properties and structure of oxidized coatings deposited onto al-cu and al-mg alloys

ISSN 1063�7842, Technical Physics, 2012, Vol. 57, No. 6, pp. 840–848. © Pleiades Publishing, Ltd., 2012.Original Russian Text © A.D. Pogrebnyak, M.K. Kylyshkanov, Yu.N. Tyurin, A.Sh. Kaverina, I.V. Yakushchenko, A.A. Borisenko, B.A. Postol’ny, I.A. Kulik, 2012, published inZhurnal Tekhnicheskoi Fiziki, 2012, Vol. 82, No. 6, pp. 106–114.

840

INTRODUCTION

Duralumin alloys, such as D�1 and D�16, arewidely used in modern industry. Along with a highstrength (400–500 MPa), they have a low density.Although the strength of aluminum alloys is lower thanthat of steels [1–3], their specific strength (ratio of theultimate tensile strength to the density) is significantlyhigher, which ensured a wide application of aluminumalloys in aviation and rocket engineering [1].

The surface of aluminum alloy articles is protectedby a heat�resistant aluminum oxide layer, which isbased on an aluminum alloy, titanium, and copper.This layer deposition process is characterized by lowenergy consumption and simple equipment. Part ofthe layer of an aluminum alloy is oxidized to formhigh�temperature aluminum oxide α�Al2O3.

The purpose of this work is to prepare equipmentfor microarc oxidation of extended aluminum alloyarticles and to develop new conditions for the elec�trodeposition of aluminum oxide along with siliconcarbide and other additions.

The anode–spark process, or the so�calledmicroarc oxidation (MAO), is characterized by thefact that the energy of electric microdischarges on thearticle surface in an electrolyte is used for processing.Numerous investigations [4–6] describe the oxide for�mation at the potentials inducing a microbreakdownof a solid material. The oxide coating thickness on thesurface of solids depends on the electric field strength

and can be 5–1000 μm [6–8]. Oxygen is released at ananode during electrolysis, is activated by an electricdischarge, and oxidizes the article material. When theoxide layer grows, the electric field must be increaseduntil microarc discharges are stabilized in order toretain electric oxidation conditions. The oxidation hasa decaying character, and its restoration requires anincrease in the electric field to the value ensuring abreakdown of the oxide layer and the formation of arcdischarges. The discharge time varies in the range 1 ×10–3–0.1 s. The onset of the breakdown of the oxidelayer has a mass character, which is accompanied by asharp increase in the electric current to 10 A/cm2. Dis�charge quenching proceeds gradually with time andincreases the thickness and dielectric strength of theoxide coating. The processing was performed for 22–25 min when the electric potential in the interelec�trode gap was increased smoothly from 150 to 300 V, andan aqueous KOH solution was used as an electrolyte.

OXIDATION SETUP AND METHOD

The technological equipment provided the oxida�tion of the surface in contact with the electrolyte,which allowed us to grow a protective coating on localregions on the article surface.

The setup for the microarc oxidation of the surfaceof an extended article contains bed 1, protective hous�ing 2, and tank 3 with electrolyte 4 (Fig. 1). The fol�lowing parts are attached to the bed: mechanism 6

Properties and Structure of Oxidized Coatings Deposited onto Al–Cu and Al–Mg Alloys

A. D. Pogrebnyaka, b *, M. K. Kylyshkanovc, Yu. N. Tyurind, A. Sh. Kaverinab, I. V. Yakushchenkob, A. A. Borisenkob, B. A. Postol’nyb, and I. A. Kulikb

a Institute of Metal Physics, National Academy of Sciences of Ukraine, Sumy, 40021 Ukraine*e�mail: [email protected]

b Sumy Institute for Surface Modification, Sumy National University, ul. Rimskogo�Korsakova 2, Sumy, 40007 Ukrainec Eastern�Kazakh State Technical University, ul. Serikbaeva 19, Ust’�Kamenogorsk, 070000 Kazakhstan

d Paton Electric Welding Institute, National Academy of Sciences of Ukraine, ul. Bozhenko 11, Kiev, 03680 UkraineReceived April 21, 2011; in final form, August 5, 2011

