Asymmetry Thermal Analyses of Self-Supporting Friction Stir Welding

Due to the inherent issue of requiring rigid back support, friction stir welding (FSW) has serious limitations for the welding of hollow structures. Self-supporting friction stir welding was proposed to join hollow aluminum extrusions, which could reduce the hindrance of the welding tool and the requirement of rigid back support. In this paper, finite element modeling analyses were carried out for the asymmetric temperature field in the process of self-supporting FSW. The peak temperature of the stir zone appeared in the upper shoulder affected zone, followed by the lower shoulder affected zone. In the upper shoulder affected zone, a peak temperature was not shown at the center of the curve due to the positive correlation between heat generation and radius and different heat dissipation rates. Considering the influence of thermal input and rotation speed on joint formation, 200 mm/min travel speed and 800 rpm rotation speed are the most proper parameters for 5-mm-thick 6082-T6 aluminum alloy self-supporting FSW butt welds.

Decipher Ultrasonic Signals from Defects in Thick Aluminum Extrusions to Identify Type and Origin of Defects

Manufacturing of thick seamless pipes of age-hardenable aluminum alloys are a specialized technology since their application is limited to specific hi-tech areas. Quality criteria for their inspection are propriety items of the very few production facilities that develop these criteria in-house. Present study relates ultrasonic signals reflecting back from non-continuities in the thickness of seamless pipes with their microstructural features. Detailed study of defects leads to the source of their formation and will ultimately help to systematically control them. Signals from ultrasonic testing trace defects as UT waves reflect back from discontinuities in the material. Defective sections of seamless pipes were cut with precision to reveal the defects. The sectioned surfaces were subjected to metallographic preparation and revealed defects were studied using Optical and Field Emission Scanning Electron Microscopes (FESEM). Defects are grouped based on the shape of UT signals as well as the defect morphology as revealed by microscopic studies. Most of the observed cracks are found to grow in the direction of extrusion. Energy Dispersive Spectroscopy (EDS) analysis was conducted to determine the composition of inclusions in the vicinity of the defects. Data from elemental analysis is used to identify the potential sources. The study recommends measures to control the defects and improve the yield.

Numerical analysis of the fatigue behaviour of friction stir welded joints in aluminum bridge decks

<p>Friction stir welding (FSW), a relatively new welding technique, has been widely used in the aero- space and manufacturing industries, showing superior mechanical and durability properties. How- ever, its application in civil engineering is very limited due to the absence of appropriate standards and quality control guidelines. FSW appears to be a promising welding solution for the fabrication of vehicular bridge decks made from aluminum extrusions, with a potential to reduce distortions and improve fatigue properties. The fatigue behaviour of common FSW joint types such as the butt FSW has extensively been investigated and documented in literature. However, certain practical configurations such as the butt-lap joint used in the fabrication of extruded aluminum bridge decks have rarely been studied, especially in the area of fatigue performance. In this context, the present research provides first an overview on the welding process of typical aluminum friction stir welded bridge deck extrusions presenting the butt-lap configuration. Then, the fatigue behaviour of butt- lap FSW joints is assessed using the effective notch stress (ENS) approach. The effect of geometrical features on the fatigue behaviour of butt-lap FSW joints is numerically investigated also by the ENS approach.</p>