Microstructural, mechanical and tribological characterization of ZrB2 reinforced AZ31B surface coatings made by friction stir processing

Among the different surface modification techniques, Friction Stir Processing (FSP) is one of the promising techniques for magnesium materials. In the present work, an AZ31B magnesium alloy is reinforced with 3 wt.% micro-sized Zirconium diboride (ZrB2) particles through the Friction Stir Processing technique. The effect of tool passes (single pass and double pass) on microstructural, mechanical, and tribological properties were investigated. The microstructural study revealed that the average grain size of double-pass AZ31B/ZrB2 surface composite was reduced from 12 to 6 mu m as compared to the AZ31B magnesium alloy. The microhardness test results revealed a 50% improvement in hardness in the double-pass AZ31B/ZrB2 surface composite than in the single-pass reinforced composite and base alloy. The tensile test result revealed a 19% improvement in the strength of the double-pass AZ31B/ZrB2 surface composite and 13.5% improvement in the strength of the single-pass AZ31B/ZrB2 surface composite in comparison to the base alloy. A ductile mode of fracture was observed in fractured tensile specimens. The friction and wear performance of base alloy and AZ31B/ZrB2 surface composites were evaluated using a pin-on-disc tribometer.Tribological behaviour exhibited that the wear rate of a double-pass AZ31B/ZrB2 surface composite was 60% lower than the base alloy. The coefficient of friction of the double-pass AZ31B/ZrB2 surface composite was 24% lower than the base alloy. SEM images of the worn surface revealed delamination, micro-cracks, and ploughing in AZ31B/ZrB2 surface composites.