Influence Of Electric Field On The Microstructures And Mechanical Properties Of Friction Welding Joint

By the means of experimental researches, theoretical analyses and mathematical modeling and calculations, the friction welding processes of similar and dissimilar materials under external electric field are studied. The influence of electric field on the dynamic recrystallization process, the critical dynamic recrystallization behaviors, the constitutive equations, the grain size and other mechanical metallurgical behaviors of the weld metal during the friction welding process are discussed. Much attention has been paid to the influence of electric field on the microstructures and mechanical properties at room temperature.The friction welding of similar and dissimilar materials under external electric field was realized for the first time. By using a specially designed temperature measurement method with thermocouple, the friction interface temperature was determined precisely, which offers important information for the welding process analysis. The strain rate in micro-zone and the friction torque have been also measured. By analyzing the dynamic behavior of dislocations in the deforming process at high temperature and high strain rate during friction welding, we have suggested the mechanism of the electric field effects on the thermal and mechanical conditions during the initial dynamic recrystallization process of the weld metal. We also have established the empirical formulae for the initial friction coefficient, the critical thermal and mechanical conditions at the initial dynamic recrystallization stage, the flow equation at the quasi-steady friction stage and the calculation model for the average recrystallization grain size. Furthermore, in terms of the electrical properties of metals, diffusion process and quantum-mechanical theories, two models for predicting the apparent activity energy and the strain-rate sensitivity exponent for the deformation of the weld metal during the friction welding process of LY12CZ alloy under external electric field have been derived respectively.The evolution of microstructure, dislocations, composition, the precipitation phases and so on during the friction welding process of LY12CZ alloy under external electric field were studied in details. Using quantitative microstructure analysis technology, the average equivalent diameter and aspect ratio of dynamicrecrystallization grains in the dynamic recrystallization zone (DRZ) and the weld zone (WZ) have been determined in the cases with and without the electric field respectively. The influences of electric field on the room temperature mechanical properties and thetorsion fracture morphology of the friction welding joint of LY12CZ alloy have been investigated. Statistic relationships between the friction welding parameters, the intensity of electric field and the room temperature torsional properties have been proposed.We have also studied quantitatively the electric field effects on the microstructure, the diffusion behavior of the main elements and the room temperature torsional properties arround the friction welding interface between T2 copper and 1Crl8Ni9Ti steel under external electric field. After that, heat treatment in external electric field for the friction welded joint between copper and stainless steel has been done. The interdiffusion coefficient and diffusion activity energy of the dominating elements around the friction welding interface of the two different materials, T2 copper and 1Crl8Ni9Ti steel, the heat treatment process both with and without the electric field have been calculated respectively. The relationship between the intensity of electric field and the diffusion activity energy has been obtained and analyzed. The interaction mechanism of external electric field on microstructure and property of the friction welding joint of dissimilar materials through diffusion process has been proclaimed...