Properties Research Of Al-Er High-Strength Thermal-resistant Conductive Aluminium Alloy

Based on the previous research of Al-Er-Zr-B series high-conductivity thermal-resistant aluminium alloy conductor,diffferent content of Mg,Si elements was added in the Al-Er-Zr-Balloy to obtainextra high-strength thermal-resistant alloy conductor.The effect of second phases,precipitation phase and aging process on the properties of Al-Er-Zr-B-Mg-Si alloy was studied,and the microstructure of the alloy in different states such as as-cast,homogenizing state,solid-solution and cold-rolled were analyzed.In the as cast alloy,coarse columnar grain is major,and there are two main existence forms of the second phases:the thick lath or spherical complex compound contain Er,hexagonal plate or agglomerationmorphological ZrB2 phase.After homogenization treatment,dendrite segregation is eliminated, the Mg and Si elements in the thick lath complex compound contain Er and long needle lath β-AlFe Si would be dissolved into Al matrix,these second phases split into fine lath or spherical phases,however the morphology of ZrB2 phase does hardly change due to its excellent thermal-resistant property.After hot extrusion and hot rolling, most second phases were broken into fine particles under the action of external stress, arraying intermittently along the direction of deformation;After cold rolling, the distance and the breaking degree of the second phase are increased with the increase of the deformation;but ZrB2 phase is not been broken up because its high hardness.The experiment used heat treatment process of T9. The main factors affecting the tensile strength and conductivity of the experimental alloys mainly include the dispersion strengthened by phase contains Er and ZrB2 particles,the precipitation hardening of Mg2 Si phase,the coherent enhancement relative to Mg2 Si,and the effect of work hardening. The main precipitation aged at 180℃ and 210 ℃ is β"phase which coherent with matrix, caused larger lattice distortion that can leads to high strength,but the plasticity and conductivity is slightly low; the main precipitation will turn into semicoherent β′ or incoherent β with the increase of aging temperature, weakening degree of crystal lattice distortion, so that the strength would rapidly decrease but the plasticity and conductivity increase. Density of precipitation increases with total amount of Mg and Si element, and the tensile strength increases.The phase transition of β" phase or β′ phase that precipitate at aging temperature of 180℃,210℃ and 240℃ will occur when a heat retention process of 230℃×1h is taken.The phase transition reduces tensile strength which means the rate ofresidual tensile strength is below 90%.The precipitation phase that aged at 270℃ and 300℃ isβ phase which has a complete prccipitation and growth so the little change of β phase when a heat retention process of 230℃×1h is taken has little influence to tensile strength,only the recovery process can affect the strength and the recrystallization nucleation on grain boundary is suppressed by ZrB2 particles.The type of precipitation phase still has an effect on the electric resistant at high temperature within short time.Electrical resistivity has a linear relationship with temperature,temperature is main factor of electric resistance. Temperature resistance coefficient is less than that of pure aluminium.The fracture mode of alloys use T9 heat treatment is ductile fracture via analysis of fracture morphology and elongation.Plasticity increases with the increase of aging temperature and decrease with the increase of Mg2 Si phase content.Elongation of alloys aging at 180℃ is the lowestwhich is between 7% to 9%.Elongation of alloys aging at 300℃ is the highestwhich is about 11%.When total amount of Mg and Si element is larger than 0.6wt%, the strength and conductivity of alloys aged at 210 ℃ ×8h and 240 ℃ ×4h match well(311MPa,55.5%IACS).Take into account the comprehensive requirements for tensile strength,electrical conductivity,thermal resistance and elongation of extrahigh-strength thermal-resistant alloy conductor,there has some alloys are satisfied.