Characteristic of temperature distributions in stirring tools during friction stir welding

The temperature distribution in stirring tools was measured by experimental method. It is shown that the characteristic of temperature distribution in stirring tools is much different from that in workpieces. At the beginning stage of friction stir welding,the softening in stirring zone reduces the friction coefficient and the friction heat between the stirring pin and the workpiece,so the temperature in stirring tools stops rising, whereas decreases in the exterior margin of the tool before the shoulder touches the workpiece. At the steady welding stage,equilibrium exists between the heat quantity delivered to and dissipated through the stirring tool,and its temperature keeps little fluctuation. The surface of the high-speed rotating tool has intensive heat exchange with the air around it,so the temperature near its axis is higher than that on the exterior margin. The stirring tools made of metal with lower specific heat capacity and higher coefficient of heat transfer lead to heat within the welding area dissipating faster.