The effects of quench rate and pre-deformation on precipitation hardening in Al-Mg-Si alloys with different Cu amounts

The effects of quench rate after solution heat treatment in combination with 1% pre-deformation on precipitation hardening in three Al-Mg-Si alloys have been investigated by transmission electron microscopy and hardness measurements during an isothermal heat treatment. The alloys contain different Cu amounts (up to 0.1 wt%) and the same amounts of other solute elements. While a Cu amount below 0.01 wt% does not affect precipitation hardening, an addition of 0.1 wt% Cu increases hardness due to the formation of a fine microstructure having a high number density of short precipitates. A double peak hardness evolution was observed during isothermal heat treatment. This effect was most pronounced for alloys with low quench rate, and less pronounced for alloys with 1% pre-deformation and 0.1 wt% Cu addition. The low quench rate also led to wider precipitation free zones. This effect was also less pronounced by 1% pre-deformation and addition of 0.1 wt% Cu.