Effects of pre-anodizing and phosphates on energy consumption and corrosion performance of PEO coatings on AA6082

A significant reduction in the energy consumption of Plasma Electrolytic Oxidation (PEO) coatings on AA6082 alloy was obtained using strategies based on electrolyte selection and a precursor anodic film. PEO coatings were developed on AA6082 in silicate-based electrolytes with different phosphate species without and with a precursor oxide layer. The electrical response and, therefore, the specific energy consumption depended on the phosphate species and most notably on the applied pretreatment. The best result was obtained after anodic pretreatment and PEO in silicate-polyphosphate electrolyte with a reduction up to ⁓66% in comparison with the most conventional treatment (direct PEO in orthophosphate electrolyte). The corrosion response is not affected significantly by the pre-anodizing treatment either for short or prolonged immersion times revealing that coatings synthesised under high-energy efficient conditions have comparable corrosion performance under aggressive corrosive environments compared to conventional PEO processes

Combination of Electron Beam Surface Structuring and Plasma Electrolytic Oxidation for Advanced Surface Modification of Ti6Al4V Alloy

The objective of this work is to study for the first time the combination of electron beam (EB) surface structuring and plasma electrolytic oxidation (PEO) with the aim of providing a multiscale topography and bioactive surface to the Ti6Al4V alloy for biomedical applications. Ca and P-containing coatings were produced via 45 s PEO treatments over multi-scale EB surface topographies. The coatings morphology and composition were characterized by a means of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The effect on the previous EB topography was evaluated by means of a 3D optical profilometry and electrochemical response via potentiodynamic polarization tests. In general, the PEO process, morphology, composition and growth rate of the coatings were almost identical, irrespective of the topography treated. Minimal local differences were found in terms of morphology, and the growth rate were related to specific topographical features. Nevertheless, all the PEO-coated substrates presented essentially the same corrosion resistance. Electrochemical tests revealed a localized crevice corrosion susceptibility of all the bare EB topographies, which was successfully prevented after the PEO treatment.Depto. de Ingeniería Química y de MaterialesFac. de Ciencias QuímicasTRUEMICINN/AEI/ FEDER, UEComunidad de MadridComunidad de MadridUCMChristian Doppler Forschungsgesellschaftpu

Layered Double Hydroxide Coatings Loaded with Corrosion Inhibitors for Corrosion Protection of AZ31 †

Layered double hydroxide (LDHs) coatings were developed for the corrosion protection of AZ31 Mg alloy. AZ31 is widely used in the transport industry due to its low mass density and good mechanical properties. LDH coatings were fabricated under co-precipitation conditions and applied under hydrothermal conditions. Two different systems Zn-Al LDH and Li-Al LDH were studied. Specimens were post-treated via immersion for 2 h at 45 °C in inhibitor aqueous baths. Na2WO4·H2O and LiNO3 inorganic inhibitors were used, respectively, to produce inhibitor-loaded systems: Zn-Al LDH(W) and Li-Al LDH(Li). The characterization of the coatings was carried out by field-emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The corrosion process was studied by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). The surface was also evaluated via the determination of water drop contact angle and the performance of a paint adhesion test using an epoxy primer. The characterization of the coating revealed two-layered coatings with a denser inner layer and a flaky outer layer. Both coatings improved the corrosion resistance of the AZ31 alloy. Loading with inhibitor further increased the corrosion resistance by one order of magnitude (bare substrate, Z10mHz~102 Ω cm2; LDH, Z10mHz~103–4 Ω cm2; LDH-inhibitor, Z10mHz~105 Ω cm2).Depto. de Ingeniería Química y de MaterialesFac. de Ciencias QuímicasTRUEFEDER/Ministerio de Ciencia e Innovación−Agencia Estatal de InvestigaciónComunidad de MadridMinisterio de Ciencia, Innovaciónpu

PLA deposition on surface treated magnesium alloy: Adhesion, toughness and corrosion behaviour

This study shows that the use of polylactic acid polymer (PLA) coatings deposited by dip-coating on AZ31 magnesium alloy can increase the integrity of the system and the fracture toughness of magnesium substrates treated by plasma electrolytic oxidation (PEO). This provides a novel and promising use of a multilayered system made of fully biocompatible materials. The maximum adhesion strength value for PLA coatings on AZ31 was >50% higher than the maximum one for AZ31/PEO/PLA, while the maximum bending strain tripled. The limitations observed in the AZ31/PEO system arise from the brittle nature of the oxides formed during PEO treatments; their negative impact is reduced when incorporating a PLA layer that is capable of filling the pores and sealing the cracks of the PEO layer. PLA coatings reduce corrosion of AZ31 and maintain the corrosion protection provided by the PEO treatments. The characteristics of the PLA coatings on AZ31 Mg alloy and on AZ31/PEO systems were evaluated by using a Taguchi design of experiment (DOE) method using the following processing parameters: (i) number of layers, (ii) withdrawal speed and (iii) polymer concentration. The effect of these three degrees of freedom and, the surface treatment has been evaluated with regards to different properties desired for the coatings, i.e., adhesion, thickness, roughness, and corrosion resistance

