Browsing by Author "Meco, Sonia"

Now showing 1 - 11 of 11
  • Thumbnail Image
    ItemOpen Access
    Comparison of continuous and pulsed wave lasers in keyhole welding of stainless‑steel to aluminium
    (Springer, 2021-10-31) Coroado, Julio; Ganguly, Supriyo; Williams, Stewart; Suder, Wojciech; Meco, Sonia; Pardal, Goncalo
    A continuous wave (CW) and a nanosecond pulsed wave (PW) lasers were used to join 1-mm thick sheets of SS304L (SS) austenitic stainless-steel to AA5251 (Al) aluminium alloy in an overlap joint configuration. The weld shape (penetration depth and width), intermetallic compounds concentration, weld quality (cracking and porosity) and mechanical strength were correlated with the process energy and compared between each laser temporal mode. Successful CW joints were produced with the SS sheet on top of the Al, but the opposite configuration revealed to be impossible for the range of parameters tested. The PW joints were successful with the Al sheet on top of SS, but all the joints cracked at the interface when the opposite configuration was used. The mechanical tests showed that even though it is possible to achieve higher tensile shear load in CW welds due to the larger bonding area, the tensile shear strength revealed to be almost 5 × higher for PW welds at similar applied energy.
  • Thumbnail Image
    ItemOpen Access
    Design of laser welding applied to T joints between steel and aluminium
    (Elsevier, 2019-01-07) Meco, Sonia; Ganguly, Supriyo; Williams, Stewart W.; McPherson, Norman
    Laser conduction welding was used to directly join DH36 steel to AA5083 aluminium alloy in a T joint configuration, each plate with 6 mm of thickness. The effect of the process energy (via power density and interaction time) on the joint integrity and quality in terms of cracking, porosity and intermetallic compound layer formation was investigated. Successful T joints were produced by melting of the aluminium plate, which was inserted into a 4 mm deep groove machined on the steel plate, with the heat generated by the laser irradiation on the steel surface. The IMC layer thickness was less than 5 μm. Although cracking was observed along the IMC layer with higher levels of energies, the joints were still strong due to the mechanical inter-locking effect resulting from the novel design of the component, whereby the IMCs were subjected to compressive state of stress while loading.
  • Thumbnail Image
    ItemOpen Access
    Effect of laser processing parameters on the formation of intermetallic compounds in Fe-Al dissimilar welding
    (Springer Intrnational, 2014-09-01T00:00:00Z) Meco, Sonia; Ganguly, Supriyo; Williams, Stewart W.; McPherson, Norman
    Fusion welding of steel to aluminum is difficult due to formation of different types of Fe-Al intermetallics (IMs). In this work, 2mm-thick steel was joined to 6mm aluminum in overlap configuration using a 8kW CW fiber laser. A defocused laser beam was used to control the energy input and allow melting of the aluminum alone and form the bond by wetting of the steel substrate. Experimentally, the process energy was varied by changing the power density (PD) and interaction time separately to understand the influence of each of these parameters on the IM formation. It was observed that the IM formation is a complex function of PD and interaction time. It was also found that the mechanical strength of such joint could not be simply correlated to the IM layer thickness but also depends on the area of wetting of the steel substrate by molten aluminum. In order to form a viable joint, PD needs to be over a threshold value where although IM growth will increase, the strength will be better due to increased wetting. Any increase in interaction time, with PD over the threshold, will have negative effect on the bond strength.
  • Thumbnail Image
    ItemOpen Access
    Fundamental understanding of the interaction of continuous wave laser with aluminium
    (Springer, 2017-07-13) Coroado, Júlio; Meco, Sonia; Williams, Stewart W.; Ganguly, Supriyo; Suder, Wojciech; Quintino, Luísa; Assunção, Eurico
    In welding, the depth of penetration, weld profile and the corresponding thermal cycle are the three basic outcomes that a user wishes to control flexibly. In laser welding applications, controlled application of power and energy density is the key to achieve predictable control of these characteristics. Creation of an analytical model is an important step towards understanding the underpinning science of laser metal interaction in controlling the depth, bead geometry and thereby temperature profile of a weld. The “power factor model”, which correlates the power applied per unit length to the laser metal interaction time, has been originally developed and validated for mild steel, guides a user on the selection laser system parameters, to achieve specific weld profile. This study is performed to extend the power factor–interaction time model to aluminium alloys by understanding the underpinning laser aluminium interaction parameters in terms of power density, interaction time, specific point energy and their correlation with the weld bead profiles. Although the power factor and interaction time showed a rectangular hyperbolic relationship, as observed in low carbon steel, for a specific weld depth and profile, the absolute magnitude and the characteristic profile of the curve is different due to the intrinsic differences in physical and thermal properties of aluminium as compared to steel. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of power and travel speed by keeping the energy input per unit length constant.
