Deep-cryogenic-treatment-induced phase transformation in the Al-Zn-Mg-Cu alloy

An aluminum alloy (Al–Zn–Mg–Cu) subjected to deep cryogenic treatment (DCT) was systematically investigated. The results show that a DCT-induced phase transformation varies the microstructures and affects the mechanical properties of the Al alloy. Both Guinier–Preston (GP) zones and a metastableη′phase were observed by high-resolution transmission electron microscopy. The phenomenon of the second precipitation of the GP zones in samples subjected to DCT after being aged was observed. The viability of this phase transfor-mation was also demonstrated by first-principles calculations.