ZK60合金ECAP-FE变形过程数值模拟研究

发布时间：2018-06-02 12:21

本文选题：ZK60镁合金 + ECAP-FE工艺　；参考：《哈尔滨理工大学》2017年硕士论文

【摘要】：镁合金因本身具有的特殊性能而被誉为“最具发展前途的新型材料”,已成为学者研究的焦点。但镁合金六方晶体结构的滑移系少,塑性成形能力差,导致加工困难。虽然传统大塑性变形工艺在细晶强化机制层面得到认可,但是仍存在单道次挤压后材料的变形量小、晶粒细化程度有限以及工艺复杂等缺陷,限制了镁合金的规模化使用。在细晶强化方面,ECAP(Equal Channel Angular Pressing)工艺由单纯的改变模具结构、挤压路径及挤压道次等因素过渡到与其他变形方式复合来提升细晶程度,与传统大变形技术相比,复合成形工艺被认为是一种更为有效的方法,也克服了传统技术的不足而提出的新的挤压方法。本次提及的新型大塑性变形工艺ECAP-FE(Equal Channel Angular Pressing-Forward Extrusion,以下简称ECAP-FE)是由等通道转角挤压(ECAP)与正挤压(FE)结合而成,即在等通道转角挤压的水平通道处连接相同横截面尺寸的正挤压通道来增加单道次挤压变形量,从而达到晶粒细化,力学性能提高的目的。首先,根据ECAP-FE工艺成形原理设计出复合模具结构,并借助DEFORM软件平台,对ECAP-FE工艺与传统ECAP、FE工艺进行等效应变的对比分析,论证了新工艺在应变累积方面的优势;然后在前处理模块合理设定的基础上,对ZK60镁合金ECAP-FE成形中的应力应变、载荷变化、微观组织等场量进行数值模拟,研究了其成形特点、场量分布规律,预测了新工艺对组织的细化效果,为研究实验的开展奠定了坚实的理论基础。最后根据单因素法,分别利用不同过渡距离、模面角、挤压比、挤压温度及摩擦因子创建了多组有限元模型,并以等效应变、载荷大小及应变不均匀系数作为衡量模具结构与成形工艺参数对ECAP-FE变形影响的标准,可以发现载荷及应变会随着模面角或挤压比的增加而增大,并且增大挤压比可减小应变不均匀系数,而过渡距离的增加只会延迟载荷变化的时间点;此外摩擦因子的增大会使载荷及等效应变增大,并且摩擦因子从0.4增至0.6时,应变不均匀系数出现上升趋势,表明较大摩擦不利于应变的均匀性分布。
[Abstract]:Magnesium alloy has been regarded as "the most promising new material" because of its special properties, which has become the focus of scholars. However, the slip system of hexagonal crystal structure of magnesium alloy is few and the forming ability of magnesium alloy is poor. Although the traditional large plastic deformation process has been accepted in fine grain strengthening mechanism, there are still some defects such as small deformation amount, limited grain refinement and complex processing after single pass extrusion, which limits the large-scale application of magnesium alloys. In the aspect of fine grain strengthening, the ECAP equal Channel Angular Pressing) process changes the die structure, the extrusion path and the extrusion path secondary to the other deformation ways to improve the degree of fine grain, compared with the traditional large deformation technology. The compound forming process is considered to be a more effective method and a new extrusion method which overcomes the shortcomings of the traditional technology. The new large plastic deformation process named ECAP-FE(Equal Channel Angular Pressing-Forward extension (hereinafter referred to as ECAP-FEP) is a combination of equal channel angular extrusion (ECAP) and forward extrusion (FEE). In order to increase the deformation of single pass extrusion, the grain refinement and mechanical properties can be improved by connecting the positive extrusion channel with the same cross section size at the horizontal channel of equal channel angular extrusion. Firstly, according to the forming principle of ECAP-FE process, the compound die structure is designed, and the comparative analysis of equivalent strain between ECAP-FE process and traditional ECAP PFE process is carried out with the help of DEFORM software platform, and the advantages of the new process in strain accumulation are demonstrated. Then, on the basis of reasonable setting of pre-processing module, the stress and strain, load change and microstructure of ZK60 magnesium alloy in ECAP-FE forming are numerically simulated, and the forming characteristics and distribution law of the field amount are studied. The effect of the new process on microstructure refinement was predicted, which laid a solid theoretical foundation for the research and experiment. Finally, according to the single factor method, several finite element models are established by using different transition distance, die angle, extrusion ratio, extrusion temperature and friction factor, and the equivalent strain is used. The influence of die structure and forming process parameters on ECAP-FE deformation can be measured by load size and strain non-uniformity coefficient. It can be found that load and strain increase with the increase of die angle or extrusion ratio. Moreover, increasing extrusion ratio can decrease the coefficient of strain inhomogeneity, but the increase of transition distance will only delay the time point of load change, in addition, the increase of friction factor will increase the load and equivalent strain, and the friction factor will increase from 0.4 to 0.6. The increasing trend of the coefficient of strain inhomogeneity indicates that the larger friction is not conducive to the distribution of strain uniformity.
【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】：2017
【分类号】：TG379

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