镁合金激光焊接过程中气孔形成的原位观察和机理研究

In Situ Observation and Mechanism Research of Pores Formation in Magnesium Alloy Laser Welding

通过自行设计的显微观察试验台对镁合金激光焊接过程中熔池内的气泡形成、长大过程进行原位观察,并采用SEM对形成的气孔的微观形貌和元素分布进行了观察检测,分析了熔池内气泡形成的机理过程,讨论了焊接速度和激光功率对气孔率的影响。结果表明：熔池内气泡形成长大主要分为三个阶段,分别是气泡形成阶段、气泡形核点增加阶段、气泡的聚合长大阶段。气孔的内外侧成分不同,内侧主要为Mg金属,而外侧为Mg O、Al2O3和Mg Al2O4等镁铝氧化物。焊接速度和激光功率都会对气孔率产生重要影响,其中气孔率随着焊接速度的提高而降低,随着激光功率的增加先升高后降低。

In situ observation of pore formation and aggregation was carried out by using self designed microscopic observation table, and the microstructure and element distribution of the porosity were studied by SEM. The mechanism of bubble formation in weld pool was analyzed, and the influence of welding speed and laser power on porosity was discussed.The results show that there are three steps during the pore formation and aggregation in weld pool, which are bubble formation stage, bubble nucleation site increasing stage, bubble aggregation and growth stage. There is chemical composition difference between the inside and outside of pores, the main chemical composition of the inner side is Mg metal, while the main chemical composition of the outer side is Mg O, Al2 O3 and Mg Al2 O4 oxides. The welding speed and laser power have a great effect on the porosity. With the increase of welding speed, the porosity decreases, and with the increase of laser power, the porosity increases firstly and then decreases.