A microplasticity-based definition of the skin in HPDC Mg–Al alloys

The hardness profiles across the thickness of tensile specimens of alloys with a range of Al contents were used in conjunction with tensile data to determine the thickness of the strongest possible outer layer for each alloy, thus defining the casting skin. As long as the skin layer remains elastic, the core of the casting is prevented from developing full plasticity. The differentiation between the skin and core regions decreases for the less concentrated alloys, leading to a thicker skin layer by this definition. An existing, complementary definition of the skin, based on the core reaching full plasticity, and by which the skin is thinner in the leaner alloys, is also discussed to provide a comprehensive description of the elasto-plastic transition for all alloy concentrations.