JP2021515108A - Selective Phosphate Treatment Method for Composite Metal Structures - Google Patents

Abstract

The present invention is a chemical pretreatment and selective phosphate of a composite metal structure comprising at least a portion made of aluminum, at least a portion made of zinc, and any additional portion made of iron. A method of treatment, (I) a surface-covering crystalline zinc phosphate layer having a coating mass in the range of 0.5-5 g / m2 on a portion made of iron and zinc in the first step. Treatment of composite metal structures with an aqueous zinc phosphate treatment composition, which results in the formation of, but does not form a zinc phosphate layer with a coating mass of at least 0.5 g / m2 on the aluminum moiety, and then intermediate water. A rinse operation is performed and (II) in the second step, the application of an aqueous acidic passivation composition having a pH in the range of 2.0 to 5.5 to a composite metal structure is included, and the acid passivation is performed. The chemical composition removes less than 50% of crystalline zinc phosphate on a moiety made of zinc and iron, but a passivation layer on an aluminum moiety that does not constitute a crystalline phosphate layer covering the surface. The zinc phosphate treatment composition in step (I) contains the contents of sodium ion and / or potassium ion, and aluminum ion, and the zinc phosphate treatment composition in step (I) is 20 to 20. As a BF4 having a temperature in the range of 65 ° C., containing a free fluoride content of at least 5 mg / l but not exceeding 200 mg / l, at least 0.04 g / l but not more than 3.2 g / l. The calculated boron in the form of a water-soluble inorganic compound is present in the zinc phosphate treated composition, and the number of points of the free acid to which KCl is added in the zinc phosphate treated composition is at least 0.6 points. Is about the method. The present invention also relates to the corresponding zinc phosphate treated composition, to the concentrate for its production, to the corresponding composite metal structure, and to its use.

Description

The present invention relates to anticorrosion treatment of composite metal structures containing metal surfaces of aluminum, zinc and any iron in a multi-step method. The method of the present invention makes it possible to selectively treat the zinc and iron surfaces of a composite metal structure with zinc phosphate without depositing a significant amount of zinc phosphate on the aluminum surface. In this way, the aluminum surface used conventional acidic and optional silane-containing passivation compositions in subsequent process steps, eg, to produce a homogeneous, thin passivation layer that provides protection from corrosion. It can be used for passivation.

In the method of the present invention, firstly, the formation of phosphate crystal clusters on the aluminum surface and secondly, the formation of specks on the zinc surface are prevented. However, in particular, the precipitation of cryolite on the surface of the composite metal structure, especially on its aluminum portion, and preferably the poisoning of the phosphate treatment bath with titanium, zirconium and hafnium is reduced.

Thus, the present invention is also sufficient to suppress the formation of spots, but in an amount not exceeding the value at which the zinc phosphate treatment loses the selectivity of the zinc and iron surfaces of the composite metal structure, the water-soluble inorganic compound of boron. Also relates to zinc phosphate treated compositions comprising.

In the field of automobile manufacturing, which is particularly related to the present invention, various metallic materials are increasingly used and bonded to composite structures. In car body structures, a wide variety of steels are still predominantly used, mainly due to their particular material properties, but also the use of lightweight metals such as aluminum, which is especially important for significantly reducing the overall mass of the car body. It has increased. To take this development into account, the objective is to develop new concepts for vehicle body protection, or to further develop existing methods and compositions for anticorrosion treatment of untreated vehicle bodies.

Therefore, there is a need for improved methods of pretreatment of the car body, including parts made of complex components such as aluminum, as well as parts made of steel and optionally galvanized steel. As a result of the overall pretreatment, a conversion or passivation layer suitable as an anticorrosion coating substrate is produced on any resulting metal surface, especially prior to cathodic electrodeposition coating.

The specification DE197353514 published in Germany proposes a two-step method, which first selectively phosphates the steel and galvanized steel surfaces of the chassis, which also has an aluminum surface, followed by the chassis. The chassis is treated with a passivation solution for anticorrosion treatment of the aluminum part of the steel. According to the teachings disclosed herein, selective phosphate treatment is achieved by reducing the pickling action of the phosphate treatment solution. To this end, in DE19735314, phosphates having a free fluoride content of hexafluorosilicates in concentrations of less than 100 ppm, especially 1-6 g, where the source of free fluoride is formed solely by water-soluble complex fluoride. Fluoride solutions are taught.

The prior art discloses another two-step pretreatment method, again in which a crystalline phosphate layer is deposited on the steel surface and any galvanized and alloyed galvanized steel surface in the first step. It also follows the concept of passivating the aluminum surface in subsequent steps. These methods are disclosed in Ref. WO 1999/012661 and WO 2002/066072. In principle, the method disclosed herein selectively phosphates the steel surface or zinc-plated steel surface in the first step and also in subsequent passivation in the second method step. The treatment is maintained but without the formation of phosphate crystals on the aluminum surface. Selective phosphate treatment of steel and zinc-plated steel surfaces is possible by limiting the proportion of free fluoride ions in the phosphate treatment solution depending on the temperature, the free acid content of which is 0. It is set within the range of ~ 2.5 points.

International application WO 2008/505726 discloses at least a one-step method for selectively phosphating the steel surface and galvanized steel surface of composite structures containing aluminum moieties. This published specification teaches a phosphating solution containing a water-soluble inorganic compound of zirconium and titanium elements, the presence of which can prevent phosphating on the aluminum surface.

European application EP2588646 discloses a method of selective phosphate treatment of steel and galvanized steel in metal components that also have an aluminum surface. In addition, this method prevents the formation of phosphate crystal clusters on the aluminum surface and the formation of dots on the galvanized steel surface. For this purpose, silicon is added to the zinc phosphate treated composition in the form of a water-soluble inorganic compound.

DE197353514 WO1999 / 012661 WO2002 / 066702 WO2008 / 055726 EP2588646

Proceeding from this prior art, the objective is to further develop selective phosphate treatment of steel and galvanized steel in the anticorrosion treatment of metal components of hybrid compositions, i.e. composite metal structures with aluminum surfaces, to increase selectivity. The specific control of the bath parameters to be controlled is to achieve the effect of achieving an improvement in process economics during phosphate treatment. Regarding the quality of the anticorrosion treatment of composite metal structures, this not only avoids the formation of phosphate crystal clusters on the aluminum surface and the formation of dots on the surface of zinc-plated steel, but also on the surface of the metal components, In particular, it involves reducing cryolite precipitation on aluminum surfaces, and preferably reducing poisoning of phosphate treatment baths with titanium, zirconium and / or hafnium.

