Softening by severe plastic deformation and hardening by annealing of aluminum–zinc alloy: Significance of elemental and spinodal decompositions

Abstract

An Al-30 mol.% Zn supersaturated solid solution alloy was severely deformed using highpressure torsion (HPT) at 300 K and subsequently annealed at 373-673 K. The hardness and tensile strength significantly decreased and the tensile ductility increased with straining by HPT and reached a steady-state level at large imposed strains. Despite this softening behavior, the lattice strain was increased, Zn-rich particles were precipitated and the initial coarse grains were refined significantly to a size of ~190 nm while being accompanied by decomposition to Al-and Zn-rich phases because of rapid atomic diffusion. The subsequent annealing led to a hardening, but microstructural observations showed that decrease in the lattice strain, increase in the grain size and reduction in the fraction of precipitates occurred by annealing. It was shown that the unusual softening/hardening behavior of the Al-Zn alloy was mainly due to the contribution of spinodal decomposition. The formation of nano-sized lamellae by spinodal decomposition resulted in increase in hardness after solution treatment and after post-HPT annealing, while this lamellar structure was destroyed by HPT which resulted in softening. The softening was less significant when the hardness was evaluated at low homologous temperatures.

Metallurgical Alchemy by Ultra-Severe Plastic Deformation via High-Pressure Torsion Process

“…These superplastic behaviors, which occurred at 0.350.36T m , are considered as the first reports on achieving room-temperature superplasticity in any Mgand Al-based alloys. It should be noted that the application of ultra-SPD was essential to achieve room-temperature superplasticity as earlier attempts using the conventional SPD processing could not lead to room-temperatures superplasticity in the MgLi 7678) and AlZn 79,80) alloys. The MgLi and AlZn processed by ultra-SPD are not so stable at room temperature and they exhibit grain coarsening and unusual hardening during time due to the weakening of grain-boundary sliding.…”

Effect of Mo addition on the microstructure and hardness of ultrafine-grained Ni alloys processed by a combination of cryorolling and high-pressure torsion

“…In the past two decades, numerous investigations were carried to study the microstructure and the mechanical properties of various SPD processed alloys, such as Al-Mg, Al-Zn-Mg, Cu-Zn, Cu-Al, Cu-Cr, Cu-Zr etc. [14][15][16][17][18][19][20][21][22][23]. However, no research was conducted to date to examine the effect of Mo solute atoms on the microstructure of UFG Ni processed by SPD, although Ni-Mo alloys have important practical applications.…”

Ultrafine Grained Structures Resulting from SPD‐Induced Phase Transformation in Al–Zn Alloys

“…But under such conditions, the final microstructures are also difficult to control because of the strong interaction between defects and solute atoms. It has even been demonstrated that in some binary systems, namely Al–Cu and Al–Zn, the quenched supersaturated solid solutions are destabilized during SPD at room temperature (RT) leading to the nucleation and growth of a large density of precipitates. It has been proposed that the atomic mobility could be significantly enhanced during SPD especially thanks to the high vacancy concentration, solute drag by dislocations, pipe diffusion along dislocations, or grain boundary diffusion .…”