Magnesium Alloy Die-Casting Process Steps

The magnesium alloy die-casting process involves a series of precision steps to transform molten magnesium into high-quality, complex-shaped components, requiring strict control of temperature, pressure, and material flow.

1. Alloy Preparation

The process begins with selecting the appropriate magnesium alloy, such as AZ91D (aluminum-zinc-magnesium) or AM60B (aluminum-manganese-magnesium), based on the component’s mechanical requirements. Raw materials—pure magnesium, aluminum, zinc, and other alloying elements—are weighed and melted in a crucible furnace under an inert gas atmosphere (usually SF₆ or CO₂) to prevent oxidation, as magnesium reacts violently with oxygen at high temperatures. The molten alloy is held at 650–700°C to ensure homogeneity, with chemical composition tested to meet specifications.

2. Die Preparation

The die, typically made of hot-work tool steel (e.g., H13), is preheated to 150–300°C to prevent rapid cooling of the molten magnesium upon contact, which could cause defects like cold shuts. The die cavity and cores are sprayed with a release agent (a water-based or oil-based lubricant) to facilitate easy ejection of the casting and protect the die from wear.

3. Injection

The molten magnesium alloy is transferred to a shot sleeve, where a plunger pushes it into the die cavity under high pressure (10–100 MPa). The injection speed is critical—too slow leads to premature solidification, while too fast causes turbulence and gas entrapment. The metal fills the cavity completely, taking the shape of the die, including fine details and thin walls (as low as 0.5 mm in some cases).

4. Solidification and Ejection

Once the cavity is filled, pressure is maintained (holding pressure) to compensate for shrinkage as the alloy solidifies. Solidification occurs rapidly, typically within seconds, due to the die’s cool surface. After solidification, the die opens, and ejector pins push the casting out. The casting, still hot, is transferred to a cooling area to stabilize its structure.

5. Trimming and Post-Processing

The as-cast component has excess material, such as sprue, runners, and flash (thin metal projections from die gaps), which are removed using trimming presses or CNC machining. Surface defects like porosity or burrs are repaired by grinding or sandblasting.

6. Heat Treatment

Depending on the alloy, heat treatment may be applied to enhance mechanical properties. For example, T6 treatment (solution annealing at 415°C followed by aging at 160°C) strengthens AZ91D by precipitating fine intermetallic particles, increasing tensile strength and hardness.

7. Surface Treatment

To improve corrosion resistance, magnesium castings undergo surface treatments such as chromating, anodizing, or painting. Chromating forms a protective oxide layer, while anodizing creates a thicker, porous layer that can be dyed for aesthetic purposes.

8. Quality Inspection

Final inspections include dimensional checks using CMMs (coordinate measuring machines), visual inspections for defects, and mechanical testing (tensile strength, hardness) to ensure compliance with standards. Non-destructive testing, such as X-ray or ultrasonic scanning, detects internal defects like porosity.

Each step in the magnesium die-casting process is critical to achieving components with high precision, strength, and surface quality, making them suitable for automotive, aerospace, and consumer electronics applications.

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