Abstract
The absolute pressure strongly affects the porosity and mechanical properties of castings produced by vacuum high-pressure die casting (V-HPDC) technology. The pore size, quantity and distribution of AlSi9Cu3 samples under three absolute pressures were evaluated by X-ray tomography and optical and electron microscopy. The paper presents an elaboration the stress concentration mechanism of pores affecting the tensile properties. According to a mathematical analysis of a sample under uniaxial stress, the greater the radius of the pore, the higher the stress value is at the pore perimeter. When the absolute pressure drops from 1013 mbar to 100 mbar, the porosity decreases from 6.8% to 2.8%, and the pore number and mean size decreases. In tensile tests, the pore sizes of the fracture surface decrease with decreasing absolute pressure, and the pore distribution becomes uniform. The tensile properties and extensibility of the sample are improved, and the microscopic fracture surface of the sample changes from cleavage fracture to quasi-cleavage fracture. The number, size and distribution of pores in die casting collectively affect the properties of the sample. Large-size or complex pores or pores with concentrated distributions produce large stress concentrations, decreasing the strength of the metal.
Highlights
The technology of high-pressure die casting (HPDC) is a special kind of casting method in modern metal processing technology involving little or no cutting
The results showed that the porosity decreased linearly with increasing degree of vacuum applied to the mold cavity
The above research indicates that the application of a vacuum system in the production process of HPDC has a great impact on the quality of die castings, and substantial research on the pores and mechanical properties of aluminum alloy die castings in vacuum applications has been conducted by scholars worldwide
Summary
The technology of high-pressure die casting (HPDC) is a special kind of casting method in modern metal processing technology involving little or no cutting. By reducing the gas entrapment of metal liquid in the filling process, we can obtain better-quality die casting products by vacuum die casting. Worldwide research on this method has focused on the effect of vacuum application on aluminum (magnesium) alloy die castings as characterized by the porosity and by the microstructural and mechanical properties. The research showed that vacuum-assisted casting strongly reduced the porosity of die castings and increased their density and mechanical properties of tensile strength and elongation. The above research indicates that the application of a vacuum system in the production process of HPDC has a great impact on the quality of die castings, and substantial research on the pores and mechanical properties of aluminum (magnesium) alloy die castings in vacuum applications has been conducted by scholars worldwide. We can better understand the effect of absolute pressure on the porosity and mechanical properties of die castings
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