硕士学位论文
TC4钛合金搅拌摩擦焊流场及动态再结晶过
程数值模拟
NUMERICAL SIMULATION OF MATERIAL FLOW AND DYNAMIC RECRYSTALLIZATION OF FRICTION STIR WELDING OF TC4
TITANIUM ALLOY
王小英
哈尔滨工业大学
2012年7月
国内图书分类号：TG453.9 学校代码：10213
国际图书分类号：621.791 密级：公开
工学硕士学位论文
TC4钛合金搅拌摩擦焊流场及动态再结晶过
程数值模拟
硕士研究生：王小英
导师：魏艳红教授
申请学位：工学硕士
学科：材料加工工程
所在单位：材料科学与工程学院
答辩日期：2012年7月
授予学位单位：哈尔滨工业大学
Classified Index: TG453.9
U.D.C: 621.791
Dissertation for the Master Degree in Engineering
NUMERICAL SIMULATION OF MATERIAL FLOW AND DYNAMIC RECRYSTALLIZATION OF FRICTION STIR WELDING OF TC4
TITANIUM ALLOY
Candidate：Wang Xiaoying
Supervisor：Prof. Wei Yanhong
中国铁建和中铁的区别Academic Degree Applied for：Master of Engineering Speciality：Materials Processing Engineering Affiliation：School of Materials Science and
Engineering
Date of Defence：July, 2012
Degree-Conferring-Institution：Harbin Institute of Technology
摘要
搅拌摩擦焊作为一种优质、高效、节能和环保的固相连接方法，在航空、航天、船舶以及车辆制造等领域均有所应用，具有广阔的应用前景。目前，国内外很多学者已经对其进行了一系列实验研究，但是搅拌摩擦焊过程是一个摩擦生热、金属流动和微观组织转变相互耦合共同作用的过程，很多物理过程和机制通过实验手段难以进行直观的观测和研究，而数值模拟的方法不仅降低了成本，而且可以对整个焊接过程进行动态观测，对实际生产过程有重要的参考价值。
本文首先采用数值模拟的方法建立了搅拌摩擦焊的热源模型，使用有限元分析软件MSC.Marc并结合Fortran语言对其二次开发，实现了对焊接过程中各个阶段的温度场模拟。模拟时将焊接过程分为三个阶段，搅拌针扎入阶段、预热阶段以及搅拌头前进阶段。焊接参数选取旋转速度为800r/min，焊接速度为0.6m/s。在此参数下发现当预热时间为15s时，搅拌头周围的温度分布基本达到了焊接所需温度，前进过程中温度场也基本保持稳定状态。从模拟结果可以看出，整体的温度场分布呈椭圆形状，而且是前面较后面的温度分布区域更小、等温线分布更加紧密，这主要与材料的导热系数有关。
随后在温度场模拟的基础上使用有限元分析软件DEFORM-3D对焊接过程中搅拌头周围金属的流动进行了数值模拟，参数选取参考温度场模拟结果。对模拟结果进行整体分析发现搅拌头周围金属的流动整体呈现漏斗状，与搅拌头的形状类似，而且金属的流动关于焊缝中心并不对称。对焊缝沿厚度方向的结果分析得到，节点的流动速度随着离焊缝中心距离的增加成线性增加，并且随着焊缝深度的增加，材料的流动能力逐渐越弱。对焊接参数对金属的流动的影响进行研究发现，旋转速度和焊接速度的大小影响焊接过程的热输入，在一定范围内，随着旋转速度的增加，热输入量增加，金属的流动能力增强，焊缝成形就较好；在一定范围内，随着焊接速度的降低，也表现出类似的特征。
最后对焊接接头焊核区的动态再结晶过程进行数值模拟，得到了不同应变和应变率下焊核区动态再结晶晶粒的变化规律。结果显示随着应变的增大，动态再结晶晶粒平均尺寸减小，动态再结晶分数增大；随应变率的增大，晶粒尺寸逐渐减小。
关键词：搅拌摩擦焊；温度场；金属流动；动态再结晶
Abstract
Friction stir welding (FSW) as an advantageous, efficient, clean and energy conserving solid state joining method, has been widely used in the manufacturing fields of aerospace, ships, airplanes and vehicles. Hitherto, scholars all over the world have already carried out a series of experimental research on it, but as a complicated process combining frictional heating, metal flowing and micro structure transforming, FSW leaves a lot of physical mechanism to be studied and illustrated, which is difficult for experiments. However, numerical modeling method not only lowers the costs, but also provides dynamic observation on the whole welding process, which is a guideline for practical production.
In this paper, FSW heat source model is firstly established by numerical modeling method applying finite element modeling (FEM) analysis software MSC.Marc and secondary development on it using FORTRAN language, fulfilling temperature field modeling in different phases. The whole welding process is divided into three phases, namely needle inserting, preheating and head marching phases. The welding head rotates at a rate of 800r/min, and marches at a spe
ed of 0.6m/s. When preheating time is 15s, temperature around welding head basically reaches the requirement for welding. During the marching phase, temperature field keeps basically stable. From computing results, the shape of temperature field is ellipsoid and in the front area temperature gradient is larger. This mainly concerns the heat conducting property of the material.
Afterword, based on temperature field modeling, the metal flow field around the welding head is simulated numerically using FEM analysis software DEFORM-3D. Parameters are set referring to temperature field modeling results. An analysis on the whole shows that the metal around the welding head flows into a hopper-like zone similar to the shape of welding head, and the flowing field is asymmetrical with the welding seam. By studying the metal flow in different horizontal cross sections, it is found that nod velocities increase linearly with the distance from seam center, and material flowing ability weakens when the welding seam is deepened. By changing the rotating rate and marching speed, heat input is affected. In some range, heat input increases with the rotating rate, leading to a
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