Phosphating Bath Research Articles

Influence of poly(methyl methacrylate) and ceria-based organic-inorganic hybrid coating mitigating saltwater corrosion of WZ44 alloys

The poly(methyl methacrylate) (PMMA)-based organic coating suffers from a poor adhesion of PMMA molecules with Mg alloy surface, necessitates the incorporation of an inorganic phase and a coupling agent, improving the adhesion and rendering a robust inorganic-organic hybrid coating to combat corrosion in Mg alloy. Therefore, the present work explores approx. ∼25 μm thick hybrid coating comprising PMMA and ceria mitigating saltwater corrosion of Mg-4.0 wt% Y-4.0 wt% Zn-0.5 wt% Zr-0.2 wt% Ca (WZ44) alloy. The specimens undergoing Ce(NO3)3 + phosphate bath treatment before PMMA (CePT→PMMA), or Ce(NO3)3 and PMMA treatment together (Ce+PMMA) displayed micro-pores and hairline cracks on coating with higher surface roughness owing to dehydration-induced tensile stress during drying. On the contrary, the specimen subjected to Ce(NO3)3 followed by PMMA (CeCC→PMMA) demonstrates a uniform, nonporous, and crack-free coating with the lowest surface roughness due to the effective closure of micro-pores/hairline cracks by PMMA molecules. Tafel polarization and electrochemical impedance spectroscopy demonstrate lowest corrosion current density (Icorr ∼0.36 µA/cm2) and highest coating (R1), polarization resistance (R2) of ∼41015 Ω.cm2 and ∼8541 Ω.cm2, respectively, for CeCC→PMMA specimen indicating superior corrosion resistance. Overall, optimization of the experimental parameter(s) of PMMA-ceria based hybrid coating minimizes corrosion of WZ44 alloy in saline water by developing ∼25 μm thick nonporous coating behaving as a shield between the reactive Mg/chlorinated solution interface.

Enhancement of low-zinc phosphate coatings with addition Ni2+ and Mn2+ cations: Structure, corrosion resistance and paint adhesion

Multi-cation phosphate coatings are used in various industries today to enhance the properties of the painting process. This study explored the impact of adding nickel and manganese ions to the low-zinc phosphating process on the properties of the resulting coating. The first step of the research examined the influence of the bath phosphating agents’ concentration, temperature and immersion time and pH on the phosphate coating on the steel 41Cr4 substrate. The second step explored the impact of varying concentrations of Zn, Ni and Mn cations in the phosphating bath and the third step compared the characteristics of zinc (single-cation), Zn–Ni (two-cation) and Zn–Ni–Mn (three-cation) phosphate. The surface thickness and weight per unit area of the phosphate coating, the total and free acid values, and the coating morphology and microstructure were measured; corrosion resistance tests including alkali solubility and salt spray tests were conducted. In addition, scratch, impact, hardness and bending tests of the paint layer were performed. The results indicated that introducing Ni2+ and Mn2+ cations into the low-zinc phosphating bath enhances the structure, corrosion resistance and paint adhesion of the phosphate coating. Scanning electron microscope images revealed that the optimal three-cation coating has a cubic and sheeted structure. Atomic force microscope analysis also demonstrated that in the tri-cation phosphate coating, compared to the zinc phosphate coating, the roughness (Ra) decreases by up to 50% and reaches 8.92 nm. The optimal three-cation coating has the highest corrosion resistance, which is attributed to the higher uniformity, lower porosity, fine crystalline structure, and high percentage of corrosion-resistant phases in the coating composition. The time to the onset of initial corrosion signs in the salt spray test, both without and with paint, increases by 50% and 225%, respectively, resulting in 11 and 180 h.

PREPARATION AND MODIFICATION OF CALCIUM PHOSPHATE CONVERSION COATING

In order to enhance the corrosion resistance of calcium-based phosphate coating, the molybdenum-modified coating was successfully prepared by adding Na2MoO4 in a phosphate bath. The prepared composite film layers were studied by EDS, XRD and SEM. The corrosion resistance performances of the films were investigated by electrochemical measurements. The results showed the main composition of molybdenum-modified film was MoO2, MoP2, and MoP4, the diameter of cracks on the surface of the coating was significantly reduced, which provided better protection to the substrate. In addition, the potentiodynamic polarization curves of the molybdenum-modified film show that the corrosion potential was positively shifted by 0.068 V compared to the calcium-based phosphate coating and the corrosion current was reduced to 2.556 × 10[Formula: see text]A ⋅ cm[Formula: see text], indicating improved corrosion resistance.