"Phosphate crystal clusters" are understood by those skilled in the art to mean the deposition of phosphate crystals individually and locally on metal surfaces (here aluminum surfaces). Such "crystal clusters" are surrounded by subsequent coating primers to form a coating heterogeneity, which can distort the uniform visual impression of the coated surface and cause point damage to the coating. ..

"Point formation" is a phenomenon in phosphate treatment, in which crystals of amorphous zinc white phosphate on the surface of otherwise treated zinc or treated zinc-plated or alloyed galvanized steel. It is understood by those skilled in the art to mean local deposition in the sex phosphate layer. Point formation is caused by a local increase in the pickling rate of the substrate. In practice, point formation should be largely avoided, as such point defects in phosphate treatment can be the starting point for the adhesive corrosive loss of subsequent organic coatings. is there.

_{Cliolite precipitation (deposition of solid Na 3} AlF ₆ and / or K ₃ AlF ₆ ) on the surface of the composite metal structure, especially on the aluminum moiety, provides sandpaper-like properties on this surface. This is not desirable as it extends below the surface of the structure to be painted immediately. As a result, paint imperfections occur, which can only be removed at great cost and inconvenience, for example by polishing the area. This, of course, is associated with corresponding effort and higher costs.

Cliolite precipitation proceeds by the following equation:
3Na ⁺ (aq) + Al ³⁺ (aq) + 6F ⁻ (aq) → Na ₃ AlF ₆ (s) ↓ or sodium ions in the phosphating composition can be added to additives, eg, additives and / or promoted. Derived from the agent. Here, the additives to be particularly mentioned are sodium fluoride, sodium nitrate, sodium phosphate and sodium hydroxide, and the accelerator to be particularly mentioned is sodium nitrite. The same applies to potassium ions. These additives are added to the bath depending on the situation and existing bath parameters. In contrast, aluminum ions are removed from the aluminum portion of the composite metal structure by pickling in an acidic medium of the phosphate-treated bath composition.

A specific minimum amount of free fluoride (fluoride ion) in the phosphate treatment bath is to ensure proper deposition kinetics for the zinc phosphate layer on the iron and zinc surfaces of the composite metal structure. is necessary. It specifically enters the zinc phosphate treated composition by simultaneously treating the aluminum surface of the composite metal structure (see above), and this is in its uncomplexed form, the iron portion of the composite structure. And because it interferes with or even prevents the formation of a uniform and homogeneous zinc phosphate layer on the zinc moiety. The free fluoride here also arises from the fluorocomplex from which the free fluoride is released in the equilibrium reaction.

However, the higher the free fluoride content (for a given sodium / potassium and aluminum content), the more pronounced the cryolite precipitation on the surface of the composite metal structure.

Poisoning of phosphating baths with titanium, zirconium and / or hafnium is especially caused by transfer systems for crust-covered composite metal structures or pre-passivated aluminum portions of the structure. There is.

Crusts on the transfer system (eg, phosphate crusts or unfired coating layers) contain titanium, zirconium, and / or hafnium. The latter unfired coating layer is passivated with a water-soluble compound containing titanium, zirconium, and / or hafnium following phosphating of the composite metal structure (see step (I)). It is derived from calcination (see step (II)) and is absorbed by the crust due to its porosity. Since the transfer system is performed periodically, the crust that was in contact with titanium, zirconium, and / or hafnium in the passivation bath is re-exposed to the acid phosphate-treated composition in the phosphate-treated bath. To. Titanium, zirconium and / or hafnium are partially redissolved in it.

The aluminum portion of the composite metal structure is often pre-passivated. This means that the aluminum moiety has already been provided with a passivation layer containing titanium, zirconium and / or hafnium by its supplier.

In both cases, as the complex is formed, titanium, zirconium and / or hafnium may leach or be pre-passivated from the crust in a fluoride-containing phosphate treatment bath. Therefore, titanium, zirconium and / or hafnium accumulate in the phosphate treatment bath. This can be wiped off on the aluminum portion of the composite metal structure, which can result in the deposition of a black layer containing amorphous zinc phosphate. The layer may later result in imperfections in the coating and may reduce protection from corrosion.

The purpose described above is the chemical pretreatment and selection of composite metal structures containing at least a portion made of aluminum, at least a portion made of zinc, and any additional portion made of iron. Achieved by the method according to the invention of target phosphate treatment, this method
(I) The first step results in the formation of a surface-covering crystalline zinc phosphate layer having a coating mass in the range of ^{0.5-5 g / m 2} on a portion made of iron and zinc. Treatment of the composite metal structure with an aqueous zinc phosphate treatment composition that does not form a zinc phosphate layer with a coating mass of at least 0.5 g / m ^{2 on the aluminum moiety, followed by an intermediate water rinse operation.} ,
(II) In the second step, the acidic passivation composition comprises the application of an aqueous acidic passivation composition having a pH in the range of 2.0 to 5.5 to a composite metal structure, and the acidic passivation composition is zinc. And removes less than 50% of crystalline zinc phosphate on the part made of iron, but forms a passivation layer on the aluminum part that does not constitute the crystalline phosphate layer covering the surface.
The zinc phosphate treatment composition in step (I) comprises a content of sodium and / or potassium ions, and aluminum ions.
The zinc phosphate treated composition in step (I) had a temperature in the range of 20-65 ° C. and contained a free fluoride content of at least 5 mg / l but not more than 200 mg / l.
_{Boron in the form of a water-soluble inorganic compound calculated as BF 4} , at least 0.04 g / l but less than 3.2 g / l, is present in the zinc phosphate treated composition, and the zinc phosphate treated composition. The number of points of the free acid to which KCl was added is at least 0.6 points.

Definition:
A "composite metal structure" in the context of the present invention is a metal component of a hybrid composition, particularly a chassis. The composite metal structure may have a zinc surface, an aluminum surface, and any iron surface as well as other metal surfaces and / or non-metal surfaces, especially plastic surfaces.

According to the present invention, the material "aluminum" is understood to mean its alloy as well. At the same time, according to the present invention, the material contains zinc and also includes zinc alloys such as zinc-magnesium alloys and zinc-plated steels and alloy zinc-plated steels, while references to iron include iron alloys, Especially steel is also included. Alloys of the above materials have an irrelevant atomic content of less than 50% by weight.

