Effect Of Nano-TiB₂ Particles On Microstructures And Mechanical Properties Of 2024 Aluminum Alloy Prepared By Selective Laser Melting

With a high content of alloy elements and a broad freezing range,2024 aluminum alloy prepared by selective laser melting?SLM?still has some problems such as hot cracks,coarse columnar grains and keyholes.In this work,nano-TiB₂/2024 composite powders were prepared by low-energy ball milling.The optimum addition amount of nano-TiB₂ and optimal SLM processing parameters were obtained by analyzing the relative density,surface roughness,microstructures and mechanical properties of samples in order to provide a technological guidance for preparing 2024 aluminum alloy with good properties by SLM.The optimum ball milling parameters for TiB₂/2024 composite powders is 125 r/min-3h,at which the Nano-TiB₂ particles can evenly adhered on the surface of 2024 aluminum alloy powders and the sphericity of powders can be well preserved.1wt.%TiB₂/2024 is the best content which has the highest density and the best comprehensive mechanical properties.The addition of 1wt.%nano-TiB₂ particles has a good heterogeneous nucleation effect,which can not only refine the grain size,but also change the grain growth mode dominated by temperature gradient.As a result,<001>preferred orientation and{001}<100>cubic texture are greatly weakened and the amount of equiaxed grains increases.The SLM processing parameters of 1wt.%TiB₂/2024 Al alloy were optimized.Relative density depends on the size and amount of spherical holes.The amount of holes is little at a low laser power?150 W?which leads to a high relative density of samples,and it is large at a high laser power which leads to a low relative density.Surface roughness is mainly affected by hot tearing and surface shrinkage.Microhardness decreases with the increasing linear energy density and affected by residual stress.Besides,grain morphology can be regulated by linear energy density.The morphology and average size of grains are finest at 1J/mm?250W-250 mm/s?.Finally,with the parameters of 150W-100mm/s,yield strength,tensile strength and ductility are significantly improved to 228.7 MPa,349.0 MPa and 12.3%,respectively.T6 heat treatment for SLMed 1wt.%TiB₂/2024 Al alloy was investigated.Solution at540?for 1 h and aging at 150?for 12 h is the best parameters,which can ensure the maximum solid solubility of Cu element and save the operation time.After heat treatment,the reticulated Al₂Cu precipitates along the grain boundary transform into lath-like precipitates,which can weaken the tendency of intergranular fracture.Besides,a large number of T-AlCuMn and S-AlCuMg phases were precipitated.As a result,yield strength,tensile strength and ductility improved to 275.5 MPa,416.9 MPa and 14.6%,respectively.