The employment of advanced fiber laser technology to weld dissimilar materials: Stainless steel and aluminum alloy using pre-placed powder-based activating flux and filler

The dissimilar materials welding was carried out between austenitic stainless steel 304 L (low carbon) and aluminum alloy 5083 by a low power single-mode continuous wave Ytterbium fiber laser in steel-on-aluminum overlapping configuration and keyhole mode. In order to compensate for both the mechanical properties and appearance deficiencies such as: underfilling, spattering, solidification cracks, excessive formation of Fe-Al intermetallic compounds in addition to lack of sufficient shear strength, various combinations of pre-placed powder-based activating fluxes including oxide- based TiO2 (titanium dioxide) and halide-based CaF2 (calcium fluoride) powders in addition to the mixture of pure iron-aluminum powder filler were utilized in order to investigate their effects on the metallurgical and mechanical properties of the joints. To characterize the joints, shear tests were carried out in order to identify the influence of laser welding parameters and powders on welded joints' strength. The elemental composition, crystallographic characteristics in addition to failure mechanism of the welded joints were evaluated using Energy-dispersive spectroscopy (EDX) and X-ray diffraction (XRD) respectively, beside that the Vickers microhardness was employed in order to identify the location of various FexAly intermetallic compound phases across the fusion, heat affected and unaffected zones. Furthermore, the microstructure and morphology of the weld fillets were characterized using Field emission scanning electron (FESEM) and Optical microscopes. The obtained results show that, the application of oxide and halide activating fluxes led to remarkable decrease in welding defects including the hot cracks, pores and inclusions which resulted in tensile properties improvement up to 1.66 and 2.14 times in average respectively compared with autogenous joints welded without any powder. The enhancement in mechanical properties and appearance of the joints is related to special mechanism of activating fluxes through which the laser plasma can be formed in a shorter period of time leading to faster laser-material coupling, shorter thermal history and better heat conduction throughout the whole thickness of welding materials, which can promote the uniform heat distribution leading to an increase in penetration depth, decrease in surface depression and material ejection, restriction of intermetallic compounds and preservation of hardness across the weld nuggets. Moreover, the enhanced convection after usage of activating fluxes led to better molten pool circulation which resulted in constitution of joints with root-shape morphology possessing mechanical interlock characteristics. Correspondingly, the severe underfilling and spattering observed during the welding process as a result of alloying elements evaporation was eliminated completely after the application of pre-placed Fe-Al powder filler which led to significant enhancement in weldments' appearance and shear strength

Severe plastic deformation of tubular AA 6061 via equal channel angular pressing

Various severe plastic deformation (SPD) processes have been developed to produce metal tubes with ultrafine grain (UFG) structures. However, most techniques are complex and limited to working with components that are short in length to avoid tube failure during SPD processes. To overcome such limitations, this study suggests the use of an equal channel angular pressing (ECAP) process for the production of tubular aluminum alloy 6061. To mitigate plastic instability effects such as tube buckling and fracture during processing, hydraulic oil was used to fill the tube cavity. Finite element analysis (FEA) using Abaqus/Explicit 6.13 was carried out to examine the feasibility of the proposed method and deformation mechanism during ECAP. A series of investigations were performed, including: microstructure analysis, torsion, and micro hardness tests to evaluate the effects of tube-ECAP treatment. Test results indicated that the resultant 60% reduction in grain size led to significant mechanical property improvements including yield shear strength, ultimate shear strength, and microhardness. However, the ductility of the material decreased slightly for the ECAP-treated samples. To resolve this issue, a heat treatment process using the T6 method was performed, leading to a notable ductility enhancement in addition to further improvements in shear strength and microhardness.the Ministry of Higher Education, Malaysia, with high impact research (HIR) grant numbers HIR-MOHE-16001-D000001. Human Resources Program in Energy Technology of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20154030200900)

The application of equal channel angular pressing to join dissimilar metals, aluminium alloy and steel, using an Ag-Cu-Sn interlayer

Joining cylindrical and bar-shaped components manufactured from dissimilar materials is frequently required in various industrial applications. The current study focuses on developing equal channel angular pressing (ECAP) as a severe plastic deformation process for solid state joining of tubular aluminium alloy 6061 components and SAE 1018 steel rods. The influence of using a 0.1 mm thick 60Ag-30Cu-10Sn interlayer in addition to annealing at 220, 320,420 and 520 degrees C for 60 min is investigated as well. Finite element analysis (FEA) is performed in order to evaluate the deformation behaviour of the workpieces during the ECAP joining process. XRD and EDX analyses as well as nanoindentation and shear tests are carried out to evaluate the joints' characteristics. The FEA outcomes show remarkable accumulation of equivalent plastic strain with relatively low strain inhomogeneity. Moreover, the experimental results indicate that with increasing annealing temperature, joint strength exhibits improvement as well. It is also revealed that the application of an interlayer at any specific annealing temperature leads to achieving higher shear strength values. According to the results, shear strength of up to 32 MPa is feasible by having an interlayer and with subsequent annealing at 520 degrees C. (C) 2015 Elsevier Ltd. All rights reserved

Employment of fiber laser technology to weld austenitic stainless steel 304 l with aluminum alloy 5083 using pre-placed activating flux

The overlapping welding was carried out in keyhole mode between austenitic stainless steel 304 l and aluminum alloy 5083 using a low power fiber laser in continuous irradiation. The significant content of magnesium as the alloying element with low boiling point and high vapor pressure inside the AA 5083 matrix can induce the spatter formation and depression on surface of the weld beads upon laser beam absorption and temperature growth which can deteriorate the mechanical properties and appearance of the joints. To reduce these defects, a variety of single and multi-components activating fluxes including oxide-based TiO2 and halide-based CaF2 flux powders were pre-placed on the surface of welding material prior to laser welding. The EDX and XRD analyses in addition to microhardness and shear tests were carried out to characterize the joints. The obtained results showed that, the oxide and halide activating fluxes can significantly improve the joints' strength up to 1.48 and 1.85 times in average respectively compared with autogenous joint. It was deduced that the simultaneous effect of significant decrease in joints' surface depression leading to welds' geometry improvement in addition to less formation of interfacial Fe-Al intermetallics, were the major causes for considerable strength improvements. (C) 2015 Elsevier Ltd. All rights reserved