耐热镁合金连续变通道直接挤压成形规律研究

发布时间：2018-05-07 20:50

本文选题：连续变通道直接挤压 + 耐热镁合金　；参考：《哈尔滨理工大学》2015年硕士论文

【摘要】：随着航空航天和汽车等领域对轻量化需求的日益渐增，镁合金作为目前可应用的最轻金属结构材料，拥有广阔的应用前景。但密排六方的晶体结构，使镁合金在常温下的滑移系较少，表现为塑性变形能力较差，不利于加工及成形。目前大塑性变形技术已被证实是镁合金晶粒细化、改善组织均匀性及提高综合性能的重要途径之一。但传统大塑性变形技术通常需要反复、多次加载或处理才能达到预期效果，工序复杂、周期长且更难于实现工业化应用等瓶颈问题凸现出来。为此，本文提出了一种可将细晶制备工序融入到挤压工艺中的新技术——连续变通道直接挤压法。该方法通过在坯料和芯模之间增设一定数量及结构的过渡模而形成一个连续变化曲率的型腔通道，金属流经时受到类似“镦-拔-镦”的持续加载变形作用，剧烈剪切变形可使微观组织形貌和力学性能发生改变，在单道次内即可实现对挤出制品形/性的一体化调控。首先，研究了连续变通道直接挤压原理及工艺特点，以此为依据，设计和研制出所需的过渡模结构及形式，推导并建立了N阶过渡模的连续变通道直接挤压通用的累积应变量理论计算模型，证明了此技术在总挤压比不变情况下增加累积应变量的可行性；随后，以耐热镁合金ZM6为例，采用数值模拟和工艺实验相结合方法，经过渡模数量及结构对连续变通道直接挤压过程影响的研究结果表明，与常规挤压相比，增设过渡模挤压后连续的剪切变形使挤后制品的动态再结晶进行更加充分，达到深度细化晶粒尺寸的实效，抗拉强度也随之提高，挤出金属的变形流动均匀性明显改善，并降低了产生表面开裂缺陷可能性；通过不同过渡模结构及组合模式的调整可深度挖掘挤压工艺的细晶强化能力，如过渡模尺寸或模角等结构设计不合理时，在变通道型腔内侧易存在死区缺陷，这使相应阶段的实际变形量与较理论计算值要小些。最后，研究了铸态和挤压态ZM6镁合金连续变通道直接挤压后，分别进行固溶、时效及固溶时效处理后微观组织演变规律的研究结果表明，挤压态ZM6经时效处理后，在晶粒内部逐渐有连续析出相产生，，并随着时效时间逐渐增多；而在固溶时效处理后，晶粒尺寸则明显增大。而随时间的增加，晶界处由少量不连续析出相出现，但增幅明显变缓。综上可知，连续变通道直接挤压工艺为大塑性变形技术真正实现工业化应用提供了实质突破的可能性，并为高性能镁合金挤压制品短流程成形技术的研究提供了重要的科学依据。
[Abstract]:With the increasing demand for lightweight in the fields of aerospace and automobile, magnesium alloys, as the most light metal structural materials available at present, have a broad application prospect. However, due to the hexagonal crystal structure, the slip system of magnesium alloy at room temperature is less, and the plastic deformation ability is poor, which is not conducive to processing and forming. At present, the technology of large plastic deformation has been proved to be one of the important ways to refine the grain, improve the microstructure uniformity and improve the comprehensive properties of magnesium alloy. However, the traditional large plastic deformation technology usually needs repeated loading or treatment to achieve the desired effect, the process is complex, the cycle is long and it is more difficult to realize the industrial application. In this paper, a new technology, continuous variable Channel Direct Extrusion, is proposed, which can integrate the fine grain preparation process into the extrusion process. This method forms a continuous cavity channel with varying curvature by adding a certain number and structure of transition modes between the blank and core die, and the metal is subjected to continuous loading and deformation similar to that of "upsetting, pulling and upsetting" as the metal flows through. Severe shear deformation can change the morphology and mechanical properties of the extruded products, and the shape / property of extruded products can be controlled in a single pass. Firstly, the principle and process characteristics of continuous variable channel direct extrusion are studied. Based on this, the structure and form of transition die are designed and developed. The theoretical calculation model of cumulative strain for continuous variable channel direct extrusion of N-order transition die is derived and established. It is proved that this technique is feasible to increase cumulative strain under the condition of constant total extrusion ratio. Then, taking heat-resistant magnesium alloy ZM6 as an example, By using the method of numerical simulation and technological experiment, the effect of the number and structure of the crossing die on the direct extrusion process of the continuous variable channel is studied. The results show that, compared with the conventional extrusion, The continuous shear deformation after extrusion by adding transition die makes the dynamic recrystallization of extruded products more fully, which can achieve the actual effect of deep refinement of grain size, the tensile strength also increases, and the deformation and flow uniformity of extruded metal is obviously improved. The possibility of producing surface cracking defects is reduced, and the fine grain strengthening ability of extrusion process can be deeply excavated by adjusting the structure of different transition die and combination mode, such as the unreasonable design of transition die size or die angle, etc. It is easy to have dead zone defects in the inner side of the variable channel cavity, which makes the actual deformation of the corresponding stage smaller than that of the theoretical calculation. Finally, the microstructure evolution of as-cast and extruded ZM6 magnesium alloys after direct extrusion with continuous variable channels was studied. The results showed that the microstructure evolution of extruded ZM6 magnesium alloy was studied after aging, aging and solution aging treatment, respectively, and the results showed that, after aging treatment, the microstructure evolution of extruded ZM6 magnesium alloy was studied. There are continuous precipitated phases in the grains, which increase with aging time, but the grain size increases obviously after solution aging. However, with the increase of time, a small amount of discontinuous precipitates appear at the grain boundary, but the increase is obviously slower. It can be concluded that the continuous variable channel direct extrusion technology provides the possibility of a real breakthrough in the industrial application of the large plastic deformation technology. It also provides an important scientific basis for the research of short-process forming technology of high-performance magnesium alloy extrusion products.
【学位授予单位】：哈尔滨理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG379

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