Effect of cooling rate on precipitation during homogenization cooling in balanced AlMg2Si alloy

The effect of the cooling rate on the precipitation process during homogenization cooling in a balanced Al0.64Mg0.32Si mass% alloy was investigated. Different cooling rates (Furnace-cooling/Air-cooling) were used. During homogenization air-cooling ( 830K/h), optical microscopy (OM) revealed that few precipitates could be observed in the matrix; however, there were many "boundaries"formed in the grains. Transmission electron microscopy (TEM) observations confirmed that these "boundaries"were caused by heterogeneous nucleation of precipitates along the dislocations during cooling, and many precipitates only grew along the [100]Al and [010]Al directions. Among the precipitates, over-aged βA/Type-B, together with string-like precipitates, were found on the dislocations. For the furnace-cooled samples (20K/h), rod/lath-like precipitates of βA and βA/Type-B were also found along the dislocations.