DE2444398A1 - PROCESS FOR CREATING A COLORED OXIDE LAYER ON ALUMINUM OR ALUMINUM ALLOYS - Google Patents

Description

Applicant: Stuttgart, September 16

Nippon Light Metal Co., Ltd. P 2935 S / kg

No. 3-5, 7-Chome, Ginza

Chuo-Ku, Tokyo, Japan

Riken Light Metal Industry Co., Ltd.

No. 2-1, 3-Chome, Magrikane

Shizuoka-Shi, Shizuoka-Ken, Japan

Process for producing a colored oxide layer on aluminum or aluminum alloys

The invention relates to a method for producing a colored oxide layer on, if necessary, already an oxide layer having parts made of aluminum or aluminum alloys, hereinafter referred to simply as aluminum parts, in an electrolytic bath containing a metal salt and in which the aluminum parts form at least one electrode.

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Several methods are known to apply colored oxide layers to the surface of aluminum parts To generate electrolysis, the aluminum parts in an electrolytic bath, which is a metal salt contains, a certain voltage is applied · In the 'known processes, an oxide layer is often first applied formed by using the aluminum parts in the electrolytic bath as an anode. Then the oxide layer colored by applying an alternating voltage to the aluminum part in an aqueous solution containing a metal salt is created «In this process, therefore, for generation, <aei? colored oxide layer two steps necessary » It is necessary that the application of an alternating current after the second step in a certain Relation to the generation of the oxide layer during the first step. Difficulties arise from this in bsd control, a low productivity, a low Area for the color tones of the colored oxide layer ■ and poor reproducibility of the color tone as well Difficulties in producing oxide layers that are always the same color.

Accordingly, the invention is based on the object of improving a method of the type described at the outset in such a way that that the production of colored oxide layers in a large color range and good reproducibility the desired colors is possible «

This object is achieved according to the invention in that on the aluminum parts © is, © pulse-shaped splits applied whose polarity is reversed according to certain 8®it © n becomes ,, There is a particular advantage of this procedure

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in that it can also be used for aluminum parts that do not yet have an oxide layer

It is particularly advantageous to use a pulse-shaped voltage that consists of a sequence of positive or negative square-wave pulses _{or the like}

The invention is described and explained in more detail below with reference to the drawing and exemplary embodiments. The features that can be derived from the description and the drawing can be used in other embodiments the invention can be used individually or collectively in any combination. Show it

1 the diagram of a pulse-shaped voltage generated by half-wave rectification of an alternating voltage has been achieved and its polarity after a predetermined number of periods is reversed "

2 the diagram of a pulse-shaped voltage obtained by phasing the pulse-shaped voltage after. Fig. 1 has been obtained,

Pig. 3 shows the diagram of a pulse-shaped voltage which consists of a sequence of pike-corner pulses, the polarity of which depends on a specific one Period number is reversed,

Fig. 4 is a diagram showing the relationships between the Duty cycle of a pulse-shaped voltage formed by Hechteck pulses, the pulse amplitude and the hue of the resulting colored oxide layer

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A diagram similar to FIG. 5. Fig. 4- for use of silver salt in the electrolytic bath,

6 shows the equivalent circuit diagram of an electrolytic bath used for the invention,

7 "and 8 are graphs showing the voltage changes between the electrodes of an electrolytic bath when using a pulse-shaped Illustrate voltage according to Fig. 5,

Figs. 9 and 10 are circuit diagrams showing devices similar to those shown in Figs Prevent the influence of discharge processes in the electrolytic bath,

Fig. 11 is a diagram showing the flow of current between the electrodes of an electrolytic bath at Use of a pulse-shaped voltage according to FIG. 5 under the influence of accessories for Electrolyser reproduces, and

Figure 12 is a diagram ₀ is generated a pulse-shaped voltage of approximately rectangular pulse waveform, the ^ by Halbweg -Grlelchrichtwig and phase control of alternating current Nets ·

To carry out the method according to the invention, an aluminum part is also subjected to a pretreatment as for a usual © electrolysis. This pretreatment

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is not directly related to the invention and can be mechanical or chemical pretreatment be. Furthermore, an aluminum part on which an oxide layer has already been created can also be used has been. In this case the mechanical or chemical pretreatment takes place before the formation of the Oxide layer and such a pretreatment does not need to be repeated.

Then the one that is free of an oxide layer or already provided with an oxide layer *. Aluminum part in one electrolytic bath, which contains a metal salt, subjected to electrolysis by adding a voltage of the to describe Kind of applied to the aluminum part that will be used as the electrode. In such a bathroom you can the aluminum parts that form one or both electrodes

The tension applied in this pail is pulse-shaped and becomes the aluminum part during a time which is longer than one pulse period, alternating with more positive and negative polarity

The pulse-shaped voltage used consists of pulses which have a short duration, the start and end values of which are equal to each other and which increase up to a predetermined value. This voltage can have the form shown in FIG -Sinua voltage is obtained, the form shown in Pig * 2 , which is carried out by

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a phase control of the voltage according to Fig. 1 with a controlled silicon rectifier or the like, is obtained, or the square wave voltage shown in Pig * 3 Other possible shapes are triangular, exponential or partially sinusoidal Voltage curve β Of these voltages is the square wave voltage the one »which is the easiest to produce industrially. By changing the characteristic With values of the square-wave voltages, colored oxide layers in a wide range of hues can be achieved.

The characteristic values for a square wave are the ImpulsdaweE ⁵ T "haw""Ca, the pulse periods T and Ta ₁ t the peak voltage Vp and Vpa and the conduction times and ta, di © in Fig. Are 3 illustrates. The metal salsa contained in the electrolytic bath is chosen with a view to the hue of the oxide layer to be obtained and can be a sulphate, a nitrate or any other salt . Furthermore, the electrolytic bath is only required to be conductive, and a sulfuric acid aqueous solution is the cheapest and therefore the most economical.

