RU2611632C2 - Method of coating thickness determination during solid-state anodisation process - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to electroplating, namely to solid-state anodisation of aluminium alloys. Method of oxide coating thickness determination during solid-state anodisation of an aluminium alloy involves measurement of current density and anodisation time, as well as voltage at the electrolytic cell, calculation of specific energy consumption

and coating thickness is calculated by the formula h=k⋅Q where Q is specific energy consumption, kW⋅h/dm², t is anodisation time, h, J is current density, A/dm², U is voltage at the electrolytic cell, V, h is coating thickness, µm, k is empirical factor defined by calibration h µm: Q, kW⋅h/dm² curve for anodised aluminium alloy and electrolytic solution.

EFFECT: improved precision of coating thickness determination.

1 tbl, 3 ex, 8 dwg

Description

The invention relates to the field of electrochemical processing, in particular to solid anodizing, and can be used to determine the thickness of the oxide coating in the process of solid anodizing of aluminum alloys.

A non-destructive gravimetric method for controlling the thickness of electrolytic coatings is known [GOST 9.302-88. Unified system of protection against corrosion and aging. Metallic and non-metallic inorganic coatings. Control methods. - M .: Publishing house of standards, 2001. S. 7], in which the part is weighed before and after coating. Then determine the average coating thickness by the formula

where m ₁ is the mass of the part after coating, g;

m ₂ is the mass of the part before coating, g;

S is the coating area, cm ² ; ρ is the density of the coating, g / cm ³ .

The disadvantage of this method is the inability to assess the thickness of the coating during its formation on the part, which can lead to insufficient or excessive coating thickness.

A known method for determining the thickness of dielectric coatings on substrates during the deposition process, which consists in constructing an anodic polarization curve of a controlled structure in an electrolyte at a given rate of substrate potential increase, they find a threshold voltage corresponding to the beginning of a linear section on the specified curve, which determines the layer thickness, and the construction of the anode polarization curve is carried out at a rate of increasing the substrate potential from 0.2 to 12 V / s in an electrolyte with an electrical conductivity of from 50 to 4 00 μS / cm [RF Patent No. 1487619, cl. G01B 7/04. Publ. 06/10/2001].

The disadvantage of this method is the low accuracy of determining the thickness of the coating, since during solid anodizing the voltage increases non-linearly in time, and the slope of the linear portion of the anode polarization curve during coating growth is quite small. Therefore, when determining the thickness of the coating, a significant error is possible due to the spread of technological parameters, leading to overexposure, the formation of a coating of excessive thickness and an unjustified increase in electricity consumption.

The closest in technical essence is a method for determining the amount of oxide formed during solid anodization, which consists in measuring the specific amount of electricity J⋅t spent on anodizing [Averyanov E.E. Handbook of Anodizing. - M .: Mechanical Engineering, 1988. S. 58]. The amount of oxide formed on a surface unit is calculated as

m = J⋅t⋅c,

where m is the mass of oxide, g / DM ² ; J is the current density, A / dm ² ;

t is the anodization time, h;

c is the electrochemical equivalent.

Knowing the actual increase in the mass of oxide, it is possible to calculate the thickness of the oxide coating

,

,

where h is the thickness of the coating;

ρ is the density of the coating.

The disadvantage of this method is the low accuracy of determining the thickness of the coating, associated with the uncertainty of the porosity of the anode coating, which is unknown during anodization, in addition, for various aluminum alloys alloyed with copper, magnesium, silicon and other elements, the electrochemical equivalents will differ.

The problem solved by the claimed invention is to reduce energy consumption due to disconnection of the technological current source upon reaching the specified thickness of the oxide coating.

The technical result is to increase the accuracy of determining the thickness of the oxide coating for the timely termination of the process of solid anodizing.

The problem is solved, and the technical result is achieved by the fact that in the method for determining the thickness of the oxide coating in the process of solid anodizing of an aluminum alloy, which consists in measuring the current density and anodizing time, according to the invention, the voltage across the cell is measured, the specific energy consumption is calculated

and the coating thickness is calculated by the formula:

h = k⋅Q,

where Q is the specific energy consumption, kW⋅h / dm ² ,

t is the anodization time, h,

J is the current density, A / dm ² ,

U is the voltage across the cell, V,

h is the thickness of the coating, microns,

k is the empirical coefficient, determined by the calibration curve of the dependence of h, μm, and Q, kW⋅h / dm ² , for the anodized aluminum alloy and the composition of the electrolyte.

