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The Effect And The Mechanism Of Static Electric Field On Aluminum Alloy

Posted on:2003-10-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:B LiuFull Text:PDF
GTID:1101360092966140Subject:Materials science
Abstract/Summary:PDF Full Text Request
The influence of a static electric field was investigated systemic in three stratifications: the electron scope of single atom, multi-atom local effect and macro-materials character based on electron theory. The multi-scope effect of electric field on metals and alloys, such as the atomic energy, solute elements, microstructure and precipitates, fracture character, mechanic and physical properties, were studied with the purpose of finding the mechanism and the nature of the electric field.Based on Thomas-Fermi theory, the effect of external electric field on atomic inner boundary potential was studied. The new atomic potential boundary condition with the influence of external electric field was established and the atomic energy and pressure were calculated with new boundary condition. The local effect of solute element under an electric field was analyzed with the electron shield model. In experiment, the DSC technique was used to analyze the effect of electric fields on the precipitate kinetic of Al-Li alloy solutionized with electric fields. The Energy spectrum, TEM and SEM techniques are employed to investigate the elements solution, precipitates, fracture character, conductivity and Vickers hardness. Also, the solidification of Al-Cu eutectic alloy was conducted with the influence of electric fields.Some new results and effects were got:Based on Thomas-Fermi theory, the influence of external electric field on atomic boundary potential is analyzed, and new boundary condition of atomic inner potential is presented. The calculation results show that the atomic energy and pressure increase with the positive external electric potential, but decrease first and then increase with negative potential. There is an extremum of the atomic energy and pressure. But the extremums are different to Al, Cu, and Li element.The Energy spectrum detect results show that electric field promotes the solution of Cu element and well distribution, and accelerates the dissolution of undissolved-phase containing Cu. The electron shield theory analysis shows that the electric field improves the solute solubility.The DSC results show that the electric fields have little influence on 8' precipitation of Al-Li alloy. There is little change of the 8' precipitate fraction and rate. But the Tj phase maximum precipitate temperature increases, the precipitate fraction decreases andVIIthe precipitate rate retards. The calculation shows that the 8' precipitate activation energy changes little but increases for Tj phase. The positive and negative electric fields have the same effects.The TEM results show that the electric fields applied during solution have little influence on precipitation of 8' phase of Al-Li alloy, but electric fields applied in aging accelerate the 8' precipitation. The electric fields decrease the size of PFZ and promote the precipitation of p' phase. The interaction of 8' and T, phases is improved and the composite phase of 8' and P' increase. Both positive and negative electric fields have the similar effects.The electric field strengthens the laminate boundary of 2090 alloy. The laminate strengthening mechanism translates into boundary strengthening and grain inner toughening with more ductility fracture and less intergranular fracture. The ductility property is enhanced with no change of intensity. The main elements distribution has no change and the TEM results show that subgrain boundary is blurred with more dislocation.The electric fields have the same effect on LY12 alloy as to 2090 Al-Li alloy with enhanced ductility and more toughness socket on fracture surface. Both positive and negative electric fields have the similar effects.The Vickers hardness is enhanced but the conductivity change little. A new relationship of Vickers hardness and conductivity is got: the Vickers hardness increases with conductivity without electric field, but decreases with electric field with the influence of electric fields. Both positive and negative electric fields have the similar effects.The el...
Keywords/Search Tags:Static electric field, Al-Li alloy, Thomas-Fermi equation, Element solution, kinetics, Microstrueture, Fracture character, properties, Conductivity, Eutectic solidification
PDF Full Text Request
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