Strengthening by the percolating intergranular eutectic in an HPDC Mg-Ce alloy

Dual beam FIB tomography was used to create a 3D model of the percolating intergranular (α-Mg)-Mg12Ce eutectic in a Mg-0.51 at% Ce alloy and its tensile deformation behaviour assessed using finite elements. The eutectic itself was modelled as a fibre reinforced composite, with the elastic constants of the Mg12Ce intermetallic determined using a first principles approach. The 3D eutectic network exhibited a very low structural stiffness, akin to that of bending-dominated cellular structures. Such high compliance implies that the 3D structure may contribute to the alloy׳s strength while sustaining limited damage by cracking, hence extending the reinforcing without compromising the ductility, up to strains in excess of 1%. Elastic stretching of the 3D network adds ~25 MPa to the overall strength of the alloy at 0.2% offset strain, a value comparable to the strengthening expected from a similar volume fraction of dispersed (isolated) elastic particles. Flash anneal of the alloy to break up the spatial interconnection confirmed that the strengthening introduced by the eutectic stemed from the combination of network reinforcement and dispersion hardening.