The quantitative investigation of mechanical properties and characterization of fractured position for friction stir lap welded A6111/A5023

•Study of the effects of material arrangement, tool plunge depth and revolutionary pitch in friction stir lap welding dissimilar aluminium alloys AA6111 and AA5023 identified key factors for bond strength.•For soft top layer, the key factor was deformed surface height.•For the hard top layer the key factor was the position of the unbonded line.

The effects of plunge depth (PD) revolutionary pitch (RP) and materials arrangement on deformation and softening material at the fractured position of a friction stir welded AA6111 to AA5023 lap joint were investigated. As a result, the main factor determining tensile shear load and fracture was different with the location of soft material. When the soft material was located on top, the softening material and the deformed surface height occurred by friction heat generation of the rotating shoulder. The main factor was the deformed surface height rather than the softening material, and the deformed surface height was decreased with increasing RP. On the other hand, when the soft material was located at the bottom, the movement of the un-bonded line and hooking occurred due to the vertical flow of the rotating probe. The crucial factor was the position of the un-bonded line rather than the height of the hook. The un-bonded line occurred along the interface between two materials affected by the lowest strength, which were deformed toward the hard material affected by a higher joint strength.

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