Wang, S.C., Starink, M.J. and Gao, N.
Overview of recent work on precipitation in Al-Cu-Mg alloys.
Materials Science Forum, 546-549, .
Recent work on Al-Cu-Mg based alloys with Cu:Mg atomic ratio close to unity is reviewed to clarify the mechanisms for age hardening. During the first stage of hardening a substantial exothermic heat evolution occurs whilst the microstructural change involves the formation of initially Cu-rich / Mg-rich clusters and later Cu-Mg co-clusters. The data show that the first stage of the age hardening is due to the formation of Cu-Mg co-clusters. The combined experimental methods show the second stage hardening is dominated by formation of S phase, which forms a dense precipitation at the peak hardness stage, whilst no significant amounts of other phases or zones are detected. S phase strengthens the alloy predominantly through the Orowan looping mechanism. These findings are incorporated into a multi-phase, multi-mechanism model for yield strength of Al-Cu-Mg based alloys.
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