Research On Microstructure And Performances Of Ce,Sc And Y Microalloyed Aluminum Alloys With High Electrical Conductivity

The aluminum alloys with high electrical conductivity（Commercial pure aluminum,Al-Fe and Al-RE alloys）and the aluminum alloys with high strength and high electrical conductivity（Al-Mg-Si alloys）have the advantages of low density,high electrical conductivity and good processing performance,which is used as the main conductor materials in the fields of overhead transmission lines,conductor rails for rail transit,etc.However,there are still some prominent issues in the current study on the aluminum alloy conductor materials:（1）The strength and electrical conductivity of the materials can not be increased simultaneously,and it is relatively difficult to obtain high strength and excellent electrical conductivity by controlling the content of impurity elements and optimizing the proportion of main alloying elements;（2）The aluminum alloy conductor materials are usually used under complex conditions,affected by various factors such as wind vibration,elevated temperature during service,industrial pollution and marine atmosphere corrosion.Poor heat resistance and corrosion resistance will definitely restrict the stability of such materials in service;（3）Breaking through the strength limit of aluminum alloy conductor materials without reducing the electrical conductivity is now becoming an essential topic of current research.Laser shock peening technology can improve the strength and plasticity of aluminum alloys,but its impact mechanism on strength,electrical conductivity and corrosion resistance is not fully revealed.Therefore,it is necessary to develop aluminum alloy conductor materials with high strength,high electrical conductivity and excellent application performances.In combination with the science and technology major project of Hunan province and the key-area research and development program of Guangdong province,trace Ce,Sc,Y and Zr elements were added separately,or in combination,to commercial pure aluminum and Al-Mg-Si alloy by comparative study,aimed to correlate the strength,electrical conductivity and the microstructure of high performance Al-RE and Al-Mg-Si-RE alloys,to investigate the damping property,heat resistance and corrosion resistance and the corresponding mechanisms,and finally to find the effect of laser shock peening on the performances and microstructure of the alloys with high electrical conductivity.High quality Al-RE alloys were prepared by melting,refining,chill casting,high temperature homogenization,hot extrusion,cold drawing and low temperature annealing.The trace Ce element slightly improved the strength and electrical conductivity of commercial pure aluminum,since the micro-sized Al₁₃Fe₃Ce and Al Ce Fe Si phases reduced the number of Fe and Si atoms dissolved in Al matrix.The electrical conductivity of Al-Ce alloy was improved by trace Y element,which could be attributed to the presence of Al₁₃Fe₃Ce phase enriched with more Y and Si atoms.The tensile property of Al-Ce alloy was greatly improved by trace Sc elements,caused by the precipitation strengthening of nano-sized Al₃Sc particles.The effect of trace Zr element on the improvement of tensile property was less obvious than Sc,which greatly reduced the electrical conductivity of the alloy.The Al-Ce-Sc-Y alloy had the fibrous grains with fewer subgrain boundaries and dislocations,the Al₃Sc particles with larger average diameter（13.5±0.9 nm）,and more micro-sized second phase with Fe and Si elements.The electrical conductivity and ultimate tensile strength of the annealed alloy were 61.77%IACS and 198 MPa,respectively.The heat resistance and damping property of Al-RE alloys and the corresponding mechanism were studied.Commercial pure aluminum and Al-Ce alloy had the worst heat resistance,and the process of recrystallization could occur when the temperature is higher than 320℃.When the temperature was lower than the recrystallization temperature,the damping mainly came from the dislocation movement.When the temperature is higher than the recrystallization temperature,it came from the nucleation and growth of the recrystallization grains.Al-Ce-Sc-Y alloy had the best heat resistance.After the alloy was exposed to high temperature from 400℃to 500℃,the diameter of Al₃Sc particles was less than 40 nm,which could effectively inhibit recrystallization of the alloy.The recrystallization temperature was higher than 500℃.After isothermal annealing at 500℃for 0.5 h,the ultimate tensile strength of Al-Ce-Sc-Y alloy was 132 MPa and the electrical conductivity was 61.71%IACS.The damping of the alloy at high temperature was mainly caused by dislocation movement,grain boundary and subgrain boundary relaxation.Due to the stable microstructure and high dislocation density,the alloy had excellent damping property.High quality Al-Mg-Si-RE alloys were prepared by melting,refining,chill casting,homogenization,hot extrusion,solution and aging treatments.The trace Ce element refined the grain of Al-Mg-Si alloy and promoted the formation of a large number of micron-sized Al Ce Si and a small amount of Al Ce Fe Si phases,which improved the strength and electrical conductivity of the alloy.The average grain size of Al-Mg-Si-Ce-Sc alloy increased while the number density and volume fraction ofβ’’precipitates decreased.The strength of the alloy decreased while the elongation after fracture increased.For Al-Mg-Si-Ce-Y alloy,the size,number density and volume fraction ofβ’’precipitates was improved.Y element was enriched with the micron-sized second phases such as Al Ce Si and Al₅Fe Si particles.Therefore,the contribution ofβ’’precipitates and solute atoms to electrical resistivity was reduced.Al-Mg-Si-Ce-Sc-Y alloy exhibited the best property,with the ultimate tensile strength,elongation after fracture and electrical conductivity of the peak-aged alloy being 336 MPa,18.4%and53.11%IACS,respectively.The heat resistance and corrosion resistance of Al-Mg-Si-RE alloy and the corresponding mechanism were studied.After long-term aging,the alloy containing Sc element had moreβ’’and coarserβ’/B’precipitates,enhancing the heat resistance of the alloys.Trace Ce and Y elements improved the corrosion resistance of Al-Mg-Si alloy.In the peak-aged Al-Mg-Si-Ce-Y alloy,the cross-sectional area and length ofβ’’precipitates were higher,and the number density ofβ’’precipitates was lower.The potential difference between the second phase containing Fe element and the Al matrix was lower.The grain boundary precipitates were discontinuous and the width of precipitate free zones is thinner.Al-Mg-Si-Ce-Sc-Y alloy obtained the best application performances.After aging at175℃for 120 h,the ultimate tensile strength and electrical conductivity of the alloy were 295 MPa and 55.71%IACS,respectively.The pitting corrosion,intergranular corrosion depth and the percentage of exfoliated grains caused by intergranular corrosion of the peak aged alloy were significantly improved.The ultimate tensile strength and elongation after fracture of Al-Ce-Sc-Y and Al-Mg-Si-Ce-Sc-Y alloys were improved by laser shock peening with slight decrease of the electrical conductivity（<0.35%IACS）.Fine-grained layer on the surface can be observed in such alloys.Dislocation cells and slip lines were evident in the near surface region,and the bulk alloy region was featured by high-density dislocations and stacking faults.Two side laser shock peening resulted in uniform gradient structure and higher dislocation density on both sides.After laser shock peening,the number,size and depth of the corrosion pits decreased in such alloys in the chloride solution,which was attributed to the more rapid repairment of the passive film due to laser shock peening.The two side laser shock peened Al-Mg-Si-Ce-Sc-Y alloy with polished surface had the lowest intergranular corrosion depth,and the intergranular corrosion cracks were finer,compared with those at the same depth observed in the alloys without laser shock peening.The corrosion products were also less than the alloy without laser shock peening.The residual compressive stress and high-density dislocations effectively enhanced the intergranular bonding force of the alloy along the thickness direction.124 Figures;24 Tables;306 References...