Preparation Of Er-containing Ultra-high Strength Al-Zn-Mg-Cu Alloy And Effects Of Heat Treatment On Microstructure And Properties

Ultra-high strength aluminum alloy thin strips have a broad application prospect in automobile,rail transit,aerospace,electronic products,among others.The Al-7.88Zn-2.05Mg-1.70Cu-0.19Er alloy hot-rolled plate is taken for experiment in this paper,and the cold rolling pass deformation rate and annealing process are reasonably designed to obtain thin sheets with a thickness of 0.5 mm.The microstructure,mechanical properties and corrosion resistance of cold-rolled sheet in different state were investigated by means of EBSD,TEM and SSRT.The main conclusions of this paper are as follows:A preferred short-procedure process for preparing a thin strip with thickness of 0.5 mm from the Er-contained ultra-high strength Al-Zn-Mg-Cu alloy hot-rolled plate with thickness of 7.5 mm is obtained.First,perform 2 cold rolling passes on the hot-rolled plate to thickness of 3.5 mm directly,with deformation rates as 33.3%and 30%,respectively.Then the cold-rolled slab is subject to annealling as 380°C×3 h+furnace cooling to100°C+air cooling,flollowing 4 passes cold rolling as 3.5 mm→2.0mm→1.2 mm→0.8 mm→0.5 mm.Solid solution treatment has a significant effect on the stamping properties of the Er-contained ultra-high strength Al-Zn-Mg-Cu alloy sheets.The optimum solution treatment for excellent formability of the thin strip is 475℃×1h,under which the YS,El,strain hardening exponent and erichsen value are 0.67,27.3%,0.21 and 8.99 mm,respectively.The excellent heat treatment for stamped parts of the test alloy is475℃×1h+forming+120℃×6 h+150℃×24 h,the hardness,UTS,YS and El are 189.7 HV,669.39 MPa,624.1 MPa and 11.2%,respectively,and the conductivity,EXCO rating,and I_SSRT are 35.5%IACS,EA and 4.07%,respectively.After double-aging heat treatment,the fine spherical Al₃（Er,Zr）phase andη’phase uniformly distribute in the grain,which affect beneficially on the ductility,strength and stress corrosion cracking resistance of the test alloy.And fine precipitates discontinuously distribute in the grain boundaries and wide precipitates free zone reduce the stress corrosion sensitivity of the test alloy.46 figures,17 tables and 103 references are contained.