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Abstract
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A non-equilibrium heat treatment was used to produce secondary phase (b) in the single phase
brass (a), which caused the modification of the grain structure and mechanical properties after
friction stir processing. For this aim, the single phase brass plate containing 37 wt pct Zn was
heated at 810 C for 1 hour, and then quenched in water, which caused the formation of
non-equilibrium secondary b phase. After the non-equilibrium heat treatment, bead on plate
friction stir processing was employed. The origin of the modification by b phase was studied
using high resolution electron backscattered diffraction and transmission electron microscopy.
The results showed that the average grain size, yield strength, and strain-hardening exponent
were changed, respectively, from 4.8 lm, 166 MPa and 0.28 to 2.1 lm, 213 MPa and 0.25 in the
presence of b phase. The b phase promoted the discontinuous dynamic recrystallization by
particle-stimulated nucleation mechanism, and then transformed to a resulting in a finer
microstructure with more random texture. In addition, the nanometer-sized b particles were
retained at the grain boundaries, which reduced their mobility and hence the grain growth was
inhibited.
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