A study of the development of micro-cracks in surface/near surface of aluminum-manganese alloys during hot rolling

The tribological aspect of the hot rolling of aluminum alloys is of particular interest, as the complex interactions between the roll and alloy surface influence the defects that are induced on the surface of aluminum alloys. These induced surface defects tend to reduce the quality of the final product. A hot rolling tribometer designed to simulate the rolling process was used to study the evolution of defects that occur on alloy surfaces during high temperature deformation. Scanning electron microscopy, energy dispersive spectroscopy, and focused ion beam microscopy were used to examine the effect of sequential rolling passes on the evolution of surface defects on an aluminum-manganese alloy. Cracks on the alloy surface were initiated mainly at grain boundaries due to rolling stresses and grain boundary sliding, causing an overlapping of grains. Cracks, which propagated along grain boundaries into the alloy subsurface, were observed on subsequent passes, with the immediate areas surrounding the cracks appearing rich in MgO in the subsurface regions. The orientation of cracks in relation to the rolling direction also influenced crack propagation.