激光深熔焊小孔型气孔的产生及其防治

小孔型气孔的产生是未穿透激光深熔焊的一个严重问题，它是由剧烈的小孔扰动所导致的，与传统冶金型气孔(H2或CO气孔等)的产生机制不同，采用传统冶金型气孔抑制措施无法有效消除该类气孔的产生。针对3～5 mm薄板的CO2激光深熔焊接，研究了脉冲调制对气孔的抑制效果及其机制。实验发现，脉冲频率低于50 Hz时，焊缝气孔随着频率的增加不断减少;当脉冲频率处于50～150 Hz的范围内，基本上可以消除小孔型气孔的产生。通过检测激光焊接过程中等离子体光辐射信号的波动可以反映小孔的稳定性，结果证明，合适频率下的脉冲调制激光焊接，由于有稳定小孔的作用，从而抑制了小孔型气孔的产生。

Formation and Prevention of Keyhole-Induced Porosity in Deep Penetration Laser Welding

Keyhole-induced Porosity formation is a severe problem in partial penetration laser welding. Different from the mechanism of traditionally metallurgical pores (e.g. H2, CO pores), the porosity is mainly caused by instability of capillary keyhole and traditional methods employed to prevent metallurgical pores are ineffective in suppressing keyhole-induced porosity. for partial penetration laser welding of 3～5 mm sheet plates the method and mechanism of porosity prevention by pulse modulation was investigated. The experimental results reveal that pulse modulated laser welding can effectively suppress keyhole-induced porosity formation. The variation of porosity ratio as pulse frequency has regularity, that is, the porosity ratio decreases with increasing pulse frequency under 50 Hz, and remains in low level when pulse frequency lies in a wide range of 50～150 Hz. In addition, the optical signal of plasma was detected in pulse modulated laser welding to explain the mechanism of porosity prevention. The results reveal that the porosity ratio varies well with the standard deviation value of plasma signal, which indicates that the mechanism of porosity suppression lies on the fact that the pulse modulated laser welding under adequate frequency can make keyhole stable.