Precipitation phenomena and strengthening mechanism of Al–Cu alloys deposited by in-situ rolled wire-arc additive manufacturing

We reported the precipitation phenomena and strengthening mechanism of Al–Cu alloys deposited by in-situ rolled wire-arc additive manufacture (WAAM) technology. The results indicated that in-situ rolling was able to eliminate most of the solidification shrinkage cavities during deposition, however, high density of fine hydrogen pores formed after T6 heat treatment, which was caused by hydrogen micropore precipitation. A slight coarsening of the pre-existed pores was mainly controlled by coalescence of micropores or Ostwald ripening. Most of the eutectic structure with continuous or semi-continuous distribution in grain boundaries dissolve into the matrix during T6. Some undissolved θ and high density of needle-like θ′ precipitates could be observed in grain interior. The UTS and YS of the alloy reached 454.4 ± 23.8 MPa and 356.6 ± 17.1 MPa after T6 treatment, which was mainly due to the precipitation strengthening. The initiation and propagation of the cracks may be ascribed to the existence of pores for the as-deposited and T6 sample. The representative transgranular fracture could be observed in T6 sample while the crack prefers to propagate along the eutectic structure with continuous distribution in grain boundaries of as-deposited sample.