Dynamic vapor and keyhole behavior, and equiaxed dendrite formation in blue laser processing of copper

Abstract

A coupled Cu vapor and keyhole numerical model including a simple virtual mesh refinement method was developed to investigated the Cu vapor and keyhole behavior in blue laser processing of a copper material. Electron backscatter diffraction (EBSD) was adopted to measure the crystal structure of the fusion zone. The Cu vapor mainly flowed upwards above the keyhole, while some downward flows were observed inside the keyhole. The recoil force and Marangoni stress caused the melt at the keyhole wall to flow downwards, and the Marangoni stress caused the melt at the pool edge to flow outwards. Owing to the multiple reflections and high absorption rate, the total blue laser energy efficiency can be as high as 83.1%. The EBSD, numerical and theoretical results indicated that the blue laser favored the fine equiaxed dendrite formation in the center of the fusion zone, which was attributed to the higher value of the cooling rate G × R, where G is the temperature gradient and R is the solidification rate, and the lower value of G/R at this location, unlike the previously studied infrared laser processing case.