Study On Microstructures And Properties Of Plasma Nitrided Layers On1050Aluminium Alloy Surface

In order to solve the poor wear and corrosion properties, aluminium nitride (AIN) layers were formed on1050aluminium alloys by using plasma nitriding technique. The composition, structure and performance of the nitride layers formed by different nitrogen sources (NH3&N2) were studied. Scanning electron microscope (SEM), X-ray diffraction (XRD) and glow discharge spectrometer (GDS) were employed to study morphology, element distribution and structure of nitride layers. The tribological performances of nitride layers and1050Al matrix were investigated and compared with each other by using reciprocating wear tester. Electrochemical measurements and corrosion weight loss analysis were performed to investigate corrosion resistance of AIN layers in simulated rainwater and3.5wt.%NaCl solution.The nitride layer was composed of large numbers of AIN and little Al, with a thickness of1-4μm. The thickness of AIN layer was increased with longer nitriding time and higher temperature. The texture of layer nitrided by N2is greyish white and metallic luster, with a flatter, thicker and more compact surface compared with layer nitrided by NH3. Under dry sliding conditions, nitride layers prepared by different process parameters could decrease the friction coefficient of1050Al (0.55) to a range of0.2-0.3. The special wear rate of nitride layers dropped to40%of matrix’s. Taken together, the nitride layer could improve the friction and wear properties of1050AL Adhesion and little abrasion wear are the main wear mechanism for1050Al matrix. While the nitride layer shows slight wear and abrasive wear.In the simulated rainwater, the corrosion potential of nitride layers shifted positively with different range, compared with1050Al’s. And the corrosion current density of nitride layers (NH3) reduced at least4μA·cm-2and that of N2layer’s reduced one order of magnitude, compared with1050Al’s (5.62μA·cm-2). After plasma nitriding process, corrosion tendency and corrosion rate of1050Al have been decreased dramatically. Both of NH3layer and N2layer improved the corrosion resistance of1050Al in simulated rainwater while the N2layer had better coating quality and properties. The corrosion mechanism of nitride layers in simulated rainwater was that the nitride layers could segregate low concentration corrosive anions and substrate. In3.5wt.%NaCl solution, nitride layers had a little change in electrochemical test results compared with1050Al matrix. But, corrosion morphology analysis showed that nitride layers could restrain the growth and development of etching hole in high concentration corrosive medium.