Investigation of nanoscale precipitates developed in Al–0·73Mg–0·45Si–0·34Cu–0·21Cr–0·20Fe alloy

Abstract

In the present work, the developed nanoscale precipitates in Al–0·73Mg–0·45Si–0·34Cu–0·21Cr–0·20Fe (wt-%) alloy have been investigated by means of differential scanning calorimetry, electron microscopy (SEM and TEM) and microhardness measurements (HV). The addition of Cu assists the formation of Q′ phase which positively changes the alloy strength. The precipitation of β′′ nanoparticles is followed by the precipitation of β′ and/or Q′ precipitates. Both coherent and semicoherent precipitates have a positive contribution to the strengthening of the alloy. The average activation energy associated with the precipitation of β(Mg₂Si)+Q phases is very close to that for Q″ and/or Q′ phase which suggests that the two phase precipitation might be characterised by the same mechanism. The reaction order of the precipitation processes suggests that β′ and/or Q′ precipitates grow radially; whereas, β-precipitates grow in the three directions.