Faculty Publications
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Item Role of interfacial microstructure on mechanical properties of cold metal transfer welded dissimilar A6061-T6 and A6082-T6 joints(Elsevier B.V., 2020) Rajeshkumar, R.; Devakumaran, K.; Banerjee, K.A6061-T6 and A6082-T6 dissimilar aluminium alloys are welded using CMT (Cold metal transfer) process and the interface microstructure of the individual alloys is correlated with mechanical properties. Microstructures indicate that dendrites next to the PMZ (Partially melted zone) of A6082-T6 side are finer than the dendrites next to the PMZ of A6061-T6 side. Liquation at grain boundaries and within the grains is clearly visible in the PMZ of A6061-T6 interface, whereas the PMZ of A6082-T6 interface does not reveal liquation phenomenon at grain boundaries and grain interiors. Among the interface regions, the A6082-T6 side shows superior mechanical properties as compared to the A6061-T6 side. © 2020 Elsevier B.V.Item Fusion boundary microstructure evolution and mechanical properties of cold metal transfer welded dissimilar A5754 and A5083 joint(Elsevier B.V., 2021) Rajeshkumar, R.; Niranjani, V.L.; Devakumaran, K.; Banerjee, K.Fusion boundary microstructure evolution and its effect on tensile properties of cold metal transfer (CMT) welded joint of dissimilar A5754 and A5083 is studied. Non-dendritic equiaxed fine zone (EQZ) is newly evolved and located between PMZ and weld metal zone (WMZ). The Si films are distributed as continuous layers at grain boundaries (GBs) of EQZ, these films are comparatively less and are distributed in a non-continuous manner at GBs of partially melted zone (PMZ). EQZ of A5083 side exhibits finer grains than A5754 side. The narrower EQZ width, finer grains at EQZ, finer dendrites at WMZ interface and larger distribution of secondary phase particles at PMZ and heat affected zone (HAZ) increase strength of A5083 side. © 2020 Elsevier B.V.Item Effect of equiaxed grains and secondary phase particles on mechanical properties and corrosion behaviour of CMT- based wire arc additive manufactured AZ31 Mg alloy(Elsevier Ltd, 2023) Manjhi, S.K.; Sekar, P.; Bontha, S.; Balan, A.S.S.Wire arc additive manufacturing (WAAM) has drawn tremendous attention for manufacturing large and complex components of lightweight material at a moderate cost due to its high deposition rate and energy efficiency. Generally, WAAM-Mg alloy comprises columnar and columnar dendrite grains due to high cooling rates and thermal gradients responsible for anisotropic mechanical properties. To overcome this challenge, in this work, CMT-WAAM, which generally uses comparatively low heat input (33% lower than conventional WAAM), was used to deposit AZ31 Mg thin wall. The metallurgical characterization of the deposited thin wall of the top (T), middle (M) and bottom (B) sections reveals equiaxed grains of average sizes ∼ 58, ∼ 63 and ∼ 38 µm, respectively. In addition, TEM results exhibit the formation of secondary phase particles, i.e., β-Mg17Al12 and ɳ-Al8Mn5. Further, the ultimate tensile strength (UTS) and % elongation (% EL) in the travel direction (UTS = 224 MPa, % EL= 23.47%) are superior to that obtained in the build direction (UTS = 217 MPa, % EL = 20.82%). The corrosion resistance of WAAMed AZ31 Mg alloy is higher than wrought (cold rolled) AZ31 Mg alloy in Hank's balanced salt solution (HBSS). The results of this study reveal the potential of CMT-WAAM to deposit different grades of Mg with desired microstructure, mechanical properties and corrosion resistance. © 2023 CIRPItem Enhancing fatigue performance of AZ31 magnesium alloy components fabricated by cold metal transfer-based wire arc directed energy deposition through LPB(KeAi Communications Co., 2024) Manjhi, S.K.; Bontha, S.; Balan, A.A.S.Cold Metal Transfer-Based Wire Arc Directed Energy Deposition (CMT-WA-DED) presents a promising avenue for the rapid fabrication of components crucial to automotive, shipbuilding, and aerospace industries. However, the susceptibility to fatigue of CMT-WA-DED-produced AZ31 Mg alloy components has impeded their widespread adoption for critical load-bearing applications. In this study, a comprehensive investigation into the fatigue behaviour of WA-DED-fabricated AZ31 Mg alloy has been carried out and compared to commercially available wrought AZ31 alloy. Our findings indicate that the as-deposited parts exhibit a lower fatigue life than wrought Mg alloy, primarily due to poor surface finish, tensile residual stress, porosity, and coarse grain microstructure inherent in the WA-DED process. Low Plasticity Burnishing (LPB) treatment is applied to mitigate these issues, which induce significant plastic deformation on the surface. This treatment resulted in a remarkable improvement of fatigue life by 42%, accompanied by a reduction in surface roughness, grain refinement and enhancement of compressive residual stress levels. Furthermore, during cyclic deformation, WA-DED specimens exhibited higher plasticity and dislocation density compared to both wrought and WA-DED + LPB specimens. A higher fraction of Low Angle Grain Boundaries (LAGBs) in WA-DED specimens contributed to multiple crack initiation sites and convoluted crack paths, ultimately leading to premature failure. In contrast, wrought and WA-DED + LPB specimens displayed a higher percentage of High Angle Grain Boundaries (HAGBs), which hindered dislocation movement and resulted in fewer crack initiation sites and less complex crack paths, thereby extending fatigue life. These findings underscore the effectiveness of LPB as a post-processing technique to enhance the fatigue performance of WA-DED-fabricated AZ31 Mg alloy components. Our study highlights the importance of LPB surface treatment on AZ31 Mg components produced by CMT-WA-DED to remove surface defects, enabling their widespread use in load-bearing applications. © 2024Item Effect of CMT-WAAM Process Parameters on Bead Geometry, Microstructure and Mechanical Properties of AZ31 Mg Alloy(Springer, 2024) Manjhi, S.K.; Sekar, P.; Bontha, S.; Balan, A.A.S.Fabrication of Mg alloys using the additive manufacturing process is quite challenging owing to high oxidation and volatile nature at high temperatures. The present study investigates the effect of wire feed speed (WFS) and travel speed (TS) on single tracks of AZ31 Mg alloy fabricated using the cold metal transfer wire arc additive Manufacturing (CMT-WAAM) process. The WFS and TS of CMT-WAAM are optimized to achieve better deposition quality. An increase in WFS increased the width, height, penetration depth, and heat-affected zone of single tracks. In addition, increasing TS decreased the deposited tracks' contact angle and height. The average grain size at the interface zone, center and top portion of single tracks are 35, 42, and 60 μm. The x-ray diffraction results show only the presence of primary phase α-Mg; interestingly, the β-Mg17Al12 and η-Al8Mn5 secondary phases are identified by SEM + EDS and TEM images. The microhardness increased from the substrate to the top section of single tracks due to the increased volume fraction of secondary-phase particles. Based on the best-chosen process parameters obtained from single-track deposition, a multilayer AZ31 Mg thin wall is deposited. The UTS, YS, and % EL of the deposited thin wall in travel direction (TD) are 222 MPa, 102 MPa, and 18%, while in build direction are 202 MPa, 110 MPa, and 14%, respectively. The tensile strength and elongation % of TD and BD samples exhibited comparable properties and were higher than cast AZ31 Mg alloy. © ASM International 2023.