Microstructure Evolution, Age‐Hardening Behavior, and Mechanical Properties of In Situ (Al 2 O 3 +TiB 2 +TiC) Reinforced A6061 and A2214 Matrix Composites

In this work, in situ (Al 2 O 3 +TiB 2 +TiC)‐reinforced A6061 and A2214 matrix composites were prepared by a combination of reactive sintering, hot extrusion, and subsequent T6 treatment. Interestingly, the T6‐treated A6061 and A2214 composites exhibited distinct differences in microstructure, age‐hardening behavior, and mechanical properties. In addition to the target reinforcing phases, a significant amount of MgAl 2 O 4 spinel formed in the T6‐treated A6061 composite due to the reaction between Mg in the A6061 matrix and the Al 2 O 3 phase. As a result, the consumption of Mg significantly suppressed the formation of Mg–Si precipitates during aging, leading to almost unchanged tensile strength of the T6‐treated A6061 composite compared to the as‐extruded A6061 composite. In contrast, fine Al–Cu precipitates were smoothly precipitated in the T6‐treated A2214 composite during aging. Moreover, several rod‐like Al 3 Ti intermediate phases were identified in the A2214 composite, revealing that the high Cu content in the A2214 matrix may inhibit the in situ reactions. Owing to the synergistic strengthening effect of in situ Al 2 O 3 , TiB 2 , TiC, Al 3 Ti phases, and nanosized Al–Cu precipitates, the T6‐treated A2214 composite exhibited a superior tensile strength of 422 MPa. This work provides new insights into the selection of suitable heat‐treatable alloy matrix for the design of high‐performance aluminum matrix composites.