Study of artificial aging in AlMgSi (6061) and AlMgSiCu (6013) alloys by Positron Annihilation

We investigate the artificial aging process of the weldable Al-alloys AA-6013 (AlMgSiCu) and AA-6061 (AlMgSi) by positron annihilation spectroscopy and Vickers micro-hardness measurements. We find a correlation between a minimum of the measured positron lifetime and the maximum hardness. To explain these findings AlZn will be discussed as a well known example of positron interaction with different types of precipitations in aluminum. Additionally, we calculate positron annihilation parameters for pure Al, Si, Mg, and Mg2Si finding support for our interpretation. For AA-6013 and AA-6061 the increase of the average positron lifetime after reaching the maximum hardness is attributed to the formation of semi-coherent precipitates. Hence, using positron annihilation it is possible to follow very sensitively the precipitation sequence even in technical aluminum alloys. Finally, we discuss which implications the aging may have on microstructural changes. C 2006 Springer Science + Business Media, Inc.