Electrodeposition and characterization of sacrificial copper-manganese alloy coatings: Part II. Structural, mechanical, and corrosion-resistance properties

Abstract

The structure and properties of electrodeposited Mn-rich Cu-Mn coatings were studied in order to assess their potential to provide sacrificial galvanic protection to steels. It is found that a small amount of codeposited copper can stabilize the ductile as-deposited centered tetragonal ␥Ј phase against roomtemperature recrystallization to the stable bcc ␣ phase. The time to transformation is increasingly delayed with increasing copper content. Phase transformation of crystalline films does not follow the Johnson-Mehl-Avrami-Kolmogorov equation for nucleation and growth transformation. Amorphous coatings do not show any structural transformation at room temperature. Nanomechanical and tribological measurements showed that Cu-Mn coatings have a lower friction coefficient than reference Cd coatings. Cu codeposition reduces the coating's hardness and elastic modulus and increases the resistance to plastic penetration with respect to pure Mn. Cu-Mn coatings show a barrier or passive behavior under anodic polarization, while the sacrificial characteristics are still preserved. The corrosion appears uniform, and the formation of MnO 2 and Cu 2 O upon anodic polarization may account for the good corrosion performance of the coatings.

The influence of substituted aromatic aldehydes on Zn-Mn alloy electrodeposition

“…% oxygen, indicating either rapid corrosion of the dendritic sample or, more probably, the inclusion of metallic hydroxides, due to the increased pH in the near-cathodic layer, as a result of fast hydrogen evolution. 27 The issue of hydroxide inclusions was reported for Mn alloy coatings obtained at high c.d.s, where the oxygen content reached even 60 at. %, 11,27 and also for pure Zn coatings, where 18 mass % of oxygen was reported.…”

“…27 The issue of hydroxide inclusions was reported for Mn alloy coatings obtained at high c.d.s, where the oxygen content reached even 60 at. %, 11,27 and also for pure Zn coatings, where 18 mass % of oxygen was reported. 28 Hence, the low oxygen percent in the coatings obtained with additives, probably means that the deposits were hydroxide-free, i.e., the hydrogen evolution process during alloy deposition is not fast enough to create alkaline media in the near-cathodic layer.…”

Electrodeposition of High-Mn Zinc-Manganese Alloys From Chloride Eectrolyte

“…Another investigation of coppermanganese electrodeposits by the same authors show similar improvement in surface morphology as deposition c.d. increases [19]. In both cases, the transition from dendritic to homogeneous and bright appearance is correlated with high Mn percentage present in the alloys.…”

Microstructural aspects of manganese metal during its electrodeposition from sulphate solutions in the presence of quaternary amines

“…The effects of these quaternary amines on the surface morphology of the manganese electrodeposits are clearly observed from their SE micrographs (Figs. [3][4][5]. It is interesting to see that introduction of 1 mg L −1 TEABr in to the electrolytic bath resulted in a bright and smooth manganese electrodeposit where manganese crystallites developed in a layered manner giving euhedral shape to the crystal with distinct triple junction points ( Fig.…”

“…The alloys of manganese with tin [1], zinc [2] and copper [3] have been found to exhibit high resistance towards corrosion. In spite of the wide use of the metal, a cost-effective technology for the production of the manganese needs to be developed.…”