【作者】 刘敦敦；

【导师】 徐向阳；

【作者基本信息】 北京交通大学 ， 材料加工工程， 2012， 硕士

【摘要】 搅拌摩擦焊具有接头质量好,应力变形小,疲劳强度高等优点,在航空、航天、船舶、车辆等载运工具制造技术领域已得到实际应用。但是热处理强化铝合金搅拌摩擦焊接头的过时效软化问题仍比较突出,通过工艺试验的方法来改善接头承载能力的效果还不明显。本文采用数字图像相关技术对6061-T6铝合金搅拌摩擦焊接头的非均匀变形行为及其机理进行了研究,对拉伸载荷作用下接头的力学响应进行了有限元模拟,对接头几何尺寸对应力应变分布规律的影响进行了分析,为优化搅拌摩擦焊工艺和改善接头承载能力提供了科学依据。拉伸载荷作用下6061-T6铝合金搅拌摩擦焊接头表现出显著的非均匀变形的特征,接头变形随载荷增大从均匀弹性变形向非均匀塑性变形转变,从接头前进侧应变集中向后退侧应变集中转变,其非均匀变形的规律取决于接头各区屈服强度大小及应变硬化能力的相对关系。采用常规的硬度测试和先进的数字图像相关应变测试结果相结合的方法,可以更为准确地确定搅拌摩擦焊接头各区的位置、尺寸、形状。基于等应力假设和全场应变测试结果,可以获得接头各区局部的力学性能和应力应变关系。在此基础上,实现了对6061-T6铝合金搅拌摩擦焊接头拉伸载荷作用下力学行为的有限元模拟,模拟结果与实验结果具有较好的一致性。采用有限元模拟的方法研究了接头各区几何尺寸形状变化对拉伸载荷作用下6061-T6铝合金搅拌摩擦焊接头的力学响应。随着接头热影响区、热塑性影响区和焊核区尺寸的减小,母材的拘束作用增强,热影响区、焊核区、热塑性影响区的应力应变减小,接头承载能力得到提高。更多还原

【Abstract】 Friction stir welding has many advantages such as good joint quality, low residual stress and distortion, and high fatigue strength, so it has been used in the manufacturing of aeronautics, astronautics, shipbuilding and vehicle. But, to heat treatment strengthening type aluminum alloy, over-aging still is a severe problem up to now and welding processing optimization has still not evident effect to the improvement of load bearing ability.In this paper, the heterogeneous deformation behavior and mechanism of friction stir welding joint of6061-T6Aluminum alloy by digital image correlation. The finite element simulation of mechanical response of joint was conducted under tensile load. The influence of joint geometry on the stress and strain was analyzed. Science foundation was established for the optimization of friction stir welding processing and the improvement of the load bearing ability of joint.The position and geometry of micro-zone of friction stir welding joint can be correctly identified by the combination of traditional micro hardness measurement and strain measurement of advanced digital image correlation. Based on iso-stress condition and the full stain results, the local mechanical properties and stress-train relation can be obtained. The finite element simulation of mechanical behavior of friction stir welding joint of6061-T6Aluminum alloy was realized under tensile load. The results of the simulation and experiment have good similarity.The influence of the geometry variation of local micro-zone of friction stir welding joint on mechanical response under tensile load was studied by finite element simulation. With the decreased the sizes of heat affect zone, thermally-mechanical zone, and welding nugget, the constraint of the base material is increased, the stress and strain of the heat affect zone, thermally-mechanical zone, and welding nugget are decreased. As a result, the load bearing ability of friction stir welding is improved.更多还原