Towards electroformed nanostructured aluminum alloys with high strength and ductility

Nanostructured Al-Mn alloys are proposed as high-strength low-density materials, which can be electroformed (i.e., produced electrolytically and removed from the substrate) from ionic liquid. A variety of current waveforms, including direct current (DC) and pulsed current (PC), are used to electrodeposit nanostructured Al-Mn alloys, with some PC methods producing significant improvements in film ductility. Transmission electron microscopy observations point to a number of structural advantages induced by PC that apparently ductilize the Al-Mn alloys: (i) grain refinement to the nanocrystalline range without the introduction of a competing amorphous phase, (ii) unimodal nanocrystalline grain size distribution, and (iii) more homogeneous structure. The significant increase in apparent ductility in the PC alloys is also apparently related to stress-or deformation-induced grain growth, which leads to alloys with unique combinations of specific hardness and film ductility.