Modeling temperature fields during friction stir welding

Abstract

In the process of friction stir welding, the temperature fields in the joint zone determine the physical possibility of the plastic flow of the heated material and obtaining a high-quality formation of the weld structure. This paper presents the results of a computational study of the temperature distribution in a plate of AMg3 aluminum alloy around and under the tool, using experimental data on heat release in linear friction stir welding when rotating tools of different diameters at different speeds of rotation and movement. For these calculations, a program has been developed in which the tool is represented by a set of elementary heating sources evenly distributed over its area. The temperature field was calculated as the sum of temperatures from each elementary (point) source and is produced using the program developed in the Mathlab package. The tool diameter is divided into 100 cells, for each of them the heat release is calculated depending on the peripheral rotation speed and the welding speed. After determining their relative velocity, the temperatures are calculated based on the scheme of a moving point source in the limiting state.

The calculation results are presented in the form of temperature fields and isotherms on the surface of a plate made of 4 mm thick AMg3 aluminum alloy for a tool with a diameter of 20 mm and the following modes – its rotation speeds of 40 and 100 rad/s and welding of 0.42 and 1.67 mm/s. After that, the area in the heating zone of the plate and inside the tool is divided into sections 2 mm wide and the dependences of the temperature distribution along the center line of welding are obtained. The main result of the performed calculations is that the highest temperature value is observed in the region of the trailing edge of the tool, while the maximum value is shifted relative to the centerline of welding by 5–8 mm in the direction opposite to the rotation of the tool. This asymmetry of isotherms is more pronounced at small radii of the tool, where its peripheral speeds are relatively low and comparable with the welding speed, as well as with a decrease in the rotation speed and with an increase in the welding speed.