焊接工艺参数对锆合金薄板YAG激光焊接气孔形成的影响及控制机理分析

Effect of Welding Processing Parameters on Porosity Formation and Prevention Mechanism Analysis of Zircaloy Sheet by YAG Laser Welding

以Zr-4和N18为研究对象,采用YAG激光焊接设备,通过抛切焊缝断面统计气孔数量,并观察焊缝中气孔位置和形貌,研究了非熔透性焊接过程中激光脉冲电流、脉冲宽度、离焦量等工艺参数以及脉冲激光调制对锆合金密集焊缝激光焊接气孔形成规律的影响。结果表明:在锆合金YAG激光非溶透性焊接过程中,气孔的形成主要源于焊接过程中匙孔的不稳定塌陷所形成的工艺型气孔,在熔池中气泡逸出熔池的速率低于熔池金属凝固速率的情况下会产生气孔。在满足焊缝熔深1.0 mm的情况下,随着激光脉冲电流、脉冲宽度的增加,气孔出现的几率逐步增加;随着离焦量的增加,气孔出现的几率逐渐减小;相比未分段编程模式,采用分段编程、电流缓降、降低焊接速度的方式,使焊缝气孔率明显降低,气孔尺寸有效控制在0.5 mm以下。

The porosity in the welded seam can be generated easily during the YAG laser nonpenetration welding of zircaloy sheet, which affects the quality of welding. This research used Zr-4 and N18 as the objects for the welding experiment. The method of cutting cross-section of weld seam was used to analyze the porosity number and observe the morphology and location of porosity in the weld. The effects of process parameters including laser pulse current, pulse width, defocusing distance and laser pulse modulation on porosity generating were discussed. The results show that the generating of porosity is due to the unstable collapse of the keyhole in the process of YAG laser nonpenetration welding of zircaloy. The porosity would be formed when the speed of bubble escaping from the weld pool is lower than that of melting metal solidifying. Under the condition of 1.0 mm penetration welding, the results also show that with the increase of laser pulse current and pulse width, the porosity number presents a gradual increase. With the increase of defocusing distance, the porosity number shows a gradual decrease. Compared with non-segmented programming model, this research uses such measures as segmented programming, slowing down the current and reducing welding speed to obtain the relatively lower porosity number, and the pore size can be controlled below 0.5 mm effectively.