Accelerating phosphating process via hydrophobic MXene@SA nanocomposites for the significant improvement in anti-corrosion performance of plain carbon steel

In this study, MXene was functionalized with stearic acid (SA) to prepare a bifunctional nano-accelerator (AMX) with phosphating acceleration and hydrophobic modification for low-temperature phosphating treatment. The AMX hybrid was incorporated into the phosphating bath to simultaneously achieve the acceleration of the phosphating process and hydrophobic treatment of the phosphate coating. The resulting phosphate coating prepared from the phosphating bath containing 0.04 g/L AMX (4-AMX/ZP) exhibited significantly enhanced hydrophobicity, with the large water contact angle (130.83°). Furthermore, the 4-AMX/ZP had the lowest porosity among all samples, which was 96.35 % lower than that of the Pure/ZP. Moreover, the results of electrochemical tests demonstrated that the |Z0.01 Hz| value of 4-AMX/ZP exhibited an increase of more than one order of magnitude when compared to the Pure/ZP, underscoring the excellent corrosion resistance of 4-AMX/ZP. In sum, the incorporation of AMX nano-accelerator into the phosphating bath accelerated the formation of the phosphate coating, simultaneously leading to the phosphate coating being hydrophobic and enhancing its corrosion resistance.

Microstructure characteristics and degradation behaviors of Se/phosphate conversion coatings on Mg-Gd-Ag-Y-Zn alloys in the Hank's electrolyte

In the present study, a selenium-phosphate based conversion coating (SPCC) was successfully developed on the dual rare-earth Mg-Gd-Ag-Y-Zn by immersion in specific acid phosphate bath. The compositions, morphologies, degradation behaviors as well as the formation/deposition mechanism of the SPCC were deeply analyzed. The results declared that the compositions of conversion coatings were the mixture of Mg3(PO4)2/η-Se, with the shallow hill-like structure and dispersive distribution, which was beneficial to enhance the adhesion and corrosion resistance. The electrochemical and static-immersion tests both revealed that the lowest corrosion dissolution rates of the SPCC coatings were realized through pretreatment at 70 °C, with higher Rct value (507.4 Ω·cm2) and lower corrosion rate of 0.603 mm/y. On the one hand, the appropriate temperature was conducive to increasing the concentrations of H2PO4−/SeO32− and accelerating the exchange rates of molecule active-movement in the conversion solution; On the other hand, the dense/stable selenium-phosphate conversion layers formed by redox reaction and hydrolysis reaction retarded the adsorption sites and penetration channels for corrosive ions.

A comparison between the titanium-based and the zinc phosphate dispersion conditionings of zinc phosphate baths

ABSTRACT Phosphating is a metallic surface treatment widely used in the industrial environment as it provides greater adhesion of the paint film to the metallic substrate and greater efficiency in inhibiting corrosion. The conditioning agents in the phosphating process contribute to reducing the time to obtain the phosphate layer and favor the refinement of the formed crystals. Commercially, the most used conditioning agent is based on titanium salts, however, it is possible that other compounds may be an alternative in optimizing the industrial process. Therefore, with the aim of reducing the time and temperature of the phosphating process, this work aims to verify the performance of using the conditioning agent based on zinc phosphate in obtaining the phosphatized layer, in terms of corrosion resistance, in comparison with to the titanium-based conditioner. For this purpose, SAE 1010 carbon steel samples were degreased and sandblasted, immersed for 1 minute in the conditioning solution (titanium or zinc phosphate) and phosphated with a commercial solution of tricationic zinc phosphate at different temperatures (40 and 50°C) and immersion times (2, 3 and 4 minutes). The deposited masses of the phosphate coatings were measured and the coatings characterized by scanning electron microscopy (SEM), through electrochemical tests of open circuit potential and potentiodynamic polarization. The results showed that the greater coverage of the substrate, with the formation of denser layers, improves the anticorrosive performance of samples phosphated with both conditioners. For the titanium-based conditioner, the optimal phosphating conditions were 3 min at 50°C, while for the zinc phosphate conditioner, they were 2 min at 40°C. Therefore, for commercial use, immersion in a zinc phosphate-based conditioner is indicated, followed by phosphating for 2 min at 40°C.

