Surface Characteristics Improvement of AZ31B Magnesium by Surface Compositing with Carbon Nano-tubes through Friction Stir Processing

In this research, compositing the surface of AZ31B magnesium alloy with CNT was studied by FSP. The investigated parameters were rotational speed (500-1500 rpm), transverse speed (12-44 mm/min), number of passes (1-4), and CNT weight fraction (0-2%). Microhardness testing, optical metallography, FESEM, and EDS analysis were used for the characterization of the samples. The suitable limits for the transverse speed and rotational speed were 12-24 mm/min and 870-1140 rpm, respectively. The highest hardness in the FSP without compositing was observed at the transverse speed of 24 mm/min, rotational speed of 870 rpm with a hardness of about 60 Vickers, and the stir region grain size of less than 5 µm. The Zener-Holman parameter was calculated and the least value was related to the conditions of the transverse speed of 12-24 mm/min and rotational speed of 870 rpm; as a result, the samples with the finest grain size were theoretically and experimentally marked. The most homogenous structure with the highest hardness was related to the three-pass processed sample with a hardness of 69 Vickers. The best rate of CNT weight was 2%, enjoying the highest hardness. The FESEM images confirmed the suitable distribution of CNTs in matrix after the performance of the three-pass processing.