Interfacial microstructure of cold gas spraying coated Al and Mg alloy substrates
Bernhard Wielage,Harry Podlesak,Thomas Grund,Andreas Wank
Microchimica Acta
Abstract
The interface between cold gas sprayed zinc-based coatings and selected light weight alloy substrates (aluminium AA7022 and magnesium AZ91) has been investigated by scanning and transmission electron microscopy in combination with energy- dispersive X-ray spectroscopy. In both cases a non- uniform interfacial zone with a thickness of up to 10 microns is evident. It consists of coating and sub- strate phases as well as an approximately 1 micron thick, partially whirled layer. For the AA7022 sub- strate the interfacial layer contains nano and submi- cron sized crystallites of the binary MgZn2 phase ( ) which are embedded in an aluminium solid solution matrix. In the case of AZ91 substrate two ternary phases, Mg5Zn2Al2 ( ) and Mg11Zn11Al6 ( ) with particle size smaller than 50 nm are evident. The for- mation of these phases during spraying cannot be ex- plained by diffusion process only, but a local melting is needed. Consequently, the assumption that the high kinetic energy of cold gas sprayed particles causes an intensive mechanical mixing of coating and substrate material accompanied by a high local temperature rise is proved.
Keywords:Cold gas spraying; zinc coating; light weight substrate; interface; microstructure
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