Magnesium Alloy Die Casting Process

In traditional die casting technology, the molten metal fills the die cavity in a high-speed turbulent and dispersed state. The gases within the cavity (air, protective gases, and mold surface lubricant vapors) cannot be expelled, leading to high-pressure micro-pores or dissolution within the alloy, or creating gas pockets during the filling process, which can interrupt the filling. The gases in the pores may separate or expand at high temperatures, causing deformation and surface blisters on the castings. Therefore, magnesium alloy parts produced with traditional die casting processes cannot be heat-treated or used at higher temperatures.

In the past 30 years, to overcome these defects, improve quality, and broaden the application range of die casting technology, researchers have developed new die casting processes, such as vacuum die casting, oxygen-filled die casting, and semi-solid die casting. Compared to traditional die casting processes, these new processes offer superior qualities in eliminating casting defects and enhancing mechanical properties, surface, and internal quality.

Vacuum Die Casting

Vacuum die casting eliminates or reduces internal pores and dissolved gases in die-cast parts by removing gases from the cavity during the casting process, thereby improving mechanical performance and surface quality. The maximum plunger speed for vacuum die casting can reach 10 m/s, with a filling time of 20s to 30s, and the minimum wall thickness of parts is 1.5mm to 2mm. Strength performance can be improved by over 10%, and toughness can increase by 20% to 50%. Moreover, vacuum die casting can enhance the elongation rate of AM50 alloy from 15% in conventional die casting to 19%. More than 20 years ago, vacuum die casting was already applied in automotive wheels and steering wheels made of AM60B alloy. However, the performance improvement for magnesium alloy parts is not as pronounced as for aluminum alloys, and thus, the development of vacuum die casting for magnesium alloys has not been vigorous.

Oxygen-Filled Die Casting

Oxygen-filled die casting, also known as pore-free die casting, involves introducing oxygen or other active gases into the cavity before filling with magnesium melt to displace the air in the cavity. The magnesium melt reacts with the active gases, generating MgO particles that are dispersed throughout the casting, thus removing gases from the casting and enabling heat treatment strengthening of magnesium alloy die castings. The oxygen-filled die casting process was first applied in the production of computer head brackets, automotive wheels, and other components.

Compression Molding

The compression molding method involves applying pressure to the entire surface of the die-cast part. Under pressure, the magnesium alloy solidifies, improving the alloy's microstructure and reducing porosity. The result is a denser and more uniform casting structure, suitable for producing magnesium alloy parts with high performance requirements and complex shapes.

Extrusion Casting

Extrusion casting is a type of pressure casting, first patented in the UK in 1819. The world's first extrusion casting machine was produced in Germany in 1931 and later widely used in the Soviet Union. It wasn’t until the 1960s that it began to be used in North America, Europe, and Japan. The North American Die Casting Association (NADAC) defines extrusion casting as a process involving low filling speeds and minimal disturbance, allowing the metal melt to solidify under high pressure to produce heat-treatable, high-density castings. Experiments have shown that with a filling speed of less than 2 m/s and a filling pressure greater than 70 MPa, good structure and performance castings can be obtained. According to incomplete statistics, in 2022, there were about 365 extrusion casting machines worldwide, mainly used for casting automotive, bicycle, air conditioner, valve, and pump parts.

In extrusion casting, the alloy melt is injected into the cavity and pressed into shape under mechanical pressure from the extrusion casting machine's plunger, solidifying under pressure. This results in dense castings with few defects such as pores or looseness, and the microstructure is fine and uniform. Sometimes, the mechanical properties of the castings are nearly equal to those of forged parts. The castings solidify and form under pressure without deformation or cracking, making the process simple, flexible, and highly automated, with a high yield rate. It is mainly used to produce parts with high strength and good air-tightness, especially thin-walled castings like various valve bodies, frames, and automotive wheels.

Lori is a manufacturer with extensive die casting production experience. We offer die casting services using various processes. If you need assistance, please contact us!