A challenge for castable Al alloys is that few elements exhibit appreciable solubility in Al. Hence, the volume fraction of any precipitated phases is low (typically less than 1 vol.%). This contrasts from the Ni-based alloys, in which Al and Ti exhibit high solubility in Ni, leading to large volume fractions (usually exceeding 50%).
Analogous to γ' in the Al system are the trialuminides (Al3M, where M is a transition element). In order to achieve superalloy-like performance in Al, the precipitated Al3M must be very small, of the order of nm. Rick and Marsha are addressing this with ternary and quaternary additions to Al3Sc. Keith is investigating Al3Zr-based alloys.