高能电脉冲处理细化AZ31镁合金机制及其组织和性能的研究

发布时间：2018-07-24 19:55

【摘要】：在当前日益严峻的能源危机背景下，人类社会对新能源新材料的需求日益旺盛，，而镁及镁合金因为其储量丰富且拥有诸如密度低、比强度高、易于回收等优点而备受瞩目。目前，镁合金的广泛应用仍旧受限于其较低的力学性能，因为细晶强化是一种有效的同时提高合金强度与塑性的强化方法，故而广泛应用于镁合金强化中。由于以热处理为代表的获得细晶组织的方法通常都在较高温度下进行，并且会导致再结晶晶粒的长大而导致材料强度与塑性的下降。因此本文以AZ31镁合金为研究对象，通过使用脉冲电源产生的高电流密度低占空比电脉冲促进了变形AZ31镁合金内部的再结晶并获得了细晶组织。本文研究了高能电脉冲处理对经过多道次轧制变形AZ31镁合金组织演化与力学性能的影响。通过使用光学显微镜(OM)、扫描电子显微镜(SEM)、电子被散射衍射(EBSD)等分析测试手段对不同参数脉冲处理进行了对比分析，研究了电脉冲的热效应与非热效应的作用，揭示了电脉冲促进再结晶的作用机理。研究结果显示，电脉冲处理加速了变形AZ31镁合金内部的再结晶过程并细化了其显微组织。经过脉宽为20μs、电流密度3.508×109A/m2、占空比为0.002的电脉冲处理320s后，在电脉冲的作用下变形AZ31镁合金在359K下发生再结晶。合金的平均晶粒尺寸由72μm降低至2μm，其抗拉强度较处理前提升85%，达到295MPa，延伸率增大到20%。通过本文的研究还指出，高电流密度低占空比电脉冲对变形AZ31镁合金的显微组织有明显的细化作用。电脉冲对金属试样主要有两方面作用，即电脉冲的焦耳热效应与非热效应。由实验数据与分析可知，非热效应在变形金属在电脉冲作用下的再结晶过程中起主要作用，其作用主要体现在增大了电脉冲处理过程中的再结晶形核率、补充了再结晶驱动力、增加了合金内部原子扩散通量。而再结晶晶粒的长大过程则与焦耳热效应有关。基于此，要想获得细晶合金组织，则必须在加强电脉冲非热效应的同时减少热效应的影响。
[Abstract]:Under the background of the increasingly severe energy crisis, the demand for new energy and new materials is increasingly strong in human society, while magnesium and magnesium alloys have attracted much attention because of their rich reserves and advantages such as low density, high specific strength, easy recovery and so on. At present, the wide application of magnesium alloy is still limited by its low mechanical properties, because fine grain strengthening is an effective strengthening method to improve both strength and plasticity of magnesium alloy, so it is widely used in magnesium alloy strengthening. As the method of obtaining fine grain structure represented by heat treatment is usually carried out at higher temperature, recrystallization grain will grow and the strength and plasticity of the material will decrease. Therefore, the high current density and low duty cycle pulse generated by pulsed power supply can promote the recrystallization of the deformed AZ31 magnesium alloy and obtain fine grain structure. The effect of high energy electric pulse treatment on microstructure evolution and mechanical properties of AZ31 magnesium alloy after multi-pass rolling has been studied in this paper. By means of optical microscope, (OM), scanning electron microscope, (SEM), electron scattering diffraction, (EBSD) and so on, the effects of thermal effect and non-thermal effect of electric pulse are studied. The mechanism of electrical pulse promoting recrystallization is revealed. The results show that electrical pulse treatment accelerates the recrystallization process and refines the microstructure of the deformed AZ31 magnesium alloy. After treatment of 320 s with pulse width of 20 渭 s, current density of 3.508 脳 10 9A / m 2 and duty cycle of 0.002, the deformed AZ31 magnesium alloy was recrystallized at 359K under the action of electric pulse. The average grain size of the alloy was reduced from 72 渭 m to 2 渭 m. The tensile strength of the alloy was increased to 295 MPA, and the tensile strength was increased to 20 渭 m. It is also pointed out that the high current density and low duty cycle electric pulse can refine the microstructure of wrought AZ31 magnesium alloy. There are two main effects of electric pulse on metal sample, namely, Joule heat effect and non thermal effect of electric pulse. From the experimental data and analysis, it can be seen that non-thermal effect plays a major role in the recrystallization process of deformed metal under the action of electric pulse, which is mainly reflected in increasing the rate of recrystallization nucleation during the treatment of electric pulse and supplementing the driving force of recrystallization. The atomic diffusion flux in the alloy is increased. The growth process of recrystallized grains is related to the Joule heat effect. Therefore, in order to obtain the microstructure of fine-grained alloy, it is necessary to reduce the effect of thermal effect while strengthening the non-thermal effect of electric pulse.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG661

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