The 2024 aluminum alloy is used extensively in the aircraft and aerospace industries because of its excellent mechanical properties. However, the weldability of 2024 aluminum alloy is generally low because it contains a high number of solutes, such as copper (Cu), magnesium (Mg), and manganese (Mn), causing solidification cracking. If high speed welding of 2024 aluminum alloy without the use of filler is achieved, the applicability of 2024 aluminum alloys will expand. Grain refining is one of the methods used to prevent solidification cracking in weld metal, although it has never been achieved for high-speed laser welding of 2024 aluminum alloy without filler. Here, we propose a short-pulsed, laser-induced, grain-refining method during continuous wave laser welding without filler. Bead-on-plate welding was performed on a 2024- T3 aluminum alloy at a welding speed of 1 m min^-1 with a single mode fiber laser at a wavelength of 1070 nm and power of 1 kW. Areas in and around the molten pool were irradiated with nanosecond laser pulses at a wavelength of 1064 nm, pulse width of 10 ns, and pulse energy of 430 mJ. The grain-refinement effect was confirmed when laser pulses were irradiated on the molten pool. The grain-refinement region was formed in a semicircular shape along the solid– liquid interface. Results of the vertical section indicate that the grain-refinement region reached a depth of 1 mm along the solid–liquid interface. The Vickers hardness test results demonstrated that the hardness increased as a result of grain refinement and that the progress of solidification cracking was suppressed in the grain refinement region.

采用Gleeble-1500 热模拟试验机对6063铝合金进行热塑性实验, 确定了合金的脆性温度区间, 并用 SEM、EDS 等测试手段分析热裂纹的产生原因。研究结果表明, 综合Rm-T曲线和Z-T曲线可得到6063铝合金母材的脆性温度区间为460～620 ℃, 表明其具有较高的焊接热裂纹倾向。热输入量增大会使材料热塑性表现为先减小再增大的变化趋势, 热输入3.0 kJ/cm时试样的热塑性达到最低。热输入2.5 kJ/cm下, 在焊缝中没有观察到热裂纹; 热输入增大至3.5 kJ/cm, 试样的焊接热塑性明显增加, 呈现出朝焊缝中心发生纵向开裂的现象; 热输入3.0 kJ/cm下, 裂纹依然表现为从焊缝中心往纵向延伸开裂, 同时在母材的部分区域中形成许多断续分布的微坑。

随着轻量化、结构功能一体化的强劲需求, 高强铝合金复杂精密零件在航天航空等领域应用广泛, 但因其焊接性能和铸造性能差, 传统加工方法难以制备。激光选区熔化成形(SLM)技术是制备该类零件的最有前景的新方法。高强铝合金对激光吸收率低、热导率高、易氧化、含大量易烧损合金元素, 有很强的热裂倾向, 成形难度极大, 因此目前其SLM成形技术远落后于其他材料。但是由于其广阔的应用前景, 近几年发展迅速。总结了国内外高强铝合金激光选区熔化成形的研究现状、发展趋势及存在的主要问题。

2198-T851铝锂合金是一种密度低、比强度高、耐腐性能和低温性能良好的新型高强铝锂合金。采用6 kW光纤激光器对1.8 mm厚的2198-T851铝锂合金薄板进行对接焊。研究填充Al-Cu系2319焊丝时焊接工艺参数对焊缝成形与焊接热裂纹的影响，观察裂纹形貌，测试接头显微硬度与力学性能，并观察分析断口形貌。结果表明，激光焊接2198铝锂合金填充2319铝铜焊丝时，在合适的激光功率、焊接速度和送丝速度条件下，可获得成形良好、无热裂纹的焊缝，接头抗拉强度272 MPa，伸延率1.6%，断裂发生在焊缝区，呈现韧性断裂特征。

激光焊接过程中较快的冷却速度可能会加剧凝固热裂纹的发生。目前对于激光焊接过程中凝固热裂纹敏感性的系统研究还较少，如何准确测量焊接凝固热裂纹发生的临界应变和温度是获得热裂纹敏感性数据的关键。利用基于高速高倍在线摄像的U型热裂纹实验，捕捉到激光焊接过程中凝固热裂纹发生的瞬间，并通过跟踪测量热裂纹尖端附近两点的位移变化获得凝固热裂纹发生的临界应变；同时，在焊接过程中采用在线观察热电偶投入法对焊接熔池后端的温度变化进行了测量。通过改变U型热裂纹实验的拉伸载荷，获得不同温度下热裂纹发生时的临界应变，从而构建表征凝固热裂纹敏感性的韧性曲线。