Studies On The Technology And Theory Of Clad Casting Of Aluminum Alloys

The aim of this study is to develop a new technology for producing the clad plates of aluminum alloys based on the need for developing clad products of aluminum alloys in China. The effects of casting equipment and technology on the metallurgical quality of clad ingots and casting process were studied. The object is to produce clad ingots with the planar and clean interface and high strength interface without porosities and inclusions.In this paper, the experiments are combined with numerical simulation to study the temperature field, flow field and heat transfer during the casting process of4045/3004two-layer clad ingots with section of420mm×160mm and4045/3004/4045three-layer clad ingots with section of500mm×420mm. The effects of distribution manner, casting temperature, casting speed, contacting height and cooling intensity of cooling plate on the temperature field and flow field during the casting process were discussed. The macro-morphologies and microstructures of the clad ingots, the temperature distribution and the element distribution in the interface zone were investigated, also the interface bonding strength was measured. Based on the above results, the optimal parameters of equipment and technology for casting clad ingots were obtained.Firstly, a mathematic model is established to describe the casting process of clad ingots. The comparison of simulation results and experiment results shows that the temperature field and flow field during the casting process can be well simulated using this model so that it can be used to study the effect of technological parameters on the casting process.By means of numerical simulation, the effects of distribution manner on the temperature field and flow field are investigated in detail using one dip tub, two dip tubs, square distributor, circular distributor and level pour distributor, respectively. The results show that the melt can flow gently and an uniform temperature distribution field can be obtained when using the square distributor in3004alloy melt and level pour distributor in4045alloy melt, so that the distribution manners were determined. The results of numerical simulations and temperature measurements show that the supporting layer which is formed on the cooling plates plays a key role in the casting process of clad ingots. A new idea of solid supporting layer was proposed, which breaks through the theory of semi-solid supporting layer proposed by Novelis. The solid supporting layer can prevent the blending of two melts by resisting the impact of alloy melt, which ensures the stable casting process and casting high quality clad ingots.There is a corner zone formed by the mold and cooling plate which is a three dimension cooling zone and leads to a bad bonding because of the low temperature melt in this region for aluminum alloy mold used in traditional process of clad ingot casting, which can be improved well by hot-top, and a solid supporting layer with uniform temperature distribution is obtained, so the bonding strength is uniform in the interface. As a result, equipment suitable for casting clad ingot is designed as hot-top graphite ring mold and hot-top lubricant mold.The relationship is obtained between the interface bonding strength and the temperature of solid supporting layer when contacted by4045alloy melt. When the temperature of supporting layer is above590℃, the interface bonding strength is higher than88MPa; when the temperature of supporting layer is below590℃, the interface bonding strength drops sharply. Based on the above results, the criterion for temperature controlling of solid supporting layer is determined.The effect of casting temperature, casting speed, the contacting height and cooling intensity of the cooling plate on the casting process were analyzed. The optimal casting parameters of4045/3004/4045three-layer clad ingots were gained, that the casting temperature of3004alloy and4045alloy is1000K, the casting speed is45mm/min, the contacting height and cooling intensity of the cooling plate is40mm and1500Wm-2K-1, respectively.The clad ingot produced using the equipment and technology developed in this study has planar and clean interface without porosities and inclusions. The elements of Si, Mn, Mg can diffuse across the interface to some extent, and the interface of two alloys is metallurgical bonding. The bonding strength of interface is between88MPa and107MPa.The clad ingot will obtain a good homogenization effect when the heating temperature is560℃and holding time is12h at which condition the alloy with low melting point will not be burnt, also the non-equilibrium constituent phases in high melting point alloy has been dissolved sufficiently.At last, the technology of hot rolling, cold rolling for clad ingot and the annealing technology for clad plates were studied. The control criterion of rolling reduction and annealing technology is established. The clad foil of4045/3004/4045aluminum alloys with good properties is obtained.These results developed a new technology with high-efficiency and economics for the progress of clad aluminum alloys products in our country.