Serrated flow and ZrB2 nanoparticle agglomerations of in-situ AA6061 alloy matrix composites

Abstract

In this paper, the roles of agglomerations of ZrB2 nanoparticles in the in-situ ZrB2-nanoparticle-reinforced AA6061 composites were investigated via the analyses of strain hardening and serrated flow behaviors during the deformation. The tensile testing demonstrates that the composite with 2 vol% of nanoparticles has a yield strength of 74.1 MPa, ultimate strength of 181.1 MPa and plastic strain of 20.2%, respectively, which are better than the composites with 1 vol% and 3 vol% of nanoparticles. The increasing values of strain-hardening coefficients suggest that the mobility of dislocations was decreased. The strain hardening rate indicates that the as-cast 2 vol% ZrB2-nanoparticles-reinforced composite has the best strain hardening ability but the composite with 3 vol% ZrB2 nanoparticles has the lowest one which is attributed to the strain concentration in the agglomerations initiating the crack through the cohesive region between ZrB2 nanoparticles. The serration analysis reveals that the population of serrations with ≤0.5 MPa of stress drop is a key feature for stabilizing plastic deformation.