The density of magnesium alloy is 1/4 of that of steel and 2/3 of that of aluminum alloy. It is the lightest metal structural material, but its low absolute strength and corrosion resistance greatly 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 can easily cause grain growth and it is difficult to obtain ultra-fine grain structure.
What's more serious is that 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. Early studies have shown that the twin structure can also be used to refine the grains and increase the strength, and the energy of the twin grain boundary is low, which will not have a significant impact on the corrosion resistance of magnesium alloys.
However, the tensile twin interface, which is the easiest to initiate 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.
Recently, researcher Xu Daokui's team from the Key Laboratory of Nuclear Materials and Safety Evaluation of the Chinese Academy of Sciences, Institute of Metal Research, Chinese Academy of Sciences, and Nanjing University of Technology Professor Xin Yunchang's team have made important progress in the preparation of high-strength and high-corrosion-resistant magnesium alloy materials.
They used the multi-pass three-way compression technique to prepare the twin crystal structure. Through the unique design of the compression path and the pass strain, using 12 passes of low-strain and high-strain cyclic compression, they successfully prepared the average plate in the AZ80 magnesium alloy. The high-density twin structure with a layer thickness of about 200 nm makes the average grain size refined from about 33 mm of the initial material to 300 nm, and its tensile strength is as high as 469 MPa, which is the highest strength reported in this series of magnesium alloys. .
The use of high-density ultra-fine twin structure to refine grains not only avoids the adverse effects of non-equilibrium grain boundaries on corrosion resistance, but also changes the morphology and distribution of 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 research results were published in "Nature Communications"