Origin of surface ridging in Ti-6Al-4V sheets produced by pack rolling and its effect on microstructural and mechanical properties

•High strength difference between Ti-6Al-4 V and S45C caused plastic flow in Ti-6Al-4 V.•Localized and uneven flow is the main mechanism responsible for surface ridging.•Choosing materials with low strength differences can reduce surface ridging.•Rolling temperature must be below the critical temperature to reduce surface ridging. Pack rolling is an effective process for manufacturing Ti-6Al-4V products, especially thin sheets; however, it tends to cause surface defects. Surface ridging is the most significant surface defect produced during the pack rolling of thin sheets. Hence, in this study, the effects of pack-rolling conditions on the origin of surface ridging on Ti–6Al–4V alloy surfaces were investigated using experimental and numerical techniques. Pack rolling was carried out at temperatures of 830, 860, 930, and 980 °C until a thickness reduction of up to 30 % was achieved. The surface ridging mechanism, microstructural evolution, and mechanical properties after pack rolling were studied using optical microscopy, scanning electron microscopy in the backscattered electron mode, microhardness tests, and the finite element method to identify the influence of pack-rolling parameters and the surface quality at various temperatures. The stress, strain, and temperature distributions after pack rolling at different temperatures revealed that the difference in the plastic flow between the core and cover resulting from the temperature rise was the mechanism controlling surface ridging on the surface of the Ti–6Al–4V plate. These results can be used for optimizing the pack-rolling processes of Ti-6Al-4V alloys.