Strain Rate-Dependent Elasto-Plastic Characterization of Stir-Cast AA6061–TiB₂ Composites via Nanoindentation and Dao Analysis for Marine Structures

Abstract

AA6061–TiB₂ metal matrix composites containing 0, 3, 6, and 9 wt.% TiB₂ were fabricated through stir casting and
investigated using nanoindentation at strain rates of 0.05–0.20 s^-1. The load–displacement response revealed enhanceddeformation resistance with increasing reinforcement and strain rate. Nanohardness increased from 1.25 to 1.65 GPa for AA6061 and from 3.40 to 4.55 GPa for AA6061 + 9 wt.% TiB₂ as the strain rate increased from 0.05 to 0.20 s^-1. Young’s modulus improved from ~69 GPa for AA6061 to ~94 GPa for the 9 wt.% TiB₂ composite. Strain rate sensitivity increased from 0.08 to 0.125 with reinforcement addition, indicating enhanced rate-dependent plasticity. For the case of significant strain-gradient strengthening, Nix–Gao analysis yielded a higher characteristic length scale, from 0.34–0.42 μm to 0.48–0.60 μm. The yield strength of the material was found to have increased significantly from 120 MPa to 290 MPa and the strain hardening capacity was almost unchanged as a result of the Dao reverse analysis. The results prove that AA6061-TiB₂ composite is suitable for the marine structural application with high local deformation resistance.