Cu-Ni-Fe合金热变形行为及其空心锭“镦粗—穿孔”挤压管材数值模拟

【作者】 周佳；

【导师】 林高用； 彭大暑；

【作者基本信息】 中南大学 ， 材料加工工程， 2007， 硕士

【摘要】 Cu-Ni-Fe合金管是制造冷凝器的关键材料,其主要采用热挤压方法进行生产,而在加工过程中因缺乏对材料流变特性的系统实验研究,热变形工艺和工模具通常是根据经验拟制和设计的,存在较大的盲目性;同时挤出管材产品常有缺陷,而生产过程的缺陷则更是无法直观地观察与考察,不利于对缺陷产生原因进行分析。本文采用物理模拟方法对Cu-Ni-Fe合金的热变形行为进行系统的研究,并采用有限体积法(FVM)对Cu-Ni-Fe合金空心锭挤压管材过程进行数值模拟研究。通过Gleeble 1500热模拟实验得到了BFe10-1-1和BFe30-1-1铜合金流变应力曲线。分析表明,在同一应变速率下,随变形温度的升高,真应力水平明显下降;在同一变形温度下,随应变速率增加,真应力升高;在低温和低应变速率的变形条件下表现出硬化现象;在高温和高应变速率的情况下,合金应力应变曲线出现波浪形,合金发生动态再结晶,且随着应变速率的提高,动态再结晶软化现象更为明显;建立了包含Arrhenius项Z参数的描述BFe10-1-1和BFe30-1-1铜合金热变形时的流变方程;在热压缩过程中温升较为明显,高应变速率下短时内温升最高可达到27℃,有利于动态再结晶的发生;组织分析表明,随着变形温度的提高,变形程度的增加,动态再结晶程度提高;在相同的应变速率和变形温度下,随着变形程度的增加,退火态晶粒变得细小,这有助于生产中后续工序的进行。采用空心锭“镦粗-穿孔”挤压管材是在传统的采用实心锭穿孔挤压管材工艺的基础上,结合空心锭管材挤压的优点提出来的,可以达到提高材料利用率、增加管材长度,减小挤压力,节约能源的目的。但在实际生产过程中,采用该方法时容易出现夹杂、分层、偏心等缺陷。本文结合生产实际,在MSC.SuperForge软件平台上,采用分步计算的方法,对BFe10-1-1铜合金的空心锭“镦粗-穿孔”挤压管材过程进行了数值模拟分析,采用空心锭进行“镦粗-穿孔”挤压铜合金管材数值模拟,获得了管材挤压过程中的金属流动规律及其应力场、应变场和温度场;得到了空心锭内孔壁在挤压过程中闭合规律,解释了内孔壁氧化皮层进入管壁形成夹杂、分层等现象;得出镦粗比例对空心锭内孔壁氧化层闭合形成缺陷影响的规律;通过改进穿孔针前端结构,在穿孔针前端设置一凹槽,可以防止空心锭内孔壁氧化层进入管壁形成夹杂。更多还原

【Abstract】 Cu-Ni-Fe alloy tube which is mainly producted by hot extrusion, cold-rolling and cold-drawing is the critical material for producing condensor. Because of lacking systemic experiment of the flow character of the deforming materials in the hot extrusion processing, the implement of technical process and the design of dies are usually finished by experiences and results in some flaws which can’t be visualized and can’t get full understanding. This paper research the hot deformation behaviors of Cu-Ni-Fe alloy adopting physical simulation, and simulate the processing of perforate extruding with hollow ingot based on finite volmue method(FVM).The true stress-true strain curves of BFe10-1-1 and BFe30-1-1 copper alloy are got under the thermal simulation experiment by the technique of Gleeble-1500. The results indicate: the true stress decreases with the increase of deformation temperature under the same strai rate, and as the strain rate rises, the true stress increases under the same deformation temperature. The Cu-Ni-Fe alloy presentes work-harding phenomenon under the low temperature and low strain rate. The true stress-true strain curves appear wave phenomenon under the high temperature and high strain rate, and the dynamic recrystallization character is obvious with the strain rate’s increasing. The flow stress equations of BFe10-1-1 and BFe30-1-1 copper alloy under hot deformation are obtained which are described by Zener-Hollomon parameter with Arrhenius model. The temperature rise is obvious in the hot compression processing, the maximum temperature rise up to 27℃which is helpful to the dynamic recrystallization.The structure analysis indicates that the dynamic recrystallization degree raises with the deformation temperature rising and deformation degree increasing, the size of grain under annealing status is refined with the deformation degree rising under the same strain rate and deformation temperature, which is helpful to the subsequent cold forming of the Cu-Ni-Fe alloy tube.The Upsetting-Perforating extrusion technical process with hollow ingot for tube producing is proposed to reach the purpose of improving ratio of material utilization, increasing length of the tube, reducing extrusion force and saving energy, but there are some defects which generate in the production process, for instances, inclusion, lamination and eccentric, et al. In this investigation, basing on software platform MSC.SuperForge, a multi-stage simulation technology of Finite Volume Method (FVM) is usd to simulate Upsetting-Perforating extrusion for BFe10-1-1 alloy tube producing adopting hollow ingot. The flow law, the field of temperature, stress and strain of the deforming materials are obtained. The closing process of the internal wall of the hollow ingot is got, which can be used to explain the phenomenon that the oxide skin which belong to the internal wall of hollow ingot occludes into the wall of extruded tube. The upsetting ratio affects the formation of these defects obviously. The defects in the wall of hot-extrued tube can be avoided by modificating the strcture of hole forming pin.更多还原