Age Hardening Response of AA7108A investigated by means of Synchrotron-based X-ray Absorption Spectroscopy (XAS) Measurements
- Resource Type
- ACADEMIC JOURNAL
- In Materials Science & Engineering A January 2018
Enhanced strengthening achieved during age hardening of 7xxx alloys, necessitated the need to study the age hardening response of Cu-free AA7108A wire, as a potential material for automobile fastener production. Age hardening response was investigated by means of Synchrotron-based X-ray Absorption Spectroscopy (XAS) measurements. Linear combination fitting (LCF), using XANES spectra of Zn K-edge showed the gradual removal of Zn atoms from the aluminum matrix of the T4 condition (where Zn is in solution and in GP zones), when subjected to one-step artificial aging treatment at 130°C and 200°C, respectively. The reduction of matrix Zn during aging at 130°C is mainly due to the precipitation of the semi-coherent η’ phase, whose number density increased with increasing aging time. η’ phase is the major phase responsible for hardness and electrical conductivity increase during aging at 130°C. Reduction of matrix Zn concentration during aging at 200°C is due to the formation and coarsening of the incoherent η-MgZn2 phase. This resulted in a dramatic decrease in hardness and an increasing trend in the electrical conductivity during aging at 200°C. Calorimetric study revealed that natural aging occurred at room temperature after solution treatment, and GP zone solvus is found to be below 130°C. In addition, precipitation of the η’ phase at 130°C is retarded, due to reduced concentration of vacancies, attributed to the presence of Zirconium (Zr) in the alloy.