Numerical Simulation Of Temperature And Flow Fields In The Melt Pool Of Selected Area Laser Melting CuCrZr Alloy

Selective Laser Melting(SLM)is a metal additive manufacturing technology that uses a high-energy laser beam to completely melt metal powder and then cool and solidify it to form a metal additive manufacturing technology.This technology has personalized custom shapes,high processing accuracy and short production cycles.And other advantages,widely used in aerospace,medical equipment,power equipment and other fields.As a complex metal forming process,the SLM process involves multi-physical field coupling,and the ultra transient nature and complexity of this physical process poses a serious challenge to resolve the underlying physics behind defect formation,and numerical simulation of melt pool dynamics in SLM is an effective way to overcome this problem.In this paper,the process and tissue properties of CuCrZr alloys prepared by SLM were investigated using a combination of numerical simulations and experimental studies at mesoscopic scale.The effects of different process parameters on the temperature distribution of the molten pool and the shape characteristics of the molten channel in the single-pass and double-pass scanning forming processes were studied,and the statistics and analysis of the molten pool size under different process parameters were carried out.As the laser power increases from 250 W to 450 W,the maximum cooling rate of the melt decreases from-0.67×10~7 K/s to-3.3×10~7 K/s;when the scanning speed increases from 0.4 m/s to0.8 m/s,the melt Maximum cooling rate reduced from-1.63×10~7 K/s to-1.91×10~7 K/s.With the increase of the laser power and the decrease of the scanning speed,the width and depth of the melt channel gradually increase,and the ripples on the surface of the melt channel gradually become significant.As the thickness of the powder layer increases,the flatness of the surface of the melting channel decreases gradually,and the melting channel appears uneven.For double-pass scanning,as the scanning distance increases,the preheating effect between adjacent melting channels gradually weakens,and the remelting phenomenon disappears.The flow process of the molten pool during single-pass and double-pass scanning was studied,and the linear energy density(LED)was introduced to evaluate the energy input of the laser.For single-pass scanning,the LED seriously affects the flow of melt bubbles in the molten pool.When the LED is 800 J/m,the bubbles in the melt can escape smoothly.At the same time,the defect analysis of the SLM process is carried out.Insufficient laser energy input causes the substrate to fail to melt and cause spheroidization.Randomly distributed powder adheres to the melt channel at the edge of the molten pool,resulting in unevenness of the single channel.For double-pass scanning,a reasonable distance between the melting channels can reduce the pores between the melting channels and improve the energy utilization rate.According to the process parameters of SLM numerical simulation,the SLM forming experiment verification of CuCrZr alloy formed parts was carried out,and the microstructure was analyzed.Due to the difference of temperature gradient in different directions,the grain size,grain orientation,and the large and small angle grain boundary distribution show the certain difference.The difference in temperature gradient makes the solidification structure form a large number of cellular crystals on the horizontal plane,and the circular molten pool makes the direction of the temperature gradient deflect greatly.A large number of columnar crystal epitaxial growth.