Characterization of Si particles and their effects on and recrystallization in a nanostructured cold rolled Al-1% Si alloy

Abstract

Abstract. An Al-1.08 vol.%Si alloy was cold rolled to a reduction of 98% (vM = 4.5) and then annealed at different temperatures up to 210C (0.52 Tm) for different times. The deformed structure is characterized by a nanoscale lamellar structure with the presence of Si particles of coarse (> 1m), medium (100 nm -1 m) and fine (< 100 nm) sizes in the microstructure. Deformation zones are formed around the coarse Si particles and the boundary spacing is finer in the deformation zone than in the matrix. The medium Si particles have little effect on the morphology and boundary spacing. The fine Si particles are aligned along the lamellar boundaries indicating a stabilizing effect on the structural refinement during cold rolling. After annealing, enhanced recovery occurs in the deformation zones around the coarse Si particles. However the reduction in stored energy during recovery and the pinning effect of fine Si particles on the boundary migration prevent the advantage of particle stimulated nucleation (PSN) of coarse Si particles in the nanoscale lamellar structure. This study also demonstrates an important effect of the fine particles in delaying both recovery and recrystallization processes. This effect diminishes with increasing annealing temperature and coarsening the fine particles especially at triple junctions. IntroductionThe effect of second phase particles on the deformation microstructure and recrystallization of Al alloys has been extensively studied in the literature [1][2][3][4][5][6][7]. It is generally observed that the recrystallization kinetics in alloys containing large particles (typically with sizes > 1 m) is accelerated while that in alloys containing fine particles is retarded. In the case of containing both coarse and fine particles, the overall kinetics of recrystallization could be retarded or accelerated depending on the relative strength of the effects from the two types of particles [3].In a recent study [8], a nanostructured Al-1%Si (or Al-1.08% vol.%Si) alloy with an ultrahigh purity Al matrix (99.9996%) was produced by heavy cold rolling to 98% thickness reduction (vM = 4.5). The nanostructured Al-1%Si alloy is characterized by a lamellar structure with an average lamellar boundary spacing of 230 nm, a fine dispersion of nanosized Si particles and a certain amount of large Si particles [8]. The Si particles of different sizes are expected to affect the structural and textural evolution during deformation and annealing of the nanostructured alloy. In this study, this effect has been analyzed separately for coarse and fine particles including their combined effect.

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