Abstract
The influence of the joint line remnant (JLR) on tensile and fatigue fracture behaviour has been investigated in a friction stir welded Al-Mg-Sc alloy. JLR is one of the microstructural features formed in friction stir welds depending on welding conditions and alloy systems. It is attributed to initial oxide layer on butting surfaces to be welded. In this study, two different tool travel speeds were used. JLR was formed in both welds but its spatial distribution was different depending on the tool travel speeds. Under the tensile test, the weld with the higher heat input fractured partially along JLR, since strong microstructural inhomogeneity existed in the vicinity of JLR in this weld and JLR had weak bonding. Resultantly, the mechanical properties of this weld were deteriorated compared with the other weld. Fatigue crack initiation was not affected by the existence of JLR in all welds. But the crack propagated preferentially along JLR in the weld of the higher heat input, when it initiated on the retreating side. Consequently, such crack propagation behaviour along JLR could bring about shorter fatigue lives in larger components in which crack growth phase is dominant.
Highlights
C onventionally, riveting has been used to join high strength aluminium plates for fuselage structures
Zigzag lines were observed in the butt weld for all weld conditions, as seen in Figs. 3(a) and (b), where the zigzag lines were highlighted with freehand lines for aid of visualization
The heat input in Friction Stir Weld (FSW) is considered to correlate with tool rotational speed and tool travel speed, where higher heat input is caused by higher tool rotational speed or lower tool travel speed, respectively [3, 19]
Summary
C onventionally, riveting has been used to join high strength aluminium plates for fuselage structures. Uematsu et al investigated the fatigue initiation site in 1050-O with JLR and showed that localized plastic deformation at the boundary between TMAZ and HAZ at the advancing side of the FSW line caused fatigue crack initiation [15]. They investigated fatigue behavior in FSWed samples of both heat-treatable and non-heat treatable alloys and concluded that fatigue fracture location was dependent on alloys due to their different microstructures and hardness distributions. Formation of the joint line remnant was examined, tensile and fatigue tests were performed and the influence of the JLR on the fracture behavior under tensile as well as fatigue loadings of the FSWed Al-Mg-Sc alloy was investigated
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