采用高功率光纤激光对铜铪合金和低碳钢进行焊接,基于熔池快速凝固保留小孔法对比研究了小孔的形貌特征。结果表明:两种材料中均可保留小孔,孔口直径明显比光斑直径大;在铜铪合金中,孔口形貌呈现为大小圆环相交的“葫芦”状,位于焊接前方的小圆环直径与光斑直径相当,大圆环的直径在毫米量级;在低碳钢中可保留小孔的激光出光时间极短,其熔池凝固时间较长,且仅保留了小孔的大圆环区域。进一步的分析表明,焊接过程中的孔口形貌可分为激光直接作用区(直径与光斑直径相当)和蒸气压力维持区(直径在毫米量级);在数值模拟中构建激光焊接热源模型时应参考小孔的形貌特征。

In this study, the Cu-Hf alloy and low carbon steel are respectively welded using a high-power fiber laser. The morphological characteristics of keyholes obtained by freezing and preserving the keyholes in a molten pool are compared. The results show that the keyholes can be retained in both materials, and the diameter of a keyhole is obviously greater than that of a spot. The shape of the keyhole retained in the Cu-Hf alloy is similar to that of a “gourd” with the intersection of big and small rings. The diameter of the small ring located in front of the welding direction is equivalent to that of the spot, and the diameter of the large ring is in the order of a millimeter. In low carbon steel, the laser output time to retain a keyhole is very short, the solidation time of the molten pool is long, and only the large circle area of the keyhole can be retained. Further analysis shows that a keyhole morphology can be divided into two parts: the laser direct-action area and vapor pressure maintaining area. In numerical simulations, the morphological characteristics of a keyhole must be considered when building a suitable heat source model for laser welding.