Modelling thermal cycles and intermetallic growth during friction melt bonding of ULC steel to aluminium alloy 2024-T3

Abstract

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.

On the Prediction of Hot Tearing in Al-to-Steel Welding by Friction Melt Bonding

“…In previous studies, van der Rest et al [9] and Crucifix et al [11] observed hot tears in the re-solidified aluminum after FMB. Such hot tears were located in the molten pool close to the aluminum-steel interface.…”

“…The simulation of the temperature field was adapted from the work of Crucifix et al [11] Four components of the weld were simulated: the steel and aluminum sheets, the backing plate, and the welding table.…”

“…where T z is the measured torque, x is the angular speed of the tool, and gð2 0; 1 ½ Þis the efficiency included in the heat input to account for the power loss, mainly by heat conduction through the tool. [23] The heat source was modeled as suggested by Crucifix et al [11] The total power introduced in the system was divided into a surface component due to friction, _ Q surf , and a volume component due to plastic deformation of the steel below the tool, _ Q vol . The surface component was distributed radially.…”

“…They observed that the commercially pure aluminum alloy AA1050 was free of hot tears, while age-hardenable AA2024 led to hot tearing. Crucifix et al [11] considered the thermal cycles when welding AA2024 to ULC steel. They observed that the number of hot tears increased as the welding speed increased.…”

“…With this as criterion, it is possible to assess the influence of alloy composition and thermomechanical parameters on the propensity of hot tear formation. [13] In the previously discussed welds performed by Crucifix et al, [11] the hot tearing susceptible alloy AA2024 was welded to steel. The combination of large cooling rates-and by extension large strain rates-seemed to be responsible for the formation of hot tears, rather than the size of the molten pool.…”