| Because of their excellent wear resistance, impact resistance, the electrochemical performance characteristics, Pb-Al composite materials have presented tremendous developing potentiality in aerospace and metallurgical industry. Especially in metallurgical industry, Pb-Al composite materials have showed attractive application due to their excellent electrochemical performance, light weight and high mechanical strength characteristic. There is the thermodynamics of solubility problem between Pb and Al in the welding process. Therefore, the solubility and weldability problems of Pb and Al are the key to block Pb-Al composite materials wide application.In order to improve the solubility of Pb and Al, the interfacial tension of Al/Sn, the enthalpy of solution of Al in Sn, the enthalpy of solution of Al in Pb and the mixing enthalpy of Pb-Sn alloy have been calculated based on Miedema Model in this paper. On the base of the previous research work, it is proved that the addition of Sn can effectively reduce the interfacial tension of Pb/Al and reduce dissolve heat in diffusion zone, which is to promote the diffusion reaction among Pb, Sn and Al.By experiments the Al/Sn and Pb/Sn diffusion dissolve layers were prepared by means of hot pressing diffusion welding technology. Based on the material dynamics and diffusion thermodynamic theories, the morphological features of the Al/Sn and Pb/Sn diffusion dissolve layers are studied, and it is researched that the diffusion reactions of Al/Sn and Pb/Sn interface zone are promoted by the addition of Sn. Meanwhile, the Pb/Sn/Al composite materials were prepared by hot pressing diffusion welding technology. Using mordent technical means, the microstructure characteristics, diffusion behavior of element near the interface, phase structure, tearing fracture surface, electric properties, mechanical properties and electrochemical performance are analyzed.The results are as follows:(1) At the heat temperature of230℃, pressure of0.5MPa and different holding time, it prior to permeate through Al grain boundary for Sn element, then spread along Al substrate. With the increase of the bond time, there exists a strong elemental diffusion and dissolution between Sn and Al, finally there is no new phases formed at interface. The interface transition layer, which is sawteeth shape, consists of Al and Sn alloy. The formation of metallurgical bonding interface comes from the solid phase diffusion, eutectic reaction, dissolution and crystallization between Al and Sn.(2) Under the heat treatment condition of200℃and different bond time, it is easy to form the diffusion dissolve layer consisting of a-Pb and (3-Sn solid solutions at the Pb/Sn interface. With the increase of the bond time, the alternant distribution interface morphology of α-Pb and β-Sn solid solutions change into another interface morphology of star β-Sn distribution into a-Pb solid solution.(3) Under the heat treatment condition of230℃, pressure of0.5MPa and the holding time of12h, the Pb/Sn/Al diffusion bonded-joints combined well can be obtained. The interfacial transition zone include Al transition layer(consist of nano Pb and Pb-Sn composite phase) and Pb transition layer(consist of α-Pb and β-Sn solid solutions). The obvious dimple-crack characters on the SEM fracture surface of the composites are observed, and the fracture mechanism is plastic fracture. Pb/Sn/Al composite samples achieve true metallurgical combination.(4) The test results of electric conductivity, the flexural strength and electrochemical properties show that the addition of Sn can effectively improve the electric conductivity and flexural strength of Pb/Sn/Al composit electrode. Compared with traditional Pb-Ag alloy, the conductivity is improved, bending strength is improved by47.5%. Due to the improvement of electric conductivity, the electrochemical properties of Pb/Sn/Al composit electrode also have been improved, which present better catalytic activity. |
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