Effect of synthetic graphite and activated charcoal addition on the mechanical, microstructure and wear properties of AZ 81 Mg alloys

In the present study, the grain refinement effects of carbon on AZ 81 (Mg8%Al) alloys were investigated through the addition of synthetic graphite and activated charcoal inoculants. The mechanical and dry sliding wear properties of AZ 81 (Mg8%Al) alloys with and without grain refiners were studied. The composition, microstructure and wear surface of the cast alloys were analyzed with the aid of atomic absorption spectroscopy, optical and scanning electron microscopes. The wear test was conducted at a speed of 5.37 m/s and two loading (20 N and 30 N) conditions in a pin on disc wear apparatus. The mean grain size of the alloy is significantly reduced from about 185 to 32 mu m when the carbon content is increased to 0.98% C. Both tensile strength and ductility increase with increasing carbon content. Also, the wear rate decreases with the increase of carbon content in the alloy. The activated charcoal with 0.98 wt% C is found to be a better grain refiner in improving the properties of tensile behaviour and wear resistance. The fracture surface morphology shows the brittle intergranular fracture. Analyses of wear surface morphology show that abrasive and delamination wear mechanisms are responsible for the wear loss in the AZ 81 alloy.