Influences of temperature and Sn-addition on microstructural evolution of Ag during FSW

ABSTRACT

The microstructural evolutions of pure Ag and Ag-0.75 wt-%Sn during rapid cooling friction stir welding (FSW) were examined. At the lower welding temperature of FSW conditions, the annealing twinning was highly suppressed and the microstructural evolution was dominated by the discontinuous dynamic recrystallisation (DDRX) via the high angle boundary (HAB) bulging. The fully recrystallised microstructure was remarkably finer than that formed through the frequent annealing twinning at the higher welding temperature. Moreover, the Sn-addition caused the HAB bulging due to the inhibition of dynamic recovery and decreased mobility of grain boundaries. With decreasing the ratio of the peak temperature to the recrystallisation temperature, the dominant grain refinement mechanism is implied to change from the annealing twinning to the DDRX.

KEYWORDS:

• Friction stir welding
• discontinuous dynamic recrystallisation
• twinning
• electron backscattering diffraction

Acknowledgements

This paper is based on results obtained from a future pioneering project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

T. Nagira http://orcid.org/0000-0002-2415-0623

X. C. Liu http://orcid.org/0000-0002-0313-6697