The influence of hot rolling on oxide development within micro-cracks of aluminum-magnesium alloys

The present study investigated the effect of hot rolling passes on the growth and morphology of transverse cracks, and the oxides formed on their surfaces, in an Al-Mg alloy. A hot rolling tribometer was used to carry out 4 rolling passes on the alloy samples. Cracks were observed on the alloy surface after the first rolling pass. These cracks occurred along and across grain boundaries and propagated to the subsurface along and within grains. MgO nanocrystalline grains with a hexagonal structure were observed on crack faces, sealing narrow regions of cracks. Crack healing was observed to begin from the initial rolling pass by the sealing of cracks with MgO. After 4 rolling passes, all cracks observed propagated along grain boundaries within the subsurface regions. The hexagonal structure of the MgO grains was no longer evident at this stage of rolling, but all cracks and damaged areas were filled with porous MgO layers. At this stage of hot rolling the microstructure of the oxides observed within cracks and at the near-surface region was similar. It was concluded that rolling stresses were contributing to the structure of MgO occurring within transverse micro-cracks during hot rolling.