Effects of annealing on periodic microstructure and mechanical properties of inter-layer hammering hybrid wire arc additively manufactured aluminum alloy

It is common to use heat treatment process to control the microstructure of additive manufacturing parts and improve the mechanical properties. However, there are few reports about the control of microstructure properties of WAAM hybrid inter-layer hammering fabricated parts by heat treatment. In this study, the effect of annealing on microstructure and mechanical properties of inter-layer hammering hybrid wire arc additively manufactured aluminum alloy was studied. The ratio variation of fine grain (FG) and coarse grain (CG) regions, grain size and dislocations were analyzed, and the strength-plasticity mechanism was revealed. The results shown that with the increase of annealing temperature, the ratio of FG and CG region changed from 4:1–1:5, grain growth and recrystallization happened in FG and CG regions, respectively, dislocations mostly retained in FG region and released in CG region. With the introduction of annealing and the increase of annealing temperature, the strength of hybrid manufactured samples gradually weakened while the plasticity first improved and then reduced. The best tensile properties of ultimate tensile stress 366 MPa and elongation 29.2% were achieved at 180 °C annealing. Compared with as-deposited sample, the synergistic enhancement of strength and plasticity in annealed samples is owing to dislocation strengthening, grain refinement, and heterogeneous structural strengthening. Compared with hammered sample, the strength retained and significant improved in plasticity of annealed sample, owing to dislocation released, grain refinement and heterogeneous structural.