Heterostructured pure aluminum produced by impact loading

Heterostructured metallic materials have drawn attention because of their superior mechanical properties compared to their homogeneous counterparts. This paper evaluates a novel and easy-to-scale approach for manufacturing gradient materials via localized impact loading and reveals the main strengthening mechanism in a high stacking-fault energy material. Impact loading caused heterogeneous strain distributions and strain hardening gradients from the surface towards the inside of the rods. The yield strength and elongation gradients of the impacted rods were 130 MPa–75 MPa and 10 %–25 %, respectively, over a depth of 0 mm–4 mm. This represents a yield strength increment of over 100 % in comparison to the homogeneous counterpart. The appearance of both microscopic and macroscopic heterostructured deformation zones was corroborated by geometrically necessary dislocation and nanoindentation profiles. In this context, the density of dislocations diminished with increasing distance from the impacted surface, leading to a concentration of dislocations in the grains adjacent to the surface. Near the impacted surface, dislocations piled up around the grain boundaries of adjoining grains, creating micro-plastic gradients that that extended into the grain interiors. The localized impact experiments resulted in a heterostructured pure Al rod with gradient properties. Specifically, 50 % of the rod's thickness achieved strengths that exceeded the as-received condition, while the remaining 50 % maintained elongations that exceeded 15 %.