Microstructures And Mechanical Properties Of ?TiH₂+TiB₂?/AA7075 Composite Powders By Selective Laser Melting

7075 aluminum alloy is one of the main materials for aerospace structural parts because of its low density,high strength and good corrosion resistance.However,due to the high content of alloy elements and a wide solidification temperature range,7075 aluminum alloy is easy to form defects such as hot tearing and pores during SLM process,which deteriorates mechanical properties of the SLMed specimen.The addition of other alloy elements or grain refiner can improve the formability of 7075 aluminum alloy during SLM process.In this work,low-energy ball milled?TiH₂+TiB₂?/AA7075 composite powders were used to prepare samples for selective laser melting.The effects of Ti H₂ addition amount,SLM processing parameters,hot isostatic pressing?HIP?and heat treatment on microstructures and mechanical properties of SLMed Ti B₂/?AA7075+Ti?composites were studied,which aims to provide technological guidance for preparing 7075 aluminum matrix composite parts with high relative density and good properties by SLM.The optimum ball milling parameters for?TiH₂+TiB₂?/AA7075 composite powders is 135r/min-3 h.Sub-micro Ti H₂ and nano-Ti B₂ particles are evenly distributed on the surface of 7075aluminum alloy powders and the good sphericity of powders can be well kept with such ball milling parameters.The effects of Ti H₂ additive amount on microstructures and mechanical properties of SLMed samples were analyzed.The results show that Ti H₂ can refine the grain size,reduce the cracks in samples,and weaken the<001>preferred orientation and{001}<100>cubic texture.When the additive amount of Ti H₂is 1.4wt%,the average grain size of AA7075matrix is 1.38?m,with no crack and best mechanical properties for SLM sample.The effects of SLM processing parameters on density,roughness,microstructure and mechanical properties of?1.4%wt.Ti H₂+0.8wt.%Ti B₂?/AA7075 composite powders were studied.With increasing laser power,pores in the samples change from irregular to round,and the relative density of samples increases first and then decreases.Surface roughness increases with increasing scanning rate.The burning loss of low boiling point elements is serious with a high laser power and a low scanning rate,which leads to less precipitation of second phases.When laser power is 180W and scanning rate ranges from 100 to 250 mm/s,the samples have high densities of more than 97.0%and the best mechanical properties.There is no spherical particle or fish scale ripple on the surface of samples,and the high relative density is obtained at the optimal scanning distance of 90?m.After hot isostatic pressing,the relative density of samples with the optimum composition and processing parameters increases from 97.1%to 99.5%,and the second phase in the microstructure changes from ring networks to dispersive particles,which enhances the bonding strength of the matrix.Therefore,tensile strength and elongation of samples increase.The optimum T6 heat treatment parameters of HIP samples are as follows:solution 1 h at 490?and aging 20 h at 120?.After heat treatment,a large number of GP?zones and?'phases precipitate,which hinders the dislocation movement.Consequently,its tensile strength,yield strength and elongation incraese to 484 MPa,395 MPa,and 16.3%,respectively.