In this context, an "aqueous composition" is primarily about water as a solvent or dispersion medium, i.e. more than 50% by weight (based on the total solvent and dispersion medium present), preferably more than 70% by weight. It is understood to mean a solution or dispersion containing to a degree, more preferably to a degree greater than 90% by weight. Therefore, the aqueous composition may include dispersed constituents as well as dissolved constituents. However, the aqueous composition preferably contains only a small amount of the solution, i.e. the dispersed constituents, preferably no dispersed constituents, but rather contains only the dissolved constituents or only the substantially dissolved constituents. It is a composition containing.

A "passivation layer" in the context of the present invention is a passivation, ie, anticorrosion, inorganic or mixed inorganic-organic thin film coating without a continuous crystalline phosphate layer. Such a passivation layer consists of, for example, oxidic compounds of titanium, zirconium and / or hafnium.

According to the present invention, the "water-soluble compound" means either one kind of water-soluble compound or two or more kinds of water-soluble compounds.

The requirement that the zinc phosphate layer not be formed on the aluminum moiety in the treatment step (I) should be understood as not forming a continuous and sealed crystalline layer there. This condition is satisfied at least when the area-based mass of zinc phosphate deposited on the aluminum moiety is less than ^{0.5 g / m 2.} Aluminum moieties are understood in the context of the present invention to mean sheets and components made from aluminum and / or alloys of aluminum.

In contrast, forming a continuous crystalline zinc phosphate layer on the surface of steel, galvanized steel and / or alloy galvanized steel is an absolute necessity of the method of the invention and the present invention. It is a feature of. For this purpose, zinc phosphate preferably has an area-based coating mass of at least 1.0 g / m ² , more preferably at least 2.0 g / m ² , but preferably 4.0 g / m ^{2 or less.} The layer is deposited on this surface of the composite metal structure in step (I) of the method according to the invention.

For any surface of the composite metal structure, the mass of the zinc phosphate coating is determined using the mass difference by weight measurement for each individual metallic material test sheet of the composite metal structure. This is done immediately after step (I) with a steel sheet and an aqueous solution of 9% by weight EDTA, 8.7% by weight NaOH and 0.4% by weight triethanolamine at a temperature of 70 ° C. for 5 minutes. This is done by contact, thus removing the zinc phosphate layer from it. Similarly, to determine the zinc phosphate coating mass of a galvanized or alloyed galvanized steel sheet, immediately after step (I), a corresponding test sheet and 20 g / l (NH ₄ ) ₂ Cr ₂ O ₇ And 27.5% by mass of _{an aqueous solution of NH 3} are brought into contact at a temperature of 25 ° C. for 4 minutes to remove the zinc phosphate layer in this way.

In contrast, the aluminum sheet is _{brought into contact with a 65% by weight aqueous solution of HNO 3 at} a temperature of 25 ° C. for 15 minutes immediately after step (I) to remove the zinc phosphate component correspondingly. The difference between the mass of the dried metal sheet after each treatment and the mass of the same untreated dried metal sheet immediately before the step (I) corresponds to the coating mass of zinc phosphate according to the present invention.

Similarly, the requirement of the present invention that less than 50% of the crystalline zinc phosphate layer on the surface of steel and zinc-plated steel and / or alloy zinc-plated steel is dissolved in step (II) is the requirement of each composite metal structure. Understood using test sheets of individual metallic materials. To this end, test sheets of phosphate-treated steel or galvanized or alloy galvanized steel in step (II) of the method of the invention are sprayed with compressed air after a rinsing step with deionized water. Weigh after drying.

The same test sheet is then contacted with the acidic passivation composition in step (II) of the method of the invention, then rinsed with deionized water, blown with compressed air to dry, and then weighed again. The zinc phosphate on the same test sheet was then added to the same test sheet with an aqueous solution of 9% by weight EDTA, 8.7% by weight NaOH and 0.4% by weight triethanolamine, or 20 g / l, as described above. Complete removal with an aqueous solution of (NH ₄ ) ₂ Cr ₂ O ₇ and 27.5 mass% NH _{3 and weigh the dry test sheet again.} Then, the percentage loss of the phosphate layer in step (II) of the method of the present invention is determined from the mass difference of the test sheet.

In step (I) of the method of the present invention, the free acid to which KCl (FA, KCl) of the zinc phosphate treatment composition represented by the point is added is determined as follows (W. Rasch "Die Phosphatierung von". "Metallen" (Phosphate Treatment of Metals), Eugen G. Leuse Verlag, 3rd Edition, 2005, Chapter 8.1, pp. 333-334):
Pipette 10 mL of the phosphate treatment composition into a suitable container, eg, a 300 mL Erlenmeyer flask. If the phosphate treatment composition contains complex fluoride, an additional 6-8 g of potassium chloride is added to the sample. Titration with 0.1 M NaOH is then performed using a pH meter and electrodes to bring the pH to 4.0. The amount of 0.1 M NaOH consumed in this titration (expressed in ml per 10 ml of phosphate-treated composition) represents the free acid value to which KCl (FA, KCl) was added in points.

The zinc phosphate-treated composition in step (I) preferably has a temperature in the range of 30 to 60 ° C, more preferably 35 to 55 ° C.

In the method of the present invention, the concentration of free fluoride in the zinc phosphate treated composition is determined by the potentiometric method. It takes a sample volume of the zinc phosphate treated composition, calibrates the combination electrode with a fluoride-containing standard solution without pH buffering, and then determines the activity of any desired commercially available fluoride selective potentiometric titration combination electrode. It is done. Calibration of the combination electrode and measurement of free fluoride are both performed at a temperature of 20 ° C.

Exceeding the critical concentration of free fluoride dependent on free acid, but in any case exceeding the concentration of 200 mg / l, causes deposition of crystalline zinc phosphate layers over the aluminum surface throughout the aluminum surface. However, the formation of such layers is undesirable due to the coating properties inherent in zinc phosphate treated substrates and is therefore not according to the present invention. However, a particular minimum amount of free fluoride is needed to ensure proper deposition kinetics for the zinc phosphate layer on the iron and zinc surfaces of the composite metal structure. This is because by simultaneously treating the aluminum surface of the composite metal structure, aluminum cations enter the zinc phosphate treatment composition in particular, which in turn inhibits the zinc phosphate treatment in its uncomplexed form. ..

Thus, the zinc phosphate treated composition is at least 5 mg / l but not more than 200 mg / l, preferably at least 10 mg / l but not more than 200 mg / l, more preferably at least 20 mg / l but 175 mg. Not exceeding / l, more preferably at least 20 mg / l but not exceeding 150 mg / l, further preferably at least 20 mg / l but not exceeding 135 mg / l, still more preferably at least 20 mg / l. Free fluoride content not exceeding 120 mg / l, particularly preferably at least 50 mg / l but not exceeding 120 mg / l, and very particularly preferably at least 70 mg / l but not exceeding 120 mg / l. Have.

