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Key points of process control for magnesium alloy high pressure die casting

2025-05-30

The demand for lightweight new energy vehicles is further increasing. The price of magnesium alloy raw materials is inverted and lower than that of aluminum alloy raw materials. Magnesium alloy die-castings replace aluminum alloys to meet the demand for further lightweighting. Therefore, the demand for magnesium alloy die-castings will gradually increase. Several articles have previously introduced Fugu's 25-year development analysis of the magnesium industry. At the same time, at the magnesium industry chain forum held in Jinhua from April 1st to 2nd, major universities and scientific research institutions were discussing the magnesium industry and jointly seeking the future development of the magnesium industry.

Magnesium alloy high Pressure Die Casting is an efficient andprecise production process. Its core is to fill the mold cavity with molten magnesium alloy at high speed and high pressure to quickly form complex parts. The key points of process control involve equipment, molds, process parameters and process management. This article mainly shares some key control points and suggestions summarized by individuals based on work experience.

1. Die-casting machine and mold control
(1).Die casting machine selection
- It is recommended to give priority to cold chamber die casting machines (commonly used for magnesium alloys) because they are suitable for high melting point alloys (molten magnesium temperature is about 620~680℃) and avoid corrosion caused by long-term contact with the melt in Hot Chamber Die Casting machines.
- The die casting machine needs to have high clamping force (matching the projected area), fast injection system and precise pressure control. Choose the appropriate die casting tonnage according to different product structures.
(2). Mold design and maintenance
- Mould material: Use high-quality steel (such as H13) that is resistant to high temperatures and thermal fatigue, and perform nitriding or chrome plating on the surface to extend its service life.
- Casting system: Use short-process fan-shaped gates or point gates to reduce turbulence and oxidation. At the same time, because the filling speed is fast and erosion is easy, the chamfer or bevel angle should be increased as much as possible to reduce obstruction; the overflow groove and exhaust groove should be reasonably designed to avoid air entrapment.
- Cooling system: Magnesium alloys have high requirements for mold temperature balance and require precise control of mold temperature. Therefore, it is recommended to configure a circulating oil circuit to control the mold temperature (usually 150~250℃). If necessary, it is recommended to use a 3D contour cooling oil circuit to balance the solidification speed and reduce shrinkage and deformation, especially in thick wall parts or special-shaped parts. Generally, an oil temperature controller is required to control the balance of the mold temperature field.

2. Process parameter control
(1).Magnesium liquid quality
- Magnesium liquid temperature: strictly controlled at 680~750℃ (specific adjustment depends on the alloy grade). If the temperature is too high, it is easy to oxidize, and the oxide impurity content is too high, which affects the corrosion resistance; if the temperature is too low, the fluidity is poor, and it will solidify prematurely and cause internal defects.
- Magnesium liquid composition: The main factors affecting the corrosion resistance of magnesium alloys are alloy composition, microstructure, and corrosive medium. Testing the corrosion rate of magnesium alloys with different contents of impurity elements such as Fe, Ni, and Cu shows that the corrosion rate of magnesium alloys decreases sharply with the increase of the content of impurity elements.

Process parameter control

Due to the sensitivity of magnesium alloy's corrosion resistance to alloy composition and microstructure, it is necessary to accurately control the alloy composition or strictly control the content of impurity elements. It is particularly important to ensure the uniformity of magnesium solution composition during casting.

(2). Injection process parameters
- Low-speed injection stage (front stage of filling): The speed is relatively low, generally 0.1~0.5m/s, to prevent metal liquid from splashing and air entrainment.
- High-speed injection stage (main filling stage): Since the magnesium liquid dissipates heat quickly to the mold, a higher filling speed can be selected to ensure rapid filling and reduce solidification defects.
- Boosting pressure: High pressure should be applied at the initial stage of solidification of magnesium liquid to compensate for shrinkage and achieve the effect of increasing density.
Compared with aluminum alloy, magnesium alloy die casting generally requires higher filling speed, earlier boost start position, and appropriately increased boost pressure. However, the specific process parameters need to be determined according to product structure, performance and other requirements to determine the optimal process parameters.

(3). Mold temperature management
- Mold preheating: Preheat to 150~200℃ before the first production to avoid mold cracking caused by thermal shock. Establish mold files and do a good job of mold maintenance.
- Mould temperature control during production: Maintain 150~250℃ through circulating water or mould temperature controller to balance heat and reduce mould sticking and cold shut.
- Barrel temperature control: Due to the low surface tension and low latent heat of solidification of magnesium, the heat transfer rate of magnesium alloy solution to the mold is faster. In order to avoid the low temperature of magnesium liquid before filling, which leads to rapid solidification, the barrel temperature should be appropriately increased and monitored.

Magnesium alloy die casting has high sensitivity to temperature, so it requires higher stability of mold and injection system temperature. Because the temperature difference between the mold and magnesium liquid is small, the magnesium alloy mold is generally higher than the aluminum alloy, but it is also based on the mold material and heat treatment.
Mold temperature management
3. Key points of process control
(1). Spraying process
- Use water-based release agent (needs low salt content), and optimize the spraying time, distance and concentration (usually spraying time 1~3s) to avoid residues that cause pores or corrode the mold.
- After spraying, dry thoroughly (blow air or evacuate) to prevent moisture from reacting with the melt to form oxide scale or hydrogen.

Key points of process control

(2). Shot curve optimization
- Through the real-time control system, key parameters such as injection speed, pressure curve, high speed and pressure start position, material handle thickness, etc. are monitored to ensure smooth filling without turbulence.
- Use vacuum-assisted die casting (vacuum degree ≤ 50mbar) to reduce gas entrapment in the cavity and improve the density of the casting.

(3). Cycle time control
- The mold opening time and ejection time must match the material solidification rate to avoid deformation or sticking caused by premature mold opening.
At present, major automobile manufacturers are gradually applying magnesium alloys to various parts. Different parts on the car have different structural strength and corrosion resistance. Therefore, different process control focus points should be selected according to the actual application environment and requirements of the parts.
Cycle time control

4. Safety and Environmental Protection
(1). Explosion and fire prevention
- The die-casting area must be equipped with a Class D fire extinguisher specifically for magnesium alloys. It is prohibited to use water or foam to extinguish fires.
- The equipment should be well grounded to prevent static electricity from igniting magnesium dust.
- Equipment valve joints should use explosion-proof valves, and oil temperature pipes should be resistant to high temperatures to prevent damage and leakage.

(2). Waste gas treatment
- SF₆ or fluorine-containing gases generated during the die-casting process must be treated by a scrubber or activated carbon adsorption to avoid environmental pollution. For specific magnesium alloy smelting and safety protection requirements, please refer to the introduction in the previous articles of the official account (magnesium alloy die-casting magnesium ingot smelting process control and safety requirements).

Summarize
The core control points of magnesium alloy high pressure die casting can be summarized as: high filling speed, high boost pressure, high mold temperature stability; magnesium liquid should have low hydrogen content and low oxidation inclusions; mold thermal field and solidification shrinkage must be balanced. In actual production, it is necessary to combine material properties, part structure and equipment conditions, through refined parameter adjustment and process monitoring, to ensure efficient and stable production of high-quality magnesium alloy die castings.