Microstructure And Texture Evolution Of Cu-24%Ag Alloy Sheets And Their Effects On The Alloy Properties

The requirements for strength and electrical conductivity of conductive materials become increasingly critical in high-field magnet and many other fields. Cu-Ag alloys prepared by in-situ compound technique possess high strength and excellent electrical conductivity. Cu-Ag alloy wires processed by cold drawing have been researched systematically, while so far few studies have been conducted on Cu-Ag alloy sheets. In the present study, Cu-24 wt.%Ag alloy sheets were processed by cold rolling and ageing technology to investigate the microstructure evolution, mechanical properties and electrical conductivity during cold rolling and heat treatment. The connection between the strengthening, conductivity and microstructure refinement of the alloy sheets was discussed, and the effect of cold rolling and ageing system on the anisotropy and orientation distribution of the alloy sheets were researched.After severe cold rolling, the microstructure develops into dual-phase multilayered structure, including Cu matrix lamellas, Ag lamellas,(Cu+Ag) eutectic lamellas and Ag precipitate-fibers embedded in Cu matrix. With increasing of rolling strain, the lamellas in longitudinal sections become curved gradually and shear bands arise. Nano-scale twins occur in both Cu matrix and Ag phase during cold rolling. The quantity of twins increases and the width decreases with increasing rolling strains.When aged at below 250℃ after cold rolled, the recovery process occurs mainly in the alloy sheets. No appreciable change is observed in the microstructure and the mechanical properties decrease slightly compared to cold-rolled alloy sheets. Local spheroidization and recrystallization occur at above 300℃. The degree of recrystallization increase and spheroidized particles aggregate and coarsen with temperature elevating. The dual-phase multilayered structure is destroyed gradually, resulting in dramatical decline of the mechanical properties. Nanometer-sized Ag phase precipitates in Cu matrix during ageing process, maintaining coherent relation with the Cu matrix. The precipitation of Ag phase can not only generate precipitation strengthening to enhance the strength but also reduce the scattering effect of solute atom to improve the electrical conductivity of the alloy sheets.The Cu-24%Ag alloy sheets with a strain of 98.9% prepared by thrice intermediate ageing technology can obtain a tensile strength of ~1043 MPa and a conductivity of 75~80% IACS. Room temperature tensile strength in excess of 900 MPa and a conductivity above 80% IACS can be achieved in the Cu-24%Ag alloy sheets with a strain of 98% processed by once intermediate ageing technology(OIAT). After aged for 0.5 h at 250℃, the alloy sheets with a strain of 98% processed by OIAT can attain a tensile strength of ~850 MPa and a conductivity of ~90% IACS.Cold rolling refines the microstructure of the Cu-24%Ag alloy and reduces the phase interface spacing continuously. When the sheets are strained to 99%, the average thickness of Cu matrix layers, Ag phase layers and eutectic lamellas are reduced to ~96 nm, ~38 nm and less than 10 nm respectively, and the thickness of Ag precipitate flat fibers decrease to ~1.5 nm. The high strength of Cu-24%Ag alloy sheets with severe plastic deformation mainly caused by Ag phase layers, Ag precipitate flat fibers and(Cu+Ag) eutectic lamellas with nanoscale thickness and spacing.After cold rolling, Cu and Ag phase of the Cu-24%Ag alloy sheets have similar orientation distribution. Strong {110}<113> texture and Goss texture are formed in both Cu and Ag phase, and the Cu phase has a higher texture intensity than the Ag phase. After aged at 450℃, Small shifts occur in the strongest orientation. When aged for 0.5~3 h at 450℃, the peak orientation moves to φ1=30° position along the α orientation fiber, and the texture intensity increases with passing of the ageing time. When aged for 8 h at 450℃, the peak orientation moves towards high φ1 value direction along the α orientation fiber, and the texture intensity declines dramatically. Whereas, the peak orientation moves towards low φ1 value direction along the α orientation fiber after aged for 12 h at 450℃. Compared with cold rolled alloy sheets, Goss texture in both Cu and Ag phase decreases substantially after aged at 450℃. The anisotropy of the mechanical properties is attributed to the texture of Cu and Ag phase and visible directional dual-phase multilayered structure and Ag fibers.