Break through the technical difficulties of magnesium alloy machining,This technology has laid a good foundation for the warm punching of high-performance magnesium alloy products.
Because of its low density, high specific strength, high specific rigidity, easy recycling and no pollution, magnesium alloy is known as one of the "21st century green and environmentally friendly engineering materials", and has attracted widespread attention. However, some inherent weaknesses of magnesium alloys have been severely restricting its development.
One is that the crystal structure of the magnesium alloy is a close-packed hexagonal structure, especially its axial ratio c/a=1.624, which makes it only have 3 independent slip systems at room temperature, resulting in poor room temperature plastic deformation ability. The second is that the absolute strength is low, and as the temperature increases, its strength and creep resistance will drop significantly.
Therefore, the research and development of effective magnesium alloy forming and machining technology and the improvement of the properties of magnesium alloy through appropriate machining and forming technology have become important topics in the research of magnesium alloys in recent years.
The emerging strong plastic deformation technology research boom provides a new development direction for the research and development of magnesium alloy machining technology. Severe plastic deformation technology is an effective method for preparing ultra-fine-grained metal materials.
A series of techniques for preparing ultra-fine-grained materials through strong plastic deformation have been proposed, including equal channel angular extrusion, cumulative rolling, high-pressure torsion, shock wave impact, repeated wrinkle-straightening, torsional extrusion, and large Extrusion ratio extrusion method, multi-directional forging method and so on.
Among them, there are more researched equal channel angular extrusion method, cumulative rolling method, high-pressure torsion method, etc., especially the strong plastic deformation method represented by the equal channel angular extrusion method can greatly refine the grain size to obtain The grain size is less than 1 micron, even reaching or less than 100 nanometers of ultra-fine grain structure, this unique microstructure will lead to excellent physical and mechanical properties.
This kind of strong plastic deformation technology can not only overcome the difficulty of magnesium alloy deformation, but also greatly improve the strength and toughness of magnesium alloy through fine-grain strengthening. At present, magnesium alloy bulk materials with ultra-fine crystal or nanocrystalline structure have been obtained by a strong plastic deformation process, which has become a very promising new machining and forming process for preparing ultra-high strength and toughness magnesium alloys.
Chinese scholars have obtained many pioneering results in this regard. According to a report from Shanghai Jiaotong University, the Mg-Y-Zn alloy was prepared by the common melting and casting process combined with the equal channel angular extrusion process. Its room temperature mechanical properties reached a tensile strength of 472.7MPa, a yield strength of 444.6MPa, and an area reduction rate of 6.24%. Comprehensive mechanical properties.
In addition, in terms of conventional deformation machining technology, it is almost impossible for magnesium alloy sheet to be stamped at room temperature. Even if it is isothermal stamping at high temperature, its formability is still poor. At present, the plastic machining methods of magnesium alloy mainly include hot extrusion, isothermal forging and isothermal rolling. In order to overcome the difficulty of poor deformability of magnesium alloys, Chinese scholar Fan Likun and others proposed a new technology of differential temperature drawing process for magnesium plates.
This technology performs differential temperature heating on different parts of the magnesium plate according to the degree of deformation during deep drawing, and accurately controls the dynamic blank holder force. It comprehensively utilizes the deformation ability of the magnesium alloy at high temperature and the work hardening ability at low temperature to achieve A higher ultimate drawing ratio is achieved at a lower forming temperature.
Through computer program control, the use of this process can make the limit drawing ratio of conventionally rolled AZ31 sheets at 180°C reach 3.2, which is close to twice the isothermal drawing under the same conditions. This technology has laid a good foundation for the warm punching of high-performance magnesium alloy products and is a promising technology. (One member)
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