The total fluoride content (F _tot. ) Of the zinc phosphate treated composition is preferably in the range of 0.01 to 0.3 mol / l, more preferably 0.02 to 0.2 mol / l.

The total fluoride content (F _tot. ) Is the total fluoride (F ⁻ ) content and is composed of complex-bound fluoride and simple fluoride. The complex-bound fluoride is a fluoride bound to Si and B, but is also bound to Al with a further complex. In contrast, simple fluorides are unbound fluorides in the complex and are composed of free fluorides that can be determined by the combination electrode, namely unbound fluorides, and fluorides that are bound as HF. ..

The higher the content of sodium ion and / or potassium ion, aluminum ion and free fluoride in the zinc phosphate treatment composition in step (I) of the method of the present invention, the higher the content on the surface of the composite metal structure, in particular. The precipitation of cryolite on the aluminum part becomes remarkable.

The content of sodium and / or potassium ions (calculated as sodium) is in the range of 1-4 g / l, especially 2-3 g / l, and the free fluoride content is 50-150 mg / l, especially 70-120 mg. If the range of / l, in the presence of aluminum ions in the form of a boron-soluble inorganic compound, the presence, especially in the form of a fluoroborate, such as HBF _4, in particular effectively reduce the deposition of cryolite It is possible to do.

The zinc phosphate treatment composition preferably has _{a concentration of boron in the form of a water-soluble inorganic compound calculated as BF 4} , 0.08 to 2.5 g / l, more preferably 0.08 to 2 g / l. It is more preferably in the range of 0.25 to 2 g / l, particularly preferably 0.5 to 1.5 g / l, and very particularly preferably in the range of 0.8 to 1.2 g / l.

The addition of the water-soluble inorganic compound containing boron according to the present invention further suppresses the formation of spots on the zinc surface. The upper limit of 3.2 g / l calculated as BF ₄ is primarily due to the economic feasibility of the method and secondly controls the process by water-soluble inorganic compounds containing such high concentrations of boron. Due to the fact that things become more difficult. This is because the formation of phosphate crystal clusters on the aluminum surface can only be suppressed to a very small extent by increasing the free acid content.

The crystal clusters result in an increase in points when the paint application is complete, which requires polishing to visually uniformly paint composite metal structures, such as automobile chassis, as desired by the customer. There is.

Surprisingly, the concentration of boron in the form of a water-soluble inorganic compound calculated as _{BF 4} to effectively suppress the formation of crystalline zinc phosphate layers and zinc phosphate crystal clusters on the aluminum surface. However, it has been found to be an important parameter essential to the success of the method of the present invention. Above the concentration of 2.0 g / l, at least individual zinc phosphate crystal clusters are already formed on the aluminum surface.

Beyond this concentration, the aluminum surface in the method of the invention is covered with a crystalline zinc phosphate layer over the entire area. Both scenarios should be avoided for successful anticorrosion pretreatment. Therefore, in step (I) of the method of the present invention, _{the boron in the form of the water-soluble inorganic compound calculated as BF 4} in each case has a value of 3.2 g / l, more preferably a value of 2.0 g / l. Use a zinc phosphate-treated composition having a concentration not exceeding.

However, in each case, the proportion of boron in the form of a water-soluble inorganic compound according to the invention is sufficient to prevent point formation on the zinc moiety treated according to the invention. Preferred boron-containing water-soluble inorganic compounds in the methods of the invention are fluoroborate, more preferably HBF ₄ , (NH ₄ ) BF ₄ , LiBF ₄ and / or NaBF ₄ . Water-soluble fluorobolates are more suitable as sources of free fluoride and are therefore introduced into bath solutions so that phosphating of the surface of steel and galvanized and / or alloy galvanized steel is still guaranteed. It serves to complex the trivalent aluminum cations.

When fluoroborate is used in the phosphate-treated solution in step (I) of the method of the present invention, _{the concentration of boron in the form of a water-soluble inorganic compound calculated as BF 4} is, of course, the concentration of boron in the form of the water-soluble inorganic compound according to claim 1 of the present invention. It should always be ensured that the value according to 3.2 g / l is not exceeded.

The zinc phosphate treatment composition in step (I) can also contain a specific content of the water-soluble inorganic compound containing silicon, as well as the water-soluble inorganic compound containing boron. The latter may be introduced into the phosphate treatment composition, for example, from the preceding method step or, if the silicon content of the aluminum moiety is high, from the composite metal structure.

However, in the context of the present invention, first of all, the content of inorganic compounds containing silicon is not desirable. This is because this increases the precipitation of cryolite on the surface of the composite metal structure, especially on its aluminum portion. This can be explained as follows:
In the case of acid pickling erosion on the surface of the composite metal structure, the protons are consumed in that they are reduced to hydrogen. This raises the pH on the surface. Surprisingly, in the context of the present invention, fluorosilicates such as hexafluoroborates, at elevated pH, significantly increase fluoride ions (free fluoride) over corresponding fluoroborates such as tetrafluoroborate. It was found to release. Therefore, in the case of fluorosilicates, the fluoride ion content on the surface is even more significantly increased, resulting in the proper content of sodium / potassium and aluminum ions, eventually resulting in the precipitation of the corresponding cryolite. Causes an increase (see Law of Mass Action).

Second, the content of inorganic compounds, including silicon, is also undesirable. It is surprising that a zinc phosphate bath composition having a free fluoride content containing silicon in the form of a water-soluble inorganic compound is a transfer system and / or structure for a crust-covered composite metal structure. Even more significant leaching of titanium, zirconium and / or hafnium can occur from the pre-passivated aluminum moiety of the, and thus significantly larger titanium, zirconium than those containing boron in the form of water-soluble inorganic compounds. It has now been found that and / or can result in poisoning of the phosphate bath with hafnium.

This also means that, as already further explained above, as a result of changes in pH on the surface of the composite metal structure, fluoride is released from the fluoride complex, complexing titanium, zirconium and hafnium. It can be explained in that it can be done. As a result, they remain soluble and can accumulate in the bath. Compared to fluorosilicates such as hexafluorosilicates, fluoroborates such as tetrafluoroborate are less likely to release fluoride ions, which means less free fluoride is available for complexing titanium, zirconium and hafnium. To do. Moreover, in the case of tetrafluoroborate, the concentration of free fluoride can be better controlled.

