Al4c3 is a brittle aluminum carbide phase characterized by blocky, lath-shaped or cuboidal crystal structures. It is a common additive to increase the strength of three-component aluminum-based alloys (Al-Si-Mg) for the manufacturing of aerospace components, machining tools and high-performance drill pipe for deep well drilling. It also can be used as a raw material to produce vacuum microelectronic devices.

The interfacial production of lath-like Al4C3 during the forming process of short carbon fiber reinforced 2024 aluminium composites (SCFs/2024 Al) causes both strengthening and weakening effects. The elongated structure of this phase enables it to absorb the stress transferred from carbon fibers and disperse it uniformly throughout the entire matrix, which can enhance the overall tensile strength (TS) of SCFs/2024 Al composites. However, the presence of this phase also causes a severe reaction between carbon fibers and the aluminum matrix at very high temperatures or after long thermal exposure time. This leads to the cutting of carbon fibers, which can reduce the overall TS of SCFs/2024 Al.

Moreover, the elongated structure of this phase may also cause local stress concentration, which results in shear fracture of the carbon fibers. However, a long duration of thermal exposure time can allow the lath-like Al4C3 to coarsen and connect, thereby reducing the stress concentration and avoiding shear fracture of carbon fibers.

The morphology of the lath-like Al4C3 and the carbon fibers at the interface in SCFs/2024 Al composites has been observed by STEM imaging. Compared with SCFs/2024 Al without addition of carbon fiber, the morphology of the interface in SCFs/2024 Al with addition of carbon fiber shows that the lath-like product coarsens and connects during the heat exposure process, which improves the distribution and volume of the interface products.