【作者】 许飞；

【导师】 李晓延； 巩水利； 陈俐；

【作者基本信息】 北京工业大学 ， 材料加工工程， 2009， 硕士

【摘要】 铝合金密度低,耐腐蚀性能好,抗疲劳性能高,以及具有较高的比强度和比刚度,是飞机结构的理想材料。激光焊接具有能量密度高、焊接变形小、生产效率高等优点,利用激光填丝焊和复合焊接技术可以降低对接装配精度、改善焊缝冶金特性、提高接头机械性能等。本文针对1.2mm厚5A06铝合金和3mm厚5A90铝锂合金激光填丝焊以及3mm厚5A90铝锂合金激光电弧复合焊接技术展开研究,为航空用铝合金的推广应用提供数据参考。激光填丝焊接时,通过焊接工艺参数(送丝速度、激光功率、焊接速度和送丝几何位置)的优化控制焊缝背宽比(焊缝的背面宽度与表面宽度之比),从而控制焊缝的成形质量。当其它优化工艺参数固定时,光丝间距必须严格控制在+0.2～+1.5mm范围,而激光复合焊由于引入电弧,两热源产生“协同效应”,对光丝间距的要求可以放宽在0～6mm范围内。优化的复合焊接工艺可以增加焊缝熔宽和熔深,但是在其它参数一定时,只有当焊接电流超过一定阈值,复合焊的优势才能充分体现。在激光填丝焊和复合焊接主要工艺参数中,优化送丝速度的选择也与输入功率有关,且母材板厚较小有利于填丝焊优化送丝速度的提高及其范围的扩大。激光填丝焊和复合焊均能有效改善激光焊接的间隙适应性,其最大间隙容许裕度均可达0.9mm以上,是激光焊的4～6倍。铝合金的主要焊接缺陷是成形不良和气孔,母材板厚较大时,焊缝中气孔数量增多且尺寸增大趋势加剧,但通过严格的焊前表面处理,并实现全熔透焊接均能获得成形较好且基本无气孔的焊缝。另外,利用高速摄像监测激光填丝焊接过程中的熔滴过渡方式,发现光丝间距+1mm时的表面张力过渡比光丝间距+0.3mm时的颗粒过渡稳定性更高;而复合焊时呈现一脉一滴的射滴过渡方式,焊接过程也相对平稳。在激光填丝焊和复合焊接过程中热源和物质的相互作用呈现周期性变化。激光填丝焊可以提高材料对激光的吸收率,增加焊缝熔宽,提高接头的拉伸性能,如与激光焊接头相比,5A06铝合金激光填丝焊接头抗拉强度提高10%左右。激光填丝焊和复合焊均有利于铝锂合金焊缝硬度的均匀化。更多还原

【Abstract】 Aluminum alloy is an ideal material for aerocraft structure, because of its light weight, superior strength-to-weight ratio, and excellent corrosion resistance. Laser welding with higher energy density can offer remarkable advantage over conventional fusion welding processes, such as minimal component distortion and high productivity. Laser welding with filling wire and laser-arc hybrid welding are new technologies, which can reduce assembled precision of butt-joint, improve metallurgic characteristic of weld bead, and enhance joints’mechanical property. In this paper, the experiments of 5A06 aluminum alloy with 1.2mm thickness and 5A90 aluminum-lithium alloy with 3mm thickness by laser welding with filling wire, and the 5A90 alloy by laser-arc hybrid welding have been investigated, which could offer data reference for joint technology of aluminum alloy in aerospace.While laser welding with filling wire, the back width to surface width ratio and the weld shaping quality are controlled by optimizing welding parameters, such as the wire feed speed, laser power, welding speed and geometry position of filling wire. With other optimized welding parameters fixed, the distance (D) between laser and wire must be controled in the range of +0.2～+1.5mm. While laser-arc hybrid welding, D is allowed to from 0mm to 6mm because of the“synergistic effect”with combining laser and arc. The optimized hybrid welding parameters can increase weld width and weld penetration. However, the advantage of hybrid welding will be sufficiently represented when the welding current exceeds some threshold value with constant other parameters. For the welding parameters of the two welding methods, the selecting wire feed speed is relative to the input power. Besides, the thinner aluminum alloy sheet demands higher wire feed speed and boarder wire feed speed range.The gap tolerance for laser welding is improved distinctively by laser welding with filling wire and laser-arc hybrid welding, and the maximal accommodable gap is enlarged above 0.9mm, which is 4～6 times wider than laser welding. The primary defects of welding aluminum alloy are defective weld appearance and porocity. The thicker aluminum sheet would cause more and larger pores in weld bead. However, the weld bead with good appearance and inside quality could be obtained by strict surface treatment and complete-penetration welding. While laser welding with filling wire, the droplet transition modes were inspected by high-velocity-camera. It was found that the surface tension transition of D=+1mm was more stable than the grain transition of D=+0.3mm. The shooting-droplet transition for hybrid welding, which was presented one droplet per pulse, was also comparatively stable. For the laser welding with filling wire and hybrid welding, the interaction between heat reservoir and material expressed periodic changing.The laser welding with filling wire could increase material’s absorptivity, weld width, and joint’s tensile property. For example, the tensile strength of joint with filling wire is increased nearly 10% than the joint by laser welding. Besides, the microhardness of Al-Li alloy weld bead is tended toward uniform by the laser welding with filling wire and laser-arc hybrid welding.更多还原