Precipitation Effects in Cast, Heat-Treated and Cold-Rolled Aluminium AA7075 Alloy with Sc,Zr-Addition

Abstract:

The commercial Al–Zn–Mg–Cu-based alloys (7xxx series) are widely used in metalworking, automotive and aircraft industries as well as in aeronautical applications. The positive effect of the Sc,Zr-addition on mechanical properties of laboratory Al-based alloys is generally known. The microstructure, mechanical and thermal properties of the conventionally cast, heat-treated and cold-rolled Al–Zn–Mg–Cu (–Sc–Zr) alloys during isochronal annealing and natural ageing were studied. Microstructure observation by scanning electron microscopy and transmission electron microscopy proved the Zn,Mg,Cu-containing eutectic phase at grain boundaries. The distinct changes in microhardness curves as well as in a heat flow of the alloys studied are mainly caused by dissolution of the clusters/Guinier-Preston (GP) zones and precipitation of particles from the Al–Zn–Mg–Cu system. An easier diffusion of Zn, Mg and Cu atoms along dislocations in the cold-rolled alloys is responsible for the precipitation of the Zn,Mg,Cu-containing particles at lower temperatures compared to the cast alloys. Microhardness values of the heat-treated alloys increase immediately from the beginning of natural ageing due to the formation of the clusters/GP zones. Addition of Sc and Zr elements results in a higher hardness above ~ 270 °C due to a strengthening by coherent secondary Al₃(Sc,Zr) particles with a good thermal stability. Sc,Zr-addition has probably no influence on the evolution of the solute clusters/GP zones.

• Periodical: Defect and Diffusion Forum (Volume 413)
• Pages: 217-224
• DOI: https://doi.org/10.4028/www.scientific.net/DDF.413.217
• Online since: December 2021
• Authors: Martin Vlach*, Veronika Kodetová, Hana Kudrnová, Michal Leibner, Sebastien Zikmund, Vladimír Šíma, Ivan Procházka, Miroslav Cieslar, Lucia Bajtošová, Jakub Čížek, Vladimír Mára, Vladivoj Očenášek
• Keywords: Al-Zn-Mg-Cu-Based Alloys, Differential Scanning Calorimetry, Homogenization, PAS, TEM

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