Mg-3Al-1Zn-2Ca (AZX312) alloy has been forged in the temperature range of 350-500°C and at speeds in the range of 0.01-10mms^-1 to produce a rib-web shape with a view to validate the processing map and study the microstructural development. The process was simulated through finite-element method to estimate the local and average strain rate ranges in the forging envelope. The processing map exhibited two domains in the following ranges: (1) 350-450°C/0.0003-0.05s^-1 and (2) 450-500°C/0.03-0.7s^-1 and these represent dynamic recrystallization (DRX) and intercrystalline cracking, respectively. The optimal workability condition according to the processing map is 425-450°C/0.001-0.01s^-1. A wide flow instability regime occurred at higher strain rates diagonally across the map, which caused flow localization that should be avoided in forming this alloy. The experimental load-stroke curves correlated well with the simulated ones and the observed microstructural features in the forged components matched with the ones predicted by the processing map.