- Pure aluminum and composite Al-Al2O3 coatings were successfully cold-sprayed onto grit-blasted steel. The very low oxygen content detected by TEM confirms that cold spray is a really protective process which only oxidized at a very fine scale. - Alumina addition decreased porosity in aluminum coatings. Spherical alumina addition strengthened the coating at nanoscale. - From a thorough TEM study, interface improvement was shown to result from alumina addition. Al/Al2O3 interfaces showed no porosity actually, unlike Al/Al interfaces which were somewhat nanoporous. - TEM nanotomography highlighted that nanopores are interconnected forming nanochannels. - TEM investigations carried out on corroded Al-Al2O3 coating highlighted that no corrosion products are present at Al/Al2O3 interfaces in contrast to Al/Al interfaces. Using electron diffraction and EDX experiments corrosion products have been identified as being probably a mixture of Al2O3 and Al(OH)3 .