J.F. dos Santos

Characterisation of electron beam welded aluminium alloys

AbstractElectron beam (EB) welding was performed on three different aluminium alloys, namely alloys 2024, 5005, and 6061 (plate thickness 5 mm except alloy 5005 which was 3 mm in thickness), to establish the local microstructure–property relationships that would satisfy the service requirements for an electron beam welded aluminium alloy component with weld zone strength undermatching. Microstructural characterisation of the weld metals was carried out by optical and scanning electron microscopy. A very low level of porosity was observed in all EB welds owing to surface cleaning before welding and the vacuum environment of the EB welding process. Extensive microhardness measurements were also conducted in the weld regions of the joints. Global tensile properties and fracture toughness properties (in terms of crack tip opening displacement, CTOD) of the EB joints were determined at room temperature. The effects of strength mismatch and local microstructure on fracture toughness of the EB joints are discuss...

Trends in laser beam welding technology and fracture assessment of weld joints

Abstract Recent advances in the industrial application of laser welding are reviewed, drawing on examples from the aerospace, automotive, shipbuilding, offshore, and white goods industries. Attempts are being made to introduce laser welding procedures into construction industry standards. The impact of the narrow, overmatched weld zone on joint properties and the difficulties this raises for quality assessment are briefly considered.

Hybrid modelling of 7449-T7 aluminium alloy friction stir welded joints

Abstract Many finite element models use adjustable parameters that control the heat loss to the backing bar, as well as the heat input to the weld. In this paper, we describe a method for determining these parameters with a hybrid artificial neural network (ANN) coupled thermal flow process model of the friction stir welding process. The method successfully determined temperature dependent boundary condition parameters for a series of friction stir welds in 3·2 mm thick 7449 aluminium alloy. The success of the technique depended on the method used to input thermal data into the ANN and the ANN topology. Using this technique to obtain the adjustable parameters of a model is more efficient than the conventional trial and error approach, especially where complex boundary conditions are implemented.

Microstructural mapping of friction stir welded AA 7075-T6 and AlMgSc alloys using electrical conductivity

Abstract AlMgSc and AA 7075-T6 alloys find applications in the aeronautic industry due to their lightweight associated with high mechanical strength and fatigue resistance. Both alloys have poor weldability when joined by fusion welding processes, which is overcome with the use of friction stir welding (FSW). Recent research work shows that electrical conductivity field analysis can be used as a material characterisation technique for solid state material welding exhibiting a microstructure gradient. This study aims to apply electrical conductivity field analysis to bead on plate FSW to identify the potential application of this technique to map and characterise microstructural transformations. The FSW was conducted on AlMgSc and AA 7075-T6 plates with different parameters, and electrical conductivity measurements were performed at half thickness, complemented by other techniques as hardness, scanning electron microscopy and energy dispersive spectroscopy. A good correlation was observed among electrical conductivity field, microstructure and hardness of different zones in FSW beads.

Progress in friction stir welding of Ni alloys

ABSTRACT In recent years, interest has been increasing in application of Nickel alloys in the oil industry. For subsea engineering, the possibility to weld high-strength materials in an effective manner is essential. Friction Stir Welding (FSW) is alternative to join several materials retaining their properties or even improving them. This fact is relevant for Corrosion-Resistant Alloys (CRA) used in deep-water exploitation of hydrocarbons. Publications up to now have focused on FSW of Inconel® series as alloy 600, 625, and 718. To provide a solid basis for development, this review discusses the crucial points for FSW. The tool materials are described, as well as the joint microstructure and properties achieved. Furthermore, the basics of the corrosion resistance and the early corrosion studies of FSW joints are presented. It is concluded that FSW is a promising process for Ni alloys, but depends on upcoming research regarding tool technology and corrosion investigations.

Residual stress and microstructural features of friction-stir-welded GL E36 shipbuilding steel

ABSTRACT The purpose of the present study was to fulfil the knowledge gap concerning residual stresses evaluation of friction stir welded GL E36 shipbuilding steel. Plates of 6u2009mm thickness were welded using two different welding speeds (1 and 3u2009mmu2009s−1) at a constant rotational speed of 500u2009revu2009min−1. This led to different thermal cycles and the objective is to analyse the resulting microstructures and residual stress states. Therefore, in this work, residual stresses were evaluated by X-ray diffraction; metallography and microhardness testing were performed to support these measurements. Results showed that welds produced with different heat inputs have distinguishable residual stress distributions. Increases in the welding speed led to higher residual stress and microhardness in the stir zone.