Why Can Squeeze Castings Be Welded?

The fundamental reason why squeeze castings can be welded lies in that through technological innovation, it has greatly eliminated the defects that make traditional die castings unweldable.

I. Why are traditional die-casting "not weldable"?

The root cause of the non-weldability of traditional die castings is "subsurface porosity."

1.Formation of Porosity:In the traditional high-pressure die-casting process, molten metal is injected into the mold cavity at an extremely high speed, in a jet-like manner. This high-speed process inevitably entraps a large amount of air and vapor from the mold release agent present in the cavity.

2.Entrapment of Porosity:Due to the rapid cooling and solidification of the metal, these entrapped gases cannot be fully expelled and become sealed just below the surface of the casting, forming numerous microscopic "subsurface pores."

3.During welding(especially high-temperature arc welding), the gas within these pores expands rapidly due to the heat:

•Generating significant internal pressure.

•Causing porosity and cracks in the weld zone.

•Leading to blistering and deformation of the casting surface.

•Resulting in extremely poor weld quality and very low strength, making it entirely unsuitable for practical use.

II. How does squeeze casting solve this problem?

Squeeze die casting prevents porosity at its root by altering the process principle. Its core technologies are "slow filling" + "high-pressure solidification."

1.Slow and Stable Filling (Solves the problem of air entrapment)

Squeeze die casting uses a relatively slow and stable speed to push the molten metal into the mold during the filling stage, as opposed to the "injection" in traditional die casting. This significantly reduces turbulence, thereby greatly avoiding the entrapment of air into the metal melt. This ensures low gas content inside the casting from the source.

2.Solidification under Extreme Pressure (Solves shrinkage porosity and compresses any residual gas)

This is the essence of squeeze die casting. After the mold cavity is filled, a special squeeze punch on the mold immediately activates, applying an extremely high and sustained pressure (can reach 100-200 MPa, more than 10 times that of traditional die casting) to the casting that is not yet completely solidified (especially in thick sections). This immense pressure produces two key effects:

a. Eliminates Micro-shrinkage (Shrinkage Porosity):The pressure forces the molten metal to feed into and compensate for shrinkage cavities that form between dendrites during solidification, resulting in an extremely dense microstructure.

b. Neutralizes Residual Gases:Even if a minimal amount of gas remains, it is compressed under this extreme pressure and dissolves into the metal matrix. This prevents it from existing as a macroscopic pore defect.

III. The specific manifestations of the weldability of squeeze castings.

Due to the process guarantees above, squeeze die castings possess the necessary conditions for welding:

1.Extremely Low Gas Content:The absence of expandable subsurface pores means the part remains stable under welding heat, preventing blisters and distortion.

2.Highly Dense Microstructure:The uniform and dense base material provides an excellent foundation for creating a high-quality, sound weld pool without defects.

3.Capability for Heat Treatment (T5/T6):This is a critical indirect proof of weldability. The ability to withstand solution heat treatment (heating to ~500°C for T6) proves the part's internal stability at high temperatures. The localized high heat of welding is a similar, though more intense, thermal challenge that these castings can now endure.

IV. Conclusion

Squeeze die castings are weldable because their 'slow filling' and 'high-pressure squeeze solidification' process transforms them into a product whose internal quality is closer to that of a forgingor a premium casting.This process fundamentally eliminates the inherent defects of traditional die casting, thereby granting the components distinctly high-performance characteristics—such as weldability and heat treatability—which are unattainable with standard die cast parts.Consequently, when designing high-strength, high-integrity aluminum alloy components that require subsequent welding and assembly, squeeze die casting is an ideal manufacturing choice."