Abstract
AbstractThe present investigation is concerned with high‐cycle axial fatigue testing of a 2‐mm AA6060‐T6 hybrid metal extrusion & bonding (HYB) butt weld produced in the solid state using AA6082 filler metal addition. The results complement the three‐point bend testing and the tensile testing done in two previous studies. In this study, optical microscope and scanning electron microscope examinations have been carried out to reveal the joint macro/microstructure and document possible surface and root defects deemed to affect fatigue life. In the as‐welded condition, the HYB weld suffers from surface irregularities at the weld face and ‘kissing’ bond formation in the root region. Despite of this, the subsequent testing shows that the fatigue properties exceed those reported for comparable AA6082‐T6 gas metal arc butt welds and matching those reported for corresponding high‐strength laser beam and friction stir weldments.
Highlights
From the optical microscope examination, it is evident that the 2-mm AA6060-T6 hybrid metal extrusion & bonding (HYB) butt joint suffers from both surface irregularities at the weld face and ‘kissing’ bond formation at the weld toe
In the extrusion zone (EZ) specimens the fatigue crack propagates from the ‘kissing bond’ defect being detected at the weld toe on the retreating side (RS), which is the weaker part of the joint
Following the elimination of the ‘kissing bond’ defect, the fatigue strength of the HYB joint approaches that of the base metal (BM) specimens, which is rather atypical for aluminium weldments
Summary
In weldments a variety of defects and geometrical discontinuities are present, which will reduce the overall fatigue life of the component.[1,2,3] In particular, aluminium fusion welds are known to be prone to fatigue failure because they suffer from gas porosity and solidification cracks.[4,5,6] they are susceptible to thermal distortions and high residual stress levels which may reduce their fatigue life.[7,8] Friction stir (FS) welded aluminium joints, on the other hand typically demonstrate superior fatigue properties compared to conventional fusion welds.[1,9,10,11,12,13,14] it is widely accepted that many of the negative effects of welding in the context of engineering design are reduced using solid state joining.[15]. The main objective of the present work is to evaluate the fatigue properties of the HYB joint in its current developed stage, with emphasis on its macrostructural features This will be done by conducting high-cycle axial fatigue testing of the joint, combined with optical microscopy and scanning electron microscopy (SEM) examination of the as-welded joint and broken specimens, respectively. To determine the crack initiation point and the subsequent propagation direction, selected fracture surfaces of FIGURE 2 Schematic drawing showing the shape and dimensions of the fatigue specimens broken fatigue specimens were examined in a Quanta FEG 450 scanning electron microscope (SEM) at different magnifications, using an acceleration voltage of 20 kV
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