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

Abstract

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.

The influence of work roll roughness on the surface/near-surface microstructure evolution of hot rolled aluminum–magnesium alloys

“…This analysis thus indicated that the roughness of the work roll also has an effect on the oxide distribution and nearsurface damage depth. This agrees with previous work by Gali et al (2015), who observed deeper near-surface damage induced by the formation of larger micro-cracks when using a rough roll (5.7 µm Ra), as compared to a smooth work roll (0.01 µm Ra).…”

“…Comparing previously reported results by Gali et al (2015) with those obtained here, a trend of increasing near-surface damage (i.e., the maximum depth of micro-cracks observed) with an increase in work roll roughness is observed. The near-surface damage, in the form of microcracks, extended to maximum depths of 1.5 µm for a 0.01 µm Ra work roll (Gali et al (2015)), 2.8 µm for the 0.1 µm Ra work roll (Fig.…”

“…Previous work of Gali et al (2015) examining the influence of work roll topography on the development of near-surface microstructure on Al-Mg alloys confirmed that a smooth work roll, with an Ra of 0.01 µm, induced no shingles, rolling marks, nor grooves on the hot rolled surface. On the other hand, a textured work roll with an Ra of 5.86 µm developed grooves and shingles, covering the sample surface.…”

“…The near-surface damage, in the form of microcracks, extended to maximum depths of 1.5 µm for a 0.01 µm Ra work roll (Gali et al (2015)), 2.8 µm for the 0.1 µm Ra work roll (Fig. 14b), 3.2 µm for the 1.1 µm Ra work roll (Fig.…”

“…Riahi et al (2012) work also involved exploring the effect of forward slip on shingle occurrence, noting that an increase in forward slip resulted in higher frequency of shingle occurrence. Preliminary studies by Gali et al (2015), who evaluated the effect of the work roll roughness, indicated that shingles were formed on rolled Al-Mg alloy samples when a WC-coated work roll with a surface roughness (Ra) exceeding 5µm was used, but none were observed with a polished work roll with a roughness of 0.01 µm. Gali et al (2015) showed that the introduction of a ground work roll in the rolling process influenced the depth of near-surface damage induced on the aluminum alloy during hot rolling.…”