Frequent Porosity in Aluminum Alloy Die Castings? In-Depth Analysis of ADC12 Material and Die Casting Process

The occurrence of a large number of gas pores in aluminum alloy die castings is not an inevitable defect of the ADC12 material itself, but rather the result of combined factors such as incomplete degassing during melting, improper setting of die casting process parameters, poor mould venting, and irregular use of coatings.

Core Cause Analysis of Gas Porosity Defects

In aluminum alloy die casting production, gas porosity is one of the most common defects. The pores have smooth surfaces, are mostly circular or elliptical, and may be distributed on the surface, subsurface, or inside the die castings. The generation of gas pores mainly stems from the following three gas sources:

• Gas precipitation from the alloy melt: The gas in the molten aluminum is mainly hydrogen. The higher the melting temperature, the greater the solubility of hydrogen, but the solubility drops sharply during solidification, and the precipitation of hydrogen forms gas pores. If the raw materials are damp or the returned scrap carries oil, the hydrogen content will increase.
• Gas entrainment during the die casting process: When the molten metal fills the cavity at high pressure and high speed, if the flow is unstable and generates turbulence, it is very easy to entrain the gas in the cavity and wrap it inside the casting.
• Gas generated by the decomposition of the die release agent: If the coating has excessive gas generation, or if the spraying process is improper resulting in excessive usage and incomplete evaporation of moisture, a large amount of gas will be generated at high temperatures after the mould is closed.

Key Influence of Die Casting Process and Mould Design

As a commonly used die casting aluminum alloy, ADC12 has good fluidity and is suitable for manufacturing complex components such as electromechanical housings, end caps, and flanges. However, to maximize the potential of ADC12, the coordination of process and mould is indispensable:

• Control of injection speed and switching point: Die casting usually adopts multi-stage injection. The first-stage slow injection helps squeeze out the gas in the shot sleeve; the second-stage fast injection is responsible for filling, but too high a speed is prone to generating turbulence and vortices. Reasonably setting the first- and second-stage injection speeds and the switching starting point is the key to reducing gas entrainment.
• Design of gating and overflow systems: If the gate position and runner shape of the mould are improperly designed, it will cause the molten metal to impact directly or generate vortices. The position and cross-sectional area of the venting slots and overflow slots must be reasonable to ensure that gas and cold, dirty molten metal can be smoothly discharged, avoiding gas entrainment in dead corners.
• Mould temperature management: If the mould temperature is too high, it will cause abnormal evaporation of the die release agent and even mould sticking; if the mould temperature is too low, the moisture in the die release agent cannot evaporate, generating a large amount of water vapor. Maintaining an appropriate mould working temperature is crucial for reducing gas porosity.

Collaborative Solutions for Purchasers and Manufacturers

For manufacturing enterprises that provide make-to-drawing/OEM and custom machining services, solving the gas porosity problem requires systematic engineering thinking, which also provides purchasers with a reference dimension for quality evaluation:

• Strict control of raw materials and melting quality: Use dry and clean ADC12 aluminum alloy ingots, strictly control the melting temperature to avoid overheating, and must carry out efficient degassing treatment to reduce the hydrogen content of the molten aluminum from the source.
• Optimization of die casting process parameters: Simulate the filling process through computer software to analyze the flow state of the molten metal. Adjust the injection pressure, slow injection speed, and pouring temperature to ensure that the molten metal fills the cavity smoothly and orderly.
• Early mould review and optimization: During the development stage of the die casting mould, the purchaser should communicate in depth with the manufacturer about the product application (such as whether subsequent custom machining, sandblasting, or powder coating is required). If the casting needs to undergo impregnation treatment or withstand high pressure subsequently, sufficient venting and overflow space must be reserved in the mould design, and the machining allowance should be controlled to avoid penetrating the dense surface layer and exposing subsurface gas pores.

In summary, the ADC12 material itself possesses excellent die casting performance, and the gas porosity problem is essentially a feedback of the manufacturing system engineering. Choosing a supplier with rich die casting mould design experience and a rigorous process control system is the core guarantee for ensuring the internal density and excellent surface quality of aluminum alloy die castings.