Recently, the team of Xu Daokui, a researcher at the Key Laboratory of Nuclear Materials and Safety Evaluation of the Institute of Metal Research, Chinese Academy of Sciences, and Nanjing University of Technology Professor Xin Yunchang's group have made progress in the research of high-strength and high-corrosion magnesium alloy materials. Researchers use multi-pass three-way compression technology to prepare twin structure. Through the unique design of compression path and pass strain, 12-pass low-strain and high-strain cyclic compression is used alternately to prepare average lamellae in AZ80 magnesium alloy. The high-density twin structure with a thickness of about 200nm makes the average grain size refined from about 33mm of the original material to 300nm, and its tensile strength is as high as 469MPa, which is the highest strength reported in this series of magnesium alloys. The high-density ultra-fine twin structure is used to refine the grains to avoid the adverse effects of non-equilibrium grain boundaries on the corrosion resistance and change the morphology and distribution of the β-Mg17Al12 phase. The β-Mg17Al12 precipitates are granular, fine and evenly distributed in the magnesium matrix, which significantly inhibits the occurrence of local corrosion and reduces the corrosion rate by an order of magnitude.
The density of magnesium alloy is 1/4 of that of steel and 2/3 of that of aluminum alloy. It is one of the lightest metal structural materials, and its low absolute strength and corrosion resistance limit its practical engineering application. The commonly used Severe Plastic Deformation (SPD) method is more effective in greatly increasing the strength of magnesium alloys, and can prepare ultra-fine-grained and ultra-high-strength magnesium alloys. However, magnesium alloys with close-packed hexagonal structure have poor cold deformability and require SPD processing under higher temperature conditions, which is likely to cause grain growth and it is difficult to obtain ultra-fine grain structure. The non-equilibrium grain boundaries formed by the ultrafine grains prepared by traditional SPD will significantly reduce the corrosion resistance of magnesium alloys. In addition, the ultra-fine-grained magnesium alloy samples prepared by traditional SPD are small in size and difficult to be applied in engineering. Previous studies have shown that the twin structure can be used to refine the grains and improve the strength, and the energy of the twin boundary is low, which will not have a significant impact on the corrosion resistance of magnesium alloys. However, the easy-to-start tensile twin interface in magnesium alloys is easy to grow and merge under stress. Therefore, the preparation of high-density ultra-fine twin structure is a key issue that needs to be solved urgently.