Effect of Annealing Heat Treatment on the Microstructural Refinement of Pure Copper by Friction Stir Processing

Recently, friction stir processing (FSP) was developed as an effective method to modify microstructural and mechanical properties of materials. During process, a rotating tool is inserted in a plate, providing frictional heating and mechanical mixing. In this investigation, the effect of annealing heat treatment on the microstructure characteristics of the nugget zone was investigated during friction stirs processing (FSP) of the pure copper. Plate with 4 mm thickness was friction stir processed at constant traverse speed of 45 mm/min and tool rotation speed of 700 rpm. Samples were processed in various annealing conditions. Results showed that by increasing the annealing duration from 45 to 180 minutes at annealing temperatures of 600°C and 800°C, the grain size and the hardness value of samples significantly decreased. At annealing temperature of 1000°C samples were exposed to extra heat, grains started to coarsen and hardness decreased. Ultrafine-grained microstructure in FSP samples was achieved using annealing heat treatment at annealing temperature of 600°C.