【摘要】：在當(dāng)前日益嚴(yán)峻的能源危機(jī)背景下，人類社會(huì)對新能源新材料的需求日益旺盛，，而鎂及鎂合金因?yàn)槠鋬?chǔ)量豐富且擁有諸如密度低、比強(qiáng)度高、易于回收等優(yōu)點(diǎn)而備受矚目。目前，鎂合金的廣泛應(yīng)用仍舊受限于其較低的力學(xué)性能，因?yàn)榧?xì)晶強(qiáng)化是一種有效的同時(shí)提高合金強(qiáng)度與塑性的強(qiáng)化方法，故而廣泛應(yīng)用于鎂合金強(qiáng)化中。由于以熱處理為代表的獲得細(xì)晶組織的方法通常都在較高溫度下進(jìn)行，并且會(huì)導(dǎo)致再結(jié)晶晶粒的長大而導(dǎo)致材料強(qiáng)度與塑性的下降。因此本文以AZ31鎂合金為研究對象，通過使用脈沖電源產(chǎn)生的高電流密度低占空比電脈沖促進(jìn)了變形AZ31鎂合金內(nèi)部的再結(jié)晶并獲得了細(xì)晶組織。 本文研究了高能電脈沖處理對經(jīng)過多道次軋制變形AZ31鎂合金組織演化與力學(xué)性能的影響。通過使用光學(xué)顯微鏡(OM)、掃描電子顯微鏡(SEM)、電子被散射衍射(EBSD)等分析測試手段對不同參數(shù)脈沖處理進(jìn)行了對比分析，研究了電脈沖的熱效應(yīng)與非熱效應(yīng)的作用，揭示了電脈沖促進(jìn)再結(jié)晶的作用機(jī)理。 研究結(jié)果顯示，電脈沖處理加速了變形AZ31鎂合金內(nèi)部的再結(jié)晶過程并細(xì)化了其顯微組織。經(jīng)過脈寬為20μs、電流密度3.508×109A/m2、占空比為0.002的電脈沖處理320s后，在電脈沖的作用下變形AZ31鎂合金在359K下發(fā)生再結(jié)晶。合金的平均晶粒尺寸由72μm降低至2μm，其抗拉強(qiáng)度較處理前提升85%，達(dá)到295MPa，延伸率增大到20%。 通過本文的研究還指出，高電流密度低占空比電脈沖對變形AZ31鎂合金的顯微組織有明顯的細(xì)化作用。電脈沖對金屬試樣主要有兩方面作用，即電脈沖的焦耳熱效應(yīng)與非熱效應(yīng)。由實(shí)驗(yàn)數(shù)據(jù)與分析可知，非熱效應(yīng)在變形金屬在電脈沖作用下的再結(jié)晶過程中起主要作用，其作用主要體現(xiàn)在增大了電脈沖處理過程中的再結(jié)晶形核率、補(bǔ)充了再結(jié)晶驅(qū)動(dòng)力、增加了合金內(nèi)部原子擴(kuò)散通量。而再結(jié)晶晶粒的長大過程則與焦耳熱效應(yīng)有關(guān)�；诖耍氆@得細(xì)晶合金組織，則必須在加強(qiáng)電脈沖非熱效應(yīng)的同時(shí)減少熱效應(yīng)的影響。
[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.
【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG661

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