Becomes an aluminum part under the conditions described subjected to electrolysis, an oxide layer consisting of aluminum oxide and a color component exists, i.e. a colored oxide layer, created on the surface of the aluminum part «

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The manner in which the colored oxide layer is produced is described below for the application of a square wave according to FIG. When the rectangular wave of Fig. 3, the positive and negative pulses are different from each other, however, · can t the peak voltages Vp and Vpa, the Pulaperioden T and Ta, the pulse durations X and Ta, and the conduction times and are selected ta equal to or symmetrical with each other. Accordingly, the square wave voltage will be described below on the assumption that the characteristic values of the two square wave voltages are identical to each other. However, the invention is not limited to this case. For example, by choosing different conduction times for the positive and negative pulses, the color of the oxide layer can be changed as required. Likewise, by selecting peak voltages, pulse periods and / or pulse durations with different values for the positive and negative pulses, the color of the oxide layer can be changed as required.

If an aluminum part is alternately applied with positive and negative pulses, as shown in Fig. are shown, the aluminum part used as an electrode becomes during the certain conduction times t and ta alternately positive and negative. While the polarity of the aluminum part is positive, the aluminum part will oxidizes because an oxide layer forms on the anode. If then the polarity of the aluminum part becomes negative, dissociated metal ions and ionized metal penetrate,

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which is present in the bath solution in the form of a metal salt, into the oxide layer. The above-mentioned metal ions and the metal become simple in the following referred to as metal salt. When the polarity of the aluminum part becomes positive again, it will again an oxide layer is formed as described above, and it is also the metal salt that is in the Oxide layer has penetrated, also oxidized. The resulting products become electrical in the oxide layer knocked down when the polarity of the aluminum part becomes negative again. That way becomes a colored oxide layer created

The mechanism described is used on the aluminum part creates a colored oxide layer. The conditions for this mechanism of coloring are determined by the Electrolysis met using a pulse-shaped voltage. Using a square wave voltage like her Fig. 3 shows it facilitates the fulfillment of such conditions.

While the negative pike-corner impulses the aluminum part are supplied for electrolysis, the metal salt penetrates into the oxide layer that is on the aluminum part during the application of the positive pike-corner pulses or has been generated in some other way beforehand · As the supplied Pulses are pike-shaped, a predetermined penetration energy is achieved, and it gets that Metal salt close to the bottom of each pore in the oxide layer.

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In other words, the pulses in FIG square wave voltage shown practically no rise time so that the penetration energy for the metal salts is supplied simultaneously with the increase in the pulse voltage As a result, the metal salt penetrates deep into the pores of the oxide layer, i.e. to the bottom the pores.

The metal salt, which has thus been introduced into the oxide layer by electrolysis, becomes during the supply of the positive square-wave pulses is again subjected to electrolysis and oxidized. While the positive square pulses are supplied, the oxidation of the metal salt is promoted, so that an excellent Coloring of the oxide layer is achieved.

When the oxide layer into which the metal salt has penetrated is electrolyzed by the application of positive pulses, the metal salt is oxidized. However, part of the resulting product and, moreover, also part of the metal salt is eluted before the oxidation. During the next negative pulse is electrically precipitated the remaining oxidized metal salt in the oxide layer and serves as a color source "In order that the colored oxide layer a clear and deep color tone assumes when it is formed by repeated application of the operations described above, it is necessary that the electric -Precipitation and the elution of the product are balanced. A square wave satisfies this requirement most easily

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and ea is in an electrolysis by a rectangular Tension makes use of an easy to adjust the pulse-shaped tension so that the conditions is sufficient.

The amount of metal salt that oxidizes during electrolysis through the application of a positive pulse namely, increases only in proportion to the peak voltage Vp shown in FIG. The amount of the oxidized product that is eluted is in proportion to the product of the peak voltage and the Pulse duration, i.e. the amount of positive charge added. In the case of the square wave voltage according to Fig. 3, the elution is proportional to Vp χ t. At the same time, the oxide layer is also created proportional to the amount of positive charges or the current that has flowed.

As a result, for an electrolytic treatment of the aluminum part in such a way that the metal salt oxidized and the electrically precipitated product is increased in an area by removing the oxide layer on the aluminum part is generated, and at the same time an elution of the product is prevented, the value of the supplied The voltage is preferably as large as possible and the amount of positive charges and the amount of current as small as be possible In the case of a rectangular bulge it is possible to apply a high voltage instantly. Also for controlling the amount of positive charges and the The peak voltage according to the above is a pike corner wave according to Fig. 3 more suitable than other pulse-shaped voltages and therefore makes it particularly good a colored oxide layer with the »desired shade achieve.

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24A4398

Fig. 4 generally illustrates the relationship between the pulse durations χ and Ta, the pulse periods T and Ta, and the peak voltage Vp and Vpa and the hue of the oxide layer in the case that an aluminum part made A0A6O63 in an electrolytic bath with a square wave of FIG _o 3 is treated in a sulfuric acid aqueous solution containing a metal salt. Fig. 5 shows similar relationships in the case of electrolysis in a sulfuric acid aqueous solution containing silver nitrate. As both diagrams show, the relationships shown in them are essentially the same. However, certain deviations can result if the chemical and physical properties of the metal salt used deviate from the type of metal salts on which FIGS. 4 and 5 are based. In Fig. 5, triangles denote a yellow, circles a light red-orange, points a reddish-orange and crosses an unclear reddish-orange hue negative impulses ©

In the diagram according to FIG. 4, the peak voltage Vp is plotted on the ordinate and the ratio n> 1 is plotted on the abscissa. The letters A, B, C and D designate zones of different colors of the oxide layer. A comparison of Figures 4 and 5 _o shows that for example in an electrolysis with a sulfuric acid aqueous solution of Ag ^ SO ^, the zones A, B and a 0

O/.

