Ball Burnishing of Friction Stir Welded Aluminum Alloy 2024-T3: Experimental and Numerical Studies

Abstract

This paper deals with the improvement of the material surface state of friction stir welding paths modified in situ by plastic deformation through ball burnishing. The metallurgical and topological states of materials joined by this welding technique are typically detrimental to the ulterior performance of the workpiece, and it is believed that ball burnishing can improve these states to enhance functioning. This study is divided into two phases. The first one is experimental and consists of welding aluminum AA2024-T3 plates while combining different tool rotations and welding speeds. Then, the welding line is deformed locally by ball burnishing. The improvement of the topology and deep hardness distribution is measured and discussed, and the evolution of mechanical properties is assessed through tensile tests. The second phase is oriented towards estimating the residual stresses by combining two pre-existing models of friction stir welding and burnishing developed by the same authors using ANSYS®. Friction stir welding experimentation and measurements show a decrease in the values of all measured mechanical properties compared to the original material. The dominant factor affecting the properties and texture of the materials is the rotational speed of the tool, with the rupture point in the tensile test located in the distinct zone with the lowest value of microhardness on the advancing side. The higher the ratio of the rotational speed to the welding speed, the lower the roughness value. Finally, ball burnishing is proven to be an effective method to enhance the surface integrity of friction stir welded joints in light of the results, achieving a reduction of 11% to 36% in average roughness and an increase of about 22% in hardness profile, along with an integrated numerical model estimation of a remarkable effect on compressive residual stresses in-depth on the retreating side of the welded samples. However, in some tests, this treatment reduced some characteristics (yield stress and failure strain).