Abstract—The results of new studies of creating protective oxide coatings based on Al2O3 (Si, Mn) anddeposited onto aluminum alloys using electrolyte–plasma oxidation are presented. An analysis is performedby scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X�ray diffraction,Rutherford backscattering of 4He+ and protons, nanoindentation, scratching, friction coefficient measure�ments, and acoustic emission measurements. The results demonstrate that the deposited coatings have a highquality, hardness, and wear resistance and a low thermal diffusivity. Apart from Al2O3, the coatings are foundto have Si, Mn, C, and Ca. The stoichiometry of the coatings is determined. The density and hardness of thecoatings are close to those of α�Al2O3 in the coating on an Al–Cu (D�16) substrate, and these values of thecoating on an Al–Mg (S006) are lower by a factor of 1.5.

DOI: 10.1134/S1063784212060217

SURFACE, ELECTRON AND ION EMISSION

TECHNICAL PHYSICS Vol. 57 No. 6 2012

PROPERTIES AND STRUCTURE OF OXIDIZED COATINGS 841

supplying articles and closed ring blocks 7. The elec�trolyte is fed from the tank with pump 8 to cathodespaces 9 and the ring gap between the tube (anode andcathode 10) surfaces. The electrolyte flow through thering gap between the cathode and article (anode) sur�faces excludes its overheating and makes it possible tooperate at high energy densities.

The setup operates as follows. The electrolyte issupplied to cathodes 7, and articles 5 are moved bymechanism 6 into the cathodes. An electric potentialis simultaneously applied to all cathodes. The poten�tial applied to the cathodes increases from 150 to 300 Vwhen an article moves in order to ensure a smoothincrease in the oxide layer thickness on the surface ofan aluminum alloy article.

The mechanism for feeding a tube is simulta�neously a current collector that supplies an electriccurrent to the aluminized tube surface. The electricpotential is applied from a special�purpose converterthrough holes in the protective housing.

We processed D�16 and S006 alloy articles up to 0.5 mlong and 0.07 m wide and cut 20 × 30 × 2.8�mm sam�ples from them to perform investigations.

The designed setup can perform oxidation at ainterelectrode gap of 20–30 mm, which decreases theenergy losses and provides the formation of a 150�μm�thick oxide layer upon heating of an electric current ata voltage of 340 V. The optimum electrolyte tempera�ture is 50–60°C and is maintained due to the electricenergy losses in the interelectrode gap of an electro�lytic cell. The electrolyte composition is 100 L H2O,300 g NaOH, 400 g Na4P2O7, 1.5 kg Na2SiO3, 1000 mLtechnical glycerol, and 5 g Al2O3. During oxidationmixed oxides of aluminum and the metals enteringinto complex electrolyte anions form [9, 10]. Metalanions can be introduced into the electrolyte due tothe dissolution of the cathode electrode and the corre�sponding alloy. Under steady oxidation conditions,the current density is 0.1–0.5 A/cm2 [11–14]. Thebasic parameters that control the electrolyte–plasmaoxidation and the properties of coatings are the elec�

trolyte concentration, the voltage, the current density,the temperature, the process time, the alloy composi�tion, and (apparently) its heat treatment [11–16].

The author of [17] comprehensively described theelectrolyte–plasma technology (EPT). Figure 2 showsthe results obtained in processing of a high�carbonsteel (AISI 1080) wire in a dynamic system, where theelectrolyte was fed at a rate of 3–5 L/min [8] and thewire moved through an EPT reactor (chamber) at aspeed of 3 m/min. At low voltages U1, the currentincreases linearly with the voltage, according to Fara�day’s law. This regime is accompanied by gas (usuallyH2) liberation (see inset b to Fig. 2). When the voltageincreases further, point U2 (>90 V), which attracts theattention of researchers studying electrolytic plasmaprocesses, is reached. This region is characterized by aglowing unstable gas, which is indicated by substantialcurrent oscillations. The current designated in Fig. 2in this regime is the average oscillation current. Insetsc and d in Fig. 2 show the instability accompanied by adiscontinuous gas glow. The appearance of a glowinggas is caused by the electrolyte evaporation near theelectrode (cathode) due to Joule heat [9–12]. Withoutsupporting Joule heat, the experimental investigationsperformed in [18] show that normal electrolysis isimpossible without glowing gas formation, since elec�trolytic gas liberation, which increases with the volt�age, is absent.

