Tensile creep behaviour of as-cast Mg-4Al-4RE (2.7La-1.3Ce) alloy

The Mg-4Al-2.7La-1.3Ce alloy was synthesized by melting in a resistance furnace at 750°C under a protective atmosphere of 98 % argon and 2 % SF6 to prevent oxidation. The cast microstructure consisted of an α-Mg matrix along with intermetallic phases such as Al₁₁(La Ce)₃ and Al₂(La Ce), exhibiting lamellar and acicular morphologies. The alloy showed a Vickers hardness of 108 ± 3 Hv. Mechanical testing revealed a yield strength (YS) of 101 ± 3 MPa, ultimate tensile strength (UTS) of 170 ± 3 MPa, and elongation of 5–7 %. Creep tests conducted at 200–220°C under 50–80 MPa stress showed a true stress exponent (n) of 2.34, suggesting a diffusion-controlled creep mechanism. Stress rupture data were compared with AE44 alloys using the Larson-Miller Parameter (LMP). The Mg-4Al-2.7La-1.3Ce alloy showed better rupture strength at stresses below 60 MPa. Fractographic analysis of tensile and creep specimens revealed cleavage and quasi-cleavage features, indicating brittle failure. Post-creep TEM examination revealed fine rod-like intermetallics at grain boundaries that acted as bridges, restricting grain boundary sliding and dislocation motion. These features contributed to improved creep resistance, making the alloy promising for high-temperature structural applications where lightweight and thermal stability are critical. • Mg-4Al alloy adding with 4 % RE (2.7 %La and 1.3 %Ce) were fabricated using a protective atmosphere. • Mechanical, microstructural, creep, and stress rupture properties studied at 220–200 °C under 50–80 MPa. • TEM analysis shows stable Al-RE precipitates enhance creep resistance; mechanism illustrated schematically.