Effect of cooling rate on precipitation during homogenization cooling in excess Si type Al–Mg–Si alloy

•Si phase and Type-A(U1) are the main precipitates after homogenization furnace-cooling.•Many “sub-boundaries” appeared in the grains after homogenization air-cooling.•The “sub-boundaries” were due to heterogeneous nucleation of precipitates on the dislocations.•Many dislocation-induced precipitates were only lying along [100]Al and [010]Al directions. The effect of the cooling rate on the precipitation during homogenization cooling in the Al-0.31 Mg-0.68Si wt.% alloy was investigated. Different cooling rates (furnace-cooling/air-cooling) were used in this work. For the samples cooled in furnace (20 K/h), the predominant phases formed in the matrix were rod/lath-like shaped and the precipitates were identified as Si phase and Type-A. For the samples cooled in air (~830 K/h), few precipitates could be observed. However, many “boundaries” appeared within the grains. In this work we confirmed for the first time that the longitudinal directions of many rod/lath-shaped precipitates forming in these “boundaries” were only along the [100]Al and [010]Al directions.