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yellowish or light red-orange or partly deep red-orange hue. In the Zone E will destroy the oxide layer when any metal salt is used

As Fig. 4 shows, is above the line I-I Zone E high the peak voltage, so that an excessively strong current flows, this causes the oxide layer broken and the hue becomes unclear. As a result, it is not practical to adjust the peak voltage to be lifted over the line I-I. In the zones below line I-I you can choose different fourths colors different from η and Vp can be obtained, as FIG. 4 illustrates.

It can also be seen that the zone below the line II-II is subdivided into zones A, B and C depending on the values of η and Vp. In each of these zones, the color of the oxide layer is only determined by the balance between the amount of the introduced and the eluted, oxidized and electrically deposited metal salt. For example, when the value of the ratio η is increased, the hue of the oxide layer changes successively from A to B and from B to 0. For example, in the zone A where the ratio η is small, the amount of flowing current is large and the The amount of the eluted metal salt is greater than that of the oxidized and electrically deposited metal salt, so that the color of the oxide layer is light and, in the case of the "5", yellowish. In zone B, in which the value dee

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Ratio η is a little greater than in the zone A, the amount of eluted metal salt somewhat smaller than in the zone A, so that the hue of the oxide layer will be slightly richer ₀ So 5, the oxide layer obtained, for example in the case of Fig. A bright, reddish-orange tone. Furthermore, the value of the ratio η in zone C is greater than in zone B _1, as a result of which the pulse duration X is short, so that the amount of positive current and thus also the thickness of the oxide layer decreases, but the peak value of the voltage remains unchanged. Accordingly, in the zone C, since the amount eluted decreases in proportion to the amount oxidized and electrodeposited, the color tone of the oxide layer becomes deeper than that in the other zones. In the case of FIG. 5, the oxide layer assumes a reddish-orange tone and is partially a deep orange-red. In Fig. 5, the lines IH-III and IV-IV are inclined obliquely upward between the adjacent zones below the line H-II. This indicates that the amount of current flowing affects the color of the oxide layer.

Furthermore, the line H-II, which separates the zones A, B and C from the zone D, is also sloping right upwards. This indicates that the line H-II exists in the presence of a certain energy level, if this is taken into account that the amount of current flow is decreased with an increase in the ratio η and dadurcji the level of total energy is decreased even if the amount of current flowing is increased by an increase in the Seheitel voltage ₀

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In zone D lying above the line H-II in FIG the color of the oxide layer becomes saturated and its thickness becomes significant regardless of the value of the ratio η elevated. In this zone D the peak voltage is high and the current density increases, so that the equilibrium between electrodeposition and oxidation as well the elution is markedly different from the equilibrium in zones A, B and 0. In particular, is in a in a large range of the ratios n, in other words in a large range of the current density, an oxide layer achieved with generally saturated colors. In the case of the figure, for example, a rich red-orange can be achieved.

In the foregoing, the ratio η and the peak stress, Which quantities are color control factors in connection with the pulse voltage treated. The size of the positive peak voltage Vp essentially influences the metal oxidation, while the magnitude of the negative peak voltage Vpa is essentially the penetration of the metal salt into the oxide layer If it is taken into account that the color of the oxide layer according to the invention is influenced by the Penetration, oxidation and electrical failure of metal salts takes place, each has a peak voltage, whether or not they is positive or negative, has a close direct relationship with the saturation of the hue of the oxide layer.

In the method according to the invention, the depth of the depends Hue of the oxide layer on the energy balance between the amount of penetrated and oxidized

ο /.

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Metal salt "and the amount eluted. Independent whether the pulse voltage is positive or negative, the areas below the line II-II become the color of the oxide layer more fully when the values of the peak voltage, the ratio η, etc. are changed in this way be that the current decreases while the color of the oxide layer becomes lighter when the above values influenced in such a way that an increase in the current takes place

As stated above, according to the invention, an aluminum part is electrolytically treated by between the two electrodes of an electrolytic bath, at least one of which is formed by the aluminum part becomes, positive and negative square-wave pulses during predetermined conduction times t and ta, as shown in Fig. are shown, are applied, whereby oxide layers of different colors can be produced «.

In the case of an electrolytic treatment of aluminum parts, as described above, are different from a conventional anodic oxidation or an alternating current electrolysis, the peak voltages Vp and Vpa instantly applied in full and imprinted during the times T and ta, then for the times of Impulse intervals Τ-χ or Ta-Ta. suppressed and then reapplied, as shown in FIG. 3.

However, when a square wave voltage with such a characteristic is applied to the electrodes of the electrolytic bath from a power source such as a pulse generator is applied, there are cases where

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24U398

the voltage between the two electrodes, at least one of which is an aluminum part, because of the influence the amount of charge contained in the electrolytic cell does not exactly correspond to the applied corner voltage corresponds o As in Pig. 6 shown schematically, an electrolytic bath 1 for the electrolytic treatment of aluminum parts has a certain electrical capacitance c and an internal resistance r. As a result, finds when the power source is on the trailing edge of a square pulse is switched off, a discharge of those charges instead of the Applying the voltages Vp or Vpa have been stored in the electrolytic bath 1, after each termination Pulse instead and the voltage does not drop in the diagram of FIG. 7 from point 2 to point 3, as it shows the solid line, but from point 2 to point 4-, as shown in Fig. 7 by the dashed line Line is illustrated. In the case shown, the decay time H is greater than the interval or the rest time h between successive pulses, so that the next pulse begins before the on previous pulse, the voltage to be fed back has reached the value zero. If so theoretically the pulse voltage should rise from zero level to the peak voltage, in practice it only rises from the value V1 to the peak voltage V, so that with large values of V1 the effect discussed above, which is based on a sharp Increase in pulse voltage is lost. It is therefore necessary to take care that the tension V1 ao as small as possible

