Situation of semi-solid die casting of magnesium alloys in China

As the country with the largest magnesium reserves, the deep processing technology of magnesium alloy is becoming mature. With the development of the new energy vehicle market, China’s magnesium alloy industry has the following advantages:

Rich — China has the largest reserves and production of magnesium in the world, and the abundance of magnesium in the earth is the eighth. Academician Pan Fusheng said that magnesium resources are inexhaustible and inexhaustible.

Light — density of aluminum alloy 2/3, 1/4 of steel;

Strong — good mechanical properties, high specific strength, high rigidity;

Flat — the normal market price is 15,000 to 20,000 yuan/ton, can compete with steel, aluminum;

Green — low melting point, low melting energy consumption, easy recycling, especially in China, there is a complete and fast magnesium alloy waste recycling system, most forms of magnesium based substances are beneficial to the environment and human health;

Cool – high resistance to electromagnetic interference, shock resistance and vibration absorption, good heat dissipation performance, good vibration and noise reduction, can be absorbed by the human body, with excellent hydrogen storage capacity, can be used as energy.

In this way, the preferred material for automotive lightweight should be magnesium alloy. At present, in China, it mainly focuses on the steering wheel skeleton and the dashboard skeleton. The average consumption of magnesium alloy in domestic models is only 2kg/ car, while in many best-selling models in Europe and America, the amount of magnesium has reached 30kg/ car. It shows that magnesium alloy has broad market prospect.

What’s the problem

“The safety, reliability and quality cost of magnesium alloy products are no longer a problem. The current obstacle is that the advanced magnesium deep processing system has long been in the hands of North American, Japanese, German and Taiwan enterprises. Even if the enterprises are located in mainland China, they do not serve the domestic market, and Chinese enterprises do more traditional die casting process, resulting in uneven quality and performance levels. “The advanced semi-solid injection molding equipment is almost all used by Taiwanese companies.”

It is understood that 80% of magnesium alloy deep processing enterprises mainly adopt traditional die casting process, which not only has high energy consumption and high pollution, but also the whole production environment is very dangerous due to the exposure of high temperature metal liquid in the production process. Especially for some small and medium-sized enterprises, small fires often occur in the workshop, and combustion and explosion accidents occur from time to time in the industry. Magnesium is a very reactive element with an ignition point below the melting point and is highly combustible. In the process of die casting of high temperature magnesium alloy, sulfur hexafluoride, which is very harmful to the environment, needs to be used as a protective gas, and the smoke is diffuse in the workshop, causing serious pollution. Therefore, the country strictly controls the application and production capacity of magnesium alloy die casting process. However, this is obviously in contradiction with the strong demand for magnesium alloy in automotive lightweight. Undoubtedly, the core of the solution lies in the innovation and improvement of magnesium alloy manufacturing process!

The safe and environmentally friendly semi-solid injection molding process is an excellent solution that can change the status quo. In fact, the semi-solid injection molding technology of magnesium alloy has only been invented for 30 years, and mature equipment has only been developed for 20 years. The equipment technology has been the exclusive monopoly of Japanese leading enterprises for a long time, and the skilled use of Chinese enterprises in Taiwan.

Due to the influence of technology monopoly, imported equipment accessories and maintenance are very expensive. It takes more than 1 million yuan to purchase a set of screw and barrel, more than 5,000 yuan for a small high temperature and high strength bolt, and even magnesium alloy particles which seem to be extremely easy to obtain now have to be imported from Japan at a high price. Subject to others, most of the domestic enterprises can only choose the relatively backward die casting process! Semi-solid injection molding as the core of magnesium alloy product processing technology and traditional die casting process has a great difference, such as plastic injection as simple, fast and safe!

The raw materials of magnesium alloy particles enter the semi-solid slurry preparation tube by negative pressure and gravity, which is quickly hot melted at about 600℃ and formed into solid-liquid two-phase mixture (semi-solid slurry) under the action of screw stirring and shearing. Then, it is injected into the mold by 100MPa high pressure, and finally, it can be discharged after cooling and shaping. It can be described as a “minimal process”. Because the solid phase becomes spherical under the action of stirring shear, the semi-solid slurry has good fluidity and good formability. The whole process, small pieces only ten seconds, big pieces only thirty or forty seconds, very efficient!

Advantages of semi-solid injection of magnesium alloys.

Safety: Compared with the die casting process, the forming process only uses a small amount of metal completely in the closed channel change, no high-temperature metal liquid exposure, transfer link, prevent burning and scald accidents;

Environmental protection: do not use harmful SF6 smelting protection gas, no smoke transpiration, no flame, no smelting waste slag, almost no waste water, waste gas, solid waste, clean working environment;

Precision: no matter how complex the shape of the workpiece can be a molding (such as half cavity parts and the thinnest part of only 0.3mm, a product on the thickest thinnest can be 100 times different), high precision (0.01mm, after processing amount is minimal;

Save money: There is no need to be heated to fully liquefied metal, no need to melt hundreds of kilograms of magnesium alloy raw materials at one time, no need to keep the raw materials in liquid state for a long time, only a very small amount of magnesium alloy raw materials required by hot melting for several parts each time. Compared with the die casting process, the temperature is 70℃ lower and there is no need for heat preservation, the energy consumption is reduced by 60%, the thermal impact on the mold is reduced, and the life of the mold is extended by 1 to 4 times. Processing surplus materials can be all recycled. Compared with die casting, the production area is 30% less;

High efficiency: single production capacity, high efficiency (1 ~ 4 pieces per minute, 24h continuous production); Due to the small amount of raw materials for heating, the startup and shutdown time of the equipment is reduced by 70% compared with that of die casting, and the replacement of raw materials is rapid;

Precision: dense metallographic structure (comparable to forgings), less product defects, mechanical index than die casting process can be improved by 20%;

Stable: long service life of consumables, reliable mechanical operation, 24h continuous operation, small inspection cycle of nearly 200,000 times;

Simple: The most simple forming process in complex metal parts, raw magnesium alloy ingot – magnesium alloy granules – semi-solid injection molding – a small amount of machining – surface treatment – coloring spraying end process;

Intelligent: high degree of automation, less labor, can realize unmanned production, remote maintenance and pre-maintenance.

These characteristics have revolutionized the manufacturing route of magnesium alloy. The whole production cost, production efficiency, product quality and management difficulty are far superior to the traditional die casting process in the past.

Our company has 3 semi-solid machines in Taishan Zhongmei, the largest machine is 650 tons, and the annual output reaches 3,000 tons of castings. We have a mature team. At present, we have cooperated with many UAV enterprises, including DJI, to produce high-precision parts of various industries with precision parts and excellent performance.