Basic situation of aluminum alloy lost foam casting

At present, the main body of lost foam castings in China is cast iron, cast steel and other alloys, and non-ferrous alloys account for a very small proportion, while aluminum alloys have many advantages and are widely used in life and production, especially in the automotive industry, the demand is very large, and the performance requirements are higher and higher, especially the complex thin-wall aluminum alloy lost foam castings have received extensive attention, Therefore, it is necessary to study the defects and technology of aluminum alloy lost foam casting. However, in view of the low qualification rate of aluminum alloy lost foam casting for a long time and many technical problems have not been solved, it still needs the continuous in-depth research of casting workers. Here, several common defects of aluminum alloy lost foam casting are analyzed and solutions are put forward.

Different from sand casting and metal casting, aluminum alloy lost foam casting is very different in technology. Dry sand filling and thermal insulation coating are the main means of casting. Melting and pouring temperature is very important in casting process. Only by ensuring that the temperature is high enough can we achieve the purpose of liquefaction and gasification of foam molds and further promote the filling of metal liquids. However, if the pouring temperature is too high or too low, it will cause serious oxygen absorption in the molten aluminum. When the temperature gradually decreases, more hydrogen will be released, and dispersed pinholes and slag holes will be formed on the surface of the alloy module. In this case, the defect rate of aluminum alloy lost foam casting parts poured, such as engine inner wall and complex parts, increases significantly. Because of the small aluminum density, it provides an opportunity for the entry of external gases. The pores produced by the reaction of aluminum liquid and foam will change to stomata when the liquid flow stops flowing, which increases the incidence of defects such as insufficient sand filling, sand sticking and deformation. It should be known that the defects of cast parts are not uniform, but different with different factors such as component structure and quality. Generally speaking, the size of parts will affect the quality. Large parts and parts with large expansion area have fewer defects due to small casting difficulty. In addition, the difficulty of solving various defects is different. Generally speaking, defects such as leakage and pinholes and pores are relatively easy to solve, because pinholes are generally evenly distributed, and pores are also relatively uniform, which are generally concentrated on the surface. The defects such as insufficient pouring, wrinkle and deformation are relatively serious, especially for complex parts. Once these problems occur, they are difficult to solve. The most difficult to solve is the bead surface or shrinkage and other defects.

In order to improve the level of lost foam casting of aluminum alloy in China, the majority of foundry workers are constantly studying and improving the process to control the occurrence of defects. However, at present, the progress is still very slow, and many technical problems have not been solved, such as aluminum alloy lost foam casting pressure solidification technology and vibration technology. In this regard, the author thinks that we should vigorously study the following aspects: first, strive to improve the quality of the foam model; two, we should thoroughly study the coatings and molding sand, and three, deepen the refining of aluminum alloy. Fourth, in-depth study of pressure solidification technology and vibration technology. It is believed that through the hard work of casting workers, China’s aluminum alloy lost foam casting technology will be pushed to a new height.

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