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For this purpose, the conditions of the electrolysis with regard to the capacity c and the internal resistance r of the electrolytic bath 1 set so that it is ensured that each pulse begins only after the Voltage of the previous pulse has decreased to essentially zero. In this case, however, remain the capacitance c and the internal resistance r of the electrolytic bath 1 during the electrolytic treatment of the aluminum part is not constant. In particular, the value of the capacitance c depends on the surface of the aluminum part and the thickness of the barrier layer formed by the oxide layer and it is almost impossible in practice determine the instant at which the pulse voltage has decreased substantially to zero.

It has been found, however, that when the time soft the pulse voltage needed to drop to 1/4 of the If the peak voltage drops, it is shorter than 1/3 of the pulse interval a h, so a sufficiently colored Oxide layer can be achieved regardless of the value of the capacitance c of the electrolytic bath. Furthermore can under these conditions the hue of the oxide layer also by changing the one on the two electrodes The voltage applied to the electrolytic bath can be determined in the desired manner »A setting of the applied voltage can only be achieved by connecting an impedance to the output terminals of a pulse generator or another source of impulses in the following described manner can be achieved.

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As shown in FIGS. 9 and 10, an impedance can be connected either in parallel or in series with the electrolytic bath between the output terminals 5 and 6 of a pulse generator or other pulse source. In such an arrangement, the impedance 7 is connected either in parallel or in series with the capacitance c and the internal resistance fc of the electrolytic cell 1. When the pulse voltage is applied to the electrolytic bath 1 and the power source is then switched off, the charges stored in the electrolytic bath are discharged via the impedance 7, so that the type of voltage drop can be influenced by changing the time constant of the impedance 7. As a result, only by setting the value of the impedance 7 in such a way that the time it takes for the pulse voltage to drop to Λ / Λ of the peak voltage Vp is shorter than 1/3 of the pulse interval h, the pulse voltage can be controlled in the manner described above will."

-In the above, the influence of the capacitance c and of the internal resistance r of the electrolytic bath 1 essentially only described in connection with the voltage, applied to the two electrodes, at least one of which is an aluminum part, or between these electrodes is measured »The reason for this is that in practice it is not necessary is to consider the current flow during electrolysis, but the consideration of the applied or measured voltage to control the coloring is sufficient and at the practical electrolysis the monitoring of the applied or measured voltage the simplest and for industrial manufacturing is the best way.

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However, if a square wave voltage as shown in Fig. 3 is shown, to the aluminum parts for electrolysis is applied in the presence of a large electrolytic current, there is a large difference between the applied Pulse voltage and current and it is necessary to take this difference into account in electrolysis.

As already mentioned, an electrolytic bath has the equivalent circuit diagram shown in FIG. 6 with a capacitance c and an internal resistance r it is shown in broken lines in FIG. 11, the current increases only slowly, as indicated by the solid line in FIG., and in some cases does not reach the possible peak value Ip. As a result, the power source is turned off before the current I has reached the peak value Ip, so that the voltage drops quickly. As can easily be seen, this considerably reduces the effect that can be achieved by applying pulse voltages.

For the method according to the invention, it is sufficient in practice, in particular for square-wave pulses, to correctly set the ratio between the peak voltage Vp or Vp ^ and the pulse duration T or X a. In particular, it is expedient to provide a ScÜeitelspannung in the range between 5 and 150 V, preferably between 10 and 80 V and a pulse duration of greater than 0.01 s to

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use when a strong electrolytic current is flowing. With normal electrolysis currents, pulses with a duration of less than 0.0 * 1 s can also be sufficient.

So if the above values for the peak voltages Vp and Vpa and the pulse durations T and ta for the voltage pulses are complied with and the Aluminum parts are treated using such pulsed voltages in an electrolytic bath " because it contains a metal salt, then it needs that given by the electrolytic bath 1 and the lines Load does not have to be particularly taken into account, but it is guaranteed that the current assumes its peak value and then falls again »So, in other words, the effect of a rapid rise and fall in voltage or current generated sufficiently well will.

As described in detail above, according to the invention, aluminum parts are placed in an electrolytic bath treated containing a metal salt by applying pulse voltage to the aluminum parts, whose polarity changes alternately from positive to negative and vice versa with a certain period thereby creating a colored oxide layer on the surface of the aluminum parts. For industrial purposes it is it is advisable to rectify a square wave by half-wave rectification and to generate phase control of AC components, for example a three-phase or other AC voltages that can be drawn from a network, for example with the aid of controlled silicon rectifiers.

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Fig. 12 shows a common six-phase alternating voltage, the components of which are shown by dashed lines. The voltages obtained by half-wave rectification and phase control of the individual AC voltage components are shown in solid lines. The one in Pig. 12 has six ripple components in the period T or Ta or during its duration Γ or Ta, which have a sawtooth-like shape. Accordingly, when a positive pulse is applied to the aluminum part, the voltage on the aluminum part rises very quickly from zero to the peak voltage Vp and the metal salt is oxidized and electrically precipitated by the pulse energy resulting from the sudden increase in voltage. Since the six sawtooth ripple components are intermittently supplied to the aluminum part, the pulse energy is supplied intermittently, which further promotes the oxidation and electrical precipitation of the metal salt. However, as the precipitation of the metal salt progresses, it is also eluted. However, since the Rppel components of the pulse shape shown in FIG. 1 accelerate the oxidation and precipitation of the metal salt, the pulse duration T need not be so long. As a result, the amount of positive charges applied to the aluminum part can be reduced and the amount of eluted metal can be kept correspondingly small. In this way, the equilibrium between the electroprecipitation and the elution can be easily maintained.

