SLM Forming Process And Performance Optimization Of TiC_p/AlSi10Mg Composite

With the rapid development of my country's aerospace technology,the integrated forming of high-performance precision complex structural components has gradually become a development trend.Among them,the thermal insulation layer of a new generation of hypersonic aircraft is represented,as the core component that connects the outer ceramic heat insulation layer and the inner aluminum alloy frame.The integrated formation of the gradient material lattice insulation layer is not only conducive to the superb The weight reduction of the aircraft is also conducive to eliminating interface mutations caused by heterogeneous materials and reducing safety hazards caused by stress mismatch.Therefore,the use of selective laser melting(Selective Laser Melting,SLM)technology to integrally manufacture gradient lattice thermal insulation components that transition from an aluminum alloy skin to an outer ceramic thermal insulation layer has important research value.AlSi10Mg,as a highly alloyed aluminum alloy material with good SLM processability,has low thermal conductivity.As a reinforcing phase,TiC nano-ceramic particles can not only refine the grains,strengthen the mechanical properties of the matrix,but also increase the thermal resistance interface and reduce the thermal conductivity.Therefore,SLM technology is used to prepare TiC_p/AlSi10Mg gradient composite components with high ceramic reinforcement phase content.However,the introduction of TiC is bound to have a significant impact on the physical and chemical properties of AlSi10Mg.Therefore,it is challenging to adjust the processing parameters of SLM to achieve mutual matching with composite materials of different components to achieve precise control of the thermodynamic properties of the material.Based on the above situation,this paper mainly carried out the process optimization of SLM forming(0 wt%,3wt%,10 wt%,15 wt%)TiC_p/AlSi10Mg composites.The effects of TiC content and distribution on the microstructure,mechanical properties,and thermal conductivity of composite materials were studied,and the microstructure and mechanical properties were controlled by heat treatment.In order to further improve the thermal performance of the composite material,plasma micro-arc oxidation(MAO)technology was used to grow a layer of ceramic on the surface of the substrate to optimize its thermal insulation capacity,and finally the transition from AlSi10Mg to 15 wt%TiC_p/Gradient composite material of AlSi10Mg.The main research conclusions are as follows:(1)The addition of TiC nanoparticles promoted the absorption of laser energy by the composite powder.Adding 3 wt%TiC reduced the laser reflectivity from 32%to 16%;adding 10 wt%and 15 wt%TiC reduced the laser reflectivity to 8%and 7%,respectively.It showed that the proper addition of TiC is helpful for SLM forming,and the addition of 3wt%TiC could expand the process window.(2)The introduction of TiC transformed the growth mode of Al matrix grains from epitaxial growth to heterogeneous nucleation,promoted the transformation of columnar crystals to equiaxed crystals,and achieved the effect of grain refinement and elimination of tissue texture.With the addition of 3 wt%,10 wt%,and 15 wt%TiC particles,the composites all transformed into equiaxed crystal structures,with average grain sizes of 0.76?m,1.8?m,and 1.78?m,respectively.(3)The tensile strength of the AlSi10Mg formed by SLM was 405 MPa,the yield strength was 253 MPa,but the elongation was only 1.8%,the strength was higher and the toughness was poor.After adding 3 wt%TiC,the yield strength increased to 309 MPa,the tensile strength was 394 MPa,and the elongation increased significantly to 7%.After adding10 wt%TiC,the composite material had a yield strength of 348 MPa,a tensile strength of400 MPa,and an elongation of 5%.It showed that the introduction of 3 wt%and 10 wt%TiC increased the yield strength and toughness of the composite material.(4)Annealing,solution aging and direct aging treatment would cause the precipitation of supersaturated solid solution Si in the 10 wt%TiC_p/AlSi10Mg composite.Annealing and solution treatment gradually transformed the eutectic Si network into spherical Si particles.After annealing,the strength of the material decreased and the toughness increased;the annealing temperature was 250°C,the holding time was 9 h,the tensile strength was 362MPa,the yield strength was 284 MPa,and the elongation increaseed to 7.8%,which was an increase of about 56%compared to the printed state.Direct aging treatment would promote the precipitation of fine Si particles in the?-Al crystals,resulting in an increase in the microhardness of the material.Due to the increase in brittleness,the tensile properties of composite materials had a downward trend at different aging temperatures.(5)Due to the precipitation of solid solution Si in the composite material and the intrinsic thermal conductivity of each phase,the thermal conductivity of TiC_p/AlSi10Mg composites showed a trend of first increasing and then decreasing with temperature changes from room temperature to 500°C.At room temperature,the thermal diffusion coefficient of3 wt%TiC_p/AlSi10Mg composite was 32.2 mm²/s,which is 21.7%lower than that of AlSi10Mg;the thermal diffusion coefficient of 10 wt%TiC_p/AlSi10Mg composite was 27.8mm²/s,which was compared with AlSi10Mg decreased by 32.4%.(6)The MAO coating prepared on the SLMed AlSi10Mg substrate was mainly composed of?-Al₂O₃,?-Al₂O₃,and Al.With the thickening of the coating,the relative content of?-Al₂O₃ increased significantly,the relative content of?-Al2O3 and Al decreased rapidly,and the bonding force of the film base increased.With the thickening of the MAO coating,the higher the density of the ceramic film,the better the heat resistance performance.Compared with the substrate,when the MAO coating was 50?m,the room temperature thermal diffusion rate decreased by about 2.5%;when the MAO coating was 100?m,The room temperature thermal diffusion rate was reduced by about 10.2%.