Microstructure Evolution and Mechanical Properties of TiB2/Al–Cu–Mn–Cd Composite with the Adoption of Two-Stage Solution and Aging Treatment

In this study, in order to obtain excellent mechanical properties in TiB2/Al–Cu–Mn–Cd composite, an optimized heat treatment, i.e., short-time solution treatment at 535 °C for 1 h following long-time solution at 523 °C for 11 h, and aging treatment, i.e., aged at 170 °C for 12 h, is proposed. In addition, this study investigated the connection between microstructure evolution and mechanical properties during heat treatment. The results show that with adoption of the optimized solution treatment, the area fraction of second and eutectic Al2Cu phases decreased from 5.08% in the as-cast state to less than 0.36% owing to improvement of dissolution efficiency in the high-temperature short-time solution. Comparing mechanical properties of the composite in the as-cast state and in the peak-aged state, average ultimate tensile strength and yield strength increased from 211.9 MPa to 523.0 MPa and from 115.8 MPa to 451.8 MPa, respectively. However, average elongation slightly decreased from 8.78% to 8.24%. Strength contribution of the peak-aged TiB2/Al–Cu–Mn–Cd composite was mainly ascribed to Cd-rich, θ″ and θ′ precipitates. In the peak-aged state, number density and average diameter of the plate-like θ″ and θ′ precipitates reached 4.266 × 1021 m3 and 64.30 nm, respectively, and severe lattice distortions occurred around the Cd-rich precipitates, providing the strongest precipitation strengthening. These findings indicate that the two-stage solution treatment successfully solved the problem of the eutectic phase at the triangular grain boundary being difficult to dissolve in a TiB2/Al-Cu-Mn-Cd composite, and excellent mechanical properties were acquired with the optimized aging treatment.