Microstructure and Mechanical Properties of FSW Lap Joint between Pure Copper and 1018 Mild Steel Using Refractory Metal Pin Tools

摘要

Friction stir welding was conducted on a copper/steel lap joint configuration. Two different W-25%Re-4% HfC pin tools, having two different pin diameters and pin lengths, were investigated to examine the combined effect of plunge depth and bonding area on joint properties. The effects of travel speeds and alternating the top and bottom sheet materials on the microstructure and mechanical properties were also investigated. Structures of the joining interface were analyzed by optical and scanning electron microscopy. Joint strength and fatigue strength were also evaluated. The results showed a "hook-like" feature on both the advancing and retreating sides, but more severe on the retreating side. The interface was bonded both by mechanical mixing between copper and steel and metallurgically as evidenced by a diffusion zone formed between Fe-Cu.