高能电脉冲作用下变形镁合金的微观组织及力学性能研究

发布时间：2018-08-02 12:13

【摘要】：在当前能源危机和人类需求多样化的背景下,镁合金作为最轻的金属结构材料和其丰富的储量而备受关注,但是由于镁合金在室温下塑性较差,而且其强度也较低,限制了它的推广应用。根据经典金属学原理可知,晶粒细化不仅可以改善材料的塑性,同时可以提高材料的强度,因此,本论文试图采用晶粒细化法改善镁合金的性能。电脉冲处理是一种新兴的材料处理方法,其具有输入能量大,效率高等特点。近年来,应用电脉冲处理细化材料的微观组织已取得了良好的效果。因此,本文应用高能电脉冲处理轧制变形态的AZ31B镁合金,首先,通过控制室温轧制变形量、脉冲宽度、脉冲时间等实验参数,利用正交试验的方法,研究电脉冲处理参数对微观组织(再结晶分数、平均晶粒尺寸)的影响,并测定力学性能。其次,通过控制脉冲宽度,考察试样的再结晶组织转变过程,并从理论上分析电脉冲处理的热效应和非热效应对变形镁合金再结晶晶粒形核与长大以及再结晶机理的影响。再结晶分数分析表明,轧制变形量和脉冲宽度对再结晶分数的影响较大,再结晶分数随着二者的增大明显升高,而脉冲时间对再结晶分数的影响相对较小;平均晶粒尺寸分析表明,轧制变形量对平均晶粒尺寸影响较大,脉冲宽度和脉冲时间对其影响相对较小;热效应分析表明,试样表面温度受脉冲宽度和轧制变形量的影响较大,随着脉冲宽度和轧制变形量的升高,试样表面温度急剧上升,而受脉冲时间的影响相对较小。通过分析选出的最优参数为室温轧制变形量38%、脉冲宽度70μs、脉冲时间10 min,在此条件下处理试样,其晶粒尺寸由原始材料的140μm细化至6.8μm,极大的改善了微观组织。力学性能测试表明,38%室温轧制变形量试样由于变形量过大而导致的内部微裂纹严重弱化了其力学性能,但是次优参数室温轧制变形量30%、脉冲宽度70μs、脉冲时间10 min试样的性能改善也非常明显,抗拉强度提升至341 MPa,伸长率达到了11.6%。组织演变分析表明,随着脉冲宽度的增大,变形组织逐渐发生再结晶,且再结晶转变过程为:孪晶再结晶、孪晶和晶界再结晶、整体再结晶、晶粒长大。再结晶机理分析表明,电脉冲处理是通过热效应与非热效应共同作用促进再结晶,且非热效应是促进再结晶的主要原因,非热效应降低了再结晶形核势垒,降低了原子扩散激活能,提高再结晶形核率,进而加速了再结晶。
[Abstract]:Under the background of the current energy crisis and the diversification of human needs, magnesium alloys, as the lightest metal structural materials and their abundant reserves, have attracted much attention. However, the plasticity of magnesium alloys at room temperature is poor, and the strength of magnesium alloys is also low. It limits its popularization and application. According to the classical metallography principle, grain refinement can not only improve the plasticity of the material, but also improve the strength of the material. Therefore, this paper attempts to improve the properties of magnesium alloy by grain refinement method. Electrical pulse processing is a new material processing method, which has the characteristics of large input energy and high efficiency. In recent years, the application of electric pulse to the treatment of fine material microstructure has achieved good results. Therefore, in this paper, high energy electric pulse is used to treat AZ31B magnesium alloy with variable shape. Firstly, by controlling the experimental parameters of room temperature rolling deformation, pulse width and pulse time, the orthogonal test method is used. The effect of electrical pulse processing parameters on microstructure (recrystallization fraction, average grain size) and mechanical properties were studied. Secondly, the process of recrystallization microstructure transformation of wrought magnesium alloy was investigated by controlling the pulse width, and the effects of thermal and non-thermal effects on the nucleation and growth of recrystallized grain and the mechanism of recrystallization of wrought magnesium alloy were analyzed theoretically. The recrystallization fraction analysis shows that the rolling deformation and pulse width have great influence on the recrystallization fraction, and the recrystallization fraction increases obviously with the increase of the recrystallization fraction, while the effect of pulse time on the recrystallization fraction is relatively small. The average grain size analysis shows that the rolling deformation has a great influence on the average grain size, while the pulse width and pulse time have relatively little effect on the average grain size, and the thermal effect analysis shows that the surface temperature of the sample is greatly affected by the pulse width and the rolling deformation. With the increase of pulse width and rolling deformation, the surface temperature of the sample increases sharply, but the influence of pulse time is relatively small. The optimum parameters are as follows: room temperature rolling deformation 38, pulse width 70 渭 s, pulse time 10 min. Under these conditions, the grain size of the sample is refined from 140 渭 m to 6.8 渭 m, which greatly improves the microstructure. The results of mechanical properties test show that the internal microcracks of 38% room temperature rolling specimens due to excessive deformation seriously weaken their mechanical properties. However, the mechanical properties of the suboptimal parameters, such as room temperature rolling deformation 30 and pulse width 70 渭 s, pulse time 10 min, were also improved obviously. The tensile strength was raised to 341 MPA, and the elongation reached 11.6 MPA. The microstructure evolution analysis shows that recrystallization occurs gradually with the increase of pulse width, and the recrystallization process is twinning recrystallization, twin recrystallization and grain boundary recrystallization, whole recrystallization and grain growth. The analysis of recrystallization mechanism shows that electrical pulse treatment promotes recrystallization through the interaction of thermal effect and non-thermal effect, and non-thermal effect is the main reason for promoting recrystallization, and non-thermal effect reduces the nucleation barrier of recrystallization. The activation energy of atomic diffusion is reduced, the nucleation rate of recrystallization is increased, and the recrystallization is accelerated.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22

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