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    • Keywords


      Two-step ageing; delayed ageing; clusters; coherency strains

    • Abstract


      In commercial practice, two-step ageing is commonly used in Al-Zn-Mg alloys to produce a fine dispersion of η′ precipitates to accentuate the mechanical properties and resistance to stress corrosion cracking. While this is true in Al-Zn-Mg alloys, two-step ageing leads to inferior properties in Al-Mg-Si alloys. This controversial behaviour in different alloys can be explained by Pashley’s Kinetic model. Pashley’s model addresses the stability of clusters after two-step ageing. In the development of the model, the surface energy term between cluster and matrix is taken into account while the coherency strains between the cluster and matrix are not considered. In the present work, a model is developed which takes into account the coherency strains between cluster and matrix and defines a new stability criterion, inclusive of strain energy term. Experiments were done on AA 7010 aluminium alloy by carrying out a two-step ageing treatment and the results fit the new stability criterion. Thus it is found that the new model for two-step ageing is verified in the case of Al-Zn-Mg alloy.

    • Author Affiliations


      K T Kashyap1 2 C Ramachandra1 B Chatterji1 S Lele1

      1. central materials and processes laboratory, foundry & forge division, hindustan aeronautics limited, bangalore - 560 017, india
      2. Department of Metallurgical Engineering, Banaras Hindu University, Varanasi - 221 005, India
    • Dates

  • Bulletin of Materials Science | News

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      Posted on July 25, 2019

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