Influence of La₂O₃ addition on structure and properties of Ni/Al composites fabricated by friction stir processing

Ni/Al and (Ni+La₂O₃)/Al composites were fabricated by adding micron Ni powder and (Ni+La₂O₃) mixed powder to the Al matrix with means of the friction stir processing. The microstructures and phase composition of the composite zone were analyzed by SEM, EDS and XRD. Mechanical properties of Ni/Al and (Ni+La₂O₃)/Al composites were tested by tensile test at room temperature. Results show that Ni/Al composites are mainly composed of Al, Al₃Ni and agglomerates of Ni powder, the size of agglomerates of Ni powder is very coarse and the morphology is core-shell structure. The core is composed of agglomerated Ni, the shell is composed of the reinforced phase layer of Al₃Ni; La₂O₃ reinforces Al-Ni in-situ reaction to produce more reinforced phase; La₂O₃ reduces the agglomeration of Ni powder by retarding the mutual adsorption and aggregated behavior of Ni powder; The tensile strength of (Ni+La₂O₃)/Al composites can reach 186 MPa. Compared with the Al matrix(tensile strength is 72 MPa), the FSPed Al(tensile strength is 90 MPa) and Ni/Al composites(tensile strength is 144 MPa), the tensile strength of (Ni+La₂O₃)/Al composites has increased by 158%, 107% and 29% respectively.