SLM Additive Manufacturing Process And Microstructure And Properties Regulation Of High Strength And Heat Resistant AlNi6TiZr Aluminum Alloy

In recent years,the demand for lightweight heat-resistant aluminum alloy materials with excellent mechanical properties in the medium temperature range of 200～300°C has become more and more vigorous in the aerospace field.However,the high temperature softening of aluminum alloys has always restricted the structural design and service safety of parts in the medium temperature range.Therefore,the industry is more inclined to use titanium alloys,which greatly increases the material and manufacturing costs.Selective laser melting(SLM)technology is used to prepare aluminum alloy components,which can improve the solid solubility of alloying elements and disperse in the matrix in the form of second phase,so that it has better heat resistance.Therefore,in this paper,the composition optimization design,forming quality control,microstructure observation,comprehensive performance test and strength and toughness mechanism of SLM formed Al-Ni-Ti-Zr alloy were studied.Firstly,the solidification interval and phase of Al-Ni-Ti-Zr alloy with different Ni,Ti and Zr contents were calculated and analyzed by Jmat Pro software.The influence of alloy element content on the solidification interval of the alloy was obtained,so that the solidification interval of the alloy was small and the thermally stable precipitated phase could be generated,which could effectively refine the grains and reduce the hot tearing tendency.Then,the effects of SLM process parameters on the surface morphology,pore defects and density of the samples were studied.It was found that when the laser energy density was 82 J/mm~3,the surface morphology and internal pore defects of the samples were the least,and the density reached the highest,which was 99.7%.Secondly,the typical microstructure and comprehensive properties of Al Ni6Ti Zr alloy were studied.A clear and arc-shaped boundary line of the molten pool can be observed in the microstructure morphology map.The fine grain zone is mainly distributed at the boundary of the molten pool,while the coarse grain zone is distributed inside the molten pool.When the laser energy density is 82 J/mm~3,the average grain size of Al Ni6Ti Zr alloy is 1.51μm,the microhardness is 145 HV,and the tensile strength is 539 MPa.Compared with SLM formed aluminum alloys with other alloy compositions,Al Ni6Ti Zr alloy exhibits good fine grain strengthening and mechanical properties.Finally,the Al Ni6Ti Zr alloy after aging treatment was studied.The microstructure,mechanical properties,heat resistance and strength and toughness mechanism were analyzed.It was found that the mechanical properties of Al Ni6Ti Zr alloy were improved most after aging treatment at 325°C for 12 h.The tensile strength was 551 MPa and the elongation was 9.7%.During the aging process,the grain size of Al Ni6Ti Zr alloy hardly grows,showing excellent thermal stability.The tensile strength of the alloy samples at200°C and 250°C is 350.2 MPa and 264.6 MPa,respectively,showing good thermal tensile properties.It is found that the three strengthening mechanisms of fine grain strengthening,second phase strengthening and solid solution strengthening have great contribution to the mechanical properties of Al Ni6Ti Zr alloy,and the strength increment caused by each strengthening mechanism is calculated respectively.