The wear resistance and dimensional stability of the aluminum casting directly affect the machine accuracy and service life; size, accuracy of mold and surface roughness of various pumps' impellers, bodies and inner cavities have direct impacts on the working efficiency of pump and hydraulic systems, energy consumption and development of cavitation, etc; strength of the aluminum castings like engine cylinder block, cylinder head, cylinder liner, piston ring and exhaust pipe as well as the resistance to shock cooling and shock thermal have direct influences on operating life of the engine.
How to guarantee the quality of aluminum casting? This requires the improvement of labor productivity, the reduction of cost and having a specific analysis on the aluminum casting so as to select a reasonable process when we determine the technical process. Aluminum castings have excellent mechanical and physical properties. They not only have a comprehensive performance of a variety of different strength, hardness, toughness, but also have one or more special properties, such as wear resistance, high temperature and low temperature resistance, corrosion resistance, etc. Aluminum castings are widely used in hardware accessories and auto parts fields because of their good properties.
Solidification forms of aluminum castings
1.Layer by layer solidification form
The solidification zone with the coexistence of liquid and solid doesn't occur in the pure aluminum or eutectic aluminum alloy solidification process, so solid of the outer surface and liquid of the inner layer of the section are clearly separated by a boundary(solidification front). With the decline of temperature, the solid layer continues to thicken and the liquid layer continues to decrease, then directly go into aluminum casting
center. This solidification method is regarded as layer by layer solidification.
2. Mushy zone solidification form
If the crystallization temperature range of the aluminum alloy is wide and the temperature distribution of the aluminum casting is relatively even, there will be no solid layer on the casting surface for a certain period of solidification; the coexistence of liquid and solid in the solidification zone penetrate the entire section, which is similar to cement setting. The process of paste and then curing, which is known as solidification with mushy zone. the solidification zone with the coexistence of liquid and solid penetrate the entire section, which is similar to cement setting, first becoming a paste and then curing, this process is known as mushy zone solidification.
3.Middle solidification form
Most solidification are between layer by layer solidification and mushy zone solidification, which is know as middle solidification. In general, the quality of aluminum casting and its solidification method are closely related to the good filling performance of the metal materials which can easily prevent shrinkage and shrinkage porosity Mushy zone solidification is the only solidification form that can help us obtain firm aluminum castings.