Effect of ultrasonic shot peening and intermediate cerium salt conversion bath treatment controlling corrosion of Mg-Y-Zn-based alloy in salt water

Ultrasonic shot peening (USP) is often regarded as beneficial in mitigating corrosion of Mg alloys. However, increasing surface roughness induced by USP promotes localized corrosion pitting. Herein, we show that an intermediate phosphate bath treatment (CePT) before USP can minimize the surface roughness and ameliorate corrosion resistance of Mg-4.0Y-4.0Zn-0.5Zr-0.2Ca alloy (wt.%) in 0.1 M NaClsolution. In this regard, WZ44 alloy was subjected to Ce(NO3)3 + NaH2PO4bath treatment followed by USP for 30 s using AISI52100 steel balls and vice versa. The sub-surface features ofspecimens analyzed using XRD, FESEM, surface topography, and Vickers hardness reveal that CePT coating before USP increases microhardness (∼142–149 HV0.05 vs ∼ 125–135 HV0.05) and decreases surface roughness (Ra = 1.91–2.38 μm vs Ra = 2.58–2.76 μm). Potentiodynamic polarizationand electrochemical impedance spectroscopy demonstrate that corrosion current decreased (Icorr ∼ 9.81–13.69 µA/cm2 vs. ∼ 23.82–26.22 µA/cm2), coating (R1), and polarization resistance (R2) increased to ∼ 1704–1907 Ω.cm2,and ∼ 1834–1902 Ω.cm2, respectively,for specimens subjected to USP + CePT treatment together indicating superior corrosion resistance.Overall, an intermediate CePT before USP can effectively minimize corrosion pitting phenomena of WZ44 alloy in chlorinated solution by developing a ceramic coating interlocked with surface acting as a barrier between the metal/solution interface.

Tuning the nucleation kinetics of phosphate chemical conversion coating on Mg-Gd-Y-Zr magnesium alloy: The effect of pretreatment and organic additive

In order to obtain a more protective phosphate conversion coating with a denser architecture, the nucleation kinetics of phosphate chemical conversion coating on Mg-Gd-Y-Zr magnesium alloy was tuned in this work. A pretreatment process was proposed and organic additives were incorporated, which aims at increasing the ionic produce (Jsp) at the interface for increasing σ, and decreasing the critical ionic product (JC,sp), respectively. Results prove that the pretreatment of bare alloys in a phosphate bath could increase the ion products of MgHPO4 / MnHPO4. The addition of benzalkonium chloride could neutralize the charges of crystals, and in turn promote the nucleation kinetics. A denser and more protective conversion coating could consequently be obtained.

KCl, KNO3, and Annealing for Modifying the Morphology and Properties of Ca-P Layers on Mg Alloy

The aim of the work was to obtain a dense and uniform calcium phosphate (Ca-P) coating on the studied magnesium (Mg) alloy using simple methods that are easy to implement on an industrial scale. In this work, Ca-P layers were prepared on the surface of a Mg alloy. The simple wet chemical method based on immersion in an aqueous solution was used to prepare the Ca-P layer on the Mg alloy (AM60) surface. The effect of chemical modification by potassium chloride (KCl) and potassium nitrate (KNO3), as well as annealing on the morphology of the phosphate layers on the AM60 alloy, was determined, as well as the impact of this layer on the evolution of hydrogen in Ringer’s solution. The addition of KCl and KNO3 to the phosphating bath caused coagulation and agglomeration of the elements of the Ca-P coating. Consequently, the flake structure of the Ca-P coating changes into two types of structures: chrysanthemum and rhombohedral. Annealing at 150 °C for 3 h allows one to obtain a dense and uniform Ca-P coating on the studied Mg alloy. The Ca-P coating obtained by annealing at 150 °C can greatly decrease the hydrogen evolution rate of AM60 alloy in Ringer’s solution to 0.02 ml/cm2/day, which is similar to the safe amount of hydrogen for the human body (H2 ≈ 0.01 ml/cm2/day).

