| The development of technology and processing technology of magnesium alloy still takes a higher cost, and the mechanical properties of magnesium alloys in the presence of plasticity is also low defects, and therefore its use is not widely popular.In this paper, only to do a very basic research for magnesium alloy tubular members which are widely used in industry, aerospace, 3C and other fields, so as to provide a theoretical reference for subsequent experiments and production.For magnesium alloy tubular members forming, there are some common pitfalls for casting magnesium alloy products, such as shrinkage, porosity, etc, which result in poor mechanical properties, low plasticity. As we all know, by plastic forming, the mechanical properties of magnesium alloys can be effectively improved. However, when using conventional plastic forming method, the improvement is very limited, and when using multi-directional forging and ECAP method, we can get a large performance increase, but the types of formed products are limited and the costs are too high. In this paper, for the magnesium alloy tubular members, based on the idea of large plastic deformation at high pressure to reverse, a method of rotating extrusion is put forward. Applying a certain conical rotation to the traditional extrusion die, thereby increasing equivalent strain deformation zone to improve the mechanical properties of material.Firstly, based on the traditional extrusion force analysis, using the way of upper bound analysis and slab analysis to research the forces of the rotating extruding tubular member and obtained required squeeze pressure in the tubular member rotating extrusion.Meanwhile, based on the research of foreign scholars, put forward the premise that the blank inner material in a certain length would occur twist with the influence of a tapered rotating extrusion die,and its twisted length has been theoretically derived, providing a reference for future experiments.By finite element simulation software DEFORM-3DV11.0 to analyze the basic process of AZ80 magnesium alloy tubular forming.Through the analysis of metal flow pattern, the equivalent strain distribution, forming study load, velocity field, forming effect and other aspects in the traditional extrusion and rotation of the extrusion process conditions of forming the tubular member, come up with the drawbacks and advantages in rotary extrusion and conventional extrusion process.Compared with conventional extrusion, axial pressure is significantly reduced when using rotary extrusion, the equivalent strain significantly increasing, through the metal flow diagram, a certain twisting of the blank will occur in a certain range.Meanwhile, when the rotational speed and extrusion speed matching improperly, for example:the rotational speed is too high and the squeeze speed is too low, the formed tubular members occur significantly wrinkling even tearing defects.Finally, by orthogonal experimental method to study the influence of various process parameters on the forming result, including rotational speed, the mold taper angle temperature, coefficient of friction, extrusion speed on forming load and equivalent strain.By comparing, the effect of various parameters on the results of the equivalent strain descending order of temperature, mold taper angle, extrusion speed, die rotation speed, the friction coefficient;influence of each parameter on the equivalent strain standard deviation descending order of extrusion speed, die cone angle, temperature, rotational speed of the die, the friction coefficient.Finally, conducted comprehensive balance analysis for the result of multiple indexes orthogonal test on the basis of analysis of each single index.For the rotation of the conical die this tubular member extrusion simulation, the optimal forming parameters as follows:the cone angle of 45°, the molding temperature of 400 ℃,the friction coefficient of 0.15,the extrusion speed of 0.1mm/s, the rotational speed of the die of 0.1rad/s. |
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