Processes and repair area properties of AA6061 repaired via additive friction stir deposition

The repair experiments of the additive friction stir deposition (AFSD) for the AA6061-T6 plates of 5 mm thickness were performed, and the influences of the repair processing parameters and groove defect sizes on the microstructures and properties of the repaired zone were explored. It is shown that adequate metallurgical bonding between the deposited layer and subtract can successfully be obtained for the groove defects with 3 mm depth and 6~24 mm widths under the rotational speed of 400 r/min and the transverse speeds of 150~300 mm/min. The fully dense and defect-free repair can be achieved when the groove width is smaller than the feed rod diameter, and the repair zone can be divided into the deposited zone (DZ), thermo-mechanically affected zone (TMAZ), heat-affected zone (HAZ), and base material (BM). The DZ is composed of refined equiaxed grains with grain sizes ranging from 9.1% to 12.8% of that of BM. The main β" strengthening phase in the DZ is almost completely dissolved, which results in the reduction of the average hardness of DZ corresponding to 71.6% of that of BM. For the AFSD parameters of 400 r/min, 300 mm/min, the tensile strength and elongation of the repaired sample with 12 mm groove width can reach the best mechanical properties of 197.4 MPa and 10.92%, respectively. The fracture sites of samples are all located at the interfaces of HAZ and TMAZ and they have the ductile fracture mode. The tensile strength and elongation of the repaired sample with the groove width of 24 mm which is greater than the feed rod diameter are the best mechanical properties of 178.9 MPa and 7.74%, while for the 400 r/min,150 mm/min AFSD parameters. In this case, the weak-bonding defects formed at the interface between the deposited layer and BM are the key factor to influence the repair property. The experimental findings provide valuable insights for developing novel repair technology via AFSD in aluminum alloys.