Research On In-situ Reacted Al₂O₃ Ceramic Reinforced Al Matrix Composites By Laser Selective Melting And Its Microstructure And Properties Control

Al-based composite materials have the characteristics of high room temperature strength,good plasticity,wear resistance and excellent high temperature performance,and are widely used in the aerospace field.However,the uneven distribution of the reinforcement phase during the preparation of Al-based composites,poor wettability with the matrix,and easy occurrence of harmful reactions to produce brittleness are the bottlenecks restricting the engineering application of this type of material.The Selective Laser Melting(SLM)forming technology developed in recent years can promote the homogenization of the enhanced phase and control the progress of harmful reactions due to its strong convection in the small laser melting pool and fast heating and cooling speeds.It is expected to solve the above-mentioned difficulties in the preparation of Al-based composite materials.In this paper,Al2O3 Ceramic Reinforced Almatrix composites were prepared by in-situ reaction using alsi10mg and nano ZnO as raw materials.The effects of the preparation process of composite powder,SLM forming process,nano ZnO content and heat treatment process on the density,microstructure,phase composition and mechanical properties of the composites were systematically studied.It provides a theoretical basis for SLM forming in-situ ceramic reinforced Almatrix composites.The main findings are as follows:(1)ZnO/AlSi10Mg composite powders with different ceramic phase content are prepared by ball milling process,and Al₂O₃ ceramics are prepared by in-situ reaction of ZnO and aluminum alloy matrix by means of laser energy in SLM forming process to strengthen the matrix.The ball milling process makes the prepared ZnO/AlSi10Mg composite powder form a rough surface,which makes the laser reflect multiple times between the powders,and reduces the reflectivity of a single AlSi10Mg to the laser.During the SLM forming process,the extremely fast cooling rate and the existence of Marangoni convection in the molten pool resulted in the formation of nm-Al₂O₃ ceramic reinforced phase at the junction of the Almatrix boundary of the cell body and the meshed Si.The introduction of the Al₂O₃ reinforcement phase and the extremely fast cooling rate make the Orowan strengthening effect,solid solution strengthening effect,and fine-grain strengthening effect occur inside the material,and can inhibit the vaporization and evaporation of the beneficial phase.When the ZnO content is1wt%,the mechanical properties of the formed composite material are:yield strength 200.7±7MPa,tensile strength 305.2±22 MPa,and elongation at break 9.2±2%.(2)In order to further optimize the structure and performance of the composite material,the heat treatment process was studied.The results show that after the heat treatment,part of the Si element in the Almatrix precipitates,and the precipitated Si gradually agglomerates and grows up.Due to the better thermal stability of Al₂O₃,there is no change before and after heat treatment.The Zn element in the matrix is uniformly distributed and significantly reduced in vaporization.No segregation occurred.After the annealing heat treatment,as the annealing temperature rises,the amount of Si precipitation increases,the toughness of the composite material increases slightly,while the tensile properties and hardness are reduced;after the aging heat treatment,the Mg₂Si phase is formed due to the age hardening effect,and the hardness of the composite material increases slightly,But the toughness is reduced;after the solution treatment,the hardness and tensile properties are greatly reduced;after the solution aging treatment,the hardness is restored,but it is still lower than that of the untreated.By controlling the ZnO content,forming process parameters and subsequent heat treatment process,the Al₂O₃ ceramic and Zn element can be controlled,and the Almatrix can be alloyed in situ through the solid solution of Zn element and transformed into Al-Si-Mg-Zn alloy.It is expected to realize the preparation of in-situ Al₂O₃ ceramic reinforced Al-based composites and promote the application of Al-based composites in the aerospace field.