Fracture behavior of a rapidly solidified thin-strip continuous cast AA5182 Al-Mg alloy with the Portevin-Le Chatelier effect under varying strain rates

Abstract

This study investigates the strain-rate triggered PLC effect and fracture behavior of a rapidly solidified thin strip (TS) cast AA5182 alloy in comparison with those of direct chill (DC) counterparts. Higher cooling rates obtained via TS casting suppress the formation of phases in Al-Mg alloys and significantly enhance the matrix solute supersaturation beyond the equilibrium level, thereby impacting the interaction dynamics of mobile dislocations and solute atoms. This in turn affects the evolution of typical stress fluctuations in Al-Mg alloys, referred to as the Portevin-Le Chatelier (PLC) effect, occurring in specific strain rate-temperature domains, i.e., with type and characteristics dependent upon the microstructure. Tensile testing demonstrated a strain-rate dependent PLC effect, also aligning with the ductility trend in both negative and positive strain-rate sensitivity domains. The characteristics of PLC bands, as well as the magnitude of stress fluctuations, were shown to evolve with strain rate, facilitating distinct fracture mechanisms. In particular, the TS sample exhibited a higher strain rate sensitivity of the fracture mechanisms and PLC band characteristics and, thus, a narrower range of deformation rates for optimum ductility (attributed to increased solute in the matrix). Controlling the deformation rate to favor predominantly Type-B serrations and ensuring their stability with minimal fluctuations was shown to postpone necking and prevent material failure. The significance of rate sensitivity in alloys with reduced microsegregation is emphasized, suggesting the need for further exploration of mechanical properties.