Numerical and Experimental Investigation on Heat Transfer Characteristics, Grain Refinement Mechanism and Mechanical Properties in Synchronous Tailing Heat Sink Assisted Laser Welding

In this paper, the influence mechanism of synchronous heat sink process on weld pool thermodynamics and weld microstructure during laser welding of SUS301L stainless steel sheet was analyzed by experiment and simulation. The dynamic characteristics of the molten pool under different heat sink process parameters were observed by a high-speed camera system, and the mechanism of the effect of heat sink on the solidification characteristics and dynamic behavior of the molten pool was preliminary revealed. In addition, based on the experimental observation, a simulation model of synchronous heat sink + laser welding (SHSLW) is established. The simulation results illustrate that heat sink will form a rapid cooling zone at the tail of weld pool, which leads to the disappearance of weld comet characteristics, and improves the temperature field at the tail of weld pool. The simulation results show that the introduction of heat sink significantly changes the temperature field of the weld seam. When the heat sink flow rate is 200ml and the distance is 5mm, the temperature gradient decreases by 305. Secondly, the impact of heat sink on the grain refinement and grain orientation of weld seams was quantitatively analyzed by EBSD, and the refinement mechanism of heat sink on microstructure was described based on the theory of constitutional supercooling (CS). This new understanding provides an opportunity to make better use of heat sink to control grain structure, and in turn to improve the mechanical properties of the welds, which is also verified by the test results of the properties of the welds. The test show that the heat sink enhances the micro hardness and improves the tensile properties of the welds significantly, exactly speaking, the tensile force increases by 12.03%, and the maximum ductility increases by about 21.37%. It can be concluded that the application of heat sink is an effective way to improve the tensile strength and toughness of the welds by laser welding of metals.