Effect of Electroless Ni–P Plating on Rotary Bending Fatigue Strength of A2017-T4 Aluminum Alloy

Abstract

In this study, A2017-T4 aluminum alloy was plated with electroless NiP with different phosphorus content and rotary bending fatigue test was conducted to investigate the effect of hydrogen by plating on fatigue properties. The fatigue strength of the low-phosphorus type NiP plated specimen was higher than that of the untreated specimen, while that of the high-phosphorus type plated specimen was much lower. It is clear that the fatigue strength differs greatly depending on the phosphorus content in the plating film. The decrease in fatigue strength of the high phosphorus type plating specimen was attributed to hydrogen induced by plating from hydrogen analysis. Thus, despite the previous report that 2000 series aluminum alloys do not exhibit hydrogen embrittlement in slow strain rate tensile tests under wet condition, it was found that A2017-T4 aluminum alloy undergo hydrogen embrittlement when the alloy is plated with high-phosphorus type electroless NiP and fatiguetested on rotary bending machine.

Evaluation of Hydrogen Embrittlement of Electroless Ni–P Plated 6061-T6 Aluminum Alloy by Three-Point Bending and Rotating Bending Fatigue Tests

“…The reduction in fatigue strength based on internal hydrogen due to the high-phosphorus-type Ni-P plating on 6061 alloys was similar to those observed for 2017 16) and 7075 alloys. 18) The reduced fatigue strengths of these alloys can be explained by the hydrogen vacancy cluster theory [19][20][21] presented below.…”

“…For other alloys, such as alloy 2017, the factor is based on hydrogen absorbed into the substrate by the plating. 15,16) According to the hydrogen analysis results in Fig. 3, there is no significant difference in the amount of hydrogen released between the low-and high-phosphorus-type plated specimens, but only the fatigue strength of the high-phosphorus-type plated specimen decreased significantly.…”

“…A fracture surface observation also showed voids of several hundred nanometers at the fatigue fracture initiation point. 16,18) For the 6061 alloy, if minute voids are formed based on the hydrogen vacancy cluster theory, a static loading, such as that in the three-point bending test, will only reduce the displacement to rupture for the minute defects. However, in fatigue tests, fine defects become a cause of stress concentration and reduce the fatigue strength, which is consistent with the results of this experiment.…”