Fabrication of Ultrathin Al Foils by Accumulative Pack Rolling: Influence of Pack Materials

Ultrathin metal foils are essential for applications requiring miniaturization across modern industry. Nevertheless, it is challenging for conventional rolling mills and conventional rolling methods to reduce the thickness of single-layer foils to a scale approaching just a few micrometers. This difficulty arises from a range of inherent factors, including the elastic modulus, diameter of the rollers, resistance of rolled materials, and friction coefficient. To address these limitations, an accumulative pack rolling (APR) method has been developed in this work to fabricate ultrathin metal foils. Al foils down to ~2 µm have been successfully fabricated by using Al, Ta, and stainless steel (SS) as pack materials. The effects of the pack sheets on surface morphology, thickness reduction, and microstructural evolution were investigated. Key surface roughening behaviors, including ridging and particle-like surface roughening, were observed on the inner surface, which influences the roughening and thinning behavior of the target Al foils. This study also provides insights into surface roughening mechanisms, including rolling marks, ridging, and particle-like roughening, and demonstrates the critical role of pack sheet materials in controlling plastic instability, achieving uniform thickness reduction in ultrathin foils, and preventing severe deterioration of surface flatness during the APR process.