Weldability and mechanical properties of AA5083-H112 aluminum alloy and pure copper dissimilar friction spot extrusion welding-brazing

This paper investigates the effect of dwell time and heat treatment on the modified friction stir clinched (MFSC) joint of AA2024-T3/AA6061-T6 Al alloys. The precipitation-hardening heat treatment method involves the combination of solution heat treatment (at 520 °C for 1 h) and aging (at 165 °C for 18 h) processes. The microstructure, failure load, hardness, and fracture behavior of the as-welded and heat-treated MFSC joints were investigated. TEM images show that re-precipitation of strengthening Al2CuMg and MgZn2 phases, dislocation density, and tangles are more pronounced in the heat-treated MFSC joint. A rise in dwell time increases the average grain sizes (1.39–6.65 μm), tensile-shear strength (101–133 MPa), and cross tension strength (59–88 MPa) of the MFSC welded 2024-T3/6061-T6 joints due to an upsurge in the in-process exposure time-induced heat input and inter-material flow. An increase in dwell time beyond 15 s is undesirable. It induces the formation of nugget cracks and micro-voids in the joints and an impaired joint failure load consequently ensues. Heat treatment processing further causes grain coarsening (2.48–9.15 μm) and improves the hardness (at the weld center), tensile-shear (146 MPa), and cross tension (102 MPa) failure strengths of the MFSC joints due to the re-precipitated strengthening phases.

Modified friction stir clinching of 2024-T3 to 6061-T6 aluminium alloy: Effect of dwell time and precipitation-hardening heat treatment

The integration of flow-induced mechanical interlocking, interlayer-controlled atomic diffusion and self-reacting brazing benefit is employed to achieve an improved load-bearing performance of the dissimilar AA2024-T3/copper joint via the use of Dieless Friction Stir Extrusion-Brazing (DFSE-B). A comparative study of the Dieless Friction Stir Extrusion-Brazing (DFSE-B) and Friction Stir Spot Welding-Brazing (FSSW-B) of the dissimilar AA2024-T3/Cu joint was investigated by using a 100 µm thick Zn interlayer. The microstructure, tensile-shear load, and fracture modes of the respective joints were examined. The results show that Zn solidification-induced voids are inevitable at the brazed zones of both joints and the DFSE-B process suppresses flow-induced defect, unlike the FSSW-B process. An improved tensile-shear load with a significant toughness is achieved by the DFSE-B process due to the absence of tool-induced keyhole, and the intrinsic mechanical interlocking of the softer Al alloy into the harder Cu alloy. The DFSE-B is a suitable welding alternative for reactive metals.

Dieless Friction Stir Extrusion-Brazing (DFSE-B) of AA2024-T3 aluminum alloy to Copper with Zn interlayer

Modified friction stir clinching (MFSC) process was employed to joint dissimilar AA2024-T3 and AA6061-T6 Al sheets by interchanging the upper and the lower sheets during the joining process. The material flow, microstructure, tensile strength and fracture behaviors of the MFSC joints were studied. The results reveal that material positioning significantly affects the material flow behavior of the MFSC joint due to the disparity in the properties (flow stress) of the AA2024-T3 and AA6061-T6 Al alloys. The flow-induced hook path and proximity of hook tip to the geometric differential flow-induced defect (at the refilled end of the keyhole) are undesirable in the welded AA6061-T6/AA2024-T3 joint as compared to the AA2024-T3/AA6061-T6 joint. The microstructure (precipitate dispersion, dislocation density, and tangles), hardness distribution, and fracture morphology of the joints are altered by the material positioning-induced flow behavior. Improved tensile strength (97.88 MPa) is obtained in the AA2024-T3/AA6061-T6 joint as compared to the AA6061-T6/AA2024-T3 joint (86.65 MPa).

Dissimilar modified friction stir clinching of AA2024-AA6061 aluminum alloys: Effects of materials positioning

Modified friction stir clinching of AA6061-T6/AA5754-O joint: Effect of tool rotational speed and solution heat treatment on mechanical, microstructure, and fracture behaviors

A. Moharrami

Papers

Modified friction stir clinching of 2024-T3 to 6061-T6 aluminium alloy: Effect of dwell time and precipitation-hardening heat treatment

Development and characterization of dissimilar joint between AA2024-T3 and AA6061-T6 by modified friction stir clinching process