Microstructural Evolutions, Hot Deformation and Work Hardening Behaviour of Novel Al–Zn Binary Alloys Processed by Squeezing and Hot Extrusion

Abstract

The main goals of this work were to manufacture novel Al–Zn extruded alloys by varying the Zn content (0, 10, 20, 30 wt%), investigate the microstructural evolutions, hot deformation, and work hardening behaviour by hot compression test at different temperatures (25 °C, 75 °C, 150 °C, 225 °C, 300 °C). Al–20Zn alloy microstructure revealed α-Al and uniform distribution of (α + η) phases, coherent (α + η) crystals in GBs with casting defect-free surfaces, and effective interactions of pinning dislocations which led to improve mechanical performance of Al–20Zn alloy, as compared to the other alloys. The observed engineering stress–strain curve results revealed the decrease of stress with increasing of temperature due to flow softening, dynamic recovery and dynamic recrystallization. These results displayed also an increase of stress value with increasing of Zn content due to the precipitation of high density (α + η) phase in the matrix and GBs, increasing of forest and mobile dislocations density with strain fields, and the formation of fine dendrites. Work hardening rate (WHR) of extruded samples displayed three stages: stage I, WHR decreased slightly with increasing of temperature up to 75 °C and decreased drastically from 75 °C to 300 °C due to softening; stage II, WHR maintained constant due to balance between dislocation generations and dislocation annihilation; stage III, WHR slightly increased due to strain hardening of (α + η) phase. WHR was observed to increase considerably with increasing of Zn content due to the formation and dispersion of high density of (α + η) phase in the Al matrix and GBs. Deformation micro-localization in terms of different characteristics was examined and reported on the deformed samples after hot-compression test through SEM micrographs.