Effect of Heat Treatment on Microstructures and Mechanical Properties of Al-Zn-Mg-Cu-Sc-Zr Alloys

The microstructures and mechanical properties of Al-Zn-Mg-Cu-Sc-Zr alloys under different treatment conditions were studied by hardness test,tensile properties and electric conductivity,optical microscope and TEM observation.The result shows that the suitable solution treatment is solution at 470℃ for 120min.The peak ageing occurs at 120℃ for 24h.When the ageing treatment is RRA treatment(Retrogression and Re-ageing): 120℃×24 h+170℃×1 h+120℃×24 h,the synthetic properties is best.At this condition,the tensile strength,yield strength,elongation and electric conductivity of studied alloy are 595.8 MPa,572.0 MPa,8.3% and 38.45%IACS respectively.The age hardening of the studied alloys is obvious.The main strengthening mechanisms of the alloy are precipitation hardening,fine-grain strengthening and substructure strengthening.The main strengthening phases are GP zone,η′ and Al3(Sc,Zr).