Dissimilar materials, aluminium 2024-T3 and ultralow carbon steel, have been welded by a novel process called friction melt bonding. A finite element thermal model is developed to predict temperature cycles and to estimate the fusion pool geometry and the intermetallic bonding layer thickness. The total mechanical power input in pseudo-steady state is inferred from in situ measurements at the tool torque and rotational speed. Temperature dependent properties, including the latent heat of fusion, and proper contact conditions between the welded plates and the backing plate are included. Predicted temperatures are in agreement with the measurements at various distances from the weld centreline. Molten pool geometries and intermetallic thicknesses, whose control is crucial to insure good weld mechanical performances, are also in accordance with the experimental observations.
Optimization of the intermetallic layer thickness and the suppression of interfacial defects are key elements to improve the load bearing capacity of dissimilar joints. However, till date we do not have a systematic tool to investigate the dissimilar joints and the intermetallic properties produced by a welding condition. Friction Melt Bonding (FMB) is a recently developed technique for joining dissimilar metals that also does not exempt to these challenges. The FMB of DP980 and Al6061-T6 is investigated using a new physical simulation tool, based on Gleeble thermo-mechanical simulator, to understand the effect of individual parameter on the intermetallic formation. The proposed method demonstrates its capability in reproducing the intermetallic characteristics, including the thickness of intermetallic bonding layer, the morphology and texture of its constituents (Fe2Al5 and Fe4Al13), as well as their nanohardness and reduced modulus. The advantages of physical simulation tool can enable novel developing routes for the development of dissimilar metal joining processes and facilitate to reach the requiring load bearing capacity of the joints.
Aluminum alloy AA6061 was welded to dual-phase steel 980 (DP980) by the friction melt bonding (FMB) process. Hot tears have been suppressed by controlling the thermomechanical cycle. In particular, the welding speed and the thermal conductivity of the backing plate have been optimized. A finite-element thermomechanical model coupled with the Rappaz-Drezet-Gremaud (RDG) criterion has been used to explain these experimental observations. The hot tear susceptibility has been reduced with large thermal gradients and with the formation of a cellular microstructure. Both effects are favored by a backing plate made of a material with high thermal conductivity, such as copper.
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