  • Thumbnail Image
    ItemOpen Access
    Investigation of dissimilar metal welds by energy-resolved neutron imaging
    (International Union of Crystallography, 2016-06-09) Tresmin, Anton S.; Ganguly, Supriyo; Meco, Sonia; Pardal, Goncalo; Shinohara, Takenao; Feller, Bruce
    A nondestructive study of the internal structure and compositional gradient of dissimilar metal-alloy welds through energy-resolved neutron imaging is described in this paper. The ability of neutrons to penetrate thick metal objects (up to several cm) provides a unique possibility to examine samples which are opaque to other conventional techniques. The presence of Bragg edges in the measured neutron transmission spectra can be used to characterize the internal residual strain within the samples and some microstructural features, e.g. texture within the grains, while neutron resonance absorption provides the possibility to map the degree of uniformity in mixing of the participating alloys and intermetallic formation within the welds. In addition, voids and other defects can be revealed by the variation of neutron attenuation across the samples. This paper demonstrates the potential of neutron energy-resolved imaging to measure all these characteristics simultaneously in a single experiment with sub-mm spatial resolution. Two dissimilar alloy welds are used in this study: Al autogenously laser welded to steel, and Ti gas metal arc welded (GMAW) to stainless steel using Cu as a filler alloy. The cold metal transfer variant of the GMAW process was used in joining the Ti to the stainless steel in order to minimize the heat input. The distributions of the lattice parameter and texture variation in these welds as well as the presence of voids and defects in the melt region are mapped across the welds. The depth of the thermal front in the Al–steel weld is clearly resolved and could be used to optimize the welding process. A highly textured structure is revealed in the Ti to stainless steel joint where copper was used as a filler wire. The limited diffusion of Ti into the weld region is also verified by the resonance absorption.
  • Thumbnail Image
    ItemOpen Access
    Laser spot welding of laser textured steel to aluminium
    (Elsevier, 2017-03) Pardal, Goncalo; Meco, Sonia; Dunn, Andrew; Williams, Stewart W.; Ganguly, Supriyo; Hand, Duncan P.; Wlodarczyk, Krystian L.
    Laser welding of dissimilar metals (steel and aluminium) was investigated with the aim to increase the maximum tensile shear load of the Fe-Al joints. The increase was achieved by texturing the surface of steel prior to the laser spot welding process which was performed in a lap-joint configuration with the steel positioned on top of the aluminium and with a texture faced down to the aluminium surface. This configuration enabled an increase of the bonding area of the joints, because the molten aluminium filled in the gaps of the texture, without the need of increasing the process energy which typically leads to the growth of the intermetallic compounds. Different textures (containing hexagonally arranged craters, parallel lines, grid and spiral patterns) were tested with different laser welding parameters. The Fe-Al joints obtained with the textured steel were found to have up to 25% higher maximum tensile-shear load than the joints obtained with the untextured steel.
  • Thumbnail Image
    ItemOpen Access
    Laser welding of steel to aluminium: thermal modelling and joint strength analysis
    (Elsevier, 2017-04-10) Meco, Sonia; Cozzolino, Luis; Ganguly, Supriyo; Williams, Stewart W.; McPherson, Norman
    The integrity of steel-aluminium dissimilar alloy joints is dependent on the thermal cycle applied during the joining process. The thermal field has a direct influence on the growth of the intermetallic compounds (IMC), which result from the reaction between iron (Fe) and aluminium (Al), but it also determines the size of the bonding area of the joint. A finite element (FE) thermal model was developed to predict the transient thermal cycle at the Fe-Al interface for different levels of applied energy by changing the power density and interaction time. The time-temperature profiles were correlated to the weld geometry, IMC layer thickness and mechanical strength. The experimental results showed that having a small bonding area is equally detrimental to the mechanical strength of the joint as having a thick IMC layer. The FE model suggested that comparing to time, the temperature is more important in laser welding of steel to aluminium as this is the factor which most contributes to the growth of the IMC layer and the formation of the bonding area. However, it was not possible to identify a thermal field able to produce simultaneously a large bonding area and a thin IMC layer to optimize the joint strength.
