Magnesium alloy is the lightest metal structural material, and it has broad application prospects in the field of automobile, aerospace and other fields. However, the crystal symmetry of magnesium is low, resulting in poor workability at room temperature. This shortcoming pushes up the production cost of magnesium alloy parts and severely weakens the competitive advantage of this material. The workability of materials is affected by two factors, the tensile elongation rate and the work hardening rate. Using traditional methods such as rare earth element addition, grain refinement, precipitation strengthening, etc., generally can only increase one of the tensile elongation or work hardening rate of magnesium alloys, and it is difficult to increase both at the same time.
The team of Researcher Wang Leyun and Professor Zeng Xiaoqin from the Institute of Light Alloys, School of Materials Science and Engineering, Shanghai Jiaotong University, China, designed a new type of Mg-Al-Ca ternary alloy under the guidance of thermodynamic calculations. By accurately setting the content of alloying elements Al and Ca and the heat treatment conditions, only Al2Ca phase is precipitated in the molding material, and Mg2Ca and Mg17Al12 phases that are harmful to plasticity are avoided. Unlike the conventional precipitation phase in magnesium, this Al2Ca phase has submicron size and its crystal orientation is random. On the one hand, these Al2Ca precipitates hinder the dislocation slip in the magnesium matrix and increase the work hardening rate of the material. On the other hand, the Al2Ca precipitated phase itself has a crystal structure similar to face-centered cubic, which can form dislocations and stacking faults on its {111} crystal plane to initiate plastic deformation. The internal plasticity of the Al2Ca phase effectively eliminates local stress concentration, enabling the material to maintain high elongation. In addition, the solutes Al and Ca inhibit twin nucleation and promote <c+a> dislocations, which are also conducive to the increase of the elongation of the material. Due to the above mechanism, the room temperature elongation of this alloy is as high as 27%, and the work hardening amount (expressed as the difference between tensile strength and yield strength) can reach 135MPa. The above combination of properties is higher than all known magnesium alloys. This new Mg-Al-Ca alloy with ultra-high workability does not need to use expensive rare earth elements, and is formed in one step through a common extrusion process, so its production cost is very low and it has a good practical application prospect.