Mechanical and tribological behavior of friction stir processed AZ61/egg shell powder/WS2 Hybrid surface composite

Abstract

Egg Shell Powder (ESP) and Tungsten Disulphide (WS2) are reinforced on AZ61 magnesium alloy through Friction Stir Process (FSP). The average particle size of ESP and WS2 are 45 μm and 10 μm, respectively. The ESP and WS2 mixed at different weight percentage (80/20, 70/30, 50/50, 30/70 and 20/80). Initially, equally spaced cylindrical holes are drilled on AZ61 alloy and then reinforcement mixture is filled in the holes using a flat head tool to secure the reinforcements. FSP tool pin with threaded profile is used to perform the friction stir process at tool rotation speed of 1000 rpm, 7 kN of axial load and 5 mm minute−1 tool transfers speed. From the micro and macro optical images, the defect free FSPed composite is obtained for the reinforcement combination of AZ61/80ESP/20WS2. The mechanical, tribological and corrosion tests are conducted on FSPed AZ61/80ESP/20WS2 composite and AZ61 base alloy according to ASTM standards. Microhardness increased twice in the nugget zone of FSPed AZ61/80ESP/20WS2 composite compared to the AZ61 base alloy because of grain refinement. The ultimate tensile strength of FSPed AZ61/80ESP/20WS2 composite increased up to 8.3% compared to AZ61 base alloy and showed ductile behaviour during the fracture. Dry wear tests conducted at three different sliding velocities (0.83, 1.7 and 2.5 m s−1) and three different loads (5 N, 10 N and 15 N) by keeping the sliding distance as 1500 m. The results showed an improvement in wear resistance of FSPed AZ61/80ESP/20WS2 composite up to 35% compared to the AZ61 base alloy. SEM images revealed that the wear mechanism changes from adhesive to abrasive under high operating conditions. The results of electrochemical corrosion test revealed that the corrosion rate of the FSPed AZ61/80ESP/20WS2 composite reduced significantly at the nugget zone because of grain refinement and reinforcement addition.