Mechanical Response of Friction Stir Welded Aluminum 2139-T8 as a Function of Loading Rate and Stress-State

Abstract

Friction stir (FS) welding is a solid state process that does not melt the base metal. This has the benefit of changing the mechanical characteristics of the original material as little as possible. This welding process is used frequently on large size aluminum plates, where the size of the welded structure prohibits heat treating of it afterward to recover pre-weld material characteristics. In this study, two plates of aluminum 2139 are FS welded together, and then machined into experimental specimens from various locations (base metal, weld material). In addition, specimens are fabricated that span from one plate to the other, including the whole weld. These are used to experimentally characterize the mechanical response and failure behavior of the weld to allow for incorporation into simulation methodology to predict the deformation and failure of the weld. In addition, these experimental observations will be used to understand the mechanisms of weld failure for FS welds under various types of high rate loading. The characterization is performed using two types of experiments: uni-axial tensile testing and a modified three-point bending experiment with distributed loading over the weld. These experiments are performed at low and high loading rates to investigate the effect of loading rate on the deformation response and failure behavior. The high rate experiments are accomplished using a tensile Kolsky bar to conduct tensile experiments, and a modified compressive Kolsky bar to perform bending experiments. Digital image correlation is used in the experiments to measure the strain field on the specimen and observe how it differs between the bulk material, heat-affected zone, and weld zone. In this paper, the experimental techniques are discussed and results are presented.