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During the negative conduction time ta, that of the positive Conduction time t follows, a negative voltage pulse is applied which has the same properties as the positive voltage pulse. The negative voltage pulse also increases from zero level to a peak voltage Vpa increases very quickly and energy is supplied to the metal salt, which the metal salt into the aluminum part drifts in. Furthermore, the presence of the six sawtooth ripple components increases the penetration of the Metal salt promoted into the oxide layer, whereby the coloring effect is further improved.

When the pulse-shaped voltage is generated by rectifying AC power as shown in Fig. 12, so becomes the pulse interval or the rest time T-f or Ta-'ta determined on the basis of the period of the network change atromes. For example, in the case of the pulse-shaped voltage shown in FIG. 12, the period of the alternating atom is the same the pulse period.

The following values are suitable for the application of a square wave voltage:

Vp, Vpa 5 to 150 V (10 to 80 V)

f »1 / T, fa = 1 / Ta 5 Ms 500 Hz (5 to 150 Hz) t, ta 0.2 to 2.4 s (3 to 50 s).

The values given above in brackets indicate preferred ranges. Pure electrolysis is common a time of about 60 minutes is sufficient.

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The above values are correct for the following reasons * If the peak voltage is less than 5 V, the coloring will be destroyed, while if the peak voltage is more than Λ $ 0 V, the rate of formation of the oxide layer is difficult to control. In terms of color, the highest possible peak voltage Vp or Vpa is generally chosen, but the peak voltage depends on the type of metal salt contained in the electrolytic bath, which was selected according to the desired color. For example, in the case of silver salts, the optimum values for the peak voltages to produce a clear and saturated color tone are 20 V and more, and in this case the electrolysis can be carried out with relatively low peak voltages «

For the sake of simplicity, the above description has essentially focused on the use of a corner stress based on the positive and negative proportions of which partially or completely matched according to the invention However, procedure can be by electrolytic treatment of an aluminum part creates a colored oxide layer and then changes its color as required when the characteristic values of the positive and negative components of the pulse-shaped voltage are completely are different from each other. In particular, by increasing the amount of charge generated during the negative Part of the pulse-shaped voltage is supplied in ■ the electrolysis of an aluminum part in a metal salt containing sulfuric acid, aqueous solution

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Degreasing or the like of the aluminum part can be achieved, unless it already had an anodic oxide layer "

Furthermore, in the preceding description, an electrolytic bath was essentially treated which contains only sulfuric acid. However, the invention is also applicable to electrolytic baths, the other contain suitable acids, such as malonic acid, malic acid, fumaric acid, sulfosalicylic acid, Sulfamic acid, tartaric acid and oxalic acid. The electrolytic Bath may contain an aqueous solution that contains one or more of the acids mentioned above, as long as it is only conductive.

In FIGS. 1, 2, 3, 7, 8, 11 and 12, the time is plotted on the abscissa, while the ordinate indicates the voltage.

The invention is described and explained in more detail below with the aid of examples.

example 1

Parts made of aluminum 1100, which were degreased in the usual way and rinsed with water, were placed in an electrolytic Bath treated, the 150 g HgSO ^ per liter of water and contained 60 mg of AglTCL · The aluminum parts were used for the two electrodes. To the electrodes

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triangular stresses were determined from the following Properties apparent from Table 1 were applied, the pulses of which had a duration of 2 ms Colored oxide layers are obtained on the aluminum parts, the color of which is also given in Table 1. For the values given in Table 1, the electrolysis time was 60 min and it had the positive and negative parts of the pulse-shaped voltage the same values.

The effect of changing the duration X or Ta of the positive and negative pulses is shown in Table. Furthermore, tests were carried out using a carbon electrode as a counter electrode to the aluminum parts under the conditions given in Table 1. It was found that essentially the same colored oxide layers as indicated in Table 1 were obtained. In the last two cases described, the electrical time was also 60 minutes. Table 2 shows that the color of the oxide layer can also be changed in the desired manner by simply changing the pulse duration »

Example 2

Degreased in the usual way and rinsed with water Parts made of aluminum 6063 were electrolytically using under the conditions shown in the table the same square wave voltage treated in example 1 was used. The aluminum parts were for both

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Electrodes "used" As a result, colored oxide layers were produced produced with the colors specified in Table 3 on the aluminum parts. The time for everyone Electrolysis lasted 60 minutes. Table 3 lists the additives used in the electrolytic bath with their Weight given in g per liter of water in the bath solution.

Aluminum part® of the same type as used in example 1 ₃ and also degreased and washed in the same way. Trax-dos, treated in the same electrolytic bath 5 as used in example 1 * In this case, however, pulverulent voltages were used which were obtained by half-wave rectification of a single-phase sine wave according to FIG. 1 and by controlling the generated half-wave according to FIG. 2 by means of a controlled silicon rectifier Table 4 specified conditions. In this way, the colored oxide layers also specified in table 4 were produced o The electrolysis time was 60 min and the frequency used was 60 Hz.

