Post-pre-ageing natural ageing stability in Al-Mg-Si alloys: the dependence on pre-ageing timeWednesday (08.11.2017) 11:40 - 12:00 Part of:
The strength of 6xxx alloys is mainly achieved via precipitation hardening during artificial ageing. However, the hardening response will be sluggish if natural ageing is introduced between solution heat treatment and artificial ageing. Pre-ageing, a thermal treatment performed after quenching but before natural ageing at an intermediate temperature (typically 100 °C) was found effective in suppressing the deleterious effect induced by subsequent natural ageing. Previous literature mainly focused on the pre-ageing temperature and its impact on artificial ageing, but less attention has been paid to the pre-ageing time and its influence on the time during which the material is stable at room temperature, the ‘stabilisation time’.
In this work, the natural ageing stability is systematically characterised by means of hardness testing, electrical resistivity measurement and differential scanning calorimetry after pre-ageing at 100 °C for various times. Stabilisation times during natural ageing are compared for the different methods. Longer stabilisation times are found for longer pre-ageing. However, for a given pre-ageing time, the stabilisation times characterised by different methods are not consistent. This can be interpreted by different sensitivities of the methods to the clustering taking place during post-pre-ageing natural ageing.