| As an Al-Cu-Mg aluminum alloy,Al 2024 aluminum alloy has the advantages of high specific strength,fatigue resistance and easy processing.It can also optimize its performance by solution aging heat treatment.It is widely used in aviation,aerospace,rail transit,automobiles and other fields.Co MPared with traditional material reduction manufacturing,additive manufacturing technology has the advantages of short processing cycle,material saving,and limited structural design.However,Al 2024 has a very strong thermal crack sensitivity,so it is of great significance to improve the stability of Al 2024 laser additive manufacturing,reduce the thermal crack sensitivity and increase the density.In this paper,the laser metal deposition（LMD）process of Al 2024 alloy and its composites was studied by LMD.The microstructure and properties evolution of Al 2024 single-layer multilayer and multi-channel multilayer samples prepared by laser metal deposition were studied.The influence mechanism of several different deposition paths and oxygen content on the microstructure and properties of laser metal deposition Al 2024 was analyzed.The heat treatment of the sample further optimizes the performance of the LMD shaped Al 2024.In order to improve the microstructure uniformity and lifting performance of Al 2024,TiB2 particles were added to Al 2024 powder to study the microstructure evolution and heat treatment microstructure of TiB2 particles in the process of LMD enhanced Al 2024 LMD.First,in a single-channel multi-layer experiment,it was found that the bidirectional deposition process has a more stable heat input than that of unidirectional deposition,and the sample has a more stable geometry and a denser structure.Under the unique heat of laser metal deposition,Al 2024 formed an equiaxed crystal region,a columnar crystal region,and a fine crystal region in the sample.The tensile properties of biaxially deposited samples were higher than those of the cast state of Al 2024.In multi-layer experiments,cross-deposition had a more stable forming process and the microstructure was more dense,reaching 98.90%.By reducing the oxygen content in the processing environment,oxidation during the forming process was suppressed,and macroscopic forming quality,density and tensile properties were improved.However,controlling the oxygen content through a limited space leaded to an increase in the temperature of the processing environment and a deterioration in heat dissipation conditions,resulting in the formation of a coarse T-Al20Cu2Mn3 phase in Al 2024,which reduces the plasticity of the material.Subsequently,in order to eliminate the tissue inhomogeneity during the LMD forming process and improve the properties of the material,the sample was subjected to solution heat treatment.After the heat treatment of T6,the T-Al20Cu2Mn3 phase of the formed sample in the low oxygen environment was not eliminated,and the TAl20Cu2Mn3 phase was formed in the atmospheric environment forming sample during the T6 heat treatment,and the performance of the sample deteriorated after the heat treatment.After 10 hours of solution treatment and 15 hours of aging treatment,the horizontal and vertical properties tend to be consistent and close to the forging level.Finally,in order to improve the Al 2024 LMD forming properties,TiB2 particles were separately added to the Al 2024 powder.At the TiB2 particle content of 0.5%,the structure is the denser and the grain is refined.The TiB2 particles effectively increase the hardness of the material,the tensile strength is improved,and the material wear performance is optimized.Through the solution heat treatment,the secondary phase in the composite material is sufficiently solid-solved;after the aging treatment,the secondary phase is dispersed.By co MParing the tissue analysis and tensile properties of the composites at different aging times,the best strengthening effect was obtained after 10 hours of aging. |
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