Different forging aluminum alloys have different forging shrinkage rates. custom Aluminum Alloy Gravity Casting Parts Even if the same alloy has different castings, the shrinkage rates are different. On the same casting, the length, width and height shrinkage rates are different. It should be determined on a case-by-case basis. (3) The thermal cracks of hot-cracked aluminum castings are mainly caused by the shrinkage stress of the castings exceeding the bonding between the crystals of the metal materials, and most of them are caused by dislocations along the crack surface. Oxidation, loss of metallic texture.

The cracks widen along the dislocation, and the appearance is jagged. Different aluminum alloy castings tend to cause different cracks. This is because the greater the difference between the temperature of the crystal structure and the condensation temperature, the greater the shrinkage ratio of the alloy, and the greater the tendency of thermal cracking. The larger the size, the hotter cracks tend to be different even for the same alloy due to the frictional resistance of the mold, the structure of the casting, and the pouring process.

In the production and manufacturing, countermeasures such as tolerance casting or improving the pouring system software of aluminum casting alloys are often used to prevent the aluminum castings from causing cracks. Generally, the hot crack ring method is used to test the hot crack of aluminum castings. (4) Airtightness The airtightness of the aluminum casting alloy refers to the watertightness of the cavity-type aluminum casting under the effect of high-pressure vapor or liquid state. The airtightness actually qualitatively analyzes the high density and purity of the inteal mechanism of the casting. The sealing performance of aluminum cast alloys is related to the characteristics of the alloy. The smaller the condensation range of the alloy, the smaller the loosening tendency is, and the smaller the precipitation vent is, the higher the sealing performance of the alloy is. The sealing performance of the same aluminum casting alloy is also related to the forging process, such as reducing the pouring temperature of the aluminum casting alloy, placing cold iron to accelerate the cooling rate and condensing crystals under working pressure, etc., all of which can make the sealing of aluminum castings Sexual enhancement. Impregnation can also be used to block leakage gaps to improve the sealing of castings. (5) Forging stress Forging stress includes thermal stress, change stress and shrinkage stress. The reasons for the various stresses are different. ① Thermal stress Thermal stress is caused by the uneven thickness of the cross-section at the intersection of the different geometric shapes of the castings, and the inconsistent cooling. Compressive stress is generated at the thick wall, resulting in residual stress in the casting. ② Change of stress

The change of stress is because some aluminum casting alloys change in the whole process of cooling after condensation, and the volume specification changes with the generation. The main reason is that the wall thickness of aluminum castings is not uniform, and different positions are changed at different times. ③Shrinkage stress When the aluminum casting shrinks, it is blocked by the mold and core and causes tensile stress. This type of stress is temporary and will subside automatically when the aluminum casting is unboxed. However, poor unpacking time often leads to thermal cracks, especially aluminum alloys cast in metal materials are usually very prone to thermal cracks under such stress effects. Residual stress in aluminum casting alloys reduces the physical properties of the alloy and jeopardizes the machining accuracy of the castings. Residual stresses in aluminum castings can be removed by annealing. Due to the good heat transfer of the alloy, there is no change in the whole cooling process, as long as the overall design of the casting is effective, the residual stress of the aluminum casting is generally small. (6) Respirable aluminum alloy is easy to digest and absorb vapor, which is the key feature of forged aluminum alloy. The composition of liquid aluminum and aluminum alloys reacts with the moisture content of retuing waste, organic combustion substances and casting molds, and the radon gas is digested and absorbed by the liquid aluminum.

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