Application Of EBSD To The Microstructure And Mechanical Properties Of A New Type Of Al-Zn-Mg-Cu-Sc-Zr Alloys

Al-Zn-Mg-Cu alloys have been extensively used for structural applications in the automobile and aerospace industries due to their light weight,excellent mechanical performances and good processability.Rare earth element scandium exhibits grain refinement,recrystallization inhibition and strengthening enhancement.However,the extensive application in aluminum alloys is limited by the high price of Sc.As another efficient element with relatively low price,zirconium can decrease the average grain size and increase tensile strength as well.Thus,a new type of aluminum alloys with high performance and low price can be obtained by adding combined additions of Sc and Zr.In this work,we designed a new type of Al-Zn-Mg-Cu-Sc-Zr alloys with different Sc and Zr additions.The effects of Sc/Zr ratio and the total amount of Sc and Zr on the microstructure and mechanical performances were investigated through the microstructure analysis and performance tests on the alloys in different states of cold rolling,homogenization annealing and aging treatments.Furthermore,the mechanism of the Al-Zn-Mg-Cu-Sc-Zr alloys was also investigated.Electron back scattering diffraction?EBSD?technology test provides more information on orientation of different phase in alloys,to deepen the understanding of alloy in recrystallization inhibition,mechanical properties and strengthening mechanism provide an advanced characterization method.The analysis technique has unique advantages in the determination of crystal orientation,microscopic parameters of texture and statistical grain boundary structure.As is well known to all,the vast majority of engineering materials is polycrystal whose performance is related to the basic properties of single crystal of the polycrystal,grain size,the crystal orientation of relationship between neighboring grain and the interface structure.This work mainly adopts the EBSD technique in the new type of aluminum alloy's microstructure analysis,the orientation figure of rolling surface is obtained to analyze the microstructure of rolling procedure,thereby mechanical properties can be explained preferably.The results indicate that combined additions of Sc and Zr?0⁰.6wt.%?exhibit excellent antirecrystallization behavior and strengthening enhancement effect.The highest strength was obtained by adding 0.22 Sc and 0.40Zr?wt.%?after aging treatment at 120? for 24 h.The maximum ultimate tensile strength and yield strengthare 668 MPa and 628 MPa,respectively.Precipitate strengthening is attributed to GP zones ? ?' phase and secondary Al₃?Sc,Zr?particles.The mainly strengthening mechanisms of Al-Zn-Mg-Cu-Sc-Zr alloys are fine grain strengthening,subgrain boundaries strengthening and precipitate strengthening.