Composite coatings created by new method of active screen plasma nitriding on aluminium alloy 6061

Abstract Active screen plasma nitriding (ASPN) is a novel method of coating, which does away with many drawbacks of conventional plasma nitriding (CPN) techniques and is widely regarded as a suitable alternative to these methods. This study aimed to investigate the effect of ASPN operation time and temperature on the surface properties of the composite coating produced through this procedure. For this purpose, a group of Al6061 samples was subjected to plasma nitriding in an atmosphere of %20H 2 –%80N 2 at temperatures of 450 °C and 500 °C for 5, 8, and 11 h. The resulting phases and microstructure were studied with Grazing Incidence X-ray Diffraction (GIXRD) device and Field Emission-Scanning Electron Microscope (FE-SEM) equipped with EDS analyzer. To investigate corrosion resistance, processed and unprocessed samples were subjected to polarization corrosion testing. The results showed that the coating formed on the surface of specimens consists of Fe 2-3 N and AlN. Microscopic images showed that the ASPN procedure conducted for 5 h at 450 °C produced a surface nitrides diameter about 38.2 nm, but when carried out in 11 h at 500 °C, it managed to produce a surface nitrides diameter about 521.4 nm. As ASPN operation time and temperature increased, the thickness of nitride layer from 0.7∓0.1 to 8.1∓0.7increased as well. The highest corrosion density 23.72 (μA/cm 2 ), the lowest corrosion potential −1130 (mV), and the highest corrosion rate 11.71 (mpy) were measured in the uncoated Al6061 sample. Also, the lowest corrosion density 5.33 (μA/cm 2 ), the highest corrosion potential −832 (mV), and the lowest corrosion rate (2.73 mpy), which signify the best corrosion resistance, were measured in the sample subjected to 11 h of APSN at 500 °C, which had an approximately 8.11 μm thick coating. The corrosion mechanism of the nitride composite coating was found to be of localized pitting corrosion type.