Third, the content of inorganic compounds, including silicon, is undesirable. This is because, particularly in _{the case of fluorosilicates such as H 2} SiF ₆ , sparingly soluble precipitates are formed in the presence of potassium ions. The formation of such precipitates is as undesirable as the precipitation of cryolite. Potassium ions are more advantageous than sodium ions as cations of salts for adjusting bath parameters, such as phosphates, hydroxides, fluorides and the like. This is because K ₃ AlF ₆ has _{better solubility than Na 3} AlF ₆ , so that the precipitation of cryolite is small. Ammonium ions that may be present in zinc phosphate treated compositions also have this advantage ( _{good solubility of (NH 4} ) ₃ AlF ₆ ), but they are more environmentally harmful than potassium ions in wastewater. .. The formation of sparingly soluble potassium-containing precipitates has not been detected for _{the corresponding boron-containing compounds, especially fluoroborates such as HBF 4.}

Therefore, _{the content of the inorganic compound containing silicon (calculated as SiF 6} ) is preferably less than 25 mg / l, more preferably less than 15 mg / l, more preferably less than 5 mg / l, and most preferably 1 mg / l. Is less than.

The zinc phosphate treatment composition in step (I) is preferably 0.6 to 3.0 points, preferably 0.8 to 3.0 points, more preferably 1.0 to 3.0 points, and most. Preferably, it has a number of points of free acid added with KCl in the range of 1.0 to 2.5 points. Adhering to the preferred range of free acids first ensures proper deposition dynamics of the phosphate layer on the selected metal surface and secondly for avoiding sludge precipitation or in the present invention. Unnecessary pickling removal of metal ions is prevented, which in turn inevitably involves intensive monitoring or post-treatment of the phosphate treatment bath for sludge disposal in the continuous operation of the method.

Furthermore, the total acid (TA) in the phosphate-treated composition in step (I) of the method of the present invention is in the range of 10 to 50, more preferably 15 to 40, and particularly preferably 20 to 35 points. Should be.

In contrast, Fisher total acid (FTA) should be in the range of 10-30, more preferably 12-25, and more preferably 15-20 points, with an A value of 0.04-0.20. It should be more preferably in the range of 0.05 to 0.15, and particularly preferably in the range of 0.06 to 0.12.

Surprisingly, both the precipitation of cryolite on the surface of the composite metal structure and the poisoning of the phosphate treatment bath with titanium, zirconium and / or hafnium are both the zinc phosphate treatment composition in step (I). Dimensionless quotient of things
(A value x T) / (F _tot. X [B] x 1000)
(In the formula, "T" represents temperature / ° C., "F _tot. " Represents total fluoride content / (mol / l), and "[B]" represents elemental boron concentration / (mol / l)). However, it has been found that it can be reduced particularly efficiently when it is in the range of 0.13 to 22.5, preferably 0.2 to 15, and more preferably 0.4 to 10.

The free acids (diluted) (FA (dir.)), Fisher total acid (FTA), total acid (TA) and A values required only for the determination of Fisher total acid (FTA) are determined as follows: Be done:
Free acid (diluted acid) (FA (dir.))
(See W. Rasch "Die Phosphatierung von Metallen", Eugen G. Leuse Verlag, 3rd Edition, 2005, Section 8.1, pp. 333-334)
To determine the free acid (dilution), 10 ml of the phosphate-treated composition is pipetted into a suitable container, such as a 300 ml Erlenmeyer flask. Then 150 ml of completely desalinated water is added. Titration with 0.1 M NaOH is performed using a pH meter and electrodes until the pH is 4.7. The value of free acid (diluted) (FA (dir.)) Is obtained in points by the amount of 0.1 M NaOH consumed in this titration, expressed in ml per 10 ml of diluted phosphate-treated composition.

Fisher Total Acid (TAF)
(See W. Rasch "Die Phosphatierung von Metallen", Eugen G. Leuse Verlag, 3rd Edition, 2005, Section 8.2, pp. 334-336)
Following the measurement of free acid (dilution), the diluted phosphate-treated composition was added to the potassium oxalate solution, followed by 0.1 M NaOH to a pH of 8.9 using a pH meter and electrodes. Titrate. In this procedure, the consumption of 0.1 M NaOH in ml per 10 ml of diluted phosphate-treated composition gives Fischer total acid (TAF) in points.

Total acid (TA)
(See W. Rasch "Die Phosphatierung von Metallen", Eugen G. Leuse Verlag, 3rd Edition, 2005, Section 8.3, pp. 336-338)
Total acid (TA) is the sum of the divalent cations present and the free and bound phosphoric acid (the latter being phosphate). Total acid is measured by consumption of 0.1 M NaOH using a pH meter and electrodes. To this end, 10 ml of phosphate-treated composition is pipetted into a suitable container, such as a 300 ml Erlenmeyer flask, and diluted with 25 ml of completely desalinated water. This is followed by titration with 0.1 M NaOH to a pH of 9. The consumption in ml per 10 ml of diluted phosphate-treated composition during this procedure corresponds to the number of points for total acid (TA).

Acid value (A value)
(See W. Rasch "Die Phosphatierung von Metallen", Eugen G. Leuse Verlag, 3rd Edition, 2005, Section 8.4, p. 338)
What is called the acid value (A value) represents the ratio of free acid to which KCl is added to Fisher total acid, that is, the ratio of (FA, KCl): FTA, and the value of free acid (FA) is the Fisher total acid value. Obtained by dividing by (FTA).

The phosphate-treated composition in step (I) preferably has a pH in the range of 2.5 to 3.5.

Total based on the elements zirconium, titanium and / or hafnium for the results of optimal phosphate treatment of metal components that have surfaces of steel and zinc-plated and / or alloy zinc-plated steel as well as aluminum surfaces. Contains 20 ppm or less, preferably 15 ppm or less, more preferably 10 ppm or less, more preferably 5 ppm or less, and most preferably a total of 1 ppm or less of water-soluble compounds of zirconium, titanium and / or hafnium, and particularly preferably any zirconium. The zinc phosphate treated composition in step (I) of the method of the present invention, which also contains no water-soluble compounds of titanium and / or hafnium, is preferred.

Therefore, the addition of water-soluble compounds of zirconium, titanium and / or hafnium to the phosphate-treated composition, in particular in step (I) of the method of the present invention, is completely omitted.

