Dislocation-obstacle interaction evolution in rate dependent plasticity of AlSi10Mg as-built microstructure by laser powder bed fusion

Abstract

Novel microstructural features obtained from laser powder bed fusion methods challenge our understanding of the rate controlling mechanisms for plasticity which are important for structural applications. The strain rate dependent plasticity of as-built AlSi10Mg laser powder bed fusion samples was systematically studied as a function of stress state (tension and compression) and strain rate at 293 and 78 K. Utilizing constant strain-rate and rate-change testing methodologies, a strong dependence of flow stress on strain rate was revealed for both stress states. The compressive yield stresses have a potent strain rate sensitivity in both quasi-static (10−4-10−1 s−1) and medium-dynamic (1-5 s−1) strain rate regimes. A positive strain rate sensitivity was observed in all strain rates except for a shift to negative values in the 10−2-10−1 s−1 range for both tensile and compression states. This negative strain rate sensitivity was correlated with the deformation-induced microstructural evolution, i.e., manifested as a gradual transition in the dominant dislocation-precipitate interaction mechanism from shearing to looping, along with the disappearance of dislocation-solute interaction in the form of dynamic strain aging (DSA). The precise measurement of activation volume evolution with flow stress further confirmed the transition from shearing to looping in the 10−2-10−1 s−1 range.