On the Sc-rich core of Al3(Sc,Er,Zr) precipitates

•Sc atoms tend to segregate at dislocations.•Two groups of precipitates are formed upon aging at 600 °C one of which has a distinct core rich in Sc.•After 2 and 4 h of aging at 600 °C trapped positrons are mostly annihilated by Zr electrons. The development of microstructure in an Al–Sc–Er–Zr alloy during aging at 600 °C was investigated utilizing microhardness measurements, positron annihilation spectroscopy (PAS) and (scanning) transmission electron microscopy ((S)TEM). The results of positron lifetime (LT) spectroscopy and coincidence Doppler broadening (CBD) indicate that Sc atoms segregate at dislocations. Two major groups of precipitates were observed after 4 h of aging at 600 °C, one having the usual Er-rich core, Sc-rich inner shell and Zr rich outer shell structure and the other having a core rich in Sc.