Effect of Cu coating on interfacial behavior of C_sf-Cu/AZ91D composites: Wettability and crack propagation mechanism

Short carbon fibers (C_sf) are modified with Cu coating to improve interfacial behavior including wettability and crack propagation of the C_sf/AZ91D composites. Wetting angle tests and in-situ tensile tests are direct approaches to characterize interfacial behavior. XPS spectra reveal that the Cu coating can increase the content of Cu element and C[dbnd]O bond, which improves the surface free energy of the C_sf by 144.8%. Wetting angle tests suggest that the Cu coating can decrease the contact angle of molten AZ91D on C_sf from 127° to 44°. In-situ SEM images show that for C_sf/AZ91D composites, most of the cracks can directly cut off the C_sf owning to the stress concentration at the interface. After the Cu coating modified C_sf, the reduction of Al₄C₃ at the interface can release the stress concentration at the interface and protect the C_sf from adverse interfacial reactions, significantly improving the ultimate tensile strength (UTS) of the composites by approximately 48.7%.