Effect of scandium micro-alloying on the creep resistance properties of Al-0.7Fe alloy cables

The effect of Sc addition on creep resistance properties in the Al-0.7Fe-0.2Sc and Al-0.7Fe alloy has been studied. The microstructures before and after creep of Al-0.7Fe and Al-0.7Fe-0.2Sc alloy were investigated by optical microscopy, electron probe micro-analysis and transmission electron microscopy. In creep tests, the steady state creep rates of Al-0.7Fe-0.2Sc alloy were much lower than that of Al-0.7Fe alloy at 90-150 °C/70 MPa, it indicates that Sc addition significantly affected the creep resistance in Al-0.7Fe alloy cables. According to EPMA data and the known formation enthalpies of Al3Fe and Al3Sc phases, both of them are thermally stable. Additionally, TEM imaging showed that Al3Fe phases non-uniformly pinned on the subgrain boundary, and the average size of Al3Fe phase is approximately 0.4 µm. The nanosized Al3Sc precipitates (25-40 nm) both pinned on subgrain boundary and dislocation, making the pinned dislocations and subgrain boundary difficult to shift. The Orowan stress increment of ∆σOr in crept Al-0.7Fe-0.2Sc alloy is 61.3 MPa, whereas the ∆σOr of crept Al-0.7Fe alloy is 30.1 MPa, indicating that Al-0.7Fe-0.2Sc alloy cables possess higher creep resistance than Al-0.7Fe alloy cables.