Aluminium Magnesium Alloy Trapezoidal Cross-section Casting
Aluminium magnesium alloy casting is an important method to produce structural parts in engineering. Aluminium magnesium alloy casting is of high strength, good integrity and accuracy, which reduces the number of welding parts, improves production efficiency and reduces production cost. Trapezoidal cross-section is a kind of casting section shape with more difficult production process. In this paper, the casting process of aluminium magnesium alloy of trapezoidal cross-section is studied.
The raw material used in the casting process of aluminium magnesium alloy of trapezoidal cross-section is aluminium magnesium alloy ingot, which is a low cost and high strength alloy material. The main components of the alloy are Al-5Mg, the content of Mg is 3.2-3.3%. The tensile strength of the material is 450-510 MPa and the yield strength is greater than 330 MPa. The crystallization temperature of the alloy is 540-540 ℃ and the density is 2.69-2.71g/cm3.
The surface finishing process of trapezoidal section is to remove excess flash before filling, to avoid defects caused by filling and reduce porosity. After surface finishing, impurities and slag inclusions should be removed and the surface should be smooth and tight.
The size of the pouring hole mainly depends on the size and weight of the casting and the amount of molten metal. Generally, the size of the overflowing hole is determined according to the formula of 1.3-1.4m³/t molten metal, and the ratio of the size of the pouring hole to the wall thickness should be designed according to the formula that the ratio of the pouring hole to the wall is 1:2.5.
In the casting process of aluminium magnesium alloy of trapezoidal cross-section, it is necessary to consider the design of gating system according to the size of each section. The gating system is mainly composed of a main gate, a snout gate, a risering system, sprue, risering gate and a pouring system. The main gate is the main path of molten metal, which is generally located in one upper corner of the pouring system. The pouring gate is the path along which the molten metal flows into the mould cavity, and the cross-sectional area is gradually increased from the pouring gate to the mould cavity. The sprue is a structure connecting the main gate and the pouring gate, which ensures the smooth flow of molten metal into the mould cavity. In order to reduce shell defects and shrinkage defects in the casting, a riser is usually added above the main gate, which acts as a reservoir of molten metal and supplies molten metal to the casting when the casting shrinks due to solidification.
In order to reduce the pores and cracks in the surface of the casting and avoid the shrinkage defect and crack in the casting, the temperature of the molten metal should be controlled. Generally, the temperature of the molten aluminium-magnesium alloy is controlled at 700-760℃. When pouring, the pouring temperature should be higher than the crystallization temperature of the alloy while the holding temperature should be lower than the crystallization temperature.
In the mould design of trapezoidal cross-section, we must also consider the solidified shrinkage rate, which is mainly affected by the shape and size of the casting. In order to properly design the mould, it is necessary to adjust the position of the main gate and the pouring gate according to the actual size of the casting and the temperature of the molten metal, so as to make the molten metal flow faster and reduce the solidified shrinkage rate.
The sand core production is mainly used for casting the internal cavities of the trapezoidal cross-section. Generally, the sand core is compacted by the dry core box and then the sand core is put into the cavity of the mould. In order to improve the surface quality of the casting and reduce the porosity and the sand inclusion, it is necessary to adopt a core coating to reduce the fluidity of the molten metal.
In order to ensure the quality of casting and reduce the production cost, the solidified and cooling process of the casting is also very important. Generally, after the casting is solidified and cooled, the mechanical strength of the casting is improved, the brittleness of the structural parts is reduced and the casting is hardened. In order to ensure the quality and performance of the casting, the cooling rate during solidification and cooling should be properly controlled and the cooling rate should be gradually increased.
In the casting process of aluminium magnesium alloy of trapezoidal cross-section, the casting process should be strictly control each process, the molten metal should be poured rapidly into the mould cavity, the proper size of the pouring hole and the design of the gating system shall be properly controlled and the position of the main gate and the pouring gate should be properly adjusted according to the actual size of the casting and the temperature of the molten metal. Moreover, the solidified and cooling process of the casting should also be properly controlled to ensure the quality and performance of the casting.
