Browsing by Author "McPherson, Norman"

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    Application of laser in seam welding of dissimilar steel to aluminium joints for thick structural components
    (Elsevier, 2015-04-01) Martins Meco, Sonia Andreia; Rodrigues Pardal, Gonçalo; Ganguly, Supriyo; Williams, Stewart W.; McPherson, Norman
    Laser welding-brazing technique, using a continuous wave (CW) fibre laser with 8000 W of maximum power, was applied in conduction mode to join 2 mm thick steel (XF350) to 6 mm thick aluminium (AA5083-H22), in a lap joint configuration with steel on the top. The steel surface was irradiated by the laser and the heat was conducted through the steel plate to the steel-aluminium interface, where the aluminium melts and wets the steel surface. The welded samples were defect free and the weld micrographs revealed presence of a brittle intermetallic compounds (IMC) layer resulting from reaction of Fe and Al atoms. Energy Dispersive Spectroscopy (EDS) analysis indicated the stoichiometry of the IMC as Fe2Al5 and FeAl3, the former with maximum microhardness measured of 1145 HV 0.025/10. The IMC layer thickness varied between 4 to 21 μm depending upon the laser processing parameters. The IMC layer showed an exponential growth pattern with the applied specific point energy (Esp) at a constant power density (PD). Higher PD values accelerate the IMC layer growth. The mechanical shear strength showed a narrow band of variation in all the samples (with the maximum value registered at 31.3 kN), with a marginal increase in the applied Esp. This could be explained by the fact that increasing the Esp results into an increase in the wetting and thereby the bonded area in the steel-aluminium interface.
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    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.
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    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.
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    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.
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    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.