A new measure to enhance the heat-resistant (4TiC + 5AlN)/Al composite by multi-scale Fe/Mn enrichment effect

Abstract

Developing high-strength Al-based alloys that can operate at 250 °C and above remains a challenge. In this study, a heat-resistant and high-strength (4TiC + 5AlN)/Al–Fe–Mn composite is designed using the liquid–solid reaction and hot extrusion. The strengthening phases, including sub-micron TiC, micron Al3(Fe, Mn), nano-sized AlN, and nano-sized Al3(Fe, Mn), in which the in–situ AlN particles are distributed in the matrix as networks, exhibit an attractive strengthening effect. Based on the results of electron backscatter diffraction, the extruded (4TiC + 5AlN)/Al–Fe–Mn composite prefers to form fiber texture in the longitudinal and cross-section:<111>Al//ED. And the average grain size of (4TiC + 5AlN)/Al–0.3Fe–0.1Mn composite is 0.69 µm. The ultimate tensile strength of the (4TiC + 5AlN)/Al–Fe–Mn composite is as high as 215 MPa at 350 °C. And the high-temperature elongation of the (4TiC + 5AlN)/Al–Fe–Mn composite is maintained while increasing the high-temperature strength. The improved performance of the (4TiC + 5AlN)/All–Fe–Mn is attributed to the synergistic effect of the multi-scale Al3(Fe, Mn) phases and particles. Furthermore, the formed micrometer Al3(Fe, Mn) phases are used to regulate the distribution of the TiC and AlN particles. The nano-Al3(Fe, Mn) dispersoids that precipitated during the homogenization can enhance the high-temperature deformation resistance of the matrix. In particular, the Fe and Mn atoms tend to aggregate at the TiC/Al interface, effectively modifying the interfaces between ex-situ TiC particles and the Al matrix. The modified interfaces of TiC/Al are beneficial to load transfer strengthening. The strengthening mechanisms of the (4TiC + 5AlN)/Al–Fe–Mn composite have been analyzed in detail, and the main strength–increasing mechanisms are calculated from the microstructural data. This work may provide an important approach to preparing heat-resistant Al matrix composites with strength-ductility matching.