Investigation of Melt Pool Geometry, Cooling Rate, and Microstructure Formation in Laser Surfacing of Al 7075 Alloy: Numerical Simulation and Experimental Analysis

The study involves numerically simulating the influence of process parameters on melt pool geometry, cooling rate, and microstructure during laser surfacing of 7075 Al alloy using COMSOL Multiphysics. Both numerical simulations and experiments show that increasing scan speeds at a constant laser power reduces melt pool dimensions and increases cooling rates. At 1000 W laser power and 15 mm/s scan speed, numerically simulated melt pool width, depth, and cooling rate are 3.8 mm, 1 mm, and 1370 K/s, closely matching experimental measurements of 4.2 mm, 1.3 mm, and 1449 K/s. Calculated thermal gradient (G) and solidification rate (R) are correlated with observed solidification morphology. The G/R ratio derived from simulations has higher values at the melt pool's bottom, gradually decreasing toward the top for a given laser power and scan speed. This pattern aligns with optical micrographs showing equiaxed dendrites at the top, and columnar and cellular dendrites in the middle and bottom of the melt pool.