Analysis of Microstructure and Mechanical Properties of Copper Friction Stir Welding Zone

This study aimed to perform friction stir welding experiments using a 2-mm-thick copper plate. The tool’s rotating speed (ω) and transversing speed were 800–1200 rpm and 200 mm/min, respectively. The impact of the tool’s transversing speed on the properties of welded copper was analyzed while keeping the transversing speed constant. Analyzing the experimental results, it is evident that the metallographic microstructure of the welding zone undergoes similar changes at different tool rotation speeds. Specifically, the grain in the welding core zone becomes refined, while the grain near the return side appears larger. The region is the thermomechanically affected zone and heat affected zone, which experiences less agitation from the tool but undergoes compression from the matrix metal, resulting in the grain size being larger than that of the welding zone but smaller than that of the matrix metal. The same was true for the advancing side. The tensile strength of the sample, which was 266.2 MPa, exhibited a high degree of consistency with that of the base metal when the tool’s ω value reached 800 rpm. The hardness of each sample exceeded that of the base metal. The hardness of the sample increased by 133.2% to 185.9 HV0.2 when the tool’s ω value was set at 1000 rpm, surpassing that of the base metal. The friction coefficient of each sample was lower than that of the base metal. The friction coefficient in the welding zone, which is merely 0.21, represents less than half of that in the base material, which is 0.55. The friction stir welding technique has significantly enhanced copper’s mechanical properties, facilitating its widespread application.