Investigation On The Creep And Corrosion Resistance Of C_f/2024Sc Aluminum Matrix Composites

C_f/Al composites has the characteristics of high specific strength,specific stiffness,good wear resistance,excellent conductivity,thermal conductivity and low coefficient of thermal expansion.It has attracted great attention from the aircraft,aerospace,automotive and electronic industries.Due to the large potential difference between C_fand Al matrix,and the high temperature environment at work,these factors will affect the performance of the materials.In this study,2024Sc aluminum matrix composites reinforced by short carbon fiber with different lengths（2mm、3mm、4mm、5 mm）and the same 3 wt.%content were investigated by casting melting technology.The effects of different lengths of short carbon fiber on the mechanical properties,high temperature creep properties and corrosion resistance of aluminum matrix composites were discussed by means of OM,SEM,Vickers hardness test,tensile test at room temperature,uniaxial tensile creep test at high temperature,polarization curve and electrochemical impedance spectrum tests.The experimental results showed that:（1）After hot extrusion of C_f/2024Sc aluminum matrix composites,short carbon fibers were distributed along the extrusion direction,and the composites of fiber and matrix was good,while the dispersion was even without obvious macroscopic defects.There were second phases of Al₂Cu Mg,Al₂Cu,W（Al Cu Sc）around the interface between carbon fiber and aluminum matrix.（2）Researched findings on heat treatment process,when the solution condition was 495℃×2 h and the two-stage aging condition was 130℃×3 h+200℃×10 h,2024Sc aluminum alloy and 2、3、4 mm C_f/2024Sc composites had the maximum hardness,while the peak aging time of 5 mm C_f/2024Sc composite was 5 h ahead.The hardness of composites was higher than that of matrix alloy.The addition of C_f reduced the tensile properties of alloy,and the brittle phase formed on the interface between the electroless copper plating and the matrix,which was easy to be brittled under stress and led to the decreased of the mechanical properties of the composites;Comparied with C_f/2024Sc composites,the tensile strength of 4 mm C_f/2024Sc composite was the best,while the yield strength,tensile strength and elongation were 370 MPa,471 MPa,5.89%respectively.（3）The creep test under the 200℃/300 MPa condition showed that 2024Sc aluminum alloy had the best creep performance under aging state（solution at 495℃for2 h,two-stage aging at 130℃×3 h+200℃×5 h）,whose creep life was 24.78 h and steady creep rate was 9.83×10^-6 s^-1.Among the composites,the creep life of 2mm C_f/2024Sc composite was 21.16 h and the steady creep rate was 1.05×10^-5 s^-1.The creep property decreased with the increased of carbon fiber length.（4）The creep tests at different temperatures（150℃,170℃,190℃）and stresses（200-400 MPa）in the under aged state（5 h）showed that,the creep apparent stress index n of 2024Sc aluminum alloy and composites was between 7.3-11.2,and the high n value indicated that the creep existed in the threshold stressσ_th.When the true stress index n was 5,it was found thatσ_th decreased linearly with the increased of temperature,the creep activation energy of 2024Sc,2 mm,3 mm,4 mm,5 mm C_f/2024Sc composite were respectively 104.2 k J/mol,83.9 k J/mol,72.9 k J/mol,63.8 k J/mol,67.4 k J/mol.SEM observation of creep fracture showed that the fracture mechanism of C_f was pull-out,and there was work hardening zone around the fiber.（5）The self-corrosion potential of C_f/2024Sc composites were less than 2024Sc.With the increased of C_f,the self-corrosion current density of C_f/2024Sc composites decreased gradually,and the capacitive arc radius of EIS increased gradually.Among them,the minimum self-corrosion current density of 5 mm C_f/2024Sc composite was4.61×10^-7 A/cm²,with the best corrosion resistance.