In situ synthesizing Al₃Ni for fabrication of intermetallic-reinforced aluminum alloy composites by friction stir processing

Ultrafine-grained in situ synthesized Al₃Ni particulate-reinforced composites were fabricated by friction stir processing (FSP) introduced Ni powder into the stirred zone of 1100-H14 aluminum alloy. The microstructures and the compositions of the composites were analyzed by SEM, EDS and XRD. The microhardness and ultimate tensile strength (UTS) were measured. The XRD and EDS analyses showed that the Al-Ni in situ synthesizing product was Al₃Ni. When the specimen was stirred 2 passes, the formed Al₃Ni was tiny to be detected. Al₃Ni subsequently became apparent when stirring 4 and 6 passes and the fine Al₃Ni particles were dispersed homogeneously in the composites, which caused significant increases of the microhardness and UTS of the composites. The effective Gibbs free energy change of formation model was proposed to predict the Al-Ni compound formation at solid-state interface and the calculation combined with kinetic factors showed that Al₃Ni was the product, which supports the experimental observation.