GP-zones in Al–Zn–Mg alloys and their role in artificial aging

✍ Scribed by L.K Berg; J Gjønnes; V Hansen; X.Z Li; M Knutson-Wedel; G Waterloo; D Schryvers; L.R Wallenberg

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 532 KB
• Volume: 49
• Category: Article
• ISSN: 1359-6454
• DOI: 10.1016/s1359-6454(01)00251-8

✦ Synopsis

The structure of GP-zones in an industrial, 7xxx-series Al-Zn-Mg alloy has been investigated by transmission electron microscopy methods: selected area diffraction, conventional and high-resolution imaging. Two types of GP-zones, GP(I) and (II) are characterized by their electron diffraction patterns. GP(I)zones are formed over a wide temperature range, from room temperature to 140-150°C, independently of quenching temperature. The GP(I)-zones are coherent with the aluminum matrix, with internal ordering of Zn and Al/Mg on the matrix lattice, suggested to be based on AuCu(I)-type sub-unit, and anti-phase boundaries. GP(II) are formed after quenching from temperatures above 450°C, by aging at temperatures above 70°C. The GP(II)-zones are described as zinc-rich layers on {111}-planes, with internal order in the form of elongated Ͻ110Ͼ domains. The structural relation to the hЈ-precipitate is discussed.