Effect of friction stir welding (FSW) parameters on strain hardening behavior of pure copper joints

Effect of tool rotation rate and traverse speed on strain hardening behavior of friction stir welded (FSWed) copper joints were investigated using hardening capacity and strain hardening exponent concepts. Kocks–Mecking type plots were used to show different stages of strain hardening. FSWed samples reveals higher hardening capacity and lower strain hardening exponent relative to base metal. With increasing rotation rate and/or decreasing traverse speed, FSWed samples show higher hardening capacity and lower strain hardening exponent. The strain hardening behavior was discussed by dislocation density and grain size variation during FSW. In addition, the microstructure and mechanical properties of the samples were investigated in detail. Four different zones were observed in microstructure of FSWed joints. The joints showed finer grain structure and weaker mechanical properties relative to base metal due to dynamic recrystallization and lower dislocation density.

► Strain hardening of friction stir welded (FSWed) copper joints were investigated.
► Base metal (BM) and FSWed samples exhibited stages III and IV of deformation.
► FSWed samples exhibited higher hardening capacity (Hc) relative to BM.
► FSWed samples exhibited lower strain hardening exponent (n∗) relative to BM.
► Increasing rotation rate or decreasing traverse speed led to higher Hc and lower n∗.