Preparation of Conductive and Corrosion Resistant Phosphate Conversion Coating on AZ91D Magnesium Alloy

The application of magnesium alloys in the 3C industry requires the coexistence of excellent corrosion resistance and good electrical conductivity. In this work, a conductive and corrosion-resistant phosphate conversion coating (PCC) on AZ91D magnesium alloy was investigated. The effects of strong oxidant (KMnO4), additive (Na2MoO4), surface-active agent (OP-10) and their content in phosphating bath on PCCs were studied, and the mechanism of action of strong oxidant was analyzed. The results showed that the optimum content for KmnO4, Na2MoO4 and OP-10 in phosphating bath was 3.0 g/L, 1.5 g/L and 1.0 g/L. The PCC formed at the phosphating bath at the optimum condition was completely covered, the coating on α phases had a bilayer structure and the β phases were protruded. The electrical contact resistance (ECR) of the PCC was as low as 4.91 Ω, the Ecorr positively shifted about 27 mV, and the icorr reduced significantly. The presence of KMnO4 inhibited the formation of phosphate crystals and made the β phases protrude from the surface to form conductive spots, which improved the conductivity of PCCs.

Electrostatic self-assembled MXene@PDDA-Fe3O4 nanocomposite: A novel, efficient, and stable low-temperature phosphating accelerator

In this study, MXene@PDDA-Fe3O4 binary hybrid (MPF) was synthesized by electrostatic self-assembly and incorporated into the low-temperature phosphating as an accelerator. MXene@PDDA-Fe3O4 with a large specific surface area exhibited excellent dispersion stability, structural stability, and the ability to selectively attract metal ions in the phosphating bath, which was conducive to the formation of the dense phosphating coating. The phosphate coating obtained from a phosphating bath containing 0.12 g/L MXene@PDDA-Fe3O4 (12-MPF coating) had the lowest porosity among all samples, which was decreased by 99.07% in comparison to the blank coating. Moreover, the EIS test revealed that 12-MPF coating exhibited the highest low-frequency impedance among all samples, which is more than an order of magnitude higher than that of blank coating, indicating that 12-MPF coating has excellent corrosion resistance. This notable improvement can be attributed to several factors, including the large specific surface area of MXene, the synergistic inhibitory effect of poly (dimethyl diallyl ammonium chloride) (PDDA) and Fe3O4 on agglomeration tendency of MXene, as well as the selective adsorption of Fe3O4 on metal ions. This study demonstrates the significant potential of the 0D/2D binary hybrid in phosphating treatment.

Preparation and Modification of Polydopamine Boron Nitride-Titanium Dioxide Nanohybrid Particles Incorporated into Zinc Phosphating Bath to Enhance Corrosion Performance of Zinc Phosphate-Silane Coated Q235 Steel.

In this work, PDA@BN-TiO2 nanohybrid particles were incorporated chemically into a zinc-phosphating solution to form a robust, low-temperature phosphate-silane coating on Q235 steel specimens. The morphology and surface modification of the coating was characterized by X-Ray Diffraction (XRD), X-ray Spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), and Scanning electron microscopy (SEM). Results demonstrate that the incorporation of PDA@BN-TiO2 nanohybrids produced a higher number of nucleation sites and reduced grain size with a denser, more robust, and more corrosion-resistant phosphate coating compared to pure coating. The coating weight results showed that the PBT-0.3 sample achieved the densest and most uniform coating (38.2 g/m2). The potentiodynamic polarization results showed that the PDA@BN-TiO2 nanohybrid particles increased phosphate-silane films' homogeneity and anti-corrosive capabilities. The 0.3 g/L sample exhibits the best performance with an electric current density of 1.95 × 10-5 A/cm2, an order of magnitude lower than that of the pure coatings. Electrochemical impedance spectroscopy revealed that PDA@BN-TiO2 nanohybrids provided the greatest corrosion resistance compared to pure coatings. The corrosion time for copper sulfate in samples containing PDA@BN/TiO2 prolonged to 285 s, a significantly higher amount of time than the corrosion time found in pure samples.

