The mechanical properties of different parts of A356 extruded castings were calculated using finite element analysis based on microstructure characteristics. By analyzing different domain sizes, mesh sizes, and FEA models, a suitable finite element model was determined. The FEA results were validated using experimental tensile results, and the influence of organizational characteristics on performance was explored. The results showed that as the length and shape factor of Si particles increased, the tensile strength and elongation both showed a decreasing trend; The increase in density and area fraction of Si particles leads to an increase in tensile strength and a decrease in elongation; The damage evolution process of alloys can be divided into three stages: Si particle fracture, crack propagation, and connection; When Si particles are small, round, and evenly distributed, the anisotropy of local mechanical properties is small. When Si particles have a large aspect ratio and exhibit obvious directionality, the anisotropy of local mechanical properties increases.
Die casting is one of the effective methods for producing complex shaped aluminum alloy castings. However, in the traditional die casting process, the liquid metal is prone to turbulent flow, which leads to the entrapment of gas and oxide film, forming pore defects and reducing the mechanical properties of the castings. Therefore, the development of high integrity casting technologies such as squeeze casting and high vacuum die casting has received widespread attention and application. Squeeze casting effectively prevents and reduces the formation of voids during the solidification process by applying extrusion pressure exceeding 50 MPa to liquid metal, resulting in castings with high integrity and excellent mechanical properties. However, during the squeezing casting process, as solidification progresses, the squeezing force gradually decreases, and the uneven wall thickness of the casting leads to different cooling rates, resulting in significant differences in the microstructure and mechanical properties of different parts of the casting. In the design of squeeze casting parts, if the differences in mechanical properties of different parts can be fully considered, the design can be optimized and the goal of structural lightweighting can be achieved. Therefore, accurate understanding of the mechanical properties of different parts of the casting is crucial. However, due to the size requirements of tensile specimens, some parts of the castings cannot be analyzed for performance through tensile testing. Therefore, it is of great significance to establish a method for calculating or predicting the local performance of extruded castings. The microstructure characteristics of extruded castings were studied, taking into account the ductile damage of α – Al matrix and the brittle fracture of Si particles. Finite element models of different parts of the castings were established; The mechanical properties of different parts of the casting were predicted, and the accuracy of FEA results was verified through tensile tests; Studied the influence of microstructure characteristics on local mechanical properties, damage behavior of A356 alloy, and anisotropy of local mechanical properties
The castings were formed using the Ube squeeze casting machine HVSC350, and the castings were analyzed using direct reading spectroscopy. The actual chemical composition of the castings is shown in Table 1. The castings were subjected to T6 heat treatment, followed by water cooling at 170 ℃ for 6 hours. Sampling for microstructure and tensile performance analysis The metallographic sample was ground and polished with sandpaper, and then corroded with HF with a volume fraction of 0.5% for 10 seconds using Leica DMC 4500 optical microscopy Characterize the microstructure and morphology of different parts of the casting using a mirror, and use a particle feature calculation program designed in Python language to quantitatively analyze the microstructure characteristics of different parts. Using the same method to characterize the microstructure of different regions of the tensile specimen (2 # 8 #), the different regions of the specimen are shown in Figure 1f, labeled as regions 1 to 6 from left to right. Perform tensile tests on the specimens using the SHIMADZ AG-X 100KN universal material testing machine, with a strain rate of 7.58 × 10-4 s-1.
The microstructure of different parts of squeeze cast parts. The studied castings were solidified and formed under 100 MPa extrusion pressure, with a dense microstructure and no micro pores were found. The Mg content in the alloy is 0.35%, and the Mg2Si phase formed during the solidification process can be completely dissolved under T6 heat treatment. After aging, it precipitates in the form of a β “phase in the α – Al matrix; The Fe content in the alloy is only 0.09%, and the intermetallic compounds containing Fe are not obvious in Figure 2. Therefore, the microstructure is mainly composed of α – Al matrix and Si particles, but there are significant differences between the two phases in different areas of the casting. Further quantitative analysis of the microstructure characteristics of the α – Al matrix and Si particles in the microstructure samples.
The prediction model for local mechanical properties of A356 alloy in squeeze casting based on organizational characteristics is effective. To ensure the accuracy and validity of the calculation results, the size of the finite element model should not be less than 100 × 100 μ m2, and the mesh size of the α – Al matrix and Si particles should be less than 1 μ m and 0.6 μ m, respectively. The actual tensile performance is slightly higher than the calculated local minimum tensile strength and elongation. The damage evolution process of alloys is mainly divided into three stages: Si particle fracture, crack propagation, and connection. The increase in tensile strain leads to an increase in stress on Si particles, resulting in fracture; As the strain continues to increase, the microcracks connecting adjacent particles become cracks of a certain length (initial microcrack propagation); When the critical strain value is exceeded, the matrix becomes unstable between particles with smaller spacing, and cracks with similar orientations connect with each other, ultimately leading to fracture. The Si particles in squeeze cast A356 alloy have a significant impact on the alloy properties. The increase in length and shape factor of Si particles reduces the tensile strength and elongation of the alloy, while the increase in density and area fraction of Si particles leads to an increase in tensile strength and a decrease in elongation. When Si particles are small, round, and evenly distributed, the stress concentration changes of particles are small under different stretching directions, and the anisotropy of local mechanical properties is small; When the aspect ratio of Si particles is large and exhibits obvious directionality, when the angle between the stretching direction and the long axis of these particles is small, the local mechanical performance is poor, while when the angle is large, the local mechanical performance is better.