线性摩擦焊接热力耦合作用周期性脉冲效应及其对接头组织性能影响研究

Linear friction welding(LFW) is mainly applied to welding of the same or dissimilar materials with noncircular section, and it is the key manufacturing technology of blisk in aero engine. Compared with the other friction welding processes, the reciprocating friction motion in linear friction welding process results in the thermo-mechanical coupling with the typical characteristics of periodic pulse, which is characterized by 3 aspects such as the pulsed heat input, the alternative friction direction and the periodic oxidation of local friction interface, has important influences on the control of microstructures and properties of the joint and the prevention of welding defects. In this project, by taking the typical materials used in aero engine as base metal, the transient mathematical model of linear friction welding according with its physical nature will be founded, the periodic pulsed thermo-mechanical coupling will be studied by numerically simulating the friction heat production, welding thermal process, plastic flow field and stress-strain field in the joint in linear friction welding process, and the influence mechanism of the periodic pulsed thermo-mechanical coupling on the microstructure evolution of thermo-mechanically affected zone will be also analyzed. At last, the effect law and mechanism of the periodic pulsed thermo-mechanical coupling on linear friciton welding process, microstructure and properties of the joint and welding quality will be revealed. The studies in this project will not only reveal the characteristics and physical nature of the thermo-mechanical coupling in linear friction welding process, improve and perfect the basic theory of linear friction weling, and has the certain significance in science, but also improve the development of the manufacturing technology of blisk of aero engine in China.

线性摩擦焊接主要用于非圆截面同种或异种材料构件的焊接，是航空发动机整体叶盘制造的关键技术。与其他摩擦焊接工艺相比，往复摩擦运动使得线性摩擦焊接热-力耦合具有典型的周期性脉冲特征，形成了脉冲性热输入、交变的材料受力方向和周期性氧化的局部摩擦界面三方面特点，对接头组织性能控制以及缺陷防控产生重要影响。本项目以典型航空材料线性摩擦焊为例，采用热-力耦合有限元方法，建立符合线性摩擦焊接物理本质的数理分析模型，分析线性摩擦焊接产热功率、热过程、摩擦界面及其附近的应力-应变场和塑性流变场等热力耦合过程，并研究周期性脉冲热力耦合对接头热力影响区组织演变的影响机制，揭示周期性脉冲热力耦合对线性摩擦焊接过程及接头组织性能和质量的影响规律和机理。项目的研究不仅揭示线性摩擦焊接过程中热力耦合的特点和本质、完善线性摩擦焊接基础理论，更将促进我国航空发动机整体叶盘制造技术水平的进步和提高。

线性摩擦焊接技术是航空发动机整体叶盘制造的关键技术。与其他摩擦焊接工艺相比，往复摩擦运动使得线性摩擦焊接热-力耦合具有典型的周期性脉冲特征，形成了脉冲性热输入、交变的材料受力方向和周期性氧化的局部摩擦界面三方面特点。本项目考虑焊接过程中库伦与剪切的混合摩擦，根据线性摩擦焊接过程热-力耦合特点，建立线性摩擦焊接热力耦合数值计算模型，数值分析焊接温度场、塑性流变场及应力应变场的演变。.线性摩擦焊接温度场的计算结果表明，初始摩擦阶段摩擦界面温度场分布不均匀，沿振动方向在两端交替出现；过渡阶段摩擦界面温度趋于一致，高温区域从中心产生；稳定摩擦阶段界面温度则保持不变。摩擦初始阶段基本无塑性金属的流动，当摩擦界面材料达到塑性状态时，摩擦界面上会形成两个具有流动中心的材料流动区域，流动区域的塑性材料的由中心点向四周流动，最终界面流场呈“X”状。.线性摩擦焊接过程中的应力演变不仅受到热、塑性材料流动的影响，还受到焊接压力的影响。摩擦过程中的应力演变受到交变力的作用应力随时间的变化存在周期性波动。摩擦初期沿着振动方向在工件两端交替出现高应力区，并不断扩大形成一个中心高应力区。保压阶段应力从工件机械约束的上方开始逐渐向工件内部中心释放。顶锻压力撤除后，接头内整体压力降低，低应力区域仍由工件中间部位向沿垂直于振动方向向两端扩展。.在整个焊接过程中接头区域不同方向上存在压应力和拉应力，Z方向上（摩擦压力方向）始终受到压应力。X、Y方向的应力则受焊接时间及焊接区域影响。随焊接时间的增加，中心区域拉应力逐渐增大而两端的压应力不断变小。冷却过程中基本上以摩擦压力越高则应力水平越高的规律变化。振幅的变化对应力演变的影响相对摩擦压力与顶锻压力较小，在振幅为2.92mm时接头的应力水平最低。.项目的研究揭示了线性摩擦焊接热力耦合物理机制、完善了线性摩擦焊接基础理论，更将促进我国航空发动机整体叶盘制造技术水平的进步和提高。