Digital Light‐Processing (DLP) 3D Printing of Magnesium Phosphate Minerals and Cements

Digital light processing (DLP) enables the fabrication of complex 3D structures based on a photopolymerizable resin usually containing a photo initiator and an UV or photo absorber. The resin and thus the final properties of the printed structures can be adjusted by adding fillers like bioceramic powders relevant for bone‐regeneration applications. Herein, a water‐based and biocompatible poly(ethylene glycol diacrylate) (PEGDA) resin containing the photo initiator lithium‐phenyl‐2,4,6‐trimethylbenzoylphosphinate (LAP) enables the production of 3D structures via DLP. The addition of calcium magnesium phosphate cement (CMPC) powder, acting as photo absorber, leads to higher accuracy of the final structures. After curing the printed construct in a diammonium–hydrogen phosphate (DAHP) bath for hardening, the resulting mechanical properties can be adjusted without post‐process sintering. Solid loading of up to 40 wt% CMPC powder is possible, and the resins are investigated regarding their rheological behavior and printability. The resulting constructs are analyzed in respect to their surface morphology using scanning electron microscope (SEM), porosity, phase composition using X‐ray diffraction (XRD) methods, as well as mechanical properties influenced by the hardening process using DAHP for different durations.

Using mixture experimental design to study the effect of phosphating bath formulation on the properties of magnesium substrate

PurposeThis paper aims to achieve phosphating via optimal features of Mg metal as a suitable base coating, which is considered for other properties such as barrier properties against the passage of several factors.Design/methodology/approachIn this research, in the phosphate bath, immersion time, temperature and the content of sodium nitrite as an accelerator were changed.FindingsAs a result, increasing the immersion time of AZ31 Mg alloy samples in the phosphating bath as well as increasing the ratio of sodium dodecyl sulfate (SDS) concentration to sodium nitrite concentration in the phosphating bath formulation increase the mass of phosphating formed per unit area of the Mg alloy. The results of the scanning electron microscope test showed phosphating is not completely formed in short immersion times, which is a thin and uneven layer.Research limitations/implicationsMg and its alloys are sensitive to galvanic corrosion, which would lead to generating several holes in the metal. As such, it causes a decrease in mechanical stability as well as an unfavorable appearance.Practical implicationsMg is used in several industries such as automobile and computer parts, mobile phones, astronaut compounds, sports goods and home appliances.Social implicationsNevertheless, Mg has high chemical reactivity, so an oxide-hydroxide layer is formed on its surface, which has a harmful effect on the adhesion and uniformity of the coating applied on Mg.Originality/valueBy increasing the ratio of SDS concentration to sodium nitrite concentration in the phosphating bath, the corrosion resistance of the phosphating increases.

Preparation of chitosan/phosphate composite coating on Mg alloy (AZ31B) via one-step chemical conversion method

The purpose of this study is to develop chitosan/phosphate composite films on magnesium alloys to improve their corrosion resistance and broaden their applications in aerospace. Phosphate/chitosan composite films were successfully prepared by adding ultra-high deacetylated chitosan in a phosphate bath. The chemical composition of the prepared composite film was investigated by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR), and the morphology and fracture of the composite film were characterized by scanning electron microscope (SEM). Potentiodynamic polarization curves and electrochemical impedance spectroscopy were used to study the corrosion behavior of the coated alloys. The results showed that when pH=2.5 and the chitosan concentration was 5.0 g/L, chitosan was deposited in the phosphate coating in the form of inclusions. In addition, the potentiodynamic polarization curves of the composite films show that the corrosion potential is positively shifted by 0.6 V compared to the monolayer phosphate coating, indicating improved corrosion resistance. This work shows that highly deacetylated chitosan can be co-deposited with phosphate to form a dense composite film on the surface of magnesium alloys in one step, thereby improving the corrosion resistance of the alloy.

A trace amount of MXene@PDA nanosheets for low-temperature zinc phosphating coatings with superb corrosion resistance

In this study, MXene nanosheets were functionalized by polydopamine to fabricate MXene@PDA (PMX) hybrid nanomaterial as an accelerator for low-temperature phosphating. PMX structure had a large specific surface area and the dispersibility of PMX in the phosphating bath was higher than that of MXene. The phosphate coating obtained by introducing 0.025 g/L PMX (0.025-PMX coating) into the phosphating bath showed excellent comprehensive properties compared to past reports of nanomaterials used as accelerators since 2010. The phosphate coating was 81.52% heavier in mass per unit area and 98.93% lower in porosity than the pure phosphate coating. Furthermore, electrochemical impedance spectroscopy (EIS) data showed that the |Z0.01 Hz| of 0.025-PMX coating was approximately two orders of magnitude higher than that of the pure coating. Subsequently, we proposed a mechanism for the positive impact of trace amounts of PMX nanosheets on phosphate coatings. This study demonstrates the importance of further studying nanomaterials as phosphating accelerators.