From WO2008 / 055726, it is known that the presence of water-soluble compounds of these elements in the phosphate treatment step also effectively suppresses the formation of crystalline phosphate layers on the aluminum surface. However, in the presence of water-soluble compounds of zirconium, titanium and / or hafnium, heterogeneous and amorphous zirconium, titanium and / or in the aluminum moiety, especially when applying the phosphating composition by spray method. It has been found that hafnium-based chemical conversion coatings are introduced relatively frequently, which causes "mapping" in the case of subsequent organic coatings.

"Mapping" is understood by those skilled in the art of dipping coating of metal components to mean a speckled visual impression of the coating coating due to the heterogeneous coating layer thickness after firing of the dipping coating.

It has been found to be advantageous to reduce the free fluoride concentration or the overall fluoride concentration in order to keep the concentration of zirconium, titanium and / or hafnium low. The effect is that layer formation on the aluminum moiety is suppressed and the process can be better controlled.

Poisoning of phosphating baths with titanium, zirconium and / or hafnium, as already described above, pre-passivates transfer systems or structures, especially for crust-covered composite metal structures. May be caused by the aluminum part that has been squeezed.

As further described, a phosphate treatment bath with titanium, zirconium and / or hafnium, depending on the boron content of the zinc phosphate treatment composition in the form of a water-soluble inorganic compound, especially on fluoroborates such as tetrafluoroborate. It is possible to reduce the poisoning of.

Moreover, when the content of free fluoride is high, leaching from the crust or pre-passivation occurs to a greater extent in acidic media. At the same time, titanium and / or zirconium are stabilized by a high free fluoride content. The result is a fluorocomplex of titanium and / or zirconium. Decreasing the free fluoride content makes the solubility of titanium and / or zirconium unstable, which precipitates and no longer constitutes poisoning of the phosphate treatment bath.

Reducing the free fluoride content does just reduce the formation of the zinc phosphate layer on the aluminum moiety. However, this is not a problem due to the subsequent passivation (see step (II)). In contrast, the low zinc phosphate on the aluminum moiety is beneficial in the corrosion and paint adhesion tests performed.

Thus, the zinc phosphate treated composition is at least 5 mg / l but not more than 200 mg / l, preferably at least 10 mg / l but not more than 200 mg / l, more preferably at least 20 mg / l but 175 mg. Not exceeding / l, more preferably at least 20 mg / l but not exceeding 150 mg / l, further preferably at least 20 mg / l but not exceeding 135 mg / l, still more preferably at least 20 mg / l. Free fluoride content not exceeding 120 mg / l, particularly preferably at least 50 mg / l but not exceeding 120 mg / l, and very particularly preferably at least 70 mg / l but not exceeding 120 mg / l. Have.

In a first preferred embodiment of the method of the invention, the transfer system for the composite metal structure comprises titanium, zirconium and / or hafnium in step (II) following step (I) phosphate treatment. Has a crust preferably derived from the passivation of composite metal structures having water-soluble compounds containing titanium, zirconium and / or hafnium. The transfer system operates preferably cyclically so that the crust contacted with titanium, zirconium and / or hafnium in step (II) is re-exposed to the acid phosphate-treated composition of step (I). ..

In a second preferred embodiment, the aluminum portions of the composite metal structure are pre-passivated, i.e. they already have a passivation layer containing titanium, zirconium and / or hafnium.

In a third preferred embodiment, the transfer system for the composite metal structure comprises titanium and / or zirconium and the titanium, zirconium and / or in step (II) following the phosphate treatment of step (I). It has a crust that is preferably derived from the passivation of composite metal structures with water-soluble compounds containing hafnium. The transfer system preferably operates periodically such that the crust produced in step (II) is re-exposed to the acid phosphate-treated composition of step (I). In addition, the aluminum portion of the composite metal structure has been passivated in advance. That is, a passivation layer containing titanium, zirconium and / or hafnium has already been provided.

The zinc phosphate-treated composition in step (I) of the method of the present invention is preferably at least 0.3 g / l, more preferably at least 0.8 g / l, but preferably 3 g / l or less. It preferably contains 2 g / l or less of zinc ions. The phosphate ion content in the phosphate treatment solution _{is calculated as P 2} O _{5 in} each case, preferably 5 to 50 g / l, more preferably 8 to 25 g / l, and more preferably 10 to 10. It is in the range of 20 g / l.

The zinc phosphate treated composition of the method of the invention may further comprise at least one of the following accelerators, similar to the zinc ions and phosphate ions described above:
− 0.07 to 0.25 g / l nitrite (calculated as sodium nitrite),
− Approximately 0.1 to 2 g / l of nitroguanidine,
− 8 to 51 mg / l hydrogen peroxide.

Such accelerators are well known in the art as components of phosphate treatment baths and are "scavengers" in that they directly oxidize hydrogen formed by acid erosion on metal surfaces. ) ”, By doing so, it is reduced in itself. The formation of a homogeneous crystalline zinc phosphate layer is significantly promoted by an accelerator that prevents the formation of gaseous hydrogen on the metal surface.

The zinc phosphate treated composition of the method of the invention may further comprise at least one of the following anions, similar to the zinc ions and phosphate ions described above:
− 0 to 2 g / l sulfate,
− 0.01 to 500 mg / l (for nickel-free zinc phosphate-treated compositions) or 0.01 to 20 g / l (for nickel-containing zinc phosphate-treated compositions) nitrate.

The proportion of nitrates of up to 5 g / l, preferably up to 3 g / l, which is customary in nickel-containing phosphate treatments, is a homogeneous continuum of crystallinity on the surface of steel and on galvanized and alloyed galvanized steel surfaces. Promotes the formation of galvanized phosphate layers.

However, in the case of nickel-free phosphate treatment, it is important to promote the layer formation reaction with nitrate. Such nickel-free phosphate treatment results in lower coating mass, especially reducing the uptake of manganese into the crystals. However, since the phosphate coating has a zero nickel content, the manganese content of the phosphate coating that is too low comes at the expense of its alkali resistance.

Alkali resistance, in turn, plays an important role during subsequent cathodic electrodeposition coating. In this method, water is electrolyzed on the surface of the substrate to form hydroxide ions. As a result, the pH rises at the substrate interface. This allows, first of all, agglomeration and deposition of the electrodeposition coating. However, elevated pH can also damage the crystalline phosphate layer.

By experiments, the corrosion protection and paint adhesion of the crystalline zinc phosphate layer produced using the aqueous phosphate treatment composition of the present invention is improved when one or more of the following cations are further present. Rukoto has been shown:
− 0.3 to 2 g / l, preferably 0.5 to 1.5 g / l of manganese (II),
− 0.3 to 2 g / l, preferably 0.8 to 1.2 g / l of nickel (II),
− 0.001 to 0.2 g / l, preferably 0.005 to 0.1 g / l of iron (III).

