SLM Forming And Performance Regulation Of （TiB₂+SiC）/AlSi10Mg Composites For Mirrors

Compared with single particle reinforced materials,hybrid reinforced aluminum matrix composites have more denser structure and better overall properties,and have a wider perspective in industrial applications.The hybrid-reinforced composites prepared by traditional casting process are prone to particle agglomeration and poor material bonding,while the selective laser melting（SLM）technology can not only reduce particle agglomeration and improve the denseness,but also achieve rapid forming of material.This technology is suitable for preparing more complex parts.Different heat treatment processes can effectively improve the mechanical properties of SLM forming specimens,but most of the relevant research is on single particle reinforced materials,so it is necessary to study the heat treatment process of hybrid reinforced aluminum matrix composites.Aluminum alloy mirrors can be quickly formed using existing machining processes,so that the advantages of aluminum alloy materials that are easy to form can be given full play.At the same time,the mirror surface of the reflector can be machined directly after using the single-point diamond turning process to obtain a smooth surface that meets the requirements of optical imaging quality,and allows the aspheric surface to be machined economically and efficiently.In this study,（TiB₂+SiC）/AlSi10Mg composites with different TiB₂contents were prepared by selective laser melting with AlSi10Mg as matrix,SiC and TiB₂ as reinforced particles.By changing laser power,the variation of structure and properties of the composites under different process conditions are studied,so as to obtain the composite material with optimal performance and finally form the reflectors.The main conclusions are as follows:（1）When the laser power is too small,the powder cannot be melted completely,and the molten metal cannot fill the gap between the two lasers,thus causing pores in the matrix,resulting in poor denseness and mechanical properties of the material.When the laser power is large,the powder gets too much energy,and the molten pool produces splashing and spheroidization,which affects the microstructure and mechanical properties of the material.The right amount of laser power can effectively improve the denseness of the material.The composites with 1%TiB₂content showed higher hardness and mechanical properties,with tensile strength of 477 MPa and elongation of 8.6%.With the increase of TiB₂ content,the mechanical properties and hardness of the composites decreased.The wear resistance and thermal expansion properties of the composites were improved.Adding an appropriate amount of TiB₂ particles to the material can improve the performance,and excessive TiB₂ particles are prone to agglomeration,and the strengthening effect is weakened.Due to the heterogeneous nucleation effect of TiB₂,the grain size of the composites decreased from 3.7μm to 3.1μm,while the selective growth orientation of the grains inside the specimens was eliminated.Compared with the common machining process,the reflector by single-point diamond processing can meet the optical performance requirements.Its surface accuracy is about 3μm and surface roughness is also lower,which provides a flatter surface for the subsequent coating process.（2）After low-temperature aging treatment,under the dual effect of solid solution strengthening and precipitation strengthening,the microstructure of specimens did not change significantly,the strength increased,and the tensile strength increased from 477 MPa to 498 MPa.While after higher temperature aging treatment,the molten pool morphology in the specimens disappeared,the grid structure was destroyed,and mechanical properties of the materials were reduced.The elongation and thermal expansion properties of the composites showed excellent properties with the increase of aging temperature,while the friction properties are opposite.After solid solution treatment,the microstructure of the specimens changed significantly,the Si particles precipitated and grew up,and the tissue morphology was destroyed,which made strength decrease and plasticity increase.In order to take into account strength and surface accuracy of the reflector,it is necessary to carry out the aging and solid solution heat treatment method.（3）Nano-SiC has smaller specific surface area compared with micron SiC,which can improve the laser absorption,resulting in finer organization and higher elongation of the composite,and the thermal expansion property was optimized.However,due to the agglomeration of nanoparticles and the generation of pores during the forming process,the strength of the material was reduced.The addition of nanoparticles increases the interface in the material,enhances the resistance to thermal deformation,and reduces the coefficient of thermal expansion.