提高焊核区细晶结构稳定性的搅拌摩擦焊接新方法及其机制

As a relatively new joining technique with advantages like high efficiency, low cost, environment-friendliness, friction stir welding (FSW) has found its broad applications in industries including airplanes, rockets, railway vehicles, and so on. However, the fine grain structure in the weld nugget (WN) is very susceptible to grain coarsening during post weld heat treatment, leading to potentially severe reduction of mechanical properties. This is already one of the critical issues in the field. High volume fraction of stable small-sized second phase particles are proved to be able to provide high enough Zener pinning effect to stabilize grain structure. In the present study, a modified FSW technique with using welding wire will be developed based on the traditional FSW. Welding wire is made from metal Me (Ti, Mn, or Zr) powder. Taking advantage of FSW features of high strain rate, severe strain, and localized temperature increase, high volume fraction of stable aluminide (TiAl3, MnAl6, or ZrAl3) nanoparticles will be produced in situ in the WN during FSW, which will fulfill the objective of stabilizing fine grain structure in the WN. The formation mechanism of in situ aluminides, their macro-/micro- distribution in the nugget, and the grain structure stabilization mechanism by these in situ particles will be studied, for further optimizing the process of this modified FSW technique and improving the welding wire fabrication. This research will provide solid fundamentals for the future application of this modified FSW.

搅拌摩擦焊接(FSW)技术在飞机、火箭、铁道车辆制造等方面已有广泛应用。以其高效率、低成本、环保节能等特性，被认为是最有前景的焊接技术之一。但是焊核细晶结构在焊后热处理过程中极易形成粗大晶粒而导致性能大幅下降，这已成为本领域研究人员非常关注的关键技术难点和科学问题。高体积分数小尺寸的稳定第二相粒子被证明对晶界有强钉扎作用(Zener Pinning)，从而能有效稳定晶粒结构。本项目提出一种能提高焊核区细晶结构稳定性的FSW新方法。此方法在待焊铝材中加入由金属Me（Ti、Mn或Zr）粉制备的焊料，利用FSW高变形速率、强变形、局部瞬时高温等特性，在焊接过程中原位生成高体积分数金属铝化物纳米粒子，从而提高焊核细晶结构热稳定性。并进一步解析铝化物粒子的原位自生机制、宏微观分布规律和对晶粒结构稳定化作用机制。这些研究将为新型FSW的工艺优化和焊料制备方法改进提供科学指导，为其推广应用提供理论基础。

搅拌摩擦焊接(FSW)技术在飞机、火箭、铁道车辆制造等方面已有广泛应用，以其高效率、低成本、环保节能等特性，被认为是最有前景的焊接技术之一。但是，焊核细晶结构在焊后热处理过程中极易形成粗大晶粒而导致性能大幅下降。针对这一问题，本项目利用搅拌摩擦焊高变形速率、强变形、局部瞬时高温的几个特性，开发出使用焊料的搅拌摩擦焊接新方法，分别采用三种方法将焊料引入搅拌摩擦焊接中。成功获得无缺陷焊缝的同时，实现了在焊接过程中外加金属颗粒的弥散化以及与铝基体原位反应生成高体积分数金属铝化物粒子。. 研究表明焊接过程金属间原位化合反应是焊接高温引起的扩散型固态相变，材料流动的机械作用大大加速了扩散和相变的进行。另外，由于搅拌摩擦焊接过程中材料宏观流动剧烈而微观流动有限，微米级金属颗粒与纳米级金属间化合物颗粒在焊核区的弥散行为存在差异。微米级外加金属颗粒随着焊接道次数的增加，弥散程度明显加剧。在多道次焊接后由原始的聚集状态转变为在焊核区弥散分布状态，而纳米粒子大多仍呈聚集状态。热处理实验结果表明，应用优化的焊接工艺，焊核区异常晶粒长大现象得到明显的抑制作用。第二相颗粒浓度高的区域，晶粒正常长大程度也低于无第二相颗粒或颗粒浓度较低的区域。原位生成的第二相粒子对晶粒结构起到明显的钉扎作用。. 本项目的研究提供了一种提高搅拌摩擦焊核区细晶结构稳定性的新方法，同时明确了焊料状态、焊接道次数、旋向组合等工艺对原位自生粒子宏微观分布、原位自生反应速度、及晶粒结构稳定化效果的作用及原因，为这种新型FSW的工艺优化和焊料制备方法改进提供了科学指导，为其推广应用提供了理论基础。.