Microstructure And Properties Of Al-Si Bi-material Fabricated By Selective Laser Melting

Al-Si alloy is widely used in aviation,aerospace,automotive and other fields because of its excellent properties,such as light weight,high strength,excellent wear and corrosion resistance.With the development of modern industry,the components of Al-Si alloy gradually transform into complex shapes,put forward new requirements for the process and dimensional accuracy.Moreover,the properties of different parts of the component are not the same.Due to the disadvantages of the traditional casting technology,it is difficult to acquire.In addition,with the increase of silicon content,the strength,wear resistance and corrosion resistance of the alloy increased.However,the ductility and thermal conductivity show the opposite trend.Therefore,the application of new methods for the preparation of a whole part with different silicon contents has gained favorable attention.Based on this,Al-?12-20?Si bi-material was fabricated by selective laser melting technology in this subject.The microstructure,mechanical properties and corrosion resistance of the bi-material and the alloy on both sides were studied.Results showed that the microstructure of selective laser melted Al-12Si,Al-20Si alloys,and Al-?12-20?Si bi-materials were nonuniform.It presented cellular morphology in the horizontal direction and semi-ellipsoidal shape in the vertical direction.The Al-?12-20?Si bi-material was composed of Al-Si eutectic,Al matrix,and Si particles.The average width of the molten pool at the Al-12Si side was about 160?m,the penetration depth was about 90?m.Whereas,The molten pool width was 204?m,depth was about87?m at the Al-20Si side.Moreover,the interface can be clearly seen.The microstructure of the Al-12Si side was composed of Al-Si eutectic,Al matrix,the microstructure of the Al-20Si side was composed of Al-Si eutectic,Al matrix and Si particles.With the increase of heat treatment temperature,the diffusion rate of Si element increased and was gradually accelerated.The microstructure of Al-12Si,Al-20Si alloys and Al-?12-20?Si bi-material gradually became uniform.X-ray diffraction analysis showed that the Al-12Si,Al-20Si alloys and Al-?12-20?Si bi-material were composed of supersaturated?-Al and Si phases.After heat treatment,the Si phase precipitates from Al matrix,and the diffraction peaks of Si phase were enhanced.The hardness of the Al-20Si side alloy(?188HV_0.1)was much greater than that of the Al-12Si side a(?131 HV_0.1)in the SLMed Al-?12-20?Si bi-material.During the heat treatment processing,the Si atoms re-diffuse,the microstructure gradually became uniform,and the hardness difference between both sides of the bi-material became small,and it tended to be consistent after 673K heat treatment for 6 h.The tensile strength of Al-?12-20?Si bi-material?ultimate tensile strength?450MPa,yield strength?300MPa?was between Al-12Si alloy?ultimate tensile strength?380MPa,yield strength?260MPa?and Al-20Si alloy?ultimate tensile strength?500MPa,yield strength?340MPa?.The strength decreased and the elongation increased for the Al-12Si,Al-20Si alloys and Al-?12-20?Si bi-material after heat treatment.The strength of Al-?12-20?Si bi-material?ultimate tensile strength?200MPa,yield strength?125MPa?was still between Al-12Si?ultimate tensile strength?130MPa,yield strength?100MPa?and Al-20Si?ultimate tensile strength?240MPa,yield strength?150MPa?alloys.Researches on the electrochemical corrosion and salt spray corrosion of Al-12Si,Al-20Si alloys and Al-?12-20?Si bi-material displayed that the formation of micro-batteries due to the potential difference between Si and Al will accelerate the corrosion Al matrix.Accordingly,a higher Si content would lead to worse corrosion resistance,and the corrosion resistance of Al-12Si alloy is better than that of Al-20Si alloy.Si particles became coarsen,and the formation of passivation films was hindered after heat treatment.The breakdown potential of the Al-12Si,Al-20Si alloys were reduced,and the blunt current increased,the corrosion resistance became worse after heat treatment.During the electrochemical test,due to the inconsistency of the materials on both sides of the Al-?12-20?Si bi-material,stable impedance and polarization curves could not be obtained,but the corrosion rate was found to be between Al-12Si and Al-20Si.