Cast near-eutectic Al-12.5 wt.% Ce alloy with high coarsening and creep resistance

Abstract

This study investigates the creep behavior of a cast, coarse-grained Al-12.5 wt.% Ce (Al-2.7 at.% Ce) alloy, consisting of an eutectic microstructure (α-Al with ~11 vol.% submicron Al11Ce3 “Chinese script” platelets) with ~3 vol.% primary, micron-scale Al11Ce3 plates. Upon aging at 322 °C for 8 weeks or at 400 °C for 12 weeks, the microhardness of the alloy remains unchanged, demonstrating excellent coarsening resistance of the strengthening Al11Ce3 phase. In addition, no coarsening of Al11Ce3 is observed metallographically after 3 weeks under compressive loads of 13–70 MPa at 260–350 °C. When tested to failure under a constant tensile stress of 23 MPa at 300 °C, the alloy shows primary, secondary and tertiary creep regimes, and fails after 19 days at 17% tensile strain, demonstrating both high creep ductility and high creep resistance. Under compressive and tensile creep conditions, the alloy exhibits high apparent stress exponents (n = 9–11), which translate into threshold stresses for dislocation creep of 34, 22, and 14 MPa at 260, 300 and 350 °C, respectively. The creep resistance of Al-12.5 wt.% Ce is higher than that of Al-Sc-Zr-based alloys (with ~0.3 vol.% of coherent nanoprecipitates) and similar to cast, eutectic Al-6 wt.% Ni (with ~11 vol.% of incoherent Al3Ni micro-fibers). For as-cast grain sizes of 2–3 mm, Al-12.5 wt.% Ce exhibits a transition from dislocation creep to diffusional creep at strain rates of ~10−7 s−1, with a threshold stress of 19 MPa in compression at 260 °C and 5 MPa in tension at 300 °C.