The glow color depends on the origin of the metalions entering into the alloy composition. For example,an orange plasma is characteristic of an NaHCO3 alloy(Na ions) and a blue plasma is characteristic of ZnSO4(Zn ions). The colors are mainly observed due to theplasma discharge at the surface of an article, wheredifferent elements emit light waves of different lengths.

When the voltage increases to U3, the cathode issurrounded by a continuous gas plasma, which is char�

−220 V −380 V−280 V−150 V+

−

1

2

3

4

56 7

8910

Fig. 1. Schematic diagram of the setup for the microarcoxidation of the surface of an extended article.

Cu

rren

t, A

Voltage, V

U1

U2

U3

Gas liberation

Spark ignition

Continuousplasma

envelope

U4Arcingregime

b

c

d

e

f

a

Fig. 2. I–V characteristic of EPT processing in the cathoderegime.

842


POGREBNYAK et al.

acterized by a significant decrease in the current. Inthis EPT regime, the plasma is stable and the articlesurface can be processed in a controlled manner(Fig. 2, inset e). This regime was discovered by Kellogand is called the Kellog region. The correlation of theformation of a stable plasma with the phenomena ofthe transition into a vapor state in boiling and “burn�ing,” which is detected in the systems where a boilingfluid interacts with a hot wall, and the use of the Helm�holtz and Taylor hydrodynamic instabilities give inter�esting results. It is known that the critical current den�sity for stable plasma conditions depends on many fac�tors, including the electrode shape (flat or circular),size, and orientation. We experimentally found that,when the anode wire diameter increases, a higher volt�age and current density are required for the formationof a stable plasma, which agrees with the results ofother researchers studying the cathode regime. Whenmoving to voltage U4, intense arcing is observed alongwith a plasma envelope (Fig. 2, inset f). This aggressiveregime can damage the article surface.

As is seen in Fig. 3, the workpiece is surrounded bya continuous gas envelope during a stable plasmaregime. A high potential between the electrodes leadsto the concentration of positive ions, which are mainlypresent in the immediate vicinity of the cathode in theelectrolyte (mainly on the surface of gas bubbles).Thus, a very high positive charge is located near thecathode, which results in a highly localized electricfield strength between the cathode and the positivecharge. As noted in [5, 17, 19], the electric field of theplasma layer during EPT can achieve 105 V/m. Atsuch a high electric field strength, the gas space insidebubbles is ionized and a plasma discharge appears[20]. Figure 3a shows an enlarged image of this work�ing surface. One gas bubble is shown for clarity. Inreality, this bubble is surrounded by a large number ofplasma bubbles. The plasma temperature can reach2000°C in some places. These hot plasma bubbles aresurrounded by a relatively cold electrolyte (about100°C), which leads to plasma quenching. As a result,a bubble bursts on the metal surface (Figs. 3b–3g).The plasma discharge time is about 10–6 s. The cath�ode surface is covered by a certain number of discreteplasma discharges at any time rather than by a contin�uous plasma layer.

The following two phenomena are possible whenbubbles burst. First, the positive ions concentratedaround a bubble grow on the cathode surface. Second,when a bubble bursts, the accumulated energy isreleased into a gas layer and the kinetic energy is trans�ferred to a liquid layer and, then, to the article surface.This energy can be very high, and the ions initiallyaccelerated by the explosion of a gas bubble then movetoward the cathode surface owing to this kineticenergy. This process leads to the deposition of themetal ions present in the electrolyte on the article sur�face (Figs. 3e, 3f). Ions in EPT mainly move due totheir acceleration through the plasma and ion absorp�

tion when a bubble bursts. EPT is a dynamic system,where high�speed electrolyte motion through thereactor leads to rapid ion transfer to a plasma layer. In[9, 12], we also wrote about hydrodynamic ion transferfrom the mass toward the article surface in similarelectrolytic plasma systems. The combination of ahydrodynamic flow with effective ion transport mech�anisms during EPT deposition results in a high depo�sition rate.

