Study On Underwater Laser Welding Mechanism And Key Technologies

Compared with other underwater welding methods,underwater laser welding has many advantages,such as less influenced by water pressure,large penetration depth of keyhole welding,and easily controlled remotely.It is expected to replace arc weld-ing as an important means of building and maintaining in underwater engineering.Since the underwater laser welding technology is in the stage of exploration,it is nec-essary to carry out systematic research on key issues such as the theory and process performance of underwater laser welding technology.Therefore,the following four aspects of research are carried out:In this study,a special micro-four inlet drain hood was designed to create a local gas phase zone to carry out research on underwater laser welding.The underwater la-ser welding mechanism and the austenitic stainless steel solidification mechanism were explored.The microstructure and performance of the back-water-soaked weld were analyzed and evaluated.The results show that there are some problems under water medium,such as the decrease of weld penetration,the deterioration of weld formation due to backside immersion,and the increase of metallurgical porosity.Compared with welding in air medium,its mechanical properties and corrosion re-sistance are reduced.The mathematical relationship of laser welding parameters,weld morphology and mechanical properties under water medium was established from the view of multivariate statistics.The results show that the established quadratic response mathematical relationship quantifies the negative shift of laser beam focusing surface caused by the negative lens,and the negative shift is about 1mm,and reveals the in-fluence law and mechanism of welding parameters on the weld morphology and me-chanical properties.The self-made underwater laser back-protecting flux and active agent were used to solve the problems of poor back forming and the weld depth decrease,respectively.The self-made underwater laser back-protecting flux not only has the physical effect of support and barrier,but also has the chemical metallurgy effect of dehydrogenation and deoxidation.It optimizes the back forming of the weld and reduces the metallur-gical pores without changing the phase composition and microhardness of the weld.It improves the mechanical properties and corrosion properties of the under-water laser welding.The self-made underwater laser active flux has the more significant effect on the penetration depth increase than the single component,and whose external weld forming is good,which also reduces the penetration power and optimizes the me-chanical and corrosion properties of the weld.B₂O₃ and TiO₂ active agents signifi-cantly increase the weld depth but reduce the weld properties.The mechanism of the underwater laser active agent increasing the penetration depth is a combination of an increase of laser absorptivity and a change of the flow direction of the molten pool.Based on digital image correlation technology?DIC?,the deformation behavior and deformation mechanism of underwater laser welding.The medium affects the amount of welding deformation,and the thickness of the plate affects the welding de-formation morphology.The temperature non-uniformity of the welding process is the root cause of the deformation.The underwater laser welding parameters and the post-weld deformation have the quadratic response relationship.Welding speed is the primary influence parameter.