Ultrasonic Laminated And Resistance Welding Combined Grain Refining Process

Ultra-fine grained materials has became one of the main stream in materials science research because of the excellent performance, such as :excellent thermals and electrical conductivity and mechanical. In recent years, sever plastic deformation for the preparation of ultra-fine grained have became the mainstream direction in the materials scientist.The process with copper as the research object achieves the ultra-fine grained copper material, and analyzes micro-structure and properties of the prepared sample. Work carried out in to achieve the following results:1. This thesis proposes the ultrasonic laminated and resistance welding combined grain refinement process, and introduces the process in detail, the whole process including: sample preparation, ultrasonic upsetting, resistance welding and ultrasonic laminated.2. The variable is specimen upsetting times of pressure in the ultrasonic upsetting experiment. The micro-structure of the specimen after upsetting pressure is observed by optical microscope and through hardness test, deep drawing experiment analyses pure copper properties. The experiment results show that, the ultrasonic upsetting can make copper grain decrease, but it is very difficult to reduce to ultrasonic level, the hardness and tensile strength is enhancing obviously, but the elongation rate decreasing. In order to obtain ultra-fine grained copper material, sample conduct ultrasonic laminated upsetting pressure, thus putting forwarding the ultrasonic laminated and resistance welding combined grain refining process.3. The variable is specimen laminated layers in the ultrasonic laminated and resistance welding combined experiment, and analyzing the copper grain refining mechanism and performance change. The experimental results show that: when the specimen is laminated to the eight layer, grain refinement to 0.96 μm, it verifies the feasibility of the process. By drawing test and hardness experiments we found that the strength and hardness of the specimen tensile strength increases at first, then slowly declined, and the increasing trend, while the elongation rate decreases at first, then increases. Through the XRD experiment analyze the change of inner micro strain and dislocation density, find that ultrasonic laminated micro strain and dislocation density is bigger than the original state of pure copper material, but with the increase of pressure superposed layers, micro strain and dislocation density variation is not obvious.