皮尔格等温轧制镁合金管材成形新工艺理论与调控机制研究

This paper presents a new theory and technology of pilger isothermal roll forming in order to solve the problems of magnesium alloy pipe that product quality and performance with existing processing methods are not stable and the key technology of forming process is unreasonable. By combing theoretical analysis, numerical simulation and experimental verification, this paper studies the process of pilger isothermal rolling of magnesium alloy tube to make the structure uniformity, eliminate the defects and establish the reasonable rolling theory and technology. The changes of microstructure and defects in the deformation process are mainly studied and determine its genetic characteristics and inheritance relationship. The relationship between the critical stress state and temperature, deformation and deformation velocity is revealed. The relation between void closure, critical stress state of inclusion cracking and temperature, deformation, deformation velocity is revealed. The damage criterion of material cracking under complex deformation is established. The ability to transform the defects with different shapes and scales and acceptance tolerance of grain size and shape difference under rolling forming process are determined. The tolerance of organization and defect under each link in the forming process is determined. The rolling process of magnesium alloy tube and the forming process parameters are optimized, the forming quality is controlled, the defects are eliminated, the grains are refined and the mechanical properties of the products are improved. In the end, the forming theory and process of pilger isothermal rolling magnesium alloy tube were established, and the processing technology of high performance magnesium alloy pipe was improved.

针对现有镁合金管材加工方法的产品质量与性能不够稳定，成形过程关键技术不合理等问题，提出一种新的皮尔格等温轧制成形的理论和工艺技术。采用理论分析、数值模拟和实验验证有机结合的方法，研究皮尔格等温轧制镁合金管材过程，确定组织均匀化、消除缺陷及对应调控方法，建立合理的轧制理论与工艺。重点研究变形过程中组织、缺陷的变化规律，确定其遗传特性和继承特性；揭示空洞闭合和夹杂开裂临界应力状况与温度、变形量和变形速度之间的关系；建立复杂变形状态下材料开裂的损伤准则；探明轧制成形工艺对不同形态、尺度的缺陷改造能力以及晶粒尺寸和形态差异度的接受容限，确定成形过程各环节对组织、缺陷的容限准则；实现镁合金管材轧制工艺创成，优化成形工艺参数，控制成形质量，消除组织缺陷，细化晶粒，提高产品的机械性能。最终建立皮尔格等温轧制镁合金管材成形理论与成形新工艺，提升我国高性能镁合金管材的加工技术。

本项目进行了皮尔格等温轧制镁合金无缝管材成形新工艺理论与协同调控机制研究:.1.建立材料内部空洞型缺陷的演变与外场应力应变的数学模型，研究金属镁变形机理。.2.研究空洞在多道次连续轧制成形过程中的演变规律及塑性变形的不均匀性对固态相变动力学的影响。研究空洞的大小及排布方式对于镁的性能的影响。.3.研究典型材料导致第一次晶粒快速长大的临界应变量和织构大晶粒对应的应变量，合金元素和第二相成分在加热过程中的变化规律，探讨控制晶粒长大的加热方法，非均匀变形组织固态相变的协调和控制机制及宏、微观偏析之间的耦合变化，成分偏析的遗传对异质相遗传的影响及温度和速率对于镁合金晶粒长大和动态再结晶的变化机理。.4.揭示异质相遗传的起始行为和非均匀晶粒的变形规律及其协调条件，提出筒形坯料原始晶粒组织的可调整窗口和容限以及遗传特性，非均匀变形组织固态相变的协调和控制机制及晶粒组织和变形的耦合不均匀性对轧制过程相变产物和相变量的影响。.5.构造满足皮尔格等温轧制管材要求的工艺参数，提出轧件控性的建模方法。建立周期送进量m值计算模型及Q值计算模型，实现了工艺参数的定量研究。.6.以控形为目标，提出典型轧件尺寸精度的评估方法，揭示金属矢量流动和工艺参数之间的关系，研究工艺参数对形状精度和形状缺陷的作用规律。.7.针对各个计算环节所设计的算法流程进行编程，软件调试，同时针对各种典型工况，对软件进行计算性验证，对比新模型的优越性。.8.研究工艺参数对最终晶粒状态的影响规律，开展多道次往复轧制变形过程数值模拟和实验研究，探讨微观组织的演化规律；研究建立典型材料的开裂条件，提出避免和减少开裂可能性的轧制工艺参数范围。提出周期式冷轧成形方式，改善冷轧镁合金管成形中出现缺陷的现象。.9.研究宏、微观偏析之间的耦合变化，成分偏析的遗传对异质相遗传的影响。对成品管进行微观组织实验及模拟，实现宏、微观的验证。