Cold-Sprayed AZ91D Coating and SiC/AZ91D Composite Coatings

Abstract

As an emerging coating building technique, cold spraying has many advantages to elaborate Mg alloy workpieces. In this study, AZ91D coatings and AZ91D-based composite coatings were deposited using cold spraying. Coatings were prepared using different gas temperatures to obtain the available main gas temperature. Compressed air was used as the accelerating gas, and although magnesium alloy is oxidation-sensitive, AZ91D coatings with good performance were obtained. The results show that dense coatings can be fabricated until the gas temperature is higher than 500 • C. The deposition efficiency increases greatly with the gas temperature, but it is lower than 10% for all coating specimens. To analyze the effects of compressed air on AZ91D powder particles and the effects of gas temperature on coatings, the phase composition, porosity, cross-sectional microstructure, and microhardness of coatings were characterized. X-ray diffraction and oxygen content analysis clarified that no phase transformation or oxidation occurred on AZ91D powder particles during cold spraying processes with compressed air. The porosity of AZ91D coatings remained between 3.6% and 3.9%. Impact melting was found on deformed AZ91D particles when the gas temperature increased to 550 • C. As-sprayed coatings exhibit much higher microhardness than as-casted bulk magnesium, demonstrating the dense structure of cold-sprayed coatings. To study the effects of ceramic particles on cold-sprayed AZ91D coatings, 15 vol % SiC powder particles were added into the feedstock powder. Lower SiC content in the coating than in the feedstock powder means that the deposition efficiency of the SiC powder particles is lower than the deposition efficiency of AZ91D particles. The addition of SiC particles reduces the porosity and increases the microhardness of cold-sprayed AZ91D coatings. The corrosion behavior of AZ91D coating and SiC reinforced AZ91D composite coating were examined. The SiC-reinforced AZ91D composite coating reveals higher corrosion potential than magnesium substrate; therefore, it serves as a cathode for the magnesium substrate, the same as the AZ91D coating on magnesium substrate. As the SiC powder is semi-conductive, the embedded SiC particles reduce the electrochemical reaction of the AZ91D coating. The addition of SiC particles increases the corrosion potential of the coating, meanwhile increasing the galvanic potential and decreasing the negative galvanic current of the coating-substrate couple.

Porosity Characterization of Cold Sprayed Stainless Steel Coating Using Three-Dimensional X-ray Microtomography

“…The difference may result from the different size of specimens and different resolution of techniques. The non-connected porosity of low level and small size promises good corrosion protection for the aluminum substrate [33,34]. In Figure 5, the porosity fraction along the certain axis is the porosity measured on the series of planes that are vertical to the assigned axis based on the grey level.…”

“…The difference may result from the different size of specimens and different resolution of techniques. The non-connected porosity of low level and small size promises good corrosion protection for the aluminum substrate [33,34].…”

Fabrication of Poly(o/m-Toluidine)–SiC/Zinc Bilayer Coatings and Evaluation of Their Corrosion Resistances

“…Bilal et al [17] and our group [18] have confirmed the excellent structure and corrosion resistance of poly(o-toluidine). As a very stable inorganic material, silicon carbide (SiC) has been widely used in the reinforcement phase of composite materials or coatings [19]. Based on that, in order to study the effect of methyl substituent on the structure and corrosion resistance of PANI, we synthesized poly(o/m-toluidine) and applied it to the surface of composite SiC/Zn coating.…”

Effect of Gas Propellant Temperature on the Microstructure, Friction, and Wear Resistance of High-Pressure Cold Sprayed Zr702 Coatings on Al6061 Alloy

“…Based on these findings, it can be seen that the FWHM gradually Figure 8 depicts the XRD patterns of the as-sprayed coatings on Al6061 alloy substrate. Visually, there appears to be no evidence of either a phase transformation or oxidation with the coatings, which is typically seen from the CS process due to the hammering effects of the particles [88] and also low temperature deposition nature of the CS process [89]. For all specimens, the crystalline planes and phase structures also seem to be the same, primarily having a hexagonal close packed (α) crystal system.…”