多向锤锻工艺对镁合金组织与性能的影响

发布时间：2018-11-19 15:14

【摘要】：近来,为降低能耗,提高资源利用率,被看作潜在“绿色金属结构材料”的镁及其合金拥有广阔的应用前景。但是镁是密排六方晶格结构,室温下滑移系少且变形过程中易形成强基面织构,致使镁及其合金室温下塑性成形性能较差,成形后各向异性显著,严格限制了镁合金的广泛应用。为此,试图通过一种简洁、高效、可靠的方法,以提高镁及其合金的成形性和力学性能是目前研究者普遍关注的热点。通过合金化或采用特殊加工工艺以细化晶粒、弱化织构进而改善镁合金的室温成形性和力学性能是目前常见的研究方式,但是大多数成果还处于实验室阶段,距工业化生产还存在较大距离,且结果并不令人满意。本文利用多向锻加工方式对AZ31B合金、Mg-Er合金以及纯镁进行预变形,而后开展了室温条件下不同程度的拉伸实验,借助各种分析手段,来研究镁及其合金在多向锻后的变形特征和变形机制,以改善镁合金室温成形性能和力学性能,取得以下结论:(1)纯镁经多向锻后塑性得到明显提高,其延伸率可达33%;纯镁在多向锻造过程中织构得到弱化,同时发生了大量的孪生行为;通过IGMA方法定性讨论,认为锻态纯镁在室温拉伸条件下启动了非基面滑移,特别是锥面滑移。(2)通过多向锻提高了AZ31B合金的力学性能,是因为多向锻过程弱化了合金织构,使得大部分晶粒取向更有利于孪生。孪生可以弱化织构,孪晶的产生以及孪晶之间的相互作用改变了初始取向。在拉伸变形初期,由于预孪生的存在,使得极易发生去孪生的行为,降低了屈服强度和出现了屈服平台,孪生的交互作用提高了材料的抗拉强度。多向锻过程中发生的动态再结晶,使晶粒得到细化,织构得到弱化。(3)力学性能测试结果显示Mg-2Er合金获得很大的延伸率,起决定作用的不是稀土元素Er的加入促进非基面滑移,而通过多向锻弱化织构来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.
【学位授予单位】：沈阳航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22;TG319

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