Experimental and numerical study on laser keyhole welding of 42CrMo under air and argon atmosphere

Abstract

Laser keyhole welding of 42CrMo in air and argon atmospheres has been studied both experimentally and numerically. Significant macroscale difference is observed for welding carried out under argon and air shielding. Fusion zone of welding under argon shielding has a "▽" shape, while it has a "U" shape for welding in air. The surface of the weldment is smoother for welding in argon when compared with that in air. Oxygen effect is proposed to account for the experimental results. A three-dimensional heat transfer model with a predefined keyhole is developed to study the heat transport and fluid flow in laser welding process. The variation of weld pool geometry and temperature history is investigated for different oxygen concentrations. It is found that a small amount of oxygen could significantly modify the weld pool dimension, while keeping the temperature history of materials, and thus the microstructure, in the fusion zone and heat-affected zone unchanged.

Effects of interface conditions on heat and mass transfer during modeling of laser dissimilar welding

“…Comparison of the simulated and observed melt pool is commonly used in the calibration of numerical model and of great significance in the modelling of heat and mass transfer inside melt pool. 14,15,[18][19][20] Both the simulated results obtained from HP-R and HR-R show good correspondence with the experimental results with a small relative error, however, the calculated dimension from HP-R is obviously more reasonable than that from HR-R because the error for HP-R is smaller according to the results. Taking the 20 mm/s situation for example, the experimentally observed melt width and melt depth are 1097 lm and 245 lm, respectively.…”

“…Resulted from the mass transfer through substrate interface in dissimilar welding, the thermal physical properties are time-dependent and change a lot in different positions, which imposes great challenges for the model convergency and simulation accuracy. 9,13,[18][19][20] In liquid phase, mass, momentum and energy are all transferred through substrate interface, thus, an accurate description of thermal physical properties for the mixture is of great importance. In this part, gas/liquid surface is assumed flat and laser absorptance is characterized by high order polynomial relation.…”

“…The gas/liquid interface of melt pool can be considered as free surface 13,16,17 or flat surface. [18][19] Generally, the melt pool configuration can be predicted more accurately considering the free surface deformation. 20 It is not difficult to understand that the boundary conditions for momentum equation are largely affected by surface curvature and surface tension at gas/liquid interface is proved the main driver for convection flow.…”

“…The melt pool for dissimilar welding is actually a mixture of liquid metals from different substrates, and its thermal physical properties are actually time-dependent and space-dependent, which imposes great challenges for the development of numerical model and makes it susceptible to many defects. 6,7,13,19 Numerical result is largely affected by the used properties, and it is thus of great importance to reasonably deal with the mixture properties inside the melt pool. There are three commonly used strategies, but no evidence shows which one is more reasonable.…”

Numerical modelling and experimental verification of thermal characteristics and their correlations with mechanical properties of double-sided laser welded T-joint

“…5d. This distinct characteristic was obviously different with that in the conventional laser welding process because of the coupling and enhancement of laser energy at this region [24,28,31,32], and resulted in the three-dimensional shape of the molten pool was changed, which should be paid enough attention.…”