Dislocation density evolution and hardening mechanism of AA7050-T7451 surface layer based on anisotropy

Abstract

Abstract Based on the modified KM (Kock–Mecking) model, a cutting constitutive model of AA7050-T7451 considering anisotropy is established in this article. With the aid of high-speed cutting FEM simulation and experiment, the micro-influence mechanism of anisotropy on high-speed cutting hardening of AA7050-T7451 was studied from three aspects: micro-morphology, residual strain, and plastic deformation. By analyzing the macro-micro correlation mechanism of dislocation density, work hardening, and cutting temperature, a “Three-Stage” model of work hardening is put forward. The results show that the work-hardening behavior of high-speed cutting AA7050-T7451 shows obvious anisotropic characteristics. And the work hardening degree is less than 0° and 90° at the material forming angle of 45°. At the 45° forming angle, the material dislocation density is the highest, and the grains are most prone to the dislocation slip. The macroscopic properties show that the microhardness of the material is small. The “Three-stage” model reveals the micro-evolution mechanism of work-hardening behavior. It is found that the dislocation density dominates the work-hardening behavior in stages I and II, and cutting temperature dominates the work-hardening behavior in stage III. The microhardness of the material increases sharply at first and then tends to be flat.