| Aluminum alloys are largely applied to the areas of aerospace,transportation, ship and equipment manufacturing, because it owns low density,high specific strength, corrosion resistance, easy to recycle, high mechanical properties and other features. SPD technology as a technology to improve material performance which imposes severe shear deformation can refine the material microstructure and improve comprehensive performance, and aluminum alloy with high strength and good mechanical properties is popular in material preparation. However, the traditional severe plastic deformation has some drawbacks, like complicated process, long circle, high costs and hard to achiave industrialized application.Therefor, this paper takes the aerospace 7A09 aluminium alloy as an example on continuous variable cross-section direct extrusion(CVCDE) spread related research. Continuous variable cross-section direct extrusion(CVCDE) is that some interim dies are added between billet and CE die to make up a cavity channel with continuous variable sections, and the flowing material subjects to intense shear deformation improves organizational performance, at the same time,the shape and properties can be solved simultaneously by a single extrusion.Compared with ordinary extrusion, interim dies play the essential effects on the extrusion. Adding different number and structure of interim dies can change local extrusion ratio and accumulative strain, which plays a key role for the organizational performance and quality of extruded product.Firstly, a dedicated mold was designed based on the principle and the characteristic of CVCDE, and finite element simulation has been employed to study the metal flow behavior in the CVCDE die cavity. Taking one,two interimdie for example, analyse systematically effects of processing parameters on the extrusion by continuous variable cross-section direct extrusion with 7A09 aluminium alloy. The research result shows that the extrusion speed has a significant influence on the maximum temperature of the billet, at the same time,both decreasing the friction factor and increasing forming temperature within a certain range are beneficial to reducing extrusion load. Both forming temperature and the extrusion speed are inversely linked to extrusion load, but the friction factor is directly proportion to extrusion load. Forming temperature has a far more important influence on extrusion load by comparison, when forming temperature increases within a certain range(380 °C~430 °C), the peak value of extrusion load decrease, and the flow uniformity of extruded product get improved. Make sure the most reasonable extrusion temperature under this process condition, which provides a reliable theoretical basis for process test.Subsequently, when retained extrusion ratio, conventional extrusion and CVCDE with one and two interim dies are applied to process test of 7A09 aluminum alloy, which can analyse the evolution of aluminum alloy microstructure and performance change under the effect of CVCDE. At the same time, the material flows through die cavity sequentially and suffers “upsettingextrusion-upsetting” continuous loading, which will result in a severe deformation. By analysis of the microstructure and mechanical properties of7A09 aluminum alloy are obtained under different conditions, it can be known that the grains become smaller and round, and the uniformity is also improved after CVCDE. Compared with conventional extrusion, the grain refinement of CVCDE with one and two interim dies increased respectively, and tensile strength and elongation also increase.To sum up, CVCDE with high efficiency, low consumption, short process and other unique advantages in obtaining high performance alloy products will be certainly raised wide concern. |
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