RESULTS AND DISCUSSION

Figure 4 shows the surface of a sample coated withan oxidized aluminum alloy. Metallographic analysisof samples (transverse and oblique polished sections)shows that an oxide layer 32–56 μm thick is densernear the aluminum substrate. The oxide layer surfacehas high porosity and consists of numerous meltedregions in the form of microcraters and drop traces ofthe melting of the oxide layer. An analysis of the exper�imental results demonstrates that a microarc processproceeds inside coating pores. The traces of localiza�tion of microarcs are also observed in the form ofmelted craters. Thus, an oxide layer with a developedsurface forms inside an aluminum alloy [8, 9].

X�ray diffraction (XRD) analysis shows that thecoating mainly consists of refractory aluminum oxideα�Al2O3 and complex oxides containing SiO2 andCaO (Tables 1, 2). Figure 4b depicts the X�ray energydispersive spectrum of the coating. It is seen that thesurface layer (2�μm�thick layer with an area 80 ×80 μm2) has a high Al concentration and lower (by afactor of 1.5) Si and O concentrations and that otherelements (K, Ca, Cr, Fe, Cl) have a concentrationlower than 1% (for a D�16 alloy sample).

Figure 5a shows an image of the alloy S006 samplesurface with a coating deposited by electron–plasmaoxidation. The surface is seen to have numerousmelted regions in the form of microcraters and droptraces of the melting of the oxide layer. Moreover, weindicated the points of integral microanalysis inFig. 5a. As follows from the spectrum shown inFig. 5b, the coating layer has high Si and O (which isnot visible in the spectrum) concentrations and low(lower than 1%) concentrations of other elements (Cl,K, Ca, Cr, Mn, Fe).

Tables 3 and 4 summarize the results of analysisperformed at various points on D�16 (Table 3) andS006 (Table 4) samples. It is seen that the Al concen�tration in the surface coating of the D�16 sample variesfrom 73.16 to 93.4%, the Si concentration varies from4.4 to 22.7%, the Cl concentration is 0.5%, and the Kconcentration is 1.2%. The Ca concentration is low(0.35%), and the Cr, Fe, or Mn concentration is verylow (Table 3). In the coating of the S006 sample, the Alconcentration is 59.8–87.7%, the Si concentration is12–35%, the Ca concentration is about 0.3%, and theconcentrations of other elements (Ti, Cr, Mn, Fe, Cu,Zn) are lower than 1%.



Figure 6 shows the Rutherford backscattering(RBS) spectra of (a) helium and (b) protons. It is seenthat the coatings on the S006 samples have a high con�tent of C, O, Al, and Ca. There is a step near theboundary of the kinematic factors of Al and O, which

indicates that Si (SiO) and calcium oxide are likely tobe present in this aluminum oxide. In the case of pro�ton spectrum (b), the curve consisting of points is verywell described by the calculated curve, which points tothe correct approach to calculating the coatings on the

(a)Surface of electrolyte

H2O H2O H2O

H2O

H2O

H2OH2O

H2OH2O

H2OH2O+

+

++ ++

+

+M+M+

M+

M+ M+

M+

M+M+

Plasma

Workpiece

Molten patch of

Negativeground

H2OH2O

H2O

H2O

H2O

H2OH2O

+ +

+ ++

+

++

++

++

+

+

Plasma begins to cool

H2O M+M+

M+

H2O

H2O

M+ M+

M+

e− e−e−

Kinetic force(rapid fluid acceleration)

Collapsingplasma bubble

Explosive surface impact

Kinetic force

M+

M+

M+

M+

e−e− e− e−

e−

Explosive surface impact

Kinetic force

M+

M+

M+

M+

e− e− e− e−

Shock wave caused by rapidexpansion of plasma

(b)

(c) (d)

(e) (f)

e−

Fig. 3. Schematic of the mechanism of electrolyte–plasma processing.

844


POGREBNYAK et al.

S006 samples. Table 5 gives the data calculated fromthe RBS curves by the model in [21] and the depthprofiles of the element concentrations.

