Research Of The Fluidity And Anodic Properties On A Novel Al-Ni-Si Casting Aluminum Alloy

Casting aluminum alloys have been widely used in automotive,aerospace,3C products and other fields because of its low density,high specific strength and excellent casting property.However,the existence of high Si content in casting aluminum alloy makes it difficult for anodization treatment.Consequently,the industrial applications of casting aluminum alloy in 3C products are hampered.Therefore,low Si-added Al-Ni-Si casting aluminum alloy was chosen as the research object in the present study.The effects of Ni,Si and RE elements on the fluidity and mechanical properties of Al-Ni-Si alloy were investigated.A novel alloy with an excellent fluidity and mechanical properties was developed.And the mechanism of various factors influencing the fluidity of Al-Ni-Si alloy was discussed by cooling curve thermal analysis technique(CCTA).Finally,the effect of the main element Ni on the performance of the anodic oxide film was discussed.The fluidity of Al-Ni-Si alloys were tested using a spiral fluidity test apparatus.It indicated that the fluidity increased with the addition of Si from 0 to 3 wt.% and Ni from 2 to 6 wt.%,and decreased slightly with increasing Ni content up to 8 wt.%.After RE modification,the fluidity of Al-Ni-Si alloy further enhanced.The tensile strength of the alloy also increased with the addition of Ni and Si.Al-6Ni-3Si alloy has the largest tensile strength,which value is 193.8MPa.The ?-Al phase and the Al-Al3 Ni eutectic phase in the alloy were obviously refined by the addition of RE,and the tensile strength and elongation of the alloy were further improved.The influence mechanism of Ni and Si on the solidification behaviors of Al-Ni-Si alloy was studied by melt thermal analysis technique.The intrinsic mechanism of alloying elements on the fluidity was analyzed by using the characteristic temperature such as solidification interval,dendritic coherency point and dendritic coherency temperature interval TP-TDCP.It was found that the addition of Ni and Si could decrease the temperature of the liquidus and narrow the solidification interval of the alloy,and increase the temperature of the dendritic coherency temperature.The increase of TP-TDCP could delay the dendritic cohenency and enhance the fluidity of the alloy.The excess Ni content causes the dendrites to rapidly coherency due to the formation of coarse Al3 Ni in the melt,which seriously hinders the flow of the liquid phase and reduces the fluidity of the alloy.The addition of RE elements refined the grain,reduced the dendritic coherency temperature,increased the solid fraction at the time of dendritic coherency,and prolonged the dendrite coherency,resulting in the increase of the fluidity.The effect of Ni element on the thickness,morphology and corrosion resistance of anodic oxide film was studied.After the anodic oxidation,the corrosion resistance of the alloy matrix was improved.With the increase of Ni in the alloy,the stable voltage in the anodic oxidation process decreased and the thickness of the film decreased gradually.Since the Al3 Ni particles in the alloy are dissolved during the anodic oxidation process,there are defects such as holes and cracks in the surface of the film,and the defects increased with the addition of Ni content in the film.