A zinc–manganese composite phosphate conversion coating for corrosion protection of AZ91D alloy: growth and characteristics

A zinc-manganese composite phosphate conversion coating (Zn–Mn PCC) was deposited on AZ91D alloy to enhance its corrosion resistance. The growth mechanism and characteristics of the Zn–Mn PCC were elucidated by adding different ZnO contents in the phosphate bath and for different phosphating times. The results indicate the PCC has a mixed phase of Mg, Mn(OH)2, Mn3(PO4)2‧3H2O, Zn, and Zn3(PO4)2‧4H2O. The Zn–Mn PCC grown on the AZ91D substrate with different ZnO contents had three structure types: island-like, clump-like, and flower-like. Increasing the ZnO content in the phosphate bath increased the coverage, thickness, elemental concentration of Zn, and reduced the cracks and pores of the coating. The contact angle result also revealed that the hydrophobic property of the coating increased with the increase in ZnO content in the phosphate bath. With ZnO modification, the corrosion resistance of the Zn–Mn PCC on the AZ91D alloy improved significantly compared with the bare alloy due to fewer cracks and pores, after especially adding 4 g/L of ZnO into the phosphate bath.

Data on zinc phosphating of mild steel and its behaviour

Surface coating of A36 mild steel using zinc phosphating method was considered in this research work. The mild steel was immersed in zinc phosphating bath which was enhanced with calcium nanoparticles (obtained from snail shells and chicken eggshells). Data on zinc phosphating of the mild steel at different coating time (50 & 60 min) and coating temperatures (60 & 80 °C) was generated. To test the adhesion level of zinc on the mild steel, the coated mild steel was subjected to corrosion tests. And data on weight loss, corrosion rate and inhibition efficiency was generated. Surface morphology of the samples subjected to coating was determined through SEM analysis using SEM (JOEL-JSM 7600F). The data on the surface morphology of the samples is stored in the Mendeley Data repository with the link https://data.mendeley.com/datasets/bpbjfg5b5t/1

Surface modification of magnesium with a novel composite coating for application in bone tissue engineering

Magnesium (Mg) and its alloys are promising candidates for use in bone tissue engineering due to their good biocompatibility and mechanical stability. Nonetheless, the fast biodegradation of Mg in physiological media inhibits its use as a bone graft material. Aiming to improve its corrosion resistance, a dicalcium phosphate dihydrate (DCPD, brushite) coating was initially deposited on the hot-rolled Mg substrates by immersion in a phosphating bath at room temperature for 24 h. Polyvinyl alcohol-bioactive glass (PVA-BG) composite coatings were then deposited by dip-coating on these materials. The samples were tested for structure, corrosion behavior, and biocompatibility. The composite coatings significantly increased the corrosion protection of Mg and also accelerated the formation of HAp on its surface when soaked in a simulated body fluid (SBF). Flow cytometry assays revealed that the composites prepared had high cell viability (over 90%) when immortalized human embryonic kidney cells were tested. The coating method investigated in this work is simple, environmentally friendly, safe, and easily scalable. It is the first time that this approach is reported in the literature, which highlights its novelty.

Improved microstructure and physiochemical properties of hopeite conversion coating by Si3N4 nanoparticles doping

The effect of nano-scaled Si3N4 particles on the microstructure, mechanical and electrochemical behavior of hopeite (Zn3(PO4)2·4H2O) conversion coating on pure titanium was investigated. Different concentrations of nanoparticles were dispersed into the phosphating bath to incorporate the process of coating deposition. The XRD results demonstrated that nano-Si3N4 were doped into the coatings without any decomposition or reaction with the hopeite phase. A finer and denser microstructure of the composite coating could be obtained at the addition of 0.5 g/L Si3N4 in comparison with the pure hopeite coating. Moreover, the composite coating presented a higher bonding strength and corrosion resistance related to the refinement of microstructure and filling of the embedded nanoparticles. It is suggested that the incorporation of nano-Si3N4 particles in conversion coating is a promising approach for performance optimization.