Recently, the BTXT Rare Earth Research Institute has developed a rare earth magnesium-zirconium grain refiner product with a zirconium particle size of less than 600nm, which fills the gap in the product of high-efficiency and low-cost magnesium alloy grain refiner.
"This provides the possibility of developing high-strength cast / deformed magnesium alloy materials for rail transportation equipment such as aircraft seats, automotive safety components, and lightweight high-speed trains." The director of the magnesium alloy project team of the BTXT Rare Earth Research Institute, Ph.D. Senior engineer Hu Wenxin told reporters.
New breakthrough in grain refiner technology
At present, the industry generally adopts magnesium-zirconium master alloys as grain refiners. Existing products in the market have low refining efficiency of zirconium elements (less than 40%), large deposits of zirconium particles, high refining agent cost, high impurity content and Many problems, such as unstable operation of chemical processes, have brought great difficulties to practical industrial applications.
"The grain size control technology of magnesium alloys is one of the most fundamental and most significant technical methods to control the performance of magnesium alloy materials. Zirconium and rare earth elements are effective refinement elements of magnesium alloys. How to make full use of these elements in The role of alloys is the focus of our research. "Hu Wenxin said.
Based on the previous research results on the coupling refinement mechanism of rare earth and zirconium elements on magnesium alloys, supplemented by a new metallurgical preparation method, the denser and smaller zirconium particles provide more adhesion opportunities for magnesium crystal cores. At the same time, the rare earth element strengthens the adhesion ability of the magnesium crystal nucleus on the surface of the zirconium particles during the crystallization process, and can achieve high-efficiency refinement of the magnesium alloy grains.
The particle size after refining is 30% of the size of the zirconium particles in the traditional magnesium-zirconium master alloy, the distribution rate of the nano-scale particles is greater than 60%, the agglomeration phenomenon between the particles is less than 5%, and the alloy grain size is reduced by 20 %, Below 35mm, the grain refinement effect is remarkable.
At present, the product has completed the research and development of a small-scale production process, and the product has been verified by the customer. The product refinement efficiency is greater than 80%, and the cost is more than 20% lower than that of the traditional magnesium-zirconium grain refiner.
"This technology is of great significance to the industrialization of rare earth magnesium alloy ingot products. It can effectively reduce the unevenness of the metal particles inside and outside the product, keep the size of the internal and external alloy particles basically the same, greatly increase the stress level of the alloy, and make the alloy More durable. "Hu Wenxin pointed to rare earth magnesium alloy products and told reporters.
Rare earth magnesium alloy product application has been newly improved
With the rapid development of new energy vehicles and domestic 5G communications, the market demand for light alloy materials that are lighter, have better heat dissipation, and have excellent corrosion resistance is strong, but the corresponding performance requirements are becoming more demanding.
"We studied the mechanism of lanthanum, cerium and other rare earth elements on the heat dissipation performance of magnesium alloys, and developed low-cost heat dissipation rare earth magnesium alloy engineering materials with thermal conductivity of 100W / (m × K). The material saves more than 5% cost than using aluminum alloy. "Hu Wenxin said confidently.
Based on the action mechanism of rare earth on the heat dissipation performance of magnesium alloys and the breakthrough in the control technology of the grain size of magnesium alloys, Baotou Rare Earth Research Institute has made some breakthroughs in the industrialization of semi-continuous casting and cold chamber die casting.
At present, there are few special researches on die casting process of rare earth magnesium alloys at home and abroad. "We, jointly with Northeastern University and Shanghai Jiaotong University, have independently developed semi-continuous casting technology, breaking through melt purification fine crystal technology, low-frequency electromagnetic casting control technology, self-flow casting control technology and other technologies. After technical integration, we have solved breakthroughs in large-scale rare earths. Magnesium alloy rods have large internal stresses, large radial grain size differences, and uneven mechanical properties. "Hu Wenxin said excitedly that this synthesis technology represents the leading semi-continuous casting technology of magnesium alloy materials in China. The low cost of high-quality forged wheels and extruded profiles lays the foundation for technology and products.
Not only that, the QC830 cold chamber die casting system introduced by the BTXT Rare Earth Research Institute has a system clamping force of 850t, a maximum injection force of 756kN, and a maximum projected area of 1242cm2. Currently, it has a large size rare earth magnesium alloy rod with a maximum diameter of 550mm The industrial preparation technology of materials, while relying on the pilot test platform, realizes the pilot-scale preparation of large-size bar products, realizes the production capacity of 300 tons / year of rare-earth magnesium alloy thin-walled devices, and accelerates the promotion of downstream end applications of rare earth magnesium alloy materials .
For future technology research and development, Hu Wenxin has his own plans. They will focus on high-performance heat-dissipating magnesium alloys and functional magnesium alloy materials for the communications engineering and civil electronics industries; carry out processing molding technologies such as low-pressure casting and semi-solid molding of magnesium alloy materials R & D to achieve demonstration applications of corresponding devices and products.