Abstract
Laser welding of metals involves with formation of a melt-pool and subsequent rapid solidification, resulting in alteration of properties and the microstructure of the welded metal. Understanding and predicting relationships between laser welding process parameters, such as laser speed and welding power, and melt-pool characteristics have been the subjects of many studies in literature because this knowledge is critical to controlling and improving laser welding. Recent advances in metal additive manufacturing processes have renewed interest in the melt-pool studies because in many of these processes, part fabrication involves small moving melt-pools. The present work is a critical review of the literature on experimental and modeling studies on laser welding, with the focus being on the influence of process parameters on geometry, thermodynamics, fluid dynamics, microstructure, and porosity characteristics of the melt-pool. These data may inform future experimental laser welding studies and may be used for verification and validation of results obtained in future melt-pool modeling studies.
Highlights
Laser is a coherent single-phase beam of lights from a single wavelength with low beam divergence and high energy content, which creates heat when it strikes a metal surface. e advent of high-power lasers in the 1970s [1] opened the door to many metal working applications, which, previously, had been done using conventional high-flux heat sources, such as reacting gas jets, electric discharges, and plasma arcs
Two adjacent or stacked metal pieces are fused together by melting the parts at the weld line; usually, the process is conducted under an inert gas flow with or without addition of material to the weld line. e moving melted volume is called the melt-pool (Figure 1). e size of this pool, which is on the order of 1 mm, is influenced by many variables, such as the material, laser power, and welding speed
The surrounding area of the melt-pool that is still in the solid state will reach temperatures high enough to change the microstructure of the material or to cause solid-state phase transformation, depending on the material thermodynamics. is area is called the heat-affected zone (HAZ)
Summary
Laser is a coherent single-phase beam of lights from a single wavelength (monochromatic) with low beam divergence and high energy content, which creates heat when it strikes a metal surface. e advent of high-power (multi-kW) lasers in the 1970s [1] opened the door to many metal working applications, which, previously, had been done using conventional high-flux heat sources, such as reacting gas jets, electric discharges, and plasma arcs. Us, the present review focuses on the following melt-pool characteristics: (1) geometrical features, such as the penetration depth, width, HAZ geometry, keyhole geometry, and MMA geometry; (2) thermodynamic characteristics, such as laser energy absorption, surface temperature, cooling rates, and temperature map in the melt-pool; (3) fluid dynamic characteristics, such as fluid flow in the melt-pool and vaporization in the keyhole; (4) resulting microstructures; and (5) porosity characteristics, including factors that influence porosity formation and methods to avoid it. In each section of the present review, we critically discuss the state of the art in determination of the considered melt-pool characteristic, its variation with process parameters, and its influence on commonly used weld quality quantifiers, such as the microstructure and mechanical properties. Ey asserted that the moving speed of the solid-liquid interface is much higher than that of the liquid-vapor interface; in other words, the melt-pool depth increases more rapidly than does the keyhole depth
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