For simplification, we divided the coating into sev�eral layers of arbitrary thicknesses. We then introduceda high Si concentration, which follows from the RBSresults for the surface and from the depth profiles (aswill be shown below), into the model. As is seen fromthe results of fitting, the experimental results coincidewith the formation of oxide Al2O3 and carbide SiC,which counts in favor of the results obtained by X�rayenergy dispersive spectroscopy (EDS) and the phasecompositions detected in the coating.

Figure 7 shows the results obtained by RBS of (a)helium and (b) hydrogen ions from samples coatedwith a D�16 (Al–Cu) coating.

As is seen from the RBS spectra, the substrate con�tains Al, O, C, and Ca. After processing the spectrawith a standard program, we obtained the depth distri�bution of elements in the coating (Table 5). We thenintroduced Si, which can hardly be separated from Albecause of a high surface roughness, into the computerprogram. As follows from the spectra and the process�ing results, SiC can form in the coating at a volumefraction of about 12%.

50 μm244 =

AlAl

Si

CaCl K K Cr Fe

478 5631.658 keV 11.489

AlSiClKCaCrFe

21855050240

330676021758

160373

103006421

500499899162125

(a)

(b)

Fig. 4. (a) SEM image of the D�16 alloy surface and (b) EDS spectrum recorded from a certain region in the surface.

50 μm216 =

Al

SiCa

Cl K Cr Fe

431 5554.058 keV 30.089

AlSiClKCaCr

Fe

(a)

(b)

Mn

Mn

Al

190010603219601060

99622

34717

111054437

301277245135

104133

12

3

4

i

Fig. 5. (a) SEM image of the S006 alloy surface and (b) EDS spectrum recorded at the points indicated by arrows.

10.0 kV×1.00k 50 μm

10.0 kV×1.00k 50 μm



Figure 8a shows the image of a polished sectionprepared at an angle of 12°–15° from a D�16 samplewith a coating and the Al–Cu substrate. There areregions with different tints (bright, dark). It is seen thatthe coating has a high density, contains a small number

of pores, and has a very high hardness (as shown byscratching of a pyramid on the polished section).

The EDS results demonstrate that, apart from Al,O, and C, the coating also contains Si (more than2.2%) and that the oxygen/aluminum ratio is far from

Table 1. XRD results for D�16 samples with an oxidized Al2O3 coating containing SiC zones

2θ θ 2θ 2sinθ d (tabulat.) Phase hkl

25.40 12.5 0.432879 3.559886 – – –

32.00 16.0 0.561274 2.795348 – – –

35.04 17.32 0.595416 2.588106 2.571 α�Mn 222

37.50 18.55 0.638264 2.421951 – – –

39.24 19.42 0.66488 2.317711 2.308 δ�Al2O3 132

43.24 21.42 0.730403 2.109794 2.101 α�Mn/SiC 330/006

44.34 22.17 0.754711 2.041844 2.043 SiC –

45.50 22.55 0.766979 2.009181 2.008 Cu 111

52.44 26.2 0.883638 1.743927 1.7401 Al2O3 024

57.34 28.52 0.95493 1.613731 1.61 Mg 110

61.14 30.37 1.011164 1.523986 1.528 α�Mn 530

65.10 32.35 1.070179 1.439946 1.435 Al –

66.50 33.25 1.096586 1.405271 1.4046 δ�Al2O3/SiC 214/009

68.15 34.07 1.12041 1.375389 1.3739 Al2O3/SiC 330/006

79.54 38.27 1.238736 1.24401 1.245 Si 331

78.15 39.07 1.260538 1.222494 1.22 Al/SiO2 –

84.25 42.17 1.342665 1.147717 1.1473 Al2O3 223

95.14 47.14 1.471485 1.047241 1.0463 Al2O3 315

101.10 50.35 1.539913 1.000706 1.001 Si 831

112.04 53.02 1.658465 0.929172 0.93 Al –

116.24 58.12 1.698312 0.907372 0.9079 Al2O3 324

127.00 63.30 1.788742 0.862464 – – –

136.10 68.05 1.85502 0.830719 0.83 Cu/SiC 305

145.00 72.42 1.906592 0.808248 0.808 Si/Cu –

2500

2000

1500

1000

500

0100 200 300 400 500 600 700

Number of channel

Yie

ld

Sample S006EHe = 2.035 MeVθ = 170°

C

O

Al

Ca

Al

Si

8000

7000

6000

5000

4000

3000

2000

1000

0400 500 600 700 800

(a) (b)

Fig. 6. RBS spectra of (a) helium and (b) protons for S006 alloy samples.

