Microstructure And Properties Of 8xxx Series Cast Aluminum Alloy In Solution Aging And Deformation

Al-0.7Fe-0.1Si-0.2Er alloy is an 8xxx series aluminum alloy.As an economical and advanced wire,8xxx series aluminum alloy can replace the ordinary steel-cored aluminum strand wire to become the wire material.The electrical conductivity of aluminum is higher,but the strength is lower,so it becomes the focus of this study to improve the strength and electrical conductivity of aluminum wire as much as possible.This research mainly through the two kinds of solid solution aging methods:550℃×1h solid solution then water quenching+180×10h ageing,550℃×1h solid solution then water quenching+180×10h aging+100℃×12h ageing and two different temperature of extrusion deformation in room temperature and 400℃temperature to explore can obtain both higher mechanical properties and of no less than 56.5%IACS electrical conductivity at the same time.The microstructure and the morphology,quantity,size and distribution of the second phase of the specimens are observed by metallographic microscope（OM）,scanning electron microscope（SEM）,transmission electron microscope（TEM）and electron backscattered diffraction（EBSD）.The properties of the samples are tested by digital metal conductivity teste,electronic vickers microhardness tester and tensile test.The cast grain size is about 660μm,in the matrix,the shape of Al_0.5Fe₃Si_0.5.5 phases are acicular and lamellar（size ranging from10μm to 25μm）,in the shape of granular,snowflake is Al₃Er phases（size is from 2μm to8μm）and the shape of Mg₂Si phases is irregular.The tensile strength is 53MPa,the yield strength is 22.7MPa,and the elongation after fracture is 26.4%.After the solid solution aging treatment,there is no coarse second phase in the aluminum alloy,and the grain boundary reticular phase is significantly reduced.The acicular AlFeSi phases are englobement with the size of about 12μm,which are distributed along the grain boundary.The precipitated phase of Mg₂Si is about 0.8μm,and the primary snowflake（Al,Er）phase disappeared,mostly became granular,and diffuse in the grain.The edge of theα-Fe phase is smoother than that of the single phase.The average grain size is about 65μm for single stage,aging and about43μm for double stage aging.Compared with the as-cast condition,the tensile strength and yield strength of single-stage aging increased respectively by about 40%,41%,1.6%,and1%respectively.Compared with that of single-stage aging,the mechanical properties of double-stage aging is slightly decreased and the electrical conductivity is slightly increased,about 1.6%.After extrusion deformation,the homogenized ingot is elongated.The grains are streamlined along the extrusion deformation direction,and the deformed alloy is subjected to shear treatment.The elongated grains are segmented under pure shear stress,and finer grains are separated.At room temperature,the grain size is about 0.54μm,the microhardness is55.71HV,and the conductivity is about 57%IACS.Under the condition of 400℃,the average grain size is about 1.3μm,and now the Al_0.5.5 Fe₃Si_0.5.5 phases changed into the size of about5μmα-Al₈Fe₂Si,the tensile strength is 156MPa,the microhardness is 45.71HV,the electrical conductivity is about 62.7%IACS.The thermal extrusion method can significantly improve the electrical conductivity.At the same time,the relationship between the tensile strength and electrical conductivity obtained by heat treatment or large deformation of other aluminum alloys in the literature is summarized,which provides guidance for production.