The development of near‐surface microstructures during hot rolling of aluminum–magnesium alloys in relation to work roll topography

The effect of the work roll topography on the surface deformation of aluminum alloys during hot rolling was examined with the use of a rolling tribo‐simulator. AISI 52100 steel work rolls with two surface conditions, smooth (polished to a surface roughness ( R a ) of 0.01 µm) and rough (WC‐coated with a surface roughness ( R a ) of 5.68 µm), were used to hot roll Al‐Mg alloy samples under similar conditions for a rolling schedule of 10 passes. The surface of the rolled samples reflected the work roll surface morphology. Surface damage for the smooth rolled samples included cracks, while shingles and grooves were observed on the rough rolled samples. Cross‐sectional examination revealed cracks extended to depths above 8 µm for the rough rolled samples, while for the smooth rolled samples, cracks were 1.5 µm deep. The oxide‐rich near‐surface layer formed on the rough rolled surfaces was discontinuous. In contrast, the near‐surface generated by the smooth roll was continuous, and near‐surface damage was uniform in comparison. A nanocrystalline grain structure was observed at the near‐surface region beneath the oxide‐rich area for the smooth rolled samples, which extended to shingles on the rough rolled samples. The nanocrystalline nature of the near‐surface region was attributed to the high strains imposed by the work roll, while the effect of the rough roll was surmised to include the formation of shingles, the redistribution of surface oxide, and the enhancement of the near‐surface damage. Copyright © 2015 John Wiley & Sons, Ltd.