Study On Microstructure And Mechanical Properties Of High Strength Al-Cu-Mg-Si Alloy Prepared By Laser Powder Bed Melting

Aluminum alloy is widely used in aerospace,vehicle engineering and ocean engineering due to its characteristics of light weight,high strength and corrosion resistance.However,the traditional casting aluminum alloy has many problems in the production of complex shape parts,such as long production cycle,high mold cost,low material utilization rate,and laser powder bed melting technology(LPBF)has the ability to integrate the forming of complex shape and precision parts.Therefore,LPBF aluminum alloy forming has great development potential.However,due to the physical characteristics of aluminum alloy itself and the characteristics of LPBF technology,LPBF aluminum alloy is easy to produce thermal cracks and holes and other defects.On the basis of summarizing the results of other researchers,the composition of Al-Cu-Mg-Si alloy was designed in this paper,and al-Cu-Mg-Si alloy was fabricated by different laser powder bed melting(LPBF)process.The effects of printing process parameters on the microstructure,phase distribution,mechanical properties,friction and wear properties and corrosion resistance of LPBF fabricated Al-Cu-Mg-Si alloy were discussed.The main research contents are as follows:(1)The influence mechanism of different laser powder bed melting(LPBF)process parameters on the densification behavior of Al-Cu-Mg-Si alloy powder was studied,and the optimal process window of LPBF-fabricated high-density and crack-free Al-Cu-Mg-Si alloy was obtained:Laser power 270W,scanning speed 300mm/s,scanning spacing 90?m,powder thickness 30?m.Under this process,the density is 99.88%,the porosity is 0.129%,and the maximum microhardness of cross section and longitudinal section is 130.1Hv and 109.2Hv,respectively.The boundary of the molten pool is dominated by ultrafine equiaxed grains with an average grain size of about 2?m.(2)LPBF-fabricated Al-Cu-Mg-Si alloy tensile strength is 435MPa,yield strength is346MPa,elongation is 12%.A large number of small and dense dimples were observed in the tensile section of Al-Cu-Mg-Si alloy and ductile fracture occurred.The higher tensile strength is mainly caused by grain boundary strengthening and second phase strengthening.Due to the rapid solidification characteristics of LPBF,the al-Cu-Mg-Si alloy fabricated by LPBF has more uniform microstructure and finer grain size,and the second phase particles such as Mg₂Si and Al₃Zr are observed in the aluminum alloy fabricated by LPBF.Under the action of tensile load,LPBF is favorable for forming small and dense dimples in the tensile section of Al-Cu-Mg-Si alloy.The wear rate and friction coefficient of Al-Cu-Mg-Si alloy fabricated by LPBF are lower than those of cast ZL205A alloy,so its wear resistance is continuous and stable.The wear resistance of LPBF fabricated Al-Cu-Mg-Si alloy is the best,the wear resistance of longitudinal section is the second,and the wear resistance of cast ZL205A is the worst.(3)The corrosion law of Al-Cu-Mg-Si alloy fabricated by LPBF is the same as that of ZL205A aluminum alloy.The pitting corrosion first occurs in the corrosion environment,and then develops into intergranular corrosion.The corrosion resistance of Al-Cu-Mg-Si alloy prepared by LPBF method is better than that of ZL205A aluminum alloy.The corrosion resistance of the horizontal section is better than that of the longitudinal section.Due to the layer-by-layer characteristics of LPBF processing,the molten pool boundary density is significantly different in horizontal and longitudinal sections.The molten pool boundary density in the longitudinal plane is much higher than that in the horizontal section.This is because the Al₂Cu in the longitudinal section is much higher than that in the horizontal section,so the corrosion resistance of the horizontal section is better than that of the longitudinal section.