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The partial weak bonding phenomenon induced by an unsuitable welding parameter often occurs at the joint interface of Al/Cu dissimilar friction stir welding (FSW). Diffusion time, temperature, and pressure are the main factors that affect the diffusion behavior at the interface. Therefore, molecular dynamics (MD) simulation is used to investigate the influence mechanism of these factors from the perspectives of diffusion thickness, total energy, and volume. The diffusion time and the temperature affect the diffusion thickness significantly, whereas external pressure has little impact. The variations of total energy and volume consist of two stages, which are caused by the combined effects of lattice transformation and atomic diffusion. The variation processes of total energy and volume are accelerated with the increase in temperature due to a higher diffusion velocity, and it is delayed by external pressure at a higher temperature because the lattice transformation is inhibited. These findings are beneficial to the choice of welding parameters in actual production.

This paper analyzes the measure principle of flexible joint stiffness and constructs the measuring system of flexible joint stiffness. It achieves the measurement of flexible joint’s torque-rotation angle stiffness through designing the measuring appliance and translocating clamp. The result shows that it is efficient to develop the measuring system and repeatability error is better than 1%.