Magnesium alloys, a highly anticipated green and environmentally friendly alloy, are gradually changing the face of the industrial sector due to their unique advantages. They possess moderate density, ranging from 1.75 g/cm³ to 1.90 g/cm³, along with excellent specific strength and specific stiffness, good dimensional stability, superior electromagnetic shielding performance, strong corrosion resistance, and significant vibration damping. Furthermore, magnesium alloys exhibit impressive machinability, being easy to process and cost-effective, with excellent filling fluidity. Even more encouragingly, with the continuous decline in prices in recent years, magnesium alloys have gradually become an ideal alternative to traditional structural materials such as steel, iron, aluminum, and plastics. Their applications in numerous fields, including automotive, electronics, home appliances, communications, instrument manufacturing, and aerospace, are becoming increasingly widespread. Although new forming methods are constantly emerging, die casting remains dominant, and many new forming technologies are derived from die casting principles.
Compared to aluminum alloys, magnesium alloys have lower density, specific heat, and latent heat of solidification, and their melting point is also relatively lower. During melting and die casting, magnesium alloys do not react with iron, resulting in lower melting energy consumption and faster solidification, thus shortening the injection cycle by 20%–30%. Furthermore, magnesium alloy die casting molds have a relatively long lifespan, generally exceeding 200,000 cycles, with some reports even suggesting up to 3 million cycles. However, magnesium alloy molten metal exhibits greater susceptibility to oxidation and combustion, and a higher tendency for hot cracking compared to aluminum alloys. This makes its melting, pouring, and mold temperature control processes more complex than aluminum alloy die casting.
Magnesium alloys can be die-cast using either cold chamber or hot chamber die casting machines. Hot chamber die casting machines are typically used to produce lightweight, thin-walled die castings, with locking forces generally below 7840 kN. Their production efficiency is approximately twice that of a cold chamber die casting machine of the same capacity. For example, a hot chamber die casting machine with a locking force of 9800 kN can die-cast a bicycle frame weighing 2.15 kg, achieving a production capacity of 70 pieces per hour. Meanwhile, WhiteMetalCasting in the United States successfully produced a 610×610mm magnesium alloy computer casing using a large hot chamber die-casting machine.
Improvements to the hot chamber die-casting machine include using an energy storage device to increase injection speed, induction heating of the gooseneck tube and nozzle to maintain optimal temperature, and dual-furnace melting and holding for precise control of the molten pool temperature. Regarding cold chamber die-casting machines, Prince in the United States developed a large magnesium alloy cold chamber die-casting machine and adopted robotic part-removal technology, making the entire unit a highly efficient die-casting production unit. This cold chamber die-casting machine achieves a maximum injection plunger speed of 819 m/s while ensuring a minimum static pressure of 419 MPa on the molten metal.
The core technology of the magnesium alloy cold chamber die-casting machine lies in its automatic pouring mechanism. Currently, this mechanism mainly employs various types, including vane pumps, pneumatic pumps, gravity pumps, and electromagnetic pumps. In automated casting, a stainless steel pump transports molten metal from the molten pool to the injection chamber via piping. Simultaneously, pressurized argon gas acts on the surface of the molten pool within a sealed crucible. The pump body, immersed in the molten pool, presses out molten magnesium alloy in quantitative increments ranging from 200 to 2000 grams. Gravity casting systems use a lifting device to raise the molten pool level above the pouring nozzle, utilizing gravity for metal pouring. Quantitative pouring is achieved through precise valve opening timing. Electromagnetic pump casting systems rely on electromagnetic force to transport molten metal. Their advantages include precise control of the pouring volume, with an error margin within 2%, and a wide adjustable range.
In actual production, components such as the dashboards of Audi cars, the right-angle bearing beams of General Motors cars, as well as car seat frames and wheel hubs, are all magnesium alloy die-cast parts produced using cold chamber die-casting machines. These components vary not only in size but also in weight and wall thickness, but all rely on efficient automated casting mechanisms and precise die-casting processes.
