| Kovar is often used for electrical packaging material as a kind of precision alloy the expansion coefficient of which is close to glass in the electronics sector and telecommunication industry,it also serves as lead wire or lead frame on transistors and integrated circuits and so on,the higher requirement is needed to its anisotropy of mechanics.Systematic research on the performance and production process of Kovar has not been attached enough importance because it not widely used just like other facecentered cubic alloys,then there is a gap in the performance of Chinese products compared with the developed countries.This paper tracked the production process of AgCu15-Kovar clad strip produced in a domestic factory,the influence of annealing temperature and other factors to the in-plane anisotropy were studied.The main process flows of clad strip consist of hot rolling,annealling,muti-pass cold rolling,finished product of 0.19 mm was obtained.This paper tracked and analysed the microstructure,texture and hardness of Kovar layer in the overlay strip firstly,some typical state samples were selected for mechanical test,and tried to explore effects of annealing temperature and time on mechanical anisotropy.The microstructure and fracture appearance of alloy were observed by optical microscope,scanning electronic microscope and transmission electron microscope,used XRD to measure the texture type,volume fraction and intensity.Mechanical properties parameters in different orientations obtained through room temperature tensile test and hardness testing.The main results were as follows:(1)The evolution of the texture of Kovar in present process is that the Cube {001} <100> texture of alloy substrate is converted into Brass R {111} <112>,<100> fiber,<011> fiber and so on,which are relatively random and weak,then transform into single N-Cube {100} <110> texture after short annealing,α fiber and β fiber are dominant in the cold rolling process.(2)When the hot-rolling bonding strip annealing at the temperature below 400°C for 1 h,strong N-Cube {100} <110> texture was obtained in Kovar during the recovery,the anisotropy of yield strength and elongation of the sample decreased after annealed at 400°C for 1 h.The texture type of the first cold rolling strip in Kovar didn’t change when annealing at the temperature below 600°C for 1 h,but recrystallization occured after annealing at 800°C for 2 h,the texture was changed to Cube {001} <100>,the first cold-rolling sample which subjected to annealing at 450°C for 1 h had the lowest mechanical anisotropy than other annealed samples.(3)The texture of final rolled sample of present process was the main factor for mechanical anisotropy,annealing at 450°C for 1 h after the first cold rolling would reduce the plastic anisotropy of the final rolled sample obviously while increasing the yield strength anisotropy slightly. |
