What is Magnesium Alloy Semi-Solid Die-Casting?

Magnesium alloy semi-solid die-casting is an advanced metal forming technology that uses magnesium alloy slurries in a semi-solid state (between solid and liquid) for die-casting, which combines the advantages of traditional die-casting and forging, and has unique technical characteristics and application value.

The key to this technology lies in the preparation of semi-solid magnesium alloy slurries. The semi-solid slurry has a non-dendritic microstructure, where the solid phase exists as fine, spherical particles, and the liquid phase fills the gaps between the solid particles. This structure gives the slurry good thixotropy, meaning that its viscosity decreases with the increase of shear rate. When it is at rest, it has high viscosity and can maintain its shape; when sheared (such as during injection), its viscosity decreases significantly, showing good fluidity, which is conducive to filling the mold cavity. The preparation methods of semi-solid slurries mainly include mechanical stirring, electromagnetic stirring, and ultrasonic treatment. Mechanical stirring uses a rotating impeller to stir the molten magnesium alloy during cooling, breaking the dendritic structure and forming spherical particles. Electromagnetic stirring generates a rotating magnetic field through an electromagnetic coil to stir the molten metal, which has the advantages of non-contact and uniform stirring. Ultrasonic treatment uses high-frequency ultrasonic waves to act on the molten alloy, using the cavitation effect and acoustic flow to refine the grains and form a semi-solid structure.

The process of magnesium alloy semi-solid die-casting is roughly as follows. First, the prepared semi-solid slurry is transferred to the injection chamber of the die-casting machine. Then, the injection punch pushes the slurry into the mold cavity at a certain speed and pressure. During the filling process, due to the thixotropy of the slurry, it can fill the complex mold cavity smoothly without splashing or turbulence, reducing the 卷入 of gas. After filling, pressure is maintained to compensate for the shrinkage of the slurry during solidification. Finally, after the product is completely solidified, the mold is opened and the product is ejected. Compared with traditional liquid die-casting, semi-solid die-casting has a lower pouring temperature, generally 10-50°C lower than the liquidus temperature of the alloy, which reduces the thermal shock to the mold, prolongs the mold life, and reduces energy consumption.

The advantages of magnesium alloy semi-solid die-casting are obvious. Firstly, the mechanical properties of the products are significantly improved. The non-dendritic microstructure makes the material have uniform properties, and the tensile strength, yield strength, and elongation are higher than those of traditional die-cast parts. For example, the tensile strength of semi-solid die-cast magnesium alloy parts can be increased by 10-20% compared with traditional die-cast parts. Secondly, the casting quality is better. Due to the low filling temperature and good fluidity of the semi-solid slurry, the defects such as porosity, shrinkage, and segregation in the castings are reduced, and the dimensional accuracy and surface quality are improved. The surface roughness of semi-solid die-cast parts can reach Ra 1.6-3.2μm, which reduces the subsequent machining allowance. In addition, the process is more environmentally friendly. The lower pouring temperature reduces the emission of harmful gases such as magnesium vapor, and the reduction in energy consumption is also in line with the requirements of green manufacturing.

Magnesium alloy semi-solid die-casting is widely used in automotive, aerospace, and 3C (computer, communication, consumer electronics) industries. In the automotive field, it can be used to produce complex parts such as engine brackets, transmission housings, and steering knuckles, which can reduce the weight of the vehicle and improve fuel efficiency. In the 3C industry, it is suitable for manufacturing thin-walled, high-precision parts such as notebook computer casings and mobile phone frames, meeting the requirements of lightweight and high strength.

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