Al–Ni intermetallic composites produced in situ by friction stir processing

Bulk Al–Ni intermetallic composites were synthesized in situ by Friction Stir Processing (FSP) at Al alloy plate with Ni powder. The microstructures and compositions of the composites were analyzed, the hardness and tensile properties of intermetallics were measured. Defect-free composites with Al3Ni and Al3Ni2 intermetallics were successfully produced by FSP and heat treatment. The initial nickel powder present three states after FSP: the coarse nickel aggregation, the sandwich-structure composite and the micron-sized Al3Ni particles. Typical microstructures of Al3Ni intermetallics after heat treatment have two microstructures, i.e. the submicron-sized equiaxed crystal when there are fine micron particles uniformly distributed in the aluminum matrix and columnar crystal when Al3Ni2 is surrounded. The grain refinement and the precipitation hardening effect of the Al3Ni intermetallics lead to a significant increase of the microhardness and tensile strength of the Al–Ni composites. The aggregated Ni powders have metallurgy reaction during FSP.