The Mg-Al-Ca Alloy System for Structural Applications at Elevated Temperatures 2007-01-1025

Solidification paths and phase stability have been investigated in the creep resistant Mg-Al-Ca based alloys for powertrain applications. The liquidus projection and isothermal sections of the Mg-Al-Ca ternary system were determined, including a ternary (Mg, Al)₂Ca intermetallic compound. The solidification of the alloys in the α-Mg primary phase field involves L→α+(Mg, Al)₂Ca eutectic reaction in a wide range of compositions and is terminated with invariant reactions that form Mg₂Ca or Mg₁₇Al₁₂ phases. The (Mg, Al)₂Ca is a high temperature phase and decomposes into Mg₂Ca and Al₂Ca phases between 773 and 673 K, but the transformation is kinetically quite slow at temperatures below 473 K. Based on this new knowledge, alloy modifications through quaternary elemental additions to improve the solid-solution strength and aging treatments to reinforce the α-Mg phase with precipitates have been demonstrated.