| Copper and copper alloys,especially high-performance copper alloys due to excellent high electrical conductivity,high thermal conductivity,corrosion resistance and as an important basic material widely used in electronic information,electrical engineering,defense equipment,automotive industry,energy materials,aerospace and other important fields.The conventional manufacturing and processing technology cannot meet the performance requirements of copper alloy parts in important fields.Laser Selective Laser Melting(SLM)is a mainstream and promising additive manufacturing technology.It uses laser as the energy source to process each layer of dispersed metal powder layer by layer to form three-dimensional parts that are difficult to process by traditional manufacturing methods and meet high performance requirements.Due to the complex material non-equilibrium physical metallurgy and thermophysical process of SLM forming process,the interaction mechanism between laser and material,the heat and mass transfer process between powder and melt pool,and the physical phenomenon of melt pool in the forming process will directly affect the quality and performance of formed metal parts.Therefore,it is important to study the laser-selective melting and forming process of copper alloys.This thesis takes CuCr-Zr copper alloy as the object of study,and deeply restores the SLM forming process through numerical simulation,investigates the melt pool dynamics and laser reflection and absorption behavior during single-pass SLM forming and multi-pass SLM forming of Cu-Cr-Zr copper alloy,deeply explores the splicing overlap region of multi-beam SLM forming,and analyzes the formation mechanism and suppression means of defects,and provides theoretical support for SLM forming of Theoretical support is provided for SLM forming of copper alloys.The main research works are shown as follows:1.The kinetic behavior of the melt pool and the laser reflection and absorption behavior of the SLM single-pass forming process were investigated at different scanning speeds and laser powers to explore the influence of scanning speed and laser power on the evolution of the melt pool,and the reliability of the numerical model was verified.The results surface that the simulated predicted melt path morphology is similar to the experimental results,and the error rate of the model is less than 7%.With the increase of laser power,the penetration depth of the depression area increases,the melt pool size increases,and the melt channel changes from discontinuous and distorted to continuous,flat and regular.With the increase of scanning speed,the energy absorbed by the melt pool is low,and the liquid melt pool forms a distorted single channel shape under the action of surface tension,while the appropriate scanning speed can effectively improve the duration of the melt pool,which makes the forming quality enhanced and reduces the probability of irregular melt channel.With the increase of laser power and the decrease of scanning speed,the average laser global absorption rate increases during the SLM forming process,and the melt pool evolution process is closely related to the laser reflection behavior.2.The melt pool dynamics and laser reflection absorption behavior during SLM multi-lane forming with different scan spacing were investigated,and the influence of scan spacing on the evolution of the melt pool was explored,and the laser reflection absorption behavior in the overlapping area of adjacent melt lanes of multi-lane SLM forming was explored in depth,and the formation mechanism of porosity defects in multi-lane SLM forming was analyzed.It is found that in multi-pass SLM forming,the first laser scan forming lane will have a preheating effect on the second laser scan lane.Under the multi-pass reciprocal scanning,there are some differences between the start and end areas of the second and the first lanes.The scan spacing has an important influence on the evolution of the melt pool,which is related to the size of the melt pool,the shape of the melt channel,and the flow rate on the surface of the melt pool.The regression curves of the global laser absorbance fit for multi-pass SLM forming show a rise,then a fall,and finally a stabilization,corresponding to the initial,development,and stabilization stages of the melt pool.The size of the scan spacing affects the laser reflection absorption,and the global absorption rate fluctuates drastically when the laser scans adjacent lap overlap regions.The porosity defects in multi-pass SLM forming are closely related to the scan spacing,and a proper scan spacing is beneficial to improve the forming quality.3.The melt pool dynamics and laser reflection absorption behavior in the spliced overlap region with different processing parameters are investigated,and the lasermaterial energy coupling mechanism in the spliced overlap region and the non-spliced overlap region is compared and analyzed.The surface morphology and porosity defects in the overlapped area were investigated in relation to the melt pool dynamics and laser reflection absorption behavior,and the processing parameters that could improve the forming quality of the overlapped area were explored.The results show that the surface morphology of the overlap region is affected by the melt pool dynamics and laser irradiation,and the melt channel width in the overlap region is larger than that in the non-overlap region,and the undulation phenomenon appears at the boundary of the overlap region.Multi-beam laser-selected melting produces porosity defects in the overlap region of the laser processing splice,and most of the porosity defects are distributed at the boundary of the overlap region.The high level of global laser absorption in the overlap region makes the melt pool prone to narrow locking holes and triggers the formation of porosity defects.Selecting reasonable processing parameters in the overlap region can effectively suppress the defect generation,and the appropriate scanning speed in the overlap region can reduce the probability of porosity formation and also get a flat and regular melt path. |
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