First, the iron (III) cation improves corrosion protection on steel and on zinc and zinc alloys. Second, the iron (III) cation improves the stability of the corresponding phosphate treatment bath. The addition of the iron (III) cation produces sludge flocs that can be filtered more easily, making it easier to remove cryolite from the bath.

As a tricationic phosphate treatment solution, an aqueous composition for chemical conversion treatment containing both manganese ions and nickel ions as well as zinc ions is known to those skilled in the art in the field of phosphate treatment, and is known to those skilled in the art. Well suited in context.

Similar to the aforementioned cations that are incorporated into the phosphate layer or have at least a positive effect on the crystal growth of the phosphate layer, the phosphate treatment solution in step (I) of the method of the present invention is sodium ion. And / or potassium ions as well as optionally ammonium ions transferred into the phosphate-treated solution to adjust the free acid content.

A water rinse operation between steps (I) and step (II) is essential. This is because the phosphate ions and metal cations that would otherwise be present in the phosphate treatment composition are associated with the passivation bath. This results in difficult-to-control changes in bath parameters and precipitation of titanium, zirconium and / or hafnium as sparingly soluble phosphates.

The water rinse operation may be one water rinse or a total of at least two water rinses.

Each rinse may be performed with completely desalinated or tap water. In each case, at least one surfactant may be present.

After the rinse water enriched with the components of the phosphate treatment bath of step (I) is post-treated, the components may be selectively recirculated into the phosphate treatment bath.

The composite metal structure is treated and rinsed in step (I) and contacted with the acidic passivation composition in step (II) by dipping or spraying the solution.

In step (II) of the method, according to the present invention, a passivation layer is formed on the aluminum surface by contacting the composite metal structure with the acidic passivation composition, and during contact with the passivation composition. In addition, the zinc phosphate layer on the steel surface or the zinc-plated and / or alloy zinc-plated steel surface dissolves to about 50% or less, preferably to about 20% or less, and more preferably to about 10% or less. In the context of the present invention, the passivation layer of aluminum is believed to passivate an inorganic or mixed inorganic-organic thin film coating that does not form a continuous crystalline phosphate layer.

The acidic passivation composition is in the range of 2.0-5.5, preferably 2.5-5.5, more preferably 3.0-5.5, and most preferably 3.5-5.5. Some pHs essentially ensure that less than 50% of the zinc phosphate layer on the steel surface or the surface of zinc-plated and / or alloy zinc-plated steel dissolves, but the aluminum surface of the corresponding composite metal structure. The passivation layer of is typically produced by a chromium-free acidic passivation composition.

The passivation composition is at least one water-soluble compound selected from water-soluble compounds of metal ions of Mo, Cu, Ag, Au, Ti, Zr, Hf, Pd, Sn, Sb, Li, V and Ce. including. The water-soluble compounds are present in concentrations in the following preferred, particularly preferred, and very particularly preferred ranges (calculated as corresponding metals, respectively):

The metal ions present in the water-soluble compound are in the form of salts containing the corresponding metal cations (eg, molybdenum or tin), preferably in at least two oxidation steps, more specifically oxyhydroxydos, hydroxides. Deposits in the form of spinels or defective spinels, or in the form of surface elements to be treated (eg copper, silver, gold or palladium).

In a first preferred embodiment, the passivation composition comprises molybdenum ions and any additional metal ions, respectively, in the form of water-soluble compounds. They are preferably molybdate, more preferably ammonium heptamolybdate, and particularly preferably in the form of ammonium heptamolybdate × 7H 2 _O, is added to the passivating composition. Molybdenum ions may also be added in the form of sodium molybdate.

Alternatively, the molybdenum ion is added to the passivation composition in the form of at least one salt containing, for example, a molybdenum cation such as molybdenum chloride, followed by a suitable oxidizing agent, eg, the accelerator described above above. It may be oxidized to molybdenum. In such cases, the passivation composition itself contains the corresponding oxidizing agent.

More preferably, the passivation composition comprises molybdenum ions in combination with copper, tin or zirconium ions.

Particularly preferably, the mobilization composition comprises a molybdenum ion in combination with a zirconium ion and is a polymer or copolymer, more specifically polyamine, polyethyleneamine, polyaniline, polyimine, polyethyleneimine, polythiophene and polypyrrylol, and these. It also optionally comprises a polymer or copolymer selected from the group consisting of mixtures and copolymers thereof, and polymer species of polyacrylic acid.

Here, the content of molybdenum ions is preferably in the range of 20-225 mg / l, more preferably 50-225 mg / l, and very preferably 100-225 mg / l (calculated as Mo), and The zirconium ion content is preferably in the range of 50-300 mg / l, more preferably in the range of 50-150 mg / l (calculated as Zr).

In a second preferred embodiment, the passivation composition comprises copper ions, in particular copper (II) ions, and any other metal ion, respectively, in the form of water-soluble compounds. Preferably, the passivation composition in that case comprises a copper ion content in the range of 100-500 mg / l, more preferably 150-225 mg / l.

In a particularly preferred embodiment, the passivation composition is in the form of a complex of Ti, Zr and / or Hf, preferably 20 to 500 mg / l, more preferably 50 to 300 mg / l, and more preferably 50. Concentrations in the range of ~ 150 mg / l (calculated as Ti, Zr and / or Hf) and any additional metal ions are included in the form of water soluble compounds. The complex is preferably a fluorocomplex, more preferably a hexafluorocomplex. In addition, the immobilized composition preferably comprises 10 to 500 mg / l, more preferably 15 to 100 mg / l, and particularly preferably 15 to 50 mg / l of free fluoride.

In the first very particularly preferred embodiment, the immobilization composition is composed of molybdenum, copper, especially copper (II), as well as in complex forms, especially Ti, Zr and / or Hf as a fluorocomplex. Includes at least one additional water-soluble compound selected from water-soluble compounds of silver, gold, palladium, tin and antimony, and lithium metal ions, preferably molybdenum and copper, particularly copper (II) metal ions. Each water-soluble compound is present in a concentration in the following preferred range (calculated as the corresponding metal):

In a second, highly preferred embodiment, the mobilization composition comprises at least one additional organosilane and / or Hf, as well as in complexed forms, especially Ti, Zr and / or Hf as a fluorocomplex. At least one of its hydrolysis products, i.e. organosilanol, and / or at least one of its condensation products, i.e. organosiloxane / polyorganosiloxane, is preferably 5 to 200 mg / l, more preferably 10 to 100 mg / l. 1 and particularly preferably at concentrations in the range of 20-80 mg / l (calculated as Si).