Example 4

Parts made of aluminum A _o Ä6063 _s which in the "known manner of a pretreatment" umLijezfwosiea x ^ er-daa warr, mircien in an electrolytic © !! Bath, which per liter of water 150 β H so., Lino 50 © g Ag _n SO ,, entiiieltr "at @ in @ r bath-

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temperature of 23 ° 0 below that given in Table 5 Conditions treated for 60 min · The pulse duration of the pulse-shaped voltage was 16 ms. By changing the values the peak voltage and the ratio η «= T / T oxide layers with the colors indicated in Table 5 were produced. By rearranging the results according to dependency of the peak voltage and the ratio η β Τ / τ, the ratios shown in FIG. 5 become achieved.

If further the aluminum parts under the conditions given in Table 6 with pulses of different duration are treated, oxide layers with the colors specified in the table are obtained. The distribution of the depth of the The hue or saturation of the colored oxide layer obtained in this case was essentially that same as that indicated in FIG. Even when the pulse width was changed as above, followed the change in color saturation of the oxide layer has essentially the same tendency as that shown in Fig. A-.

The values of the current density given in Tables 5 and 6 were determined using a moving coil amplifier.

_{If HAuCl., Na 2} SeO ,, OuSO., SnSO ^, NiSO ^ or GoSO ^ is added to a sulfuric acid aqueous bath solution instead of the above-mentioned metal salt and the peak voltage Vp and the ratio η «T / T are changed, the values in the Table 7 achieved colors.

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2U4398

If parts are made from aluminum alloys different from A.A6O63, like A0AIO99, 1100, 2011, 2014, 2024, 3003, 4043, 5OO5, 5086, 5357, 6061 and 7075 of an electrolysis are subjected and the peak voltage Vp and the ratio η = Τ / τ are varied, so are essentially achieved the same results as the Pig. 5 and 5 illustrate, although the colors of the generated Oxide layers are slightly different from one another because this aluminum alloy * «! other compositions and consequently have different electrical properties depending on the alloy metals »

The influence of the peak tension and the ratio on the change in hue had the same tendency, as shown in Fig. 4, although little influence by factors such as the power source, the voltage setting device, the geometric shape of the electrolytic bath, for example the electrode gap, the bath capacity, etc., the leakage current and the like. apart from the quality of the aluminum used and the type of metal salt.

For example, if one or more of the above factors is changed, the size and shape of zones A, B and O in FIG. 4 may change, or zone D oo may become narrow that it was not necessary to note the existence of a zone D between zones A, B and C on the one hand and zone E on the other hand in practical electrolysis. Under other conditions, however, the width of zone D was also increased «

509813/0840

Furthermore, the above factors are related to at least some of the electrolysis conditions, "for example with regard to the height of the lines I-I and II-II as well as their inclination. In any case, however, remains the basic tendency illustrated in FIG. 4 when the method according to the invention is used on which this procedure is based.

Example 5

Parts made of aluminum 1100, degreased in the known manner, rinsed with water and neutralized, were placed in an electrolytic bath containing 150 g H ^ SO and 50 mg AgoSO per 1 V / water. contained, treated at a temperature of 25 ° C with a ^ real corner stress according to FIG. The aluminum parts were used for the two electrodes of the bath. In this case, as shown in FIG. 9, an impedance in the form of a resistor was connected in parallel to the electrolytic bath. Changing the resistance value changed the current in the parallel circuit. The results obtained are shown in the table. The frequency of the pulse-shaped voltage was 50 Hz. As can be seen from Table 8, if the parallel resistance is large, the color quality of the oxide becomes poor if the time until the pulse voltage drops to 1/4 of the Seheitel voltage is greater than 1 / 3 of the pulse duration · This applies in particular to a resistance value of 500 ohms for the two samples with surfaces of 50 and 100 cm ² .

509813/0840

Example 6

Parts made of aluminum A _o A6036 chemically pretreated in a known manner were electrolytically treated in an aqueous solution containing 150 g of HoSO _{2 and 50 mg of AgpSO ^ per liter of water.} The aluminum parts were used for both electrodes. In this case, a pulse-shaped voltage was used, which was obtained by half-wave rectification of a six-phase alternating current as shown in FIG. The results of this treatment are listed in Table 9, Table 9 shows that when the voltages Vp and Vp ^ are increased, the color of the oxide layer becomes more saturated, while at the same frequency, i.e. when the pulse periods T and Ta are the same , an increase in the pulse duration χ or Ta causes the color of the oxide layer to change to a lighter color «

Example 7

Parts made of aluminum 1100 were degreased, rinsed with Waasex · and then neutralized, were about its surface to clean · These aluminum parts are then in an aqueous solution containing 1 1 Water 150 g HgSO ^ and _z 50 mg Ag2S0, electrolytically treated. The aluminum parts were used for both electrodes. A pulse-shaped voltage according to FIG. 3 was applied and the electrolysis was carried out with a current of 100 A for 60 minutes. The results are shown in Table 10. The positive and negative parts of the pulse-shaped voltage

509813/0840

2444338

were the same in terms of duration and the absolute values of the peak stresses. Among all in Table 10 under the specified conditions, the current peaked and oxide films became sufficiently colored achieved.

In the method according to the invention, the frequency the pulse-shaped voltage used is determined in relation to the pulse width, but it is sufficient if it is below 100 Hz.

Although the foregoing description relates essentially to cases in which parts made of aluminum A.A1100 and A.A6063 have been used, they can easily Can also be used in conjunction with other aluminum alloys · A change in the composition and However, the electrical properties of the aluminum alloys has a change in the color of the oxide layer contributing to it Episode. If, for example, under the conditions in which aluminum A.A1100 has an orange oxide layer is produced, parts made of aluminum A.A.3003, Α.Α4Ό43, -A.A5052, A.A6061 and A.A6063 are treated, then gray-orange, dark orange, light-orange, dark-orange-red and orange-colored oxide layers produced

It goes without saying that many modifications and changes to the examples described are possible without to leave the scope of the invention.

