Modelling microplastic flow in an hpdc Mg-Al alloy

A numerical micromechanistic model is used to simulate the progressive development of microplastic flow across the cross section of cast to shape tensile specimen of a Mg-Al alloy, accounting for the strong gradient of yield strength between the softer core and the harder periphery of the section, or skin. While maintaining iso-strain and iso-stress conditions across the entire section, the onset of microyielding at the core increasingly sheds load onto the elastic skin, which reacts by applying an increasing elastic constraint on the core. In the process the skin becomes thinner while the core expands. The speed of the interface between the plastic core and elastic skin that moves outwardly with the applied stress can be quantified and the onset of full plasticity across the entire cross section readily identified.