高能電脈沖作用下變形鎂合金的微觀組織及力學性能研究
發(fā)布時間：2018-08-02 12:13
【摘要】：在當前能源危機和人類需求多樣化的背景下,鎂合金作為最輕的金屬結構材料和其豐富的儲量而備受關注,但是由于鎂合金在室溫下塑性較差,而且其強度也較低,限制了它的推廣應用。根據(jù)經(jīng)典金屬學原理可知,晶粒細化不僅可以改善材料的塑性,同時可以提高材料的強度,因此,本論文試圖采用晶粒細化法改善鎂合金的性能。電脈沖處理是一種新興的材料處理方法,其具有輸入能量大,效率高等特點。近年來,應用電脈沖處理細化材料的微觀組織已取得了良好的效果。因此,本文應用高能電脈沖處理軋制變形態(tài)的AZ31B鎂合金,首先,通過控制室溫軋制變形量、脈沖寬度、脈沖時間等實驗參數(shù),利用正交試驗的方法,研究電脈沖處理參數(shù)對微觀組織(再結晶分數(shù)、平均晶粒尺寸)的影響,并測定力學性能。其次,通過控制脈沖寬度,考察試樣的再結晶組織轉變過程,并從理論上分析電脈沖處理的熱效應和非熱效應對變形鎂合金再結晶晶粒形核與長大以及再結晶機理的影響。再結晶分數(shù)分析表明,軋制變形量和脈沖寬度對再結晶分數(shù)的影響較大,再結晶分數(shù)隨著二者的增大明顯升高,而脈沖時間對再結晶分數(shù)的影響相對較小;平均晶粒尺寸分析表明,軋制變形量對平均晶粒尺寸影響較大,脈沖寬度和脈沖時間對其影響相對較小;熱效應分析表明,試樣表面溫度受脈沖寬度和軋制變形量的影響較大,隨著脈沖寬度和軋制變形量的升高,試樣表面溫度急劇上升,而受脈沖時間的影響相對較小。通過分析選出的最優(yōu)參數(shù)為室溫軋制變形量38%、脈沖寬度70μs、脈沖時間10 min,在此條件下處理試樣,其晶粒尺寸由原始材料的140μm細化至6.8μm,極大的改善了微觀組織。力學性能測試表明,38%室溫軋制變形量試樣由于變形量過大而導致的內部微裂紋嚴重弱化了其力學性能,但是次優(yōu)參數(shù)室溫軋制變形量30%、脈沖寬度70μs、脈沖時間10 min試樣的性能改善也非常明顯,抗拉強度提升至341 MPa,伸長率達到了11.6%。組織演變分析表明,隨著脈沖寬度的增大,變形組織逐漸發(fā)生再結晶,且再結晶轉變過程為:孿晶再結晶、孿晶和晶界再結晶、整體再結晶、晶粒長大。再結晶機理分析表明,電脈沖處理是通過熱效應與非熱效應共同作用促進再結晶,且非熱效應是促進再結晶的主要原因,非熱效應降低了再結晶形核勢壘,降低了原子擴散激活能,提高再結晶形核率,進而加速了再結晶。
[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.
【學位授予單位】：太原理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.22
本文編號：2159401
[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.
【學位授予單位】：太原理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.22
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