509813/0840

- 32 Table 1

Electrolysis conditions Shit
telspar
tion
V = Y '
P: Pa
(V) Mean
re
current
density
(A / dm ² • Leadership
Time
t = ta Generated oxide layer hue
Munsell system
I.
f frequency
1 1
f- _T - _{T &}
(Hz) 30th 1.2 5 layer
thickness
(/ * m) 1.4Y
5.6 / 7.2 50 20th 0.6 5 11.3 5.6YR
4 / 8.8 • 40 10 0.2 5 3.9 2Y
4.1 / 5.1 30th 30th 1.1 5 1.3 lOYR
5.2 / 4.8 20th 20th 0.5 5 10.3 6.8YR
4.1 / 6.9 10 30th 10.6 3.0 2.5Y
5.7 / 7.9 20th 0.5 7.1 3.8YR
3.4 / 0.1 10 6.16 3.0 1.5Y
4.2 / 4 30th 1.0 1.0 0.9Y
5.3 / 8.7 20th 0.5 4.2 5.4YR
3.8 / 8.7 30th 0.8 2.5 7YR
3.9 / 8.7 20th 0.4 3.3 2.4YR
3.1 / 5.8 2.0

13/0840

- 33 Table 2

Electrolysis conditions frequency
^{f β} ί "la
(Hz) Shit
tel-
tension Mitt
lere
g electricity Line
Time
t - t _a
(s) Generated oxide layer - Hue
Munsell
system 6.9 / 1/5 pulse
duration
τ * ta
(ms) (V) density
(A / dm ² ] layer
thickness
(/ λβι) 7.8YR
4.6 / 5.4 3.4Ϋ
5.8 / 2.9 2 40 1.9 5 22.6 9.9YR 8.9Y
5.2 / 5.8 3 100 30th 1.6 17.2 5Y
7.4 / 6.1 20th 0.6 5 3.8 7.4YR
■ 4.5 / 8.5 2 40 3.6 28.3 1.4Y
5.6 / 7.2 30th 2.1 5 12.8 5.6YR
4 / 8.8 20th 0.7 5.9 2.7G
4.9 / 5.6 3 40 1.4 13.5 3.5Y
6.1 / 5.6 30th 1.2 5 11.3 5Y
6.3 / 2.4 20th 0.6 3.9 40 2.0 20.0 30th 1.3 6.8 20th 0.6 4.3

509B 13/0840

- 34 Table 3

Bathroom together i
settlement metal Electrolysis conditions frequency Divorce Mitt Generated Oxide layer Color IY 8YR Basic i salt - Pulse- ""* tel- lere Lei Stokes volume 6.7 / 7.2 / 2 solution period 1
JL CL f Tt \ span
iung
Vp or
fpa current
density
(A /
dar) tion thickness Munsel]
system 2.4 T ^β Q?
(ms) (V) Time
t or
ta
(s) (,at the) HAuCl ₄ 3.5RP H ₂ SO ₄ 50 25th 0.98 100 2 5 6th 4.2 / 150 mg / £ 7.1 g / A Na ₃ SeO ₃ 25th 0.6 H ₂ SO ₄ 2 5 4.6 5 g / A 25th 11.0 150 6th 5 10.4 g / A

509813/0840

Table 4-

244A398

Electrolysis Conditions Pulse
period
T = Ka
(ms) Shit
tel-
span
tion
Vp = JVpa
(V) Mitt!
lere
current
density
(A / dm ² ) Line
Time
t = ta
(s) Generated oxide layer hue
Munsell
system Type of
laid chip
tion 5.7 30th 2 .. 4 5 layer
thickness
(/ om) 2.9Y
6.2 / 8.2 Half waves
one
Single phase
Alternating voltage
tion
Controlled
Half waves
one
Single phase
Bill of exchange
tension 2.6
1.4
1.6 20th 1.14 5 15.0 3.0Y
• 5.9 / 7.6 10 0.64 5 4.8 4.1Y
5.7 / 3.5 30th 1.8 5. 1.5 9.4YR
5.2 / 8.8 20th 0.24 5 14.8 3.1YR
3.8 / 7.4 10 0.30 5 1.5 8.5YR
4.1 / 6.3 0.8

509813/0840

- 56 Table 5

Electrolysis conditions η «
T / f PuIs-
period
T = Ta
(ms) Medium
Current density
(A / dm ² ) Generated oxide layer hue Apex
tension
Vp j ^ -) Vpa 10
8th 100
80 0.32
0.37 layer
thickness
(/ Km) Orange red
U 6th 60 0.44 1.7
2.0 Il 20th 4th 40 0.64 2.5 bright orangeroi; 2 20th 1.18 4.0 yellow 10 100 0.54 7.8 Orange red 8th 80 0.60 4.0 Il 6th 60 0.80 5.0 bright orange
Red 25th 4th 40 1.12 5.2 Il 2 20th 2.04 6.7 yellow ! 8th 80 0.88 15.0 bright orange
Red 4th 40 1.60 6th yellow 27.5 2 20th 2.52 11.5 Il 10 100 0.88 19th bright orange
Red 8th 80 0.98 6.7 It 6th 60 1.32 7.5 Il 30th 4th 40 1.64 10.7 Orange red 2 20th 2.46 15.1 ti ^v 6th 60 1.16 21.7 dirty
Orange red 4th 40 3.04 11 Il 32.5 2 20th 3.28 24 Orange red 10 10 1.50 30th Orange red 8th 80 2.28 17.8 It 6th 60 2.86 24.4 dirty
Orange red 35 4th 40 3.08 28.2 / 08A0 ²⁹ 50981

- 37 - Table

Electrolysis conditions • Shit
tel-
tension n =
T / r Pulse
period
T = Ta
(ms) Medium
current
density
(A / dm ² ) Generated Oxide layer pulse
duration
T = Ta
(ms) 15V
20th
25th 2
8th
4th 10
40
20th 0.7
0.5
1.4 layer
thickness hue 5 30th 2 10 3.0 3.9
2.2
10.5 yellow
Orange red
light orange red 35 10 50 1.52 25.7 Orange red 25th
25th 3
7th 48
118 0.69
0.4 21.5 Il 30th 2 32 2.3 5.5
2.5 yellow
light orange red 16 33 2 32 2.2 11.5 Orange red 33 4th 64 1.8 22.0 11 10.0 Il

Table 7

No.

