Micromechanism And Prediction Criterion Of Hot Crack Formation In Low Pressure Casting Of ZL205A Casting

The domestic high-strength casting aluminum alloy of ZL205A is widely used in the national pillar industry due to its escellent performance.But there will always be different degrees of hot cracking defects in the low-pressure casting process,especially for cylindrical castings.It can be seen that the cylindrical casting which is a common type of casting have speaial geometric characteristics that create favorable conditions for the generation of hot cracking defects.Therefore,studying the hot cracking defects of cylindrical castings is useful for clarifying the influence of the geometric characteristics of castings on casting defects.It is of great significance,and it has practical guiding significance for engineers to find the control method of casting defects in the geometric characteristics of castings.Based on the numerical simulation technology,the geometric characteristics of the cylindrical casting and the change law of the stress field during the solidification process are studied.The resistance factor represents the resistance of the cylindrical casting during the solidification process.The maximum effective stress of the cylindrical casting increases with the decrease of the resistance factor.When the resistance factor is 0.0784,the maximum effective stress at the center position of the cylindrical casting reaches 130.96 MPa.The modulus of the cylindrical casting represents the solidification time and feeding condition of the cylindrical casting.The maximum effective stress of the cylindrical casting gradually decreases with the increase of the modulus.When the modulus is 22.7273 mm,the maximum effective stress of the cylindrical casting is only 25.42 MPa.Based on low-pressure casting pouring experiments,the influence of lowpressure casting process parameters on the formation characteristics of hot cracks in cylindrical castings are studied.With the increase of boost pressure,the length of hot cracks of cylindrical castings shows a tendency to decrease and then increase.The areas with the greatest hot cracking tendency are in the vertical cylinder area and the inner and outer cold iron areas.The transverse cracks are caused by the axial tensile stress.Longitudinal cracks are caused by radial tensile stress.Sand core strength has a significant impact on the hot cracking behavior of cylindrical castings.The length of hot cracks gradually increases with the increase of sand mold strength.The use of furan resin sand cores can significantly reduce the hot cracking tendency of cylindrical castings.Based on the molecular dynamics method,the microscopic mechanism of ZL205A alloy's hot cracking at the atomic scale was studied.It was found that the uniformly distributed disordered structure in the alloy system continuously moved and aggregated under the action of stress,and nucleated in the local atomic stress and atomic energy.The larger position expands along the direction perpendicular to the tensile stress under the action of tensile stress,and the stress induces the surrounding ordered atoms to rapidly transform to disordered atoms under the action of the stress,until the alloy system fractures and fails.The thermal cracking information database of ZL205A alloy cylindrical castings containing the geometric and technological characteristics of cylindrical castings was initially established through low-pressure pouring experiments.The BP neural network was used to fit the multiple nonlinear factors affecting the thermal cracking behavior of cylindrical castings.A data-driven ZL205A cylindrical casting hotcracking prediction criterion was developed,and the prediction criterion was verified by the actual information of the cylindrical casting,and the mean square error was 32.538.