【摘要】：近來,為降低能耗,提高資源利用率,被看作潛在“綠色金屬結(jié)構(gòu)材料”的鎂及其合金擁有廣闊的應(yīng)用前景。但是鎂是密排六方晶格結(jié)構(gòu),室溫下滑移系少且變形過程中易形成強(qiáng)基面織構(gòu),致使鎂及其合金室溫下塑性成形性能較差,成形后各向異性顯著,嚴(yán)格限制了鎂合金的廣泛應(yīng)用。為此,試圖通過一種簡潔、高效、可靠的方法,以提高鎂及其合金的成形性和力學(xué)性能是目前研究者普遍關(guān)注的熱點。通過合金化或采用特殊加工工藝以細(xì)化晶粒、弱化織構(gòu)進(jìn)而改善鎂合金的室溫成形性和力學(xué)性能是目前常見的研究方式,但是大多數(shù)成果還處于實驗室階段,距工業(yè)化生產(chǎn)還存在較大距離,且結(jié)果并不令人滿意。本文利用多向鍛加工方式對AZ31B合金、Mg-Er合金以及純鎂進(jìn)行預(yù)變形,而后開展了室溫條件下不同程度的拉伸實驗,借助各種分析手段,來研究鎂及其合金在多向鍛后的變形特征和變形機(jī)制,以改善鎂合金室溫成形性能和力學(xué)性能,取得以下結(jié)論:(1)純鎂經(jīng)多向鍛后塑性得到明顯提高,其延伸率可達(dá)33%;純鎂在多向鍛造過程中織構(gòu)得到弱化,同時發(fā)生了大量的孿生行為;通過IGMA方法定性討論,認(rèn)為鍛態(tài)純鎂在室溫拉伸條件下啟動了非基面滑移,特別是錐面滑移。(2)通過多向鍛提高了AZ31B合金的力學(xué)性能,是因為多向鍛過程弱化了合金織構(gòu),使得大部分晶粒取向更有利于孿生。孿生可以弱化織構(gòu),孿晶的產(chǎn)生以及孿晶之間的相互作用改變了初始取向。在拉伸變形初期,由于預(yù)孿生的存在,使得極易發(fā)生去孿生的行為,降低了屈服強(qiáng)度和出現(xiàn)了屈服平臺,孿生的交互作用提高了材料的抗拉強(qiáng)度。多向鍛過程中發(fā)生的動態(tài)再結(jié)晶,使晶粒得到細(xì)化,織構(gòu)得到弱化。(3)力學(xué)性能測試結(jié)果顯示Mg-2Er合金獲得很大的延伸率,起決定作用的不是稀土元素Er的加入促進(jìn)非基面滑移,而通過多向鍛弱化織構(gòu)來提高塑性更具有有效的作用。
[Abstract]:Recently, in order to reduce energy consumption and improve resource utilization, magnesium and its alloys, which are regarded as potential "green metal structural materials", have broad application prospects. However, magnesium is a closely packed hexagonal lattice structure, with few slip systems at room temperature and easy to form strong basal texture during deformation, which results in poor plastic forming properties of magnesium and its alloys at room temperature, and obvious anisotropy after forming. The wide application of magnesium alloys is severely restricted. Therefore, a simple, efficient and reliable method to improve the formability and mechanical properties of magnesium and its alloys is the focus of attention. It is a common research method to refine grains, weaken texture and improve the room temperature formability and mechanical properties of magnesium alloy by alloying or adopting special processing technology, but most of the results are still in the laboratory stage. There is still a long distance from industrial production, and the results are not satisfactory. In this paper, AZ31B alloy, Mg-Er alloy and pure magnesium were predeformed by multi-direction forging, and then tensile experiments were carried out at room temperature to different extent, with the help of various analytical methods. To study the deformation characteristics and deformation mechanism of magnesium and its alloys after multi-direction forging, in order to improve the room temperature formability and mechanical properties of magnesium alloys, the following conclusions are obtained: (1) the plasticity of pure magnesium is obviously improved after multi-direction forging, and its elongation can reach 33%; The texture of pure magnesium is weakened and a large number of twinning behaviors occur in the process of multi-direction forging. Through qualitative discussion by IGMA method, it is considered that forged pure magnesium starts non-basal slip, especially cone slip, under room temperature tensile condition. (2) the mechanical properties of AZ31B alloy are improved by multi-direction forging, because the texture of the alloy is weakened during multi-direction forging. It makes most grain orientation more favorable to twins. The twinning can weaken the texture, and the formation of twins and the interaction between twins change the initial orientation. In the early stage of tensile deformation, due to the existence of pre-twinning, it is easy to occur the behavior of removing twinning, which reduces the yield strength and the yield platform, and the interaction of twinning improves the tensile strength of the materials. The dynamic recrystallization in the process of multi-direction forging results in the refinement of grain and the weakening of texture. (3) the results of mechanical properties test show that the elongation of Mg-2Er alloy is very large. It is not the addition of the rare earth element Er that promotes the non-basal slip, but the more effective way to improve the plasticity by weakening the texture through multi-direction forging.
【學(xué)位授予單位】：沈陽航空航天大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG146.22;TG319

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