Friction Stir Welding of Die Cast Aluminum

As die-cast-components are subjected to major production deviations, considerable linear misalignments and gaps along the joint line have to be handled regarding butt joints. Furthermore the porosity of the base material has an impact on the welding process. Thus, this paper deals with the influence of linear misalignments and gaps as well as the quality of the base material on the mechanical properties of friction stir welded die-cast-aluminum-alloys.

Welds, performed as butt joints, with 4 mm thick plates of EN AC-AlSi10MnMg show that a linear misalignment Dh up to 0.5 mm can be bridged, using a tool shoulder with 13 mm diameter. Applying an additional lateral tilt angle β of the tool a misalignment of 2 mm is possible as the following cross section micrographs reveal (fig. 1).

The influence of Dh and β is examined on the basis of static tensile tests. Inverting advancing and retreating side with respect to the position of the upper plate doesn't show any effect.

Investigations concerning the gap, using the same plates and welding tool as described above, exhibit that a gap up to 0.6 mm can be bridged. Further tests are performed varying the plate thickness and weld parameters, such as rotation and welding speed. Micrographs and tensile tests serve as a basis for analysis.

To examine the impact of defects of the base material – in the case of die-cast-components these are often pores – on the weld quality, boreholes with diameters form 1.5 to 2.5 mm and distances from 5 to 15 mm in between are applied to the joint surface (fig. 2). This way it is possible to create samples with artificial but reproducible porosity, which can be varied orderly. Analyzing cross section micrographs the maximum allowed porosity can be determined, at which defect free welds are achievable.