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7397 |
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Wednesday, May 04, 2022, Hall D 2:00 PM Automotive Industry |
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Deposition of HVOF-sprayed coatings on Mg alloys |
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Giovanni Bolelli* / Department of Engineering "Enzo Ferrari", University of Modena and Reggio Emilia, Italy Stefania Morelli / Department of Engineering , Italy Veronica Testa/ Department of Engineering , Italy Luca Lusvarghi/ Department of Engineering , Italy Mattia Lopresti/ Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale “A. Avogadro”, Italy Giuseppe Rombolà/ Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale “A. Avogadro”, Italy Luca Palin/ Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale “A. Avogadro”, Italy Marco Milanesio/ Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale “A. Avogadro”, Italy |
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Mg alloys have been acquiring increasing engineering relevance especially for lightweight structural design, due to their low density and high strength/density ratio. Their widespread application in transports might results in significant energy savings. However, their applicability is limited by their low hardness and poor corrosion resistance. Thermal spray coatings could help overcoming these issues by providing surface protection against wear and corrosion, but these approaches were rarely explored for Mg alloys protection. The goal of the present work is therefore to study the deposition of two kinds of HVOF-sprayed coatings onto commercial Mg alloy substrates: a WC-10Co4Cr hardmetal and a Cu-9Al-1Fe bronze. Each of these materials has distinct but technologically relevant applications against wear and corrosion. The AZ31 alloy was selected as substrate material as it is frequently used e.g. in the automotive field. For each coating material, different samples were obtained by varying stand-off distance and pitch spacing, aiming to find a good compromise between the quality of the deposited layer and the need to control the heat input to the Mg alloy substrates. Coatings were also sprayed onto both grit-blasted and as-supplied substrates to verify whether the high-energy impact of semi-solid particles during the HVOF-spray process can provide good mechanical interlocking even without prior roughening. Morphological and compositional analyses were carried out by SEM and XRD, before and after corrosion tests. The practical adhesion of the coatings onto the substrate plates was verified qualitatively by cyclic impact testing. The quality of the coatings was verified by depth-sensing micro-indentation testing. Finally, the protectiveness of the layers against corrosion was verified both by electrochemical polarization testing in a 3.5% (wt./vol.) NaCl aqueous solution and by the Corrodkote test (ASTM B380). Corrosion tests were also performed on samples with polymeric coatings as reference. Finally, a multivariate analysis of corrosion and indentation data as a function of deposition conditions was carried out to devise optimal conditions. |