Solid-state additive manufacturing of dispersion strengthened aluminum with graphene nanoplatelets

Additive friction stir deposition (AFSD) successfully deposited graphene nanoplatelets (GNP) at concentrations of 0.0, 0.4, 0.8, and 1.1 wt% with AA6061 powders. Each concentration of GNP-AA6061 consisted of four consecutive layer-by-layer depositions on AA6061-T6 substrate. The hardness of the deposits varied from 48 Hv to 55 Hv, where a critical concentration of GNP appears to be required for a notable increase in hardness to occur (>0.8 wt%). This hardness response scaled with the tensile responses, with the highest yield and ultimate strengths belonging to the 1.1 wt% GNP of 104 +/- 6 MPa and 195 +/- 0.9 MPa respectively. The changes in strength are linked to grain refinement with increasing GNP content as well as a higher amount of dispersion strengthening from the GNPs within the grains. Unlike prior research on AFSD where consolidated AA6061 feedstock bars with GNPs are used, the hardness and strength is higher with this powder mixture approach.