Study On Improving Laser Absorption Rate Of Copper Powder And Density And Properties Of Selected Laser Melted Copper

Copper is widely utilized in the aerospace industry due to its favorable electrical and thermal conductivity.However,the conventional processing of copper parts with complex geometries is challenging.Selective laser melting(SLM)is an additive manufacturing technique that utilizes a high-energy laser beam to trace a predefined trajectory based on a discrete digital model.SLM represents a new opportunity for the formation of intricate copper components.However,it is difficult to form high density samples processed by selective laser melting forming because of the high thermal conductivity and low laser absorption of copper.The main determinant for forming high-density copper elements in the selective laser melting process is the rate of laser absorption by pure copper powder.To enhance the laser absorption rate,three different particle size ranges(5-35μm,15-53μm,and53-105μm)of pure copper powders were chosen,and the effect of particle size on laser absorption rate and the formability of selective laser melting were investigated.Based on this examination,the powder was further modified to enhance the laser absorption rate of the pure copper powder.Subsequently,the modified powder was tested using selective laser melting forming experiments to explore alternative methods for improving the density and traits of selective laser melted copper.The main findings are as follows:(1)According to our investigation,the absorption rate of laser increases as the particle size of the powder decreases.However,the density of the sample formed is not solely reliant on the absorption rate of the laser by the powder.Selective laser melting experiments indicate that the powder with a particle size range between 15-53μm has better formability.Moreover,this powder size resulted in higher density compared to other sizes under the same process parameters.(2)Following the modification of the powder with graphite,the laser absorption rate of the powder increased in proportion to the added graphite content.Nonetheless,we discovered that after selective laser melting forming,the graphite was imperfectly distributed on the copper powder surface after mechanical mixing,leading to numerous voids following laser sintering.This adversely affected the forming of the modified powder.(3)We subjected the powder to oxidation to investigate the effect on laser absorption rate.After holding the powder at 150℃ for 5 minutes,there was no significant enhancement in the laser absorption rate of the powder.However,when held at 200℃ for the same duration,the absorption rate of the powder increased by35% and the absorption rate was not further improved after continuing to increase the oxidation temperature.Proper oxidation of the powder was conducive to the improvement of laser absorptivity.(4)Results of surface modification with nano copper on pure copper powder demonstrate that the effect of particle size range on laser absorption varies after addition of nano copper.Larger particle sizes led to more significant enhancement effects on laser absorption after modification.The modified powder with a particle size of 53-105 μm demonstrated the most notable improvement in laser absorption rate,resulting in enhanced density after forming.However,formed samples still contained large pores,which made it difficult to achieve high-density samples through powder bed gap filling when coated with large particle sizes.Addition of 0.6 wt% nano copper to the 5-35 μm sized particle powder resulted in a formed sample density of 96.4%,a6% improvement over unmodified samples.Additionally,the Brinell hardness,electrical conductivity,and thermal conductivity reached 79 HB,81.4% IACS,and172.3 W/(m·K),respectively,demonstrating the potential for copper nanoparticle modification to enhance the density and performance of selectively laser melted copper.