Mechanism study on the effects of power modulation on energy coupling efficiency in infrared laser welding of highly-reflective materials

• Published in: Materials & design Vol. 178; p. 107871
• Main Authors: Ning, Jie, Zhang, Lin-Jie, Yin, Xian-qing, Zhang, Jian-Xun, Na, Suck-Joo
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.09.2019; Elsevier
• Subjects: Highly-reflective materials; Keyhole; Laser welding; Magnesium alloy; Power modulation; Recoil pressure; Keyhole; Power modulation; Highly-reflective materials; Recoil pressure; Laser welding; Magnesium alloy
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2019.107871

High-reflectivity of materials, such as magnesium, copper and aluminum, results in low thermal efficiency of their infrared laser welding processes. AZ31 magnesium alloy was selected to study the effects of power modulation on energy coupling efficiency in laser welding of highly-reflective materials. A model for the relationship between energy coupling efficiency and modulation parameters was obtained. The energy coupling efficiency in optimized modulated-power laser welding was about 1.58 times that in constant-power welding. The mechanism was explored by analyzing keyhole evolution and the resulted pressure distribution along keyhole wall during welding. The keyhole evolutions in laser continuous welding of common material (Q345 steel, reflectivity of 65%) and highly-reflective material (AZ31, reflectivity of 85%) were observed through high-speed imaging by utilizing a half sandwich method. The results indicated that the secret of improving energy coupling efficiency of laser welding process of highly-reflective materials through power modulation was the formation of a deep keyhole and its long life. When instantaneous power decreased from the peak, there was still enough recoil pressure at the bottom of keyhole to resist surface tension and hydrostatic pressure of liquid metal, which was the fundamental reason for the long time existence of keyhole with a large depth. [Display omitted] •Energy coupling efficiency in infrared laser welding of high-reflective material was greatly increased by power modulation.•The empirical model between energy coupling efficiency and modulation parameters was obtained.•Half-sandwich specimen of dissimilar metals was designed to compare keyhole evolutions through high speed imaging.•The mechanism of improving energy coupling efficiency of highly reflective material by laser power modulation was analyzed.