The structure transformation in an Al–Li–Zn–Mg–Cu–Zr alloy

The precipitation behavior in an Al–Li–Zn–Mg–Cu–Zr alloy has been studied by transmission electron microscopy (TEM) and Vickers hardness tester during artificial aging. Aging was performed at 393, 433 and 473 K for different time respectively. For samples aged at 393 K, only precipitation of δ′ particles was observed under TEM, and the efficient hardening came from δ′ particles. Samples aged at 433 K hardened in two stages separated by a hardness plateau on the aging kinetics curve. In the first stage, hardening comes from δ′ particles only and, in the second stage, the hardening is a result of precipitation of both δ′ particles and X particles. For samples aged at 473 K, there was only one aging peak on the aging kinetics curve, and the hardening is a consequence of precipitation of both δ′ particles and X particles. alysis indicated that δ′ phase with lower nucleation activation energy and Li with higher vacancy-bond energy contributes to the different precipitation response in the alloy at 393, 433 and 473 K.