Precipitation on grain boundaries in Al-Mg-Si alloys: The role of grain boundary misorientation

The application of Al-Mg-Si alloys is growing in fracture critical applications such as transportation. The formation of grain boundary precipitates during cooling after solution treatment is an important factor in controlling low energy intergranular fracture modes. A systematic study was conducted on the effects of grain boundary misorientation and cooling rate (between 3 and 1000 degrees C/s) on the size and density of grain boundary precipitates before and after artificial ageing. It was found that precipitates on high angle grain boundaries were approximate to 3 times larger than those formed on low angle boundaries. The grain boundary precipitate size decreased by a factor of 3 when the cooling rate increased from 3 to 80 degrees C/s with no precipitates observed at 1000 degrees C/s. However, even for a cooling rate of 1000 degrees C/s, grain boundary precipitation was observed during subsequent artificial ageing. The effects of grain boundary misorientation and cooling rate were rationalized by enhanced diffusion at grain boundaries. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The application of Al-Mg-Si alloys in fracture critical applications is increasing, and the formation of grain boundary precipitates plays an important role in controlling low energy intergranular fracture. The study shows that precipitates on high angle grain boundaries are approximately 3 times larger than those formed on low angle boundaries. The size of grain boundary precipitates decreases by a factor of 3 with increasing cooling rate, and almost no precipitates are observed at a cooling rate of 1000 degrees C/s. However, grain boundary precipitation is still observed during subsequent artificial ageing.