A multi modal approach to microstructure evolution and mechanical response of additive friction stir deposited AZ31B Mg alloy

Current work explored solid-state additive manufacturing of AZ31B-Mg alloy using additive friction stir deposition. Samples with relative densities >= 99.4% were additively produced. Spatial and temporal evolution of temperature during additive friction stir deposition was predicted using multilayer computational process model. Microstructural evolution in the additively fabricated samples was examined using electron back scatter diffraction and high-resolution transmission electron microscopy. Mechanical properties of the additive samples were evaluated by non-destructive effective bulk modulus elastography and destructive uni-axial tensile testing. Additively produced samples experienced evolution of predominantly basal texture on the top surface and a marginal increase in the grain size compared to feed stock. Transmission electron microscopy shed light on fine scale precipitation of Mg17Al12 within feed stock and additive samples. The fraction of Mg17Al12 reduced in the additively produced samples compared to feed stock. The bulk dynamic modulus of the additive samples was slightly lower than the feed stock. There was a similar to 30 MPa reduction in 0.2% proof stress and a 10-30 M Pa reduction in ultimate tensile strength for the additively produced samples compared to feed stock. The elongation of the additive samples was 4-10% lower than feed stock. Such a property response for additive friction stir deposited AZ31B-Mg alloy was realized through distinct thermokinetics driven multi-scale microstructure evolution.