In this study, the effect of electroless Ni P plating on the mechanical properties of an Al 1.2Si alloy was investigated. As results, the following points were clarified. (1) Fatigue strength of the specimen subjected to zincate treatment only after furnace cooling treatment was almost the same as the furnace cooling only. (2) Fatigue strength of the specimen subjected to Ni P plating after furnace cooling treatment, was reduced overall, except for high stress region, rather than one of non processing materials. (3) Fatigue strength of the specimen subjected to Ni P plating after aging treatment showed a clear increase in comparison with one of non processing materials. (4) Tensile strength of the specimen subjected to Ni P plating after aging treatment or furnace cooling treatment was improved by about 10 in comparison with one of non processing materials. (5) Breaking elongation of the specimen subjected to Ni P plating after aging treatment showed no significant changes in comparison with one of non processing materials. On the other hand, breaking elongation of the specimen subjected to Ni P plating after furnace cooling treatment reduced by half in comparison with one of non processing materials. Especially, it seems that poor fatigue strength and ductility of plating materials are mainly caused due to interaction between surface precipitates and hydrogen gas.

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