Effects of Surface Structure and Hydrogen on the Fatigue Strength of Electroless Nickel-Phosphorus Plated Al-2%Cu Alloy

In this study, the effect of the surface structure and hydrogen on the fatigue strength of electroless Ni-P plated Al-2%Cu alloy was investigated. As the results, the following points were clarified. Large precipitates were recognized near the specimen surface of the furnace-cooled Al-Cu alloy, but these were not recognized in the aged Al-Cu alloy. Fatigue strength of the Al-Cu alloy specimen subjected to Ni-P plating after a furnace cooling treatment was overall reduced rather than one of the non-processed specimens. Fatigue strength of the Al-Cu alloy specimen subjected to Ni-P plating after the aging treatment showed a clear increase in comparison to one of non-processed materials. In the Al-2%Cu alloy specimens subjected to Ni-P plating after the furnace cooling treatment or aging treatment, a clear hydrogen desorption was recognized. On the other hand, there was only hydrogen desorption from a few of the non-processed specimens. It is considered that the poor fatigue strength of the plating materials is mainly due to the interaction between the surface precipitates and hydrogen gas.