846


POGREBNYAK et al.

Table 2. XRD results for S006 samples with an Al2O3 (Si, Ca) coating

2θ θ 2sinθ d (calc.) d (tabulat.) Phase hkl

34.00 17.0 0.584743 2.637054 – – –

39.39 19.49 0.667285 2.310858 2.308 δ�Al2O3 132

41.24 20.42 0.697798 2.209807 – – –

44.24 22.12 0.753095 2.04755 – – –

45.39 22.49 0.765044 2.015569 2.008 Cu 111

56.54 28.27 0.947254 1.627863 1.628 δ�Al2O3 211

60.44 30.22 1.006643 1.531824 1.53 SiO2 324

64.54 32.27 1.067819 1.444064 1.445 δ�Al2O3 214

66.54 33.27 1.09717 1.405434 1.405 δ�Al2O3 440

77.59 39.0 1.258641 1.225131 1.22 SiO2 622

79.24 39.42 1.27 1.214173 1.21 Si –

80.54 40.27 1.292781 1.192778 1.193 α�Al2O3 217

96.24 48.12 1.489089 1.035532 1.0356 δ�Al2O3 252

98.49 49.24 1.514902 1.017888 1.017 CuO 024

102.24 51.12 1.556925 0.990414 0.994 α�MnO2 712

111.39 55.49 1.648055 0.935649 0.932 α�MnO2 213

116.10 58.05 1.69702 0.908651 0.9079 Al2O3 324

121.24 60.42 1.739335 0.886546 0.885 α�MnO2 413

136.54 68.27 1.857878 0.829979 0.83 Mg/Cu –

137.24 68.42 1.85981 0.829117 – – –

145.24 75.42 1.935594 0.796655 0.808 Si/Cu –

Table 3. EDS results (in vol %) for a D�16 (Al–Cu) alloy sample performed at certain points

Microanalysis points

D�16

Al Si Cl K Ca Cr Mn Fe In total

i 73.157 22.671 1.118 2.173 0.516 0.096 0.000 0.269 100

1 81.767 15.541 0.224 1.872 0.179 0.000 0.000 0.417 100

2 92.525 6.089 0.320 0.848 0.113 0.003 0.000 0.103 100

3 93.385 4.444 0.595 0.783 0.383 0.018 0.016 0.377 100

Table 4. Element concentrations (vol %) in the coating deposited onto an S006 (Al–Mg) alloy sample

Microanaly�sis points

D�16

Al Si Cl K Ca Ti Cr Mn Fe Cu Zn In total

i 62.944 35.02 0.382 0.689 0.402 0.000 0.025 0.142 0.396 0.000 0.000 100

1 59.797 38.78 0.216 0.603 0.240 0.133 0.087 0.098 0.039 0.000 0.000 100

2 87.724 12.01 0.000 0.000 0.039 0.089 0.064 0.034 0.033 0.000 0.000 100

3 68.223 31.01 0.046 0.324 0.118 0.000 0.058 0.1244 0.091 0.000 0.000 100

4 81.512 17.45 0.018 0.259 0.277 0.030 0.012 0.055 0.025 0.244 0.118 100



the stoichiometry of aluminum oxide Al2O3 (the oxy�gen content is higher). Therefore, the coating is likelyto contain SiO. It follows from the subsequent analysisthat the carbon concentration decreases by an order ofmagnitude, the coating has oxygen and aluminum,and a low Si concentration and about 7% Cu (from thesubstrate) are present in the coating. The ratio of O toAl in the coating differs from the stoichiometric oneinsignificantly. The spectrum of the substrate exhibitsthe presence of 93% Al and 7% Cu; no other impuri�ties were detected.

Figure 8b shows the image of an oblique polishedsection prepared from an S006 sample with a coating(the same resolution).

