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sγl,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rδ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。
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.
出处
《中国激光》
EI
CAS
CSCD
北大核心
2011年第4期76-80,共5页
Chinese Journal of Lasers
基金
国家重大资助项目(2009DFB50350)
上海市重点资助项目(ZX08089)资助课题
关键词
激光技术
激光焊接
热裂纹机理
树枝晶桥接
殷瓦合金
laser technique
laser welding
hot tearing mechanism
dendrite crystal impinging
invar alloy
