Precipitation of a new platelet phase during the quenching of an Al-Zn-Mg-Cu alloy

Yong Zhang; Matthew Weyland; Benjamin Milkereit; Michael Reich; Paul A Rometsch

doi:10.1038/srep23109

Precipitation of a new platelet phase during the quenching of an Al-Zn-Mg-Cu alloy

Sci Rep. 2016 Mar 16:6:23109. doi: 10.1038/srep23109.

Authors

Yong Zhang¹, Matthew Weyland^{1

2}, Benjamin Milkereit^{3

4}, Michael Reich³, Paul A Rometsch¹

Affiliations

¹ Department of Materials Science and Engineering, Monash University, Clayton, VIC 3800, Australia.
² Monash Centre for Electron Microscopy, Monash University, Clayton, VIC 3800, Australia.
³ Chair of Materials Science, Faculty of Marine Technology and Mechanical Engineering, University of Rostock, 18051 Rostock, Germany.
⁴ CALOR - Research Competence Center Calorimetry and Thermal Analysis Rostock, Faculty for Interdisciplinary Research, Department Light, Life and Matter, University of Rostock, 18051 Rostock, Germany.

Abstract

A previously undescribed high aspect ratio strengthening platelet phase, herein named the Y-phase, has been identified in a commercial Al-Zn-Mg-Cu alloy. Differential scanning calorimetry indicates that this phase only precipitates at temperature and cooling rate of about 150-250 °C and 0.05-300 K/s, respectively. This precipitate is shown to be responsible for a noticeable improvement in mechanical properties. Aberration corrected scanning transmission electron microscopy demonstrates the minimal thickness (~1.4 nm) precipitate plates are isostructural to those of the T1 (Al2CuLi) phase observed in Al-Cu-Li alloys. Low voltage chemical analysis by energy dispersive X-ray spectroscopy and electron energy loss spectroscopy gives evidence of the spatial partitioning of the Al, Cu and Zn within the Y-phase, as well as demonstrating the incorporation of a small amount of Mg.