  • No Thumbnail Available
    ItemOpen Access
    Laser welding of steel to aluminium: Thermal modelling and joint strength analysis
    (Cranfield University, 2017-11-15 16:12) Meco, Sonia; Cozzolino, Daniel; Ganguly, Supriyo; Williams, Stewart; McPherson, Norman
    Data generated by the FE model and experimental data used in the accompanying article.Files created in SigmaPlot 11.0.
  • Thumbnail Image
    ItemOpen Access
    Light-weight Mg/Al dissimilar structures welded by CW laser for weight saving applications
    (Springer, 2017-08-25) Gao, Qiong; Meco, Sonia; Wang, Kehong
    With the increasing demand of light-weight alloys, such as magnesium (Mg) and aluminum (Al), the need for joining these two alloys is unavoidable. In this study, AZ31B Mg and 1060 Al alloys were joined by continuous wave laser micro-welding using a 0.05 mm thick Cu/Zn interlayer. The microstructure and phases constituent of the weld seam were examined by optical microscope, SEM and EDS. The formation and distribution of the intermetallic compounds (IMCs) and the relationship between these structures and the micro-hardness of the weld were discussed in detail. The effect of Cu/Zn interlayer on the performance of Mg/Al joint was also analyzed. The results showed that Mg/Al IMCs were formed in the weld, which indicates that the Cu/Zn foil could not prevent the reaction between Mg and Al. However, the addition of Cu and Zn into the weld pool refined the microstructure by improving the number of eutectic structures. The micro-hardness of Mg/Al IMCs in the middle of the weld was very high which can be detrimental to the toughness of the Mg/Al joints.
  • Thumbnail Image
    ItemOpen Access
    New phenomenological model for comparison of lasers with different temporal outputs
    (Springer, 2022-04-06) Coroado, Julio; Williams, Stewart W.; Suder, Wojciech; Ganguly, Supriyo; Meco, Sonia; Pardal, Goncalo
    Laser welding is distinguished by low heat input, low distortion, high travel speeds and accuracy. Traditional high-power pulsed wave (PW) lasers are being replaced by high-frequency low-pulse energy fibre lasers. However, as these lasers operate at very high frequencies, near continuous wave (CW) operation, it is not clear the benefit of such frequencies in comparison to CW lasers for micro-welding. In this project, two lasers, one in high-frequency PW and another in CW are operated at the same conditions, including average power, average peak power, spot size and travel speed, and the differences in material response are investigated. It has been shown that frequency is one of the important parameters that affect the heat loss between individual pulses, referred to as inter-pulse losses. At low frequency, the PW laser provided lower melting efficiency and higher penetration efficiency than CW. On the other hand, at high frequency, the PW resulted in lower melting and penetration efficiency than CW. In addition, a new definition of interaction time has been proposed to capture conduction losses by travel speed and heat inter-pulse losses due to periodic lack of laser power. This allows a like-for-like comparison of CW and PW lasers and can be used to predict penetration depth with processing parameters.
  • Thumbnail Image
    ItemOpen Access
    Selection of parameters in nanosecond pulsed wave laser micro-welding
    (Springer, 2021-05-31) Coroado, Julio; Ganguly, Supriyo; Suder, Wojciech; Williams, Stewart; Meco, Sonia; Pardal, Goncalo
    The digital control of the latest nanosecond pulsed wave (PW) fibre lasers allows very high flexibility in controlling the application of the total energy to a workpiece, which brings several advantages to the joining process. By choosing different pulse shapes in different spatial profiles, it is possible to apply low energy per pulse with high precision and accuracy resulting in lower heat input. Since the energy of each pulse is insufficient to generate melting, these lasers operate at very high pulse repetition frequencies near continuous wave (CW) regime. Nevertheless, the peak powers of PW lasers are much higher than CW. In this research, the effect of peak power, pulse energy, pulse width, pulse repetition frequency and duty cycle has been studied. The experimental work was conducted in bead on plate of austenitic stainless steel to investigate the effect of laser on the weld geometry, i.e. depth of penetration and width. An empirical model, previously established for CW mode, which enables the achievement of a particular penetration depth independent of the beam diameter, was redesigned and tested for PW mode. The “pulse power factor model” allows the laser user to select a weld profile that meets certain quality and productivity requirements independent of the laser system. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of different system parameters by keeping a constant trade-off between pulse power factor and interaction time.