ZL114A belongs to Al-Si alloy. A certain amount of Mg is added to Al Si alloy to form Al Si Mg alloy. During heat treatment and aging, mesophase Mg2Si compound is precipitated from the structure and is in dispersion of 5 kPa / s.
After the casting was cleaned and the sand fell, it was found through X-ray inspection that shrinkage defects in varying degrees appeared in the diaphragm, oil circuit and middle annular structure. Due to the complex structure at the diaphragm, the defect location could not be accurately found, which caused damage to the distribution of casting state α The crystal lattice of solid solution is distorted (distorted), so as to improve the strength. The content of Mg in ZL114A alloy is high, and the content of Mg is between 0.4% ~ 0.75%. The increase of Mg content can improve the tensile strength and elastic modulus (yield point). However, the addition of high content of Mg in molten aluminum is easy to cause oxidation, increase the oxide scale involved in the alloy liquid, reduce the fluidity of molten aluminum, and easily form pinholes, oxidation slag inclusion and other casting defects in the pouring process. In traditional gravity casting, the pouring speed is difficult to control, and it is easy to get involved in air during pouring. Although the mold filling speed in the pouring process of low-pressure casting can be adjusted, the air in the mold cavity will be heated and expanded during the mold filling of liquid aluminum, so that the gas back pressure of liquid aluminum can not be controlled, so it is difficult to accurately control the mold filling speed of liquid aluminum. Moreover, when the aluminum liquid solidifies under low pressure, it is easy to have casting defects such as pinhole, air hole, shrinkage cavity, shrinkage porosity and oxidation slag inclusion, which is difficult to meet the technical requirements of the product. Therefore, the differential pressure casting process scheme is selected for pouring, and the original process is shown in the figure.
The filling pressure of aluminum liquid in differential pressure casting and the gas back pressure in the mold cavity can be adjusted at will, which can make the filling speed of aluminum liquid reach the best state. Due to the high gas back pressure in the mold cavity, it is not easy to cause splashing and spraying of liquid aluminum and can fill the mold smoothly, which provides powerful conditions for casting high-quality large-scale complex castings; During differential pressure casting, the metal liquid crystallizes and solidifies under high pressure, which inhibits the precipitation of hydrogen atoms in the aluminum liquid, improves the feeding capacity of the pouring system, and greatly reduces the pinhole, shrinkage cavity and shrinkage porosity in the casting, so as to obtain the casting with dense structure and high mechanical properties, and avoid the possibility of leakage in the later leakage and sealing detection of the casting. The process parameters of differential pressure casting are as follows: synchronous pressure 600 kPa, liquid rising speed 45 mm / s, liquid rising pressure 20 kPa, mold filling speed 50 mm / s, mold filling pressure 75 kPa, crusting time 1 s, crusting pressurization pressure 5 kPa, crusting pressurization speed 5 kPa / s, crystallization time 720 s, crystallization pressurization pressure 15 kPa, crystallization pressurization speed, slice anatomy and determine the defect location.