Aging- and creep-resistance of a cast hypoeutectic Al-6.9Ce-9.3Mg (wt.%) alloy

A ternary Al-6.9Ce-9.3Mg (wt.%) hypoeutectic alloy, consisting of equal amounts of α-Al(Mg) solid-solution regions and Al(Mg)-Al₁₁Ce₃ eutectic colonies, is investigated in terms of its aging and creep resistance. The eutectic regions exhibit a microhardness of 1230 MPa, which is thrice the value of Al-Al₁₁Ce₃ eutectic regions in a binary Al-12.5Ce (wt.%) near-eutectic alloy, demonstrating that Mg in solid-solution enhances the strengthening provided by the micron-scale highly-branched Al₁₁Ce₃ phase. X-ray diffraction measurements during ambient-temperature tensile testing reveal that load is being transferred from the Al(Mg) matrix to the Al₁₁Ce₃ phase, confirming that the fine eutectic microstructure displays composite strengthening in addition to the expected precipitation- and solid-solution strengthening. The hardness remains effectively unchanged after aging at 450 °C for up to 8 weeks, indicating excellent coarsening resistance of the Al₁₁Ce₃ phase. The ternary alloy exhibits creep resistance at 300 °C slightly inferior to the near-fully eutectic binary Al-12.5Ce (wt.%) alloy, consistent with the presence of large regions of fast-creeping primary Al(Mg) solid-solution matrix between the strong Al(Mg)-Al₁₁Ce₃ eutectic colonies in the hypoeutectic ternary alloy.