At least one organosilane preferably has at least one amino group. Particularly preferred are those capable of hydrolyzing aminopropylsilanol and / or 2-aminoethyl-3-aminopropylsilanol and / or bis (trimethoxysilylpropyl) amines.

In a third very particularly preferred embodiment, the immobilization composition comprises molybdenum, copper, especially copper (II), as well as in complexed forms, especially Ti, Zr and / or Hf as a fluorocomplex. At least one additional water-soluble compound selected from water-soluble compounds of silver, gold, palladium, tin and antimony, and lithium metal ions, preferably molybdenum and copper, especially copper (II) metal ions, and at least. One organosilane and / or at least one of its hydrolysis products, namely organosilanol, and / or at least one of its condensation products, ie, organosiloxane / polyorganosiloxane, preferably 5 to 200 mg / l. , More preferably in the range of 10-100 mg / l, and particularly preferably in the range of 20-80 mg / l (calculated as Si). Each water-soluble compound is present in a concentration in the following preferred range (calculated as the corresponding metal):

The method of the present invention for anticorrosion treatment of composite metal structures assembled from metallic materials and also having an aluminum surface to at least to some extent, after cleaning and activating the metal surface, first involves the surface and zinc phosphate in step (I). The treatment composition is carried out by contacting the treatment composition at a temperature in the range of 20 to 65 ° C. for a period suitable for the application mode, for example by a spraying method or a dipping method. Experiments have shown that surface spot formation in galvanized and / or alloy galvanized steel in conventional immersion phosphate treatment is particularly pronounced. Therefore, the phosphate treatment in step (I) of the method of the present invention is particularly suitable for a phosphate treatment facility operating according to the principle of the dipping method. This is because the method of the present invention suppresses point formation.

It is advantageous to first wash the composite metal structure and especially degreas it before treating it with the zinc phosphate treatment composition in step (I). For this purpose, it is particularly possible to use acidic, neutral, alkaline or strongly alkaline cleaning compositions, but optionally more acidic or neutral pickling compositions are also possible. ..

Here, alkaline or strongly alkaline cleaning compositions have been found to be particularly advantageous.

The aqueous cleaning composition may optionally include a detergent builder and / or other additives such as a complexing agent, as well as at least one surfactant. It is also possible to use an activating detergent.

After washing / pickling, the composite metal structure is preferably at least rinsed with water. In that case, the water may be optionally mixed with a water-soluble additive such as nitrite or surfactant.

It is advantageous to treat the composite metal structure with the activating composition before treating the composite metal structure with the zinc phosphate treated composition in step (I). The purpose of the activation composition is to deposit a large number of ultrafine phosphoric acid particles as seed crystals on the surface of the portion made of zinc and iron. These crystals are particularly crystalline with a large number of densely placed fine phosphate crystals in the zinc and iron moieties that are in contact with the phosphate treatment composition in subsequent method steps. Phosphate layers, or nearly continuous phosphate layers, help to form, preferably without rinsing in between.

The activation composition contemplated in this case particularly comprises an acidic or alkaline composition based on titanium phosphate or zinc phosphate.

However, it is also advantageous to add an activator, in particular titanium phosphate or zinc phosphate, to the cleaning composition, in other words, to perform the cleaning and activation in one step.

In a further step following step (II), the composite metal structure is provided with a primer coating, preferably an organic immersion coating, particularly an electrodeposition coating, preferably components treated according to the present invention without prior oven drying. It's okay. After the primer coating, it is possible to apply a top coating, which may be a powder coating or a wet coating.

The present invention further relates to zinc phosphate treated compositions for selective phosphate treatment of steel, zinc plated steel and / or alloy zinc plated steel surfaces in composite metal structures comprising moieties made of aluminum. The zinc phosphate treated composition is calculated as at least 0.6 points of KCl-added free acid, and preferably a pH in the range 2.5-3.5, and (a) P ₂ O _5. And 5 to 50 g / l phosphate ion,
(B) 0.3 to 3 g / l of zinc ion,
(C) Free fluoride of at least 5 mg / l but less than 200 mg / l, and (d) Water-soluble inorganic compounds calculated as _{BF 4 of at least 0.04 g / l but less than 3.2 g / l.} Has a form of boron,
The zinc phosphate treated composition further comprises a content of sodium and / or potassium and aluminum ions.

Preferably, the free fluoride content is 10 to 200 mg / l, more preferably 20 to 175 mg / l, still more preferably 20 to 150 mg / l, still more preferably 20 to 135 mg / l, still more preferably 20 to 120 mg / l. l, particularly preferably in the range of 50-120 mg / l, and very particularly preferably in the range of 70-120 mg / l.

Surprisingly, both the precipitation of cryolite on the surface of composite metal structures and the poisoning of phosphate treatment baths with titanium, zirconium and / or hafnium are the dimensionless quotients of zinc phosphate treatment compositions. (A value x T) / (F _tot. X [B] x 1000)
(In the formula, "T" represents temperature / ° C., "F _tot. " Represents total fluoride content / (mol / l), and "[B]" represents elemental boron concentration / (mol / l)). However, it has been found that it can be reduced particularly efficiently when it is in the range of 0.13 to 22.5, preferably 0.2 to 15, and more preferably 0.4 to 10.

In a preferred variant, the zinc phosphate treated composition of the present invention, based on the elements zirconium, titanium and / or hafnium, has a total of 20 ppm or less, preferably 15 ppm or less, more preferably 10 ppm or less, more preferably 5 ppm or less. , And most preferably no more than 1 ppm water-soluble compounds of zirconium, titanium and / or hafnium, and particularly free of water-soluble compounds of zirconium, titanium and / or hafnium.

Further advantageous configurations of the zinc phosphate treated compositions of the present invention have already been clarified above in the methods of the present invention.

The present invention also relates to concentrates, wherein the zinc phosphate treated composition of the present invention can be obtained by diluting with a suitable solvent and / or dispersion medium, preferably with water, and optionally adjusting the pH.

The dilution factor here is preferably 2 to 100, preferably 5 to 50.

Finally, the present invention relates to a corrosion-protected composite metal structure that comprises at least a portion of aluminum, at least a portion of zinc, and an additional portion of any iron and can be obtained by the methods of the invention.

The composite metal structures protected from corrosion by the methods of the present invention correspond to the supplier industry for automobiles, the body structure of automobile manufacturing, the mechanical structure for agