Investigation of developed precipitates in Al–1·1 wt-%Mg2Si balanced alloy by DSC and SEM techniques

Abstract

The effect of temperature on the sequence of the hardening precipitates in Al–1·1 wt-%Mg2Si balanced alloy has been investigated by means of differential scanning calorimetry, scanning electron microscopy and hardness measurements. The non-isothermal DSC thermograms exhibited seven reaction peaks. Out of these seven peaks, five are exothermic (representing precipitation) and two are endothermic (representing dissolution). The activation energy associated with the individual precipitates is calculated. The activation energy of nucleation of GP zones (54·3 kJ mol−1) is close to the migration energy of Si in Al (52·7 kJ mol−1). The activation energy associated with the precipitation of β″ is determined as 77·6 kJ mol−1 and that for the formation of β′ precipitates is 145·3 kJ mol−1. The latter value is close to that for Si diffusion in Al (124 kJ mol−1) and that of Mg diffusion in Al (131 kJ mol−1). It can be concluded that the precipitation of β′ particles might be characterised by both the diffusion of Mg and Si atoms in Al to form β′ precipitates.