We can see the structure of the coating, intermedi�ate zone 2, and the structure of substrate 3. In thiscase, the coating thickness is significantly smaller thanthat of the D�16 sample, and the hardness of this coat�ing is noticeably lower (by almost 20%) than that onD�16.

Microanalysis performed near the coating surfaceshows that the coating has 35% Al, 47% O, 12% Si,1.6% Cr, 3.2% C, and other elements (Na, K, Mg)whose concentration is lower than 1%.

The Al concentration at the coating–substrateinterface is ≈70%, and the other concentrations are25% O, 3% Si, 1.35% Cr, and 0.5% C. In other words,this layer is less oxidized than the coating volume.

Moreover, it is seen that Mg is likely to penetrateinto the coating from the substrate due to diffusionduring electrolysis (oxidation) and an increase in thetemperature in local zones (the substrate is cold owingto heat removal due to heat conduction and cooling bya flowing electrolyte).

The substrate of the S006 sample has 98.9% Al and1.1% Mg, which corresponds to the typical concentra�tions of the Al–Mg alloy [1–3].

The nanohardness measurements performed onthe coated samples show that the nanohardness of the

coating on (Al–Cu)D�16 alloys varies from 9.87 ± 1.13to 14.8 ± 0.86 GPa on an 80% area and that there existregions where the nanohardness is 26.7 ± 2.4 GPa, whichis close to the hardness of bulk SiC. The nanohardness

Table 5. Depth profiles of the element concentrations in anoxidized layer obtained from RBS data using a standardprogram

Layer 1, thickness 50 (1 × 1016 atoms/cm2)

Element Atomic parameters Concentration

Ca Z = 20, M = 40.0800 0.0096Si Z = 14, M = 28.0860 0.1000Al Z = 13, M = 26.9810 0.1200O Z = 8, M = 15.9990 0.5102C Z = 6, M = 12.0110 0.2601






Ca Z = 20, M = 40.0800 0.0099Si Z = 14, M = 28.0860 0.1500Al Z = 13, M = 26.9810 0.1900O Z = 8, M = 15.9990 0.6501

2500

2000

1500

1000

500

0200 400 600

Number of channel

Exp

erim

ent

Sample D�16EHe = 2.035 MeVθ = 170°

C

O

Al

Ca

AlSi

500

0400 500 600 700 800

(a) (b)

Fe Zn

1000

1500

2000

2500

3000

3500

900800

СO

CaFeZn

Sample D�16Ep = 2.012 MeVθ = 170°

Number of channel

Yie

ld o

f ba

cksc

atte

red

ion

s

Fig. 7. RBS spectra of (a) helium and (b) protons for D�16 alloy samples.

848


POGREBNYAK et al.

of the coating deposited on an (Al–Mg)S006 alloy is9.6–11.2 GPa, which is likely to indicate a high homo�geneity of the coating composition.

CONCLUSIONS

We developed electrolyte–plasma oxidation condi�tions to deposit high�quality coatings on Al–Cualloys. These coatings have a low porosity, a high hard�ness, and higher adhesion to the substrate as comparedto the coatings deposited onto Al–Mg alloys. Thecompositions (stoichiometry) of both types of coatingsare close to aluminum oxide, but the Al2O3 coatingalso has regions containing SiO2 and SiC. The coat�ings were shown to exhibit good characteristics.

ACKNOWLEDGMENTS

We thank A.P. Kobzev (Joint Institute for NuclearResearch, Dubna), Yu.V. Shestakov (SELMI, Sumy),and V.S. Kshnyakin (Sumy State Pedagogical Univer�sity, Sumy) for assistance.

This work was supported in part by the programNanotechnologies, Nanomaterials, and Nanosystemsof the National Academy of Sciences of Ukraine.

REFERENCES

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3. L. P. Luchikov, Deformable Aluminium Alloys for High�Temperature Operation (Metallurgiya, Moscow, 1965).

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Translated by K. Shakhlevich

2 mm 500 μm

1

2

3

1

2

3

(a) (b)

Fig. 8. SEM images of the surfaces of (a) D�16 (Al–Cu) and (b) S006 (Al–Mg) alloys. The points indicate EDS analysis sites.

properties and structure of oxidized coatings deposited onto al-cu and al-mg alloys

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