Microstructures and tensile properties of a high-strength die-cast Mg–4Al–2RE–2Ca–0.3Mn alloy

• Combinative addition of Ca and RE has a very good cell refinement effect.
• The Al-RE phases are disparate from those in the conventional AE44 alloy.
• The studied alloy has much higher yield strength than the similar magnesium alloys.
• The intermetallic skeleton plays a key role on the tensile properties.

Microstructures and tensile properties of a high-pressure die-cast Mg–4Al–2RE–2Ca based alloy were thoroughly investigated. The results indicate that the combinative addition of Ca and RE has a good cell refinement effect and can clearly change the intermetallic constituents. In the studied alloy, the intermetallic phases mainly consist of (Mg,Al)2Ca, Al11RE3, Al8RE3, Al2.12RE0.88, and Al10RE2Mn7, wherein the Al11RE3 phase has fully disparate morphologies from the conventional one in the Mg–Al–RE based alloys, the Al8RE3 phase is an unknown phase, and the Al2.12RE0.88 phase contains twins and numerous staking faults. However, the Al2RE phase is absent in the studied alloy. On the other hand, substituting half RE with Ca can also obviously further improve the tensile strength at both room temperature and high temperatures, but will also result in low plasticity simultaneously at lower temperatures (≤ 200 °C), to which the key is the highly interconnected and strong intermetallic skeleton.