高强度纳米晶纯铜管材成形模拟研究

发布时间：2018-02-28 13:18

  本文关键词： 纯铜管材 TECAP工艺 模具结构 微观组织 成形模拟　出处：《山东建筑大学》2017年硕士论文　论文类型：学位论文

【摘要】：纯铜管材具有良好的耐蚀性,高温下亦可正常工作,常用于较为复杂的环境。但是纯铜挤压管材质地较硬,作为结构件时,受到周期载荷的情况下,纯铜管材寿命较差,限制了管材的进一步应用。为了改善管材性能,提高其强韧性,研究新型工艺,而管的等通道转角挤压工艺(TECAP)作为一种新型的剧烈塑性变形方法。其工艺是在材料受到三向压应力的作用下,管坯发生纯剪切变形,具有较好的变形效率。可以实现管坯材料的纳米化,具有较高的研究价值。现阶段,TECAP工艺正处于研发阶段,本文通过对TECAP工艺理想状况和三维情况进行数值模拟,并对模拟结果进行分析研究,为管材TECAP工艺更加深入系统研究打下良好的基础。首先,在二维理想状况下对管坯进行等通道转角挤压数值模拟,发现管坯流动规律和应力应变分布情况。在理想情况下,材料在经过一道次的TECAP挤压以后,部分管坯发生了较大的剪切变形,产生了良好的效果。在模拟过程中,经过一道次TECAP变形后,靠近拐角处的管坯应变最为明显,最小变形处位于管坯的下端面远离拐角的位置。除此之外,材料与芯部填充物之间的接触条件对试样变形分布有着重要影响。接触条件越稳定变形质量越好,因而在变形过程中摩擦因子选取0.6变形效果较好。在选择填充材料时,应该选择力学性能和管坯材料力学性能相近的金属材料或非金属材料。其次,在三维状况下对纯铜管材进行了TECAP的数值模拟分析,得到不同模具结构下,材料的流动规律以及应力应变分布情况。发现圆心角Ψ=20°时,拐角Φ=90°的情况下,管坯的等效应力应变较大,均匀性较好,管坯一道次变形综合成形质量较好。为了验证TCP模型和文中的TECAP模型变形情况,构建了TCP模拟模型,对比了TECAP的Ψ=20°时,Φ分别为90°、135°模具结构,在室温,低速变形过程中,TCP等效应变均值大于TECAP变形量。但是TCP对于模具质量要求较高,变形质量要由于TECAP变形质量,但是管坯的外表面受损较为严重。除此之外,对管坯TECAP一道次变形不同变形速度、温度以及润滑条件下,材料的应力应变分布,发现和棒材具有一致性,在T=200℃时,摩擦因子≤0.2时,材料一道次TECAP变形效果较好。最后,对材料的微观组织进行了模拟,参考了位错变形机制和剪切变形机制,利用3D-deform软件自带的微观组织模拟系统,研究在再结晶温度以下,材料晶粒、晶界以及位错的变化情况,分析验证Φ=90°,Ψ=20°时,摩擦因子为0.12的情况下,管坯在T=250℃外界环境下,材料一道次TECAP变形后,管坯微观组织演化效果较为明显。通过对微观组织模拟,发现晶粒演化存在位错的增加和消失,亚晶界向大角度晶界的演化,因而TECAP实现管坯的晶粒细化,同时位错的变化强化了管坯的力学特征。总而言之,管坯实现了一定程度的强化。
[Abstract]:Pure copper pipes have good corrosion resistance and can work normally at high temperature. They are often used in more complicated environments. However, pure copper extruded pipes have a hard texture. When they are used as structural parts, the life of pure copper pipes is poor when they are subjected to periodic loads. In order to improve the properties of pipes and improve their strength and toughness, a new technology is studied. As a new method of severe plastic deformation, the equal channel angular extrusion (TECAP) of the tube is a pure shear deformation of the tube billet under the action of triaxial compressive stress. It has good deformation efficiency, can realize the nanocrystalline material of tube blank, and has high research value. At present, the TECAP process is in the research and development stage, the ideal condition and three-dimensional condition of TECAP process are numerically simulated in this paper. The simulation results are analyzed and studied, which lays a good foundation for the further and systematic study of pipe TECAP process. Firstly, the equal channel angular extrusion numerical simulation of tube blank is carried out under the two dimensional ideal condition. It is found that the flow law and the stress and strain distribution of the tube billet. In ideal case, after a TECAP extrusion, some of the tube billets have a large shear deformation, which has a good effect. After a secondary TECAP deformation, the strain of the tube billet near the corner is the most obvious, and the minimum deformation is located at the lower end of the tube blank far from the corner. In addition, The contact condition between the material and the core filler has an important effect on the deformation distribution of the specimen. The more stable the contact condition, the better the deformation mass, so the friction factor 0.6 is better in the process of deformation. Metal or non-metallic materials with similar mechanical properties and similar mechanical properties should be selected. Secondly, the TECAP numerical simulation analysis of pure copper pipes is carried out under three dimensional conditions, and different die structures are obtained. It is found that when the center angle is 20 掳and the corner is 90 掳, the equivalent stress and strain of the tube billet is larger and the uniformity is better. In order to verify the deformation of the TCP model and the TECAP model in this paper, a TCP simulation model is constructed, and the die structure of 桅 is 90 掳~ 135 掳at room temperature. During low speed deformation, the mean equivalent strain of TECAP is greater than that of TECAP. However, TCP requires higher die quality, and the deformation quality is due to TECAP deformation quality, but the outer surface of tube billet is damaged seriously. It is found that the stress and strain distribution of the material is consistent with that of the bar under different deformation rates, temperatures and lubrication conditions of the TECAP secondary deformation of the tube billet. When the friction factor is less than 0.2, the deformation effect of the material is better than that of the steel bar. Finally, the stress strain distribution of the material is similar to that of the bar under different deformation rates, temperature and lubrication conditions. The microstructure of the material was simulated, and the change of grain, grain boundary and dislocation under recrystallization temperature was studied by using 3D-deform software's system of microstructure simulation, referring to the mechanism of dislocation deformation and shear deformation. The results show that under the condition of 桅 90 掳, 蠄 20 掳and friction factor 0.12, the microstructure evolution effect of tube billet is obvious after the material is deformed together with secondary TECAP under the external environment of T _ (250 鈩，

本文编号：1547458