated that the clad slab had excellent rellability, and well metallurgical bonding was maintained at the bonding interface.
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