| Kovar alloy has good electrical conductivity,welding,structural stability,welding performance and anti-atomic oxygen oxidation characteristics,and has been widely used in the aerospace field.Ag/Kovar/Ag is a space battery interconnect material with significant application requirements.However,the traditional coating method is limited by the defect of the preparation method,and cannot be rolled to coil preparation,and the stability and reliability of the prepared materials is poor.This paper combines the technical requirements of continuous high-performance Ag/Kovar/Ag interconnect materials proposed by Shanghai Academy of Spaceflight Technology,and carries out the process and theoretical research on the preparation of Ag/Kovar/Ag composite strip by rolling composite method.This paper mainly studies the composite process of room temperature rolling Ag/Kovar/Ag strip and the subsequent diffusion annealing process.The effect of rolling composite with different sizes of silver was analyzed.The effect of composite process and diffusion annealing on the microstructure and interfacial bonding of composite interface was studied by means of optical microscope,scanning electron microscope,energy spectrum analysis.The mechanical properties of the annealed Ag/Kovar/Ag strip were tested by room temperature tensile test.The effects of microstructure and interfacial bonding on the mechanical properties of the composite strips after annealing were discussed.The main conclusions are as follows:For the rolling billet with Ag/Kovar thickness ratio of 15:50,brass wrapping is beneficial to stable rolling.Compared with the ratio of Ag/Kovar thickness of 15:50 and 50:50,the interface bonding effect and layer thickness of composite strip with thickness ratio of 100:50 are better,and there is no obvious layer or void between layers.The peeling test and characterization results of the composite samples show that the bonding of the rolled composite samples is better with the increase of reduction ratio,and the metal extrusion volume in the Ag layer is higher than that in the Kovar layer at the interface position.The composite strip with 100:50 thickness of Ag/Kovar was annealed in the annealing temperature range of 800℃～900℃.The annealing time was 10 h～14 h.SEM and EDS analysis of the annealed samples showed that no intermetallic compounds were formed at the interface,but metallurgical bonding was formed.The diffusion depth of Kovar alloy to Ag side was about 1μm.Tensile tests at room temperature with strain rate of 1.11×10-4s-1 for the composite strip show that the yield strength and tensile strength of the diffusion annealed sample are lower than those of the rolled sample,and the elongation is significantly increased.The yield strength,tensile strength and elongation of the composite strip annealed at 850℃for 12 h are 108.7 MPa,166.3M Pa and 7.86%,respectively.The tensile fracture can be a typical dimple morphology,indicating that the fracture form is ductile fracture.The annealed composite strip exhibited a coordinated deformation effect during the stretching process.There was a partial bonding point between the Ag layer and the Kovar layer after the breaking,indicating that the diffusion annealing effectively improved the interfacial bonding effect of the sample.The inheritance of the heterogeneity of the composite layer in the surface treatment stage is obvious for the preparation of micro-scale layer thickness composite strip.During rolling and bonding,the localized Kovar will be embedded in the Ag layer.After annealing,the diffusion layer of the Ag/Kovar in these areas will be deeper,which is beneficial to improve the mechanical properties of the composite thin strip. |
