Traditional aluminum die castings often encounter mechanical performance bottlenecks due to internal defects such as porosity and shrinkage. Squeezing casting adopts the mechanisms of “liquid forging” and “solidification under high pressure”, effectively eliminating defects and refining eutectic silicon phase through full pressure, transforming it from needle-like to granular form, thus achieving forging level in key indicators such as strength, elongation, and hardness.
Following the logical chain of “process principles – defect elimination – microstructure optimization – property performance,” this article systematically analyzes how squeeze casting, by controlling the solidification process of molten aluminum, comprehensively improves the performance of aluminum alloy castings and overcomes the limitations of traditional die casting.
Overview of the Technical Advantages of Squeeze Casting
Principle of Squeeze Casting Process
The Transition from “Liquid Filling” to “Liquid Forging”
Traditional die casting fills the mold cavity with aluminum liquid through high-speed injection, and the aluminum liquid is filled in a turbulent state, which is prone to being entrained with gases and oxides.
Squeezing casting adopts low-speed smooth filling, and after the aluminum liquid fills the mold cavity, a continuous mechanical pressure of 50-200MPa is applied through a punch.
This transformation enables molten aluminum to form under plastic deformation rather than simple flow, fundamentally avoiding the defect generation mechanism of traditional die casting.
The following figure shows the process flow of squeeze casting:
Squeeze Casting Process Flow
The Physical Essence of “Solidification Under High Pressure”
The core of squeeze casting lies in the solidification process of metal under continuous high pressure. When high pressure is applied, the melting point of the metal will increase accordingly.
Taking aluminum alloy as an example, for every 100 MPa increase in pressure, the melting point rises by about 20 ℃.
This means that at the same pouring temperature, the aluminum liquid is actually in a greater supercooled state.
The significant increase in undercooling promotes the instantaneous formation of a large number of crystalline cores within the melt, rather than just nucleating at certain specific locations.
The result is a significant refinement of the solidified structure, with finer and more uniform grains, providing a fundamental guarantee for obtaining high-density castings.
How Does Pressure Suppress Air Porosity and Shrinkage Porosity
The Physical Mechanism of Air Porosity Suppression
The high pressure of 100MPa applied by squeeze casting significantly increases the solubility of casting gases such as hydrogen in the aluminum liquid, and gas molecules are forced to “lock” in the aluminum liquid, making it difficult for them to aggregate and nucleate.
At the same time, the high-pressure environment promotes the existing microbubbles to re-dissolve into the aluminum liquid under tremendous pressure, preventing the formation of pores from the source.
This dual function ensures that the interior of the casting achieves extremely high density.
Feeding Mechanism for Eliminating Shrinkage Porosity
During solidification, the tiny channels formed between dendrites require sufficient feeding pressure to fill.
The sustained high pressure provided by squeeze casting (often more than 10 times the feeding pressure of conventional casting) overcomes the flow resistance between dendrites, ensuring that the feeding molten aluminum reaches every microscopic shrinkage cavity.
This mechanism effectively eliminates the microscopic shrinkage porosity caused by insufficient feeding in conventional casting.
Internal Quality of CEX Casting’s Squeeze Casting Parts
Through X-ray non-destructive testing analysis, the squeeze casting parts produced by CEX Casting exhibit a highly dense internal structure without defects such as porosity and shrinkage.
In sharp contrast to the common porous structure of traditional die casting parts, this densification feature directly translates into a significant improvement in the mechanical performance indicators of the castings.
The following figure shows a comparison of X-ray inspection between traditional die casting parts and squeeze casting parts produced by CEX Casting:
Porosity in Die Castings & Porosity-Free in Squeeze Castings
How Does Squeeze Casting Promote the Refinement and Rounding of the Eutectic Silicon Phase?
The Fundamental Reason for Silicon Phase Refinement
Under the high-pressure environment of squeeze casting, the undercooling of the molten aluminum during solidification increases significantly.
According to classical nucleation theory, every 10°C increase in undercooling increases the nucleation rate by approximately one order of magnitude.
This high-pressure condition promotes the formation of a large number of evenly distributed crystallization nuclei in the melt, allowing the eutectic silicon phase to precipitate in a fine, dispersed manner, rather than growing coarsely in a few locations.
The Transformation Process of Silicon Phase Morphology
In conventional casting, silicon atoms have ample time and space to preferentially grow along specific crystal directions, forming sharp, needle-like structures.
However, under the high-pressure and rapid cooling conditions of squeeze casting, the anisotropic growth of silicon crystals is significantly suppressed.
Furthermore, the rapid solidification limits the long-range diffusion of silicon atoms, forcing the silicon phase to grow evenly in all directions, ultimately forming a rounded, granular morphology.
The figure below compares the needle-like silicon phase in conventional die casting parts with the granular silicon phase in squeeze casting parts:
Needle-Like Silicon Phase vs. Granular Silicon Phase
Mechanical Properties of CEX Casting Squeeze Castings
According to a third-party test report (see the figure below), CEX Casting’s squeeze casting parts, made of AlSi7Mg material combined with T6 heat treatment, exhibit excellent performance in key mechanical properties:
Hardness
The Brinell hardness test was conducted on the flat bar sample, and the results of three measurements were 96.1HB, 96.1HB, and 95.0HB, with an average hardness of 95.7HB.
This hardness level fully reflects the strengthening effect of T6 heat treatment (solid solution+artificial aging), proving that the material has good resistance to plastic deformation.
Tensile Properties
The test results of the round bar sample show more outstanding comprehensive performance: the tensile strength reaches 320MPa, the yield strength is 260MPa, and the elongation rate is as high as 14.5%.
This data combination indicates that under T6 heat treatment, AlSi7Mg material achieves an ideal balance between strength and plasticity through the squeeze casting process, and its performance has exceeded the typical level of traditional casting.
Process Advantage Verification
The actual test data fully prove the technical advantages of the “squeeze casting+T6 heat treatment” process route.
The 14.5% elongation rate indicates that there are very few internal defects in the material, and the eutectic silicon phase is effectively rounded.
The tensile strength of 320MPa combined with the yield strength of 260MPa indicates that the material has both high load-bearing capacity and good resistance to plastic deformation.
The ideal combination of high strength and high plasticity is a direct manifestation of the microstructure optimization achieved through the high-pressure solidification mechanism in squeeze casting.
CEX Casting Squeeze Casting Mechanical Properties Test Report
Conclusion
Squeeze casting, through its fundamental breakthrough of “high-pressure solidification,” systematically addresses the technical bottlenecks of traditional casting at the fundamental level of solidification physics.
From gas dissolution mechanisms to feeding dynamics, from nucleation theory to phase transformation mechanisms, the scientific principles of each process underpin its exceptional performance.
CEX Casting, leveraging its extensive experience in aluminum alloy casting and patented squeeze casting technology, ensures the full realization of these theoretical advantages in practical production.
If you’re looking for performance enhancements for your next aluminum alloy casting project, please contact us for professional technical solutions and customized services.