1 2

5 6 ·

Coloring metal

Au Se

Cu Sn

Ni Co

Metal salt

Na ₂ SeO ₃

CuSO ₄ SnSO,

NiSO

CoSO,

3Jl

Color of

purple

cream

deep red to brown white to dark brown amber to black!

Il II It

Rn / OR /, 0 -

- 38 Table 8

sample
Mr. pulse
duration
τ = τ a
(s) Pulse-
interval
h = ha
(s) Parting
tension
Vp - hfpa,
(ν) ^: 'Ί
Rehearse-,
upper
area :
(cm ² ), resistance 1 2x10 ~ ³ 18xl0 ~ ³ 20V 50 10 2 Il Il Il Il 40 3 Il Il Il Il 54 4th Il Il Il M. 100 5 Il Il Il Il 150 6th Il Il ■ ' Il 220 7th Il M. Il Il 500 8th Il Il Il 100 10 9 Il Il Il Il 150 10 Il Il It Il 500

Middle Current in 1 Time until , ". ,, sample electro
lyt! see
(A) Parallel
Bathroom circle
• (A) Waste of the
Tension on
Vp / 4 or Vpa / 4-
(s) Color of No. 0.21 O.3xlO ~ ³ Oxide layer 1 0.23 0.85xl0 ~ ³ dark brown 2 0.20 l.lxio " ³ Il 3 0.22 2. OxIO " ³ Il 4th 0.25 2.5 x 10 ^-3 medium brown 5 0.23 4.3xl0 " ³ Il 6th 0.23 9xl0 ~ ³ Brown 7th 0.44 0.5xl0 " ³ brownish yellow 8th 0.39 5xlO ~ ³ dark brown 9 0.41 14.5 x 10 ~ ³ light brown 10 brownish yellow 0.22 i 0.07 0.06 0.04 0.03 0.03 0.02 0.27 0.04 0.015

509813/0840

- 59 - Table 9

No. Characteristic - impulse
duration
1 T = Ta Sizes of the pulse-shaped spans Line
Time
t = ta
(s) y
3
middle
current
density
(A / dm ² ) Color of
Oxide layer 1 Parting
tension
Vp Ά | V _E 16x10 ~ ³ Pulse period
T = Ba-
(s) 5 0.63 rich yellow 2 25th 33xl0 " ³ 48xlO ~ ³ Il 0.62 Il 3 25th 16x10 ~ ³ 132x10 ~ ³ Il 0.44 bright yellow 4th 20th 33x10 ~ ³ 48xlO ~ ³ • 0.43 Il 5 20th 16x10 ~ ³ 132x10 ~ ³ Il 1.50 rich orange 6th 33 33x10 ~ ³ 16x10 ~ ³ Il 1.40 Il 7th Il 50xl0 ~ ³ 33x10 ~ ³ It 1.50 Il 8th
9 Il 16x10 ~ ³
33x10 ~ ³ 50xl0 " ³ Il
Il 1.20
1.00 light orange
Il 10 20th
Il 50xl0 " ³ 64xl0 " ³
132x10 ~ ³ Il 1.30 Il 11 Il 16x10 ~ ³ 200xl0 ~ ³ ■ 1 1.00 orange 25th 64x10 ~ ³

509813/0840

- 40 table

Electrolysis conditions

frequency

Ta

ücheitel-

! voltage Tp = i

Pulse duration (s)

Color of the oxide layer

(Hz) 20th 20xl0 ~ ³ yellow 10 25th 4OxIO "* ³ bright orange 5 30; 60xl0 ~ ³ orange 3 full 30th 200x10 " orange 1

50981 3/0840

Claims (8)

Claims 1. Method for producing a colored oxide layer on parts that may already have an oxide layer made of aluminum or aluminum alloys (aluminum parts) in an electrolytic bath containing a metal salt contains and in which the aluminum parts form at least one electrode ", characterized in that a pulse-shaped voltage is applied to the aluminum parts, the polarity of which is determined by " Times is reversed » 2. The method according to claim 1, characterized in that that a sequence of positive or negative pike-corner pulses is used as a pulse-shaped voltage will ο 3. The method according to claim 2, characterized in that the pike-corner pulses by rectifying a usual alternating voltage and a period related to the period of the ΐ / echs el voltage exhibit. 4. The method according to any one of the preceding claims, characterized in that the pulse-shaped voltage by phase control of an alternating voltage is obtained. 5. Method according to one of the preceding claims, characterized in that a sulfuric acid bath is used. 509813/0840 24U398 6. The method according to any one of the preceding claims, characterized in that the duty cycle
and / or the peak voltage of the pulse-shaped
Voltage can be changed. 7ο Method according to one of the preceding claims, characterized in that a pulse-shaped
Voltage is used, the pulses of which have a
Have a duration of at least 0.01 s 8. "The method according to any one of the preceding claims, characterized in that a pulse-shaped
Voltage is used at which the fall time
the pulse from the peak value to ΊΓ / 4 of the peak value is at most 1/3 of the interval between two pulses. 509813/0840 Blank page