Abstract

In the present research, the hydrogen embrittlement (HE) susceptibility of an industrial Zinc-Nickel (Zn-Ni) brush plating process was investigated according to the ASTM F519 standard. Plated notched round bar samples were subjected to 200 h long sustained load test (SLT) to evaluate the HE susceptibility of the plating process. The results of the SLT indicated significant embrittlement in the absence of baking. However, baking for 24 h at 190°C according to industry standards relieved embrittlement completely. In addition, it was found that baking at a significantly lower temperature of 100°C relieved embrittlement as well. Change in plating parameters also failed to mitigate HE as samples plated at various current densities fractured in a similarly catastrophic manner under the SLT test. However, it was shown that by avoiding sandblasting in the pre-plating sample preparation stage, the results of the SLT improve significantly. Samples without sandblasting passed the SLT while those sandblasted failed after 11 h only. Another important finding was the outward diffusion of hydrogen at room temperature. This was shown by the fact that samples similar to those which failed the SLT managed to pass after being kept at room temperature for a week. The fracture surfaces of the embrittled samples showed intergranular fracture features at the crack initiation point and dimples and voids throughout the rest of the surface but the presence and visibility of these features varied among different samples.