Fatigue properties of nickel-foam reinforced aluminum alloy.

Nickel-foam reinforced aluminum alloy (NFRA) has recently attracted special interest as one of the metal matrix composites. Nickel foam is easily integrated with aluminum alloy because of high porosity, and its specific surface area is large enough to improve the wetability and adhesion and to form a Ni-Al intermetallic compound which is helpful in improving wear resistance.The aim of this investigation was to evaluate the strength of NFRA and to clarify the fatigue behavior of this material. Cantilever-type rotating bending fatigue tests and tensile tests were carried out on two types of NFRA and AC8A aluminum alloy. Two types of NFRA of which nickel-foam is squeeze-casted with AC8A aluminum alloy were prepared and heat treated in accordance with T6 processing; one has 2mm pore diameter of nickel foam, another has 0.4mm. It was observed by a microscope that two types of intermetallic compounds were formed at the interface between nickel foam and base metal. These hardness were about ten times harder than that of base metal.The fatigue life, and crack initiation and propagation behavior of NFRA were discussed in detail. From the experimental results, the fatigue life and tensile strength of NFRA decreased significantly as compared with those of AC8A-T6 aluminum alloy. Many cracks were initiated at the interface between intermetallic compound and base metal during the fatigue process, and crack initiation behavior was related to the shape and size of nickel foam. Fatigue cracks of NFRA propagated with coalescence of many microcracks, of which mechanism was very different from a homogeneous material such as AC8A aluminum alloy.