The efficiency of interfacial ion mixing is measured for metal/Al (metal=Ti, Cr, Ni, and Mo) thin‐film bilayers irradiated with 285 keV Xe+ions near 77 K. The results indicate that, as a group, mixing of 3d‐metal/Al pairs irradiated by Xe can be explained by neither a pure binary collision cascade nor a pure thermal spike model. Such a situation should exist; that it should be found at the average atomic numbers of the present bilayers is consistent with recent theoretical predictions.