中国激光, 2011, 38 (4): 0403001, 网络出版: 2011-03-24   

殷瓦薄板高速激光焊接的热裂纹敏感性

Hot Tearing Susceptibility of High Speed Laser Welding Invar Sheet
作者单位
上海交通大学上海市激光制造与材料改性重点实验室, 上海 200240
摘要
以2.2 m/min激光扫描速度,采用对接和搭接两种方式高速焊接0.7 mm薄板殷瓦合金。借助金相显微镜和扫描电子显微镜观察焊缝显微组织,讨论焊缝中心的热裂纹形成机理,对比分析不同接头形式的热裂纹敏感性。实验结果显示,殷瓦合金的高速激光焊缝为铸态单相奥氏体树枝晶。对接焊缝中心出现热裂纹,而搭接焊缝未发现热裂纹。分析认为,在树枝晶凝固最后阶段,焊缝两侧树枝晶粒的大角度晶界能γgb大于2倍液态薄膜固/液界面能γsl,液态薄膜完全桥接需要临界过冷度ΔTb。殷瓦合金散热系数低,过冷度不足,焊接残余拉伸应力δr将导致液态薄膜开裂。对接时容易出现热裂纹。而搭接时开裂的液态薄膜有上层液态金属流入补充,能有效降低焊缝的热裂纹敏感性。
Abstract
0.7 mm thickness invar alloy sheet is welded at 2.2 m/min laser scanning speed by using butt and lap joint. Microstructure analysis is conducted by optical microscope and scanning electric microscope. Hot tearing mechanism and susceptibility of butt and lap joint are discussed, respectively. Results show that the weld metal is composed of as-cast single phase dendrite austenite. Some hot tearing is in the weld center of butt joint, but none is in the lap joint. At the last solidifying stage of impinging dendrite, generally, dendrite grain boundary energy γgb is always two times larger than liquid/solid interfacial energy γsl of liquid film. The liquid film coalescence will not occur until adequate undercooling ΔTb, which results in hot tearing of butt joint under welding residual tensile stress. However, the remained liquid of upper weld pool can flow down and fill into torn liquid film, then lap joint has a lower hot tearing susceptibility.

倪加明, 李铸国, 吴毅雄. 殷瓦薄板高速激光焊接的热裂纹敏感性[J]. 中国激光, 2011, 38(4): 0403001. Ni Jiaming, Li Zhuguo, Wu Yixiong. Hot Tearing Susceptibility of High Speed Laser Welding Invar Sheet[J]. Chinese Journal of Lasers, 2011, 38(4): 0403001.

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