Electrochemical deposition of NiCo magnetic layer on the aluminum substrate

The NiCo magnetic materials have been deposited on an aluminum substrate using a multi-step electroplating, preventing Al from being self-reactive and oxidized during the process. The hydrogen bubble evolution due to the galvanic displacement reaction (GDR) driven by the reduction potential difference usually degrades adhesion between Al and electro-deposited layer. In order to suppress the hydrogen evolution at the interface, we performed a two-step electroplating, of which first step was an electro-deposition at 5 °C where the gas evolution was minimized. Then, in the second step, the thicker NiCo film was electro-deposited at 40 °C by increase of metal-ion activity. After this two-step electro-deposition process, the NiCo magnetic materials were evenly deposited on the aluminum substrate with the good adhesion. We also investigated the magnetic properties of the deposited NiCo layer, according to various metal composite ratios obtained at different current-densities during the electro-deposition. When current density was increased, the ratio of nickel relative to that of cobalt increased. It is because the nickel has a higher reduction potential than that of cobalt. In addition, the analysis data of vibrating sample magnetometer (VSM) showed an increase of saturated magnetization and a decrease in coercivity, which were observed when films were electro-deposited at higher current densities. We also optimized experimental conditions with regard to film thickness, the ratio of magnetic materials, and magnetic properties to fabricate magnetic thin films suitable for application in induction heating cookers.