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Precipitation processes and structural evolutions of various GPB zones and two types of S phases in a cold-rolled Al-Mg-Cu alloy

Abstract

The Guinier–Preston–Bagaryatsky (GPB) zone and the S phase are the key strengthening precipitates in Al-Cu-Mg alloys. However, how their respective structures evolve during aging has not been fully understood. In this work, the age-hardening behavior and the precipitates in an Al–3Mg–1Cu (wt.%) alloy were investigated by means of Vickers hardness measurements, differential scanning calorimetry, transmission electron microscopy, and density functional theory calculations. A series of common GPB zones and a novel type of GPB zone named “GPBX” were observed in the cold-worked samples aged at 443 K for 20 min. In the subsequent aging, two types of S phases were found to coexist, labeled S-I and S-II phases. Density functional theory calculation results indicate that GPBX zone is stable and the S-I and S-II phases have almost the same formation enthalpy. Common GPB zones transform to S-I phases, while S-II phases are formed from GPBX zones preferentially along dislocation lines. The misorientation angles and morphologies of the S phases are also discussed. GPB zones were confirmed to be structurally linked to β” and U2 precipitates reported in 6xxx (Al-Mg-Si) series Al alloys. The revealed precipitate structures and their interrelationships may provide insights into future alloy design.

Category

Academic article

Language

English

Author(s)

Affiliation

  • SINTEF Industry / Materials and Nanotechnology
  • Norwegian University of Science and Technology
  • Tokyo Institute of Technology

Date

01.01.2021

Year

2021

Published in

Materials & design

ISSN

0264-1275

Volume

199

View this publication at Norwegian Research Information Repository