Calcium Doped Flash-PEO Coatings for Corrosion Protection of Mg Alloy

This study demonstrates a significant improvement of the corrosion resistance of an AZ31B magnesium alloy achieved by the application of 1 um-thin coatings generated by an environmentally friendly flash plasma electrolytic oxidation (FPEO) process in Ca-containing electrolytes. Two compounds with different solubility, calcium oxide (CaO) or calcium glycerophosphate (CaGlyP), were used as sources of Ca in the electrolyte. Very short durations (20–45 s) of the FPEO process were employed with the aim of limiting the energy consumption. The corrosion performance of the developed coatings was compared with that of a commercial conversion coating (CC) of similar thickness. The viability of the coatings in a full system protection approach, consisting of FPEO combined with an inhibitor-free epoxy primer, was verified in neutral salt spray and paint adhesion tests. The superior corrosion performance of the FPEO_CaGlyP coating, both as a stand-alone coating and as a full system, was attributed to the formation of a greater complexity of Ca2+ bonds with SiO2 and PO4 3- species within the MgO ceramic network during the in situ incorporation of Ca into the coating from a double chelated electrolyte and the resultant difficulties with the hydrolysis of such a network. The deterioration of the FPEO_CaGlyP coating during immersion was found over ten times slower compared with Ca-free flash-PEO coating

Biotribology and biocorrosion of MWCNTs-reinforced PEO coating on AZ31B Mg alloy

Over the last two decades, various methods have been developed for surface modification of Mg alloys among which plasma electrolytic oxidation (PEO) is one of the most effective methods for tailoring surface properties. However, PEO coatings still need to be improved in various aspects, including mechanical and corrosion performances. In the current study, multi-walled carbon nanotubes (MWCNTs) were incorporated into a PEO coating structure via one-step process. Characterization techniques in this study included scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffraction (XRD). Corrosion behavior was evaluated by electrochemical tests taking into account quasi-in vivo conditions in order to get closer to implant degradation rates in human body. Dry-wear and tribocorrosion in SBF were also evaluated in reciprocal ball-on-plate mode. According to the findings, MWCNTs induced several microstructural modifications in PEO coating such as formation of ~ 1 μm homogeneous dense barrier layer and irregular-shape porosities. Reinforcement significantly improved pitting corrosion resistance of the PEO coating, yielded a low friction coefficient and decreased wear-related damage by 60%

Hard Anodizing and Plasma Electrolytic Oxidation of an Additively Manufactured Al-Si alloy

Plasma Electrolytic Oxidation (PEO) and Hard Anodizing (HA) coatings are investigated on an Additively Manufactured (AM) Al10Si1Mg alloy obtained via Direct Metal Laser Sintering (DMLS). Results are compared to those obtained for a conventional A361 cast alloy. Findings revealed that the microstructure of the AM alloy, consisting of α-Al cells enclosed in a Si network, produces coatings that are more uniform –in terms of morphology, thickness and roughness of the coating/substrate interface– than those obtained on the cast alloy. However, enhanced oxidation of the fine Si network in the AM alloy results in softer coatings. In both alloys, PEO coatings demonstrate superior wear protection than HA due to the presence of mullite in the former. The anisotropy in the microstructure of the AM alloy influences the tribological behaviour of studied coatings, with the XZ plane showing superior wear performance

Effect of cerium (IV) on thin sulfuric acid anodizing of 2024-T3 alloy

Chromic acid anodizing (CAA) is still being used today for corrosion protection of fatigue-critical components in the aeronautic industry due to the lack of feasible alternatives. Ce-containing sulfuric acid anodizing (SAA) has been identified as a promising strategy for the development of alternatives to toxic CAA. This work explores thin sulfuric acid anodizing (TSAA) focusing on the following effects: (i) current density and voltage values; (ii) concentration of Ce(IV). Screening of the optimum combination in search of minimum thickness and the best corrosion resistance was performed using electrochemical impedance spectroscopy (EIS). Two Ce-containing anodic films were selected and further investigated in comparison with the inhibitor-free film in terms of morphology (FEG-SEM, TEM), composition (RBS), corrosion resistance (EIS, NSST), high-cycle fatigue and paint adhesion. The results indicate that the path to approach the CAA performance lies through thin (<1 μm) SAA-Ce films formed at low current density

Manual del Profesor como Complemento a la Asignatura Laboratorio Integrado de la Titulación Grado en Ingeniería de Materiales

El fin principal de este proyecto es la creación de un Manual del Profesor con inclusión de cuestionarios, gráficos, muestras-tipo, etc. La generación de estos recursos didácticos adicionales permitirá al profesorado del Departamento de Ingeniería Química y de Materiales, anteriormente denominado Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica, una mejor preparación de las prácticas de la asignatura Laboratorio Integrado de tercer curso del grado Ingeniería de Materiales impartido en la Facultad de Ciencias Físicas. Actualmente esta asignatura cuenta con un total de 24 prácticas, clasificadas en cuatro bloques, a saber: tratamientos térmicos de aceros, metalografía, corrosión y procesado. En este proyecto se abordarán las prácticas relativas a Anodizado, Niquelado y Cobreado correspondientes al bloque de Procesado de Materiales