The Effect of Preaging Deformation on the Precipitation Behavior of an Al-Mg-Si Alloy

Transmission electron microscopy (TEM) studies were performed on an undeformed and a 10 pct predeformed condition of a commercial Al-Mg-Si alloy (AA6060) to investigate the effect of deformation prior to aging 300 minutes at 463 K (190 °C) on precipitate microstructure and precipitate types. Homogeneous precipitation of β″-type precipitates, many of them disordered, was observed in the undeformed condition. Heterogeneous precipitation was found in the predeformed condition with fewer, coarser precipitates nucleated on dislocation lines producing a higher volume fraction compared with the undeformed condition. The precipitation sequence changed in the presence of dislocations, with most precipitates in the predeformed material being of post-β″ type. These microstructure findings were correlated with the tensile strength properties of the material. For the tensile tests, the undeformed and 10 pct predeformed materials were subsequently aged at 463 K (190 °C) for 0, 10, 100, and 300 minutes before testing at room temperature. The results show that the yield strength of the tested conditions was higher with predeformation for all aging times despite the relatively lower contribution of the precipitates to the total yield strength. Furthermore, it was shown that the maximum yield strength was reached for the predeformed material after shorter annealing times.