Study on Plastic Response Under Biaxial Tension and Its Correlation with Formability for Wrought Magnesium Alloys

The mechanical response and microstructural changes under biaxial tension of two magnesium alloy sheets, ZE10 and AZ31, have been investigated. The forming limit diagram (FLD) of the two alloys was further assessed using the Marciniak–Kuczynski (M–K) model combined with two constitutive models: (a) crystal plasticity finite element (CPFE), and (b) phenomenological yield. The FLDs predicted by the combined CPFE and M–K model were in excellent agreement with the experimental data. The phenomenological yield models using the mechanical data at small plastic work led to poor prediction results. However, these could well reproduce the experimental FLDs when the mechanical data at larger plastic work were used for parameter identification. In-depth analyses revealed that the evolution of the anisotropic strain hardening during biaxial tension and significant evolution of the r-value during uniaxial tension were the main sources of the error in the predictions by the phenomenological models using the material data at smaller plastic work.