FIG. 1 is a graph of voltage changes during the process of solid anodizing of alloys AK6, AK7ch

FIG. 2 is a graph of the change in the specific amount of electricity during the process of solid anodizing of alloys AK6, AK7ch

FIG. 3 is a graph of the change in specific energy consumption during the process of solid anodizing of alloys AK6, AK7ch

FIG. 4 is a graph of changes in coating thickness during the process of solid anodizing of alloys AK6, AK7ch

FIG. 5 - the results of a statistical analysis of the results of experimental studies of the processing of aluminum alloys AK6, AK7ch, D16T

FIG. 6 - calibration curve of the dependence of h, μm and Q, kW⋅h / dm ² for AK6 alloy

FIG. 7 - calibration curve of the dependence of h, μm and Q, kW⋅h / dm ² for AK7ch alloy

FIG. 8 - calibration curve of the dependence of h, μm and Q, kW⋅h / dm ² for alloy D16T

The essence of the method is illustrated by drawings. In FIG. Figure 1 shows the change in voltage U (t) for various aluminum alloys, the graph of which has a generally growing character, but may have growth areas with different speeds, as well as dips, which is associated with the current state of the surface, the appearance of defects in the structure of the oxide film, and other changes . In FIG. Figure 2 shows the change in the curve of the specific amount of electricity J⋅t, which, being an integral over time, smoothly increases with time, reflects an increase in the coating thickness, however, with the same program of changing the current density for different alloys, these curves are not distinguishable, and the thickness coverings are different. In FIG. Figure 3 shows the change in the curve of specific energy consumption, which is a combination of voltage and the amount of electricity and has a smooth growing character, as well as a graph of the increase in coating thickness. The specific energy consumption is different for different alloys, as well as for different process implementations at the same current density on the same alloy, as well as the increase in coating thickness. In FIG. 4 shows the change in coating thickness h during the process of hard anodizing for various aluminum alloys. In FIG. Figure 5 presents the results of a statistical analysis of the results of experimental studies of the processing of aluminum alloys AK6, AK7ch, D16T in the form of scattering diagrams showing that the pair correlation coefficient r of specific energy consumption with the coating thickness is significantly higher compared to the amount of electricity. In FIG. 6, 7, 8 are examples of calibration curves that allow one to determine the empirical coefficient k for various alloys.

Concrete implementation example

Example 1

Samples of AK6 aluminum alloy were treated by solid anodization according to GOST 9.305-84 in an aqueous solution of sulfuric acid with a concentration of 300-380 g / l at an electrolyte temperature of -4 ... -6 ° C at a current density of 2.5 A / dm ² for 90 minutes in an automated installation that allows you to register electrical process parameters. The current density J and the anodizing time t were measured, the voltage across the electrolyzer U was additionally measured, and the specific energy consumption was calculated

and the coating thickness was calculated by the formula:

h = k⋅Q,

where k = 312 ± 17 μm / (kW⋅h / dm ² ).

After processing, the thickness of the oxide coating on the samples was measured on metallographic sections with a relative error of 7%, according to the proposed method, the relative measurement error was 5.6%.

The measurement results are shown in the table.

Example 2

Samples of AK7ch aluminum alloy were processed by solid anodization according to GOST 9.305-84 in an aqueous solution of sulfuric acid with a concentration of 300-380 g / l at an electrolyte temperature of -4 ... -6 ° C at a current density of 2.5 A / dm ² for 120 minutes in an automated installation that allows you to register electrical process parameters. The current density J and the anodizing time t were measured, the voltage across the electrolyzer U was additionally measured, and the specific energy consumption was calculated

and the coating thickness was calculated by the formula:

h = k⋅Q,

where k = 258 ± 31 μm / (kW⋅h / dm ² ).

After processing, the thickness of the oxide coating on the samples was measured on metallographic sections with a relative error of 7%, according to the proposed method, the relative measurement error was 6.7%.

The results are shown in the table.

Example 3

Samples of aluminum alloy D16T were processed by solid anodization according to GOST 9.305-84 in an aqueous solution of sulfuric acid with a concentration of 300-380 g / l at an electrolyte temperature of -4 ... -6 ° C at a current density of 2.5 A / dm ² for 105 minutes in an automated installation that allows you to register electrical process parameters. The current density J and the anodizing time t were measured, the voltage across the electrolyzer U was additionally measured, and the specific energy consumption was calculated

and the coating thickness was calculated by the formula

h = k⋅Q,

where k = 332 ± 30 μm / (kW⋅h / dm ² ).

After processing, the thickness of the oxide coating on the samples was measured on metallographic sections with a relative error of 7%, according to the proposed method, the relative measurement error was 5.6%.

The results are shown in the table.

Analysis of the table shows that the thickness of the oxide coating, determined during solid anodization using the proposed method, within an error of ± 5 μm, coincides with the thickness determined using independent measurements after processing.

Thus, the claimed invention allows to determine the thickness of the oxide coating in the process of solid anodizing, as well as to reduce the energy consumption of the process by turning off the technological current source when the specified coating thickness is achieved.

Claims (10)

A method for determining the thickness of an oxide coating in the process of solid anodizing of an aluminum alloy, comprising measuring current density and anodizing time, characterized in that the voltage across the electrolyzer is measured, specific energy consumption is calculated

and the coating thickness is calculated by the formula h = k⋅Q, where Q is the specific energy consumption, kW⋅h / dm ² , t is the anodization time, h, J is the current density, A / dm ² , U is the voltage across the cell, V, h is the thickness of the coating, microns, k is the empirical coefficient determined by the calibration curve of the dependence of h, μm, and Q, kW⋅h / dm ² , for the anodized aluminum alloy and the composition of the electrolyte.

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