大厚度6061-T6铝合金板搅拌摩擦焊研究

【作者】 罗维；

【导师】 贺地求；

【作者基本信息】 中南大学 ， 机械制造及其自动化， 2010， 硕士

【摘要】 6061-T6铝合金属A1-Mg-Si系可热处理强化铝合金,具有中等强度、良好的塑韧性、耐腐蚀性和挤压性等优点,在航空航天、航海以及轨道车辆等领域被广泛使用。目前针对6061-T6铝合金的传统焊接方法存在易产生焊接裂纹和气孔、焊接变形大、焊缝力学性能不高等问题,大厚度焊接则更加困难。搅拌摩擦焊作为一种新型固相连接方法为6061-T6铝合金厚板焊接提供了一种新的解决途径。搅拌摩擦焊温度场和流场是影响焊缝微观组织和力学性能的重要因素,本文应用流体动力学理论和计算流体分析软件FLUENT构建了不同厚度与不同工艺参数的6061-T6铝合金板搅拌摩擦焊的温度场和流场模型。数值仿真的结果和试验结果基本吻合。在数值仿真的基础上,分别对厚度为22mm和60mm6061-T6铝合金板进行了单道与双道搅拌摩擦焊接试验,在22mm6061-T6铝合金板的焊接试验中,采用了多种焊接速度,结果表明焊接速度对焊缝成形与力学性能有重要影响；在60mm 6061-T6铝合金板的双道搅拌摩擦焊试验中,当旋转速度为1000r／min、焊接速度为80mm／min时,焊接接头强度达到218MPa,为母材的70%。本文对焊缝进行了力学性能测试,并选取显微硬度较低的点进行组织强化相观察,结果表明黑色Mg2Si相是6061-T6铝合金的主要强化相,它的尺寸、形态和含量对焊接头力学性能有较大影响,由焊接热循环引发的强化相重固溶和过时效是导致焊接头力学性能下降的重要原因；对不同厚度的微观组织进行光学和电镜观察,结果表明由于焊接区温度分布沿厚度方向存在较大差异,焊接过程中焊缝组织沿厚度方向的发生了较大改变,是大厚度铝合金板焊接困难和力学性能不高的关键原因。在22mm和60mm 6061-T6铝合金板搅拌摩擦焊接试验基础上,摸索出较为成熟的焊接规律与工艺参数,将搅拌摩擦焊接技术推广到多种厚度6061-T6铝合金板的焊接工艺上,最大焊接厚度达到70mm,并成功应用于大型直流电机铝合金板的焊接。更多还原

【Abstract】 6061-T6 aluminum alloy, a heat-treatable strengthened aluminum alloy of Al-Mg-Si alloys, with the advantages of medium strength, good plasticity and toughness, corrosion and crumpling resistance,has been widely used in the fields of aerospace, marine, railway vehicles,etc. However, due to the problems such as welding cracks and pores, large welding deformation, and low mechanical properties of welds raised in the traditional welding method for 6061-T6 aluminum alloy, the large thickness welding becomes more difficult Friction stir welding (FSW), a new solid-state welding technique,provides a new solution for thick 6061-T6 aluminum alloy plate connection.The temperature field and flow field in the FSW welding process are important factors affecting the micro-structure and mechanical properties of welded joint, hydrodynamic theory and computational fluid dynamics software FLUENT are applied to construct the flow and temperature field model of 6061-T6 friction stir welding. The numerical modeling results are in basic agreements with the experiment results.Based on numerical model, Friction-stir-weld on 6061-T6 in 22mm and 60mm thickness were separately carried out successfully by single and dual pass. Different welding speeds are used in the welding experiment of 22mm 6061-T6 plate, the results show that the welding speed plays an important role in the formation and physical property of the weld joint. In the dual pass weld experiment of 60mm 6061-T6 plate, when the rotating speed is 1000r/min and welding speed is 80mm/min, the weld’s tensile strength reaches 218MPa, is 70% of the base metal. Compare the microstructure and mechanical property of the joint, the result demonstrates that the strengthening phrase’s "Re-solution" and "over-aging" caused by welding thermal cycle are the main reason of the degradation of the physical property of the welding joint. The metallography and electron microscope of the microstructure of the joint with different thickness are observed, the results indicate that due to the huge different temperature distribution in the thickness direction along the welding zone, the morphology and distribution of the microstructure have undergone major changes, which was a big challenge of the aluminum alloy plate welding with large thickness.Base on 22mm and 60mm 6061-T6 aluminum alloy plates friction stir welding, we explored more sophisticated welding process parameters and laws of friction stir welding technique,extended it to the welding process of different thickness 6061-T6 aluminum alloy plate,moreover the maximum welding thickness was raised to 70mm, and successfully applied to the welding of large DC motor aluminum alloy plates.更多还原