Transformation of structure and properties of Al–Zn–Mg–Cu alloy under complex processing. Part. I. Microstructure

Keywords

7075 alloy, twin-roll casting, hot rolling, quenching, aging, microstructure.

Cite as

Pryhunova A. H., Nohovitsyn О. V., Aiupova Т. А., Abolikhina O. V., and Nosko О. А. Transformation of structure and properties of Al–Zn–Mg–Cu alloy under complex processing. Part. I. Microstructure. Physicochemical Mechanics of Materials. 2025. 61(2), 005-013.

https://doi.org/10.15407/pcmm2025.02.005

Abstract

The structure formation of the 7075 Al–Zn–Mg–Cu alloy with a maximum allowable zinc content (6.1 mass%) and a crystallization range of 162°C was studied during the complex technological process “twin-roll casting–hot rolling–heat treatment”. It is shown that the structure of the cast strip during twin-roll casting is non-dendritic, with dispersed inter­metallic precipitates present within the grains. At the grain boundaries, non-equilibrium eutectics are formed. Hot rolling with a deformation degree of ε = 64–88% causes the orientation of the primary solid solution (Al) crystals in the rolling direction process and a reduction in their size in the plane perpendicular to the strip surface. The volume fraction and size of intermetallics decrease monotonically due to the mechanical effects of rolling and the partial dissolution of strengthening phases in the solid solution (Al). During heat treatment, the size and shape parameter of dendritic cells (Al) and intermetallics de­crease due to recrystallization and spheroidization processes. After quenching and natural aging, the supersaturation of the solid solution increases as a result of the dissolution of the strengthening phases located on the grain boundaries (Al), the iron-containing intermetal­lics of crystallization genesis and spheroidization of secondary intermetallics being pre­ser­ved. During artificial aging, the quantity and size of eutectic and secondary intermetallics increase, but their shape parameter decreases. This structural transformation differs from that observed in traditional processing technology, with smaller grain size, higher disper­sion, and a more uniform distribution of intermetallic phases, as well as the absence of macrosegregations of casting heterogeneities. This is primarily due to the hereditary in­fluence of high cooling rate from the liquid state (v ≈ 10³ °С/s) at the initial stage of the complex process.

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