Control of the r -value in aluminium alloy sheets through plastic working: Processing routes, mechanistic framework, and industrial implications

Plastic anisotropy strongly governs sheet formability in aluminium alloy sheets, and its control is essential for improving deep drawability and suppressing earing. The Lankford coefficient, or r -value, quantifies plastic anisotropy, while the derived parameters r ¯ and Δ r represent thickness strain resistance and in-plane anisotropy, respectively. This review re-examines plastic working processes from the perspective of r -value control, treating the r -value as a primary design target rather than a secondary outcome of texture evolution. Various processing routes, including asymmetric rolling, cross rolling, severe plastic deformation, and their combinations with intermediate annealing, are systematically analysed based on their strain path characteristics and their effects on r ¯ and Δ r . Particular emphasis is placed on the role of crystallographic texture, especially the development of <111>//ND fibre and Cube components, as well as on through-thickness texture gradients arising from shear deformation. A mechanistic framework is presented in which r -value evolution is interpreted through the combined effects of strain path, stored energy distribution, recrystallisation behaviour, and particle-stimulated nucleation. The distinct, and often competing, requirements for increasing r ¯ and reducing |Δ r | are critically discussed, highlighting the limitations of existing processing strategies. Furthermore, the scalability and practical applicability of each processing route are evaluated in the context of industrial sheet forming.