Permanent Mold Casting and Creep Behavior of Mg - 4 Al - 4 X: (Ca, Ce, La, Sr) Alloys 2007-01-1027

Creep-resistant magnesium alloys for automotive powertrain applications offer significant potential for vehicle weight reduction. In this study permanent mold casting, microstructure and creep behavior have been investigated for a series of ternary magnesium alloys (Mg-4Al-4X (X: Ca, Ce, La, Sr) wt%) and AXJ530 (Mg-5Al-3Ca-0.15Sr, wt%). A permanent mold was instrumented with twelve thermocouples and mold temperature was monitored during the casting process. Average mold temperature increased from 200°C to 400°C during a typical alloy casting series (fifteen to twenty castings). The cast microstructure for all alloys consists of primary α-Mg globular phase surrounded by eutectic structure which is composed of intermetallic(s) and α-Mg magnesium phases. The primary cell size of the AXJ530 increased from 18 to 24 μm with increasing mold temperature and a similar trend is expected for all alloys. The cast alloys were subsequently subjected to constant load creep tests in the stress ranges of 40 to 90 MPa. Mold temperature in permanent mold casting had a significant effect on the creep behavior of some alloys and insignificant effect on others, and can be related to precipitation of Al₂Ca in the primary phase during solidification.