Increased σ3 boundaries: Effects of friction stir and post heating on pure copper

This research explored the mechanisms of increased electrical conductivity in pure copper (Cu) which was first joined with aluminum via micro friction stir blind riveted and then exposed to post heating. The increased E3 boundaries with reduced random grain boundaries are the main reason contributing for this improvement. In this research, microstructural characterization, resistance measurement, and hardness testing were performed at the stir zone (SZ) and thermomechanical affected zone (TMAZ) of Cu in as-fabricated and heat-treated joints. A ratio between the fraction of E3 boundaries to total fraction of E9 and E27 boundaries was introduced to confirm that the increases of E3 boundaries in TMAZ at 300 degrees C were caused by the twinning mechanism whereas were through the regeneration mechanism in the SZ (heated at both 300 degrees C and 500 degrees C) and TMAZ (heated at 500 degrees C). Although electrical conductivity was improved by this grain boundary engineering approach, the hightemperature heating caused a dramatic reduction in microhardness due to the substantial strain relief and grain growth.

Automated summary

This study investigated the mechanisms behind the increased electrical conductivity in pure copper joined with aluminum via micro friction stir blind riveted and post-heating. The increase in E3 boundaries and reduction in random grain boundaries were identified as the main contributing factors. While this grain boundary engineering approach led to improved electrical conductivity, high-temperature heating resulted in a significant reduction in microhardness due to strain relief and grain growth.