Surface Friction Stir Method to Improve Formability and Spring-back of AA5052-H32 Sheets

A process to improve formability and spring-back was developed for AA5xxx-H temper sheets based on the surface friction stir (SFS) method. When the sheet surface is stirred by the rotating probe which advances on the surface, plastic deformation and heat resulted by friction and deformation incur changes in the microstructure and macroscopic mechanical properties of the stirred zone and, therefore, ultimately the formability and spring-back performance of the overall sheet. When applied to AA5052-H32 automotive sheets, the process improved formability and spring-back, as experimentally and numerically confirmed in uni-axial tensile, limit dome height (LDH) and unconstrained bending tests. For numerical simulations, the non-quadratic anisotropic yield function, Yld2000–2d, was employed along with isotropic hardening, while formability was evaluated using theoretical forming limit diagram (FLD) based on Hill’s bifurcation and M-K theories.