Nitriding of aluminium alloy (AlFe1.8Zn0.8) in nitrogen and nitrogen-helium mixture was carried out by using 100 Hz-pulsed DC glow discharge. Samples are treated for different durations, namely 4 h, 8 h and 12 h, in nitrogen plasma as well as in a mixture of nitrogen-helium plasma for the same processing duration of 4 h. All nitriding treatments are carried out at an input power of 100 W, filling ... [Show full abstract] pressure of 1 mbar and substrates temperature of 250oC. X-ray diffraction (XRD) results show an expansion in lattice spacing and consequently shift of diffraction peaks towards lower angle with the addition of helium in nitrogen plasma. Surface morphology of the treated sample is investigated by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Vickers micro-hardness testing results show increases in surface hardness with processing duration as well as with the addition of helium in nitrogen plasmas. This increase of surface hardness may be attributed to the diffusion of nitrogen content in the surface layer generating internal stresses. It is observed that the addition of helium positively affects the nitriding of samples.