Investigating the Hall-Petch Constants for As-Cast and Aged AZ61/CNTs Metal Matrix Composites and Their Role on Superposition Law Exponent

Abstract

AZ61/carbon nanotubes (CNTs) (0, 0.1, 0.5, and 1 wt.%) composites were successfully fabricated by using the stir-casting method. Hall–Petch relationship and superposition of different strengthening mechanisms were analyzed for aged and as-cast AZ61/CNTs composites. Aged composites showed higher frictional stress (108.81 MPa) than that of as-cast (31.56 Mpa) composites when the grain size was fitted directly against the experimentally measured yield strength. In contrast, considering the superposition of all contributing strengthening mechanisms, the Hall–Petch constants contributed by only grain-size strengthening were found (σ0 = 100.06 Mpa and Kf = 0.3048 Mpa m1/2) for as-cast and (σ0 = 87.154 Mpa and Kf = 0.3407 Mpa m1/2) for aged composites when superposition law exponent is unity. The dislocation density for the as-cast composites was maximum (8.3239 × 1013 m−2) in the case of the AZ61/0.5 wt.%CNT composite, and for aged composites, it increased with the increase in CNTs concentration and reached the maximum value (1.0518 × 1014 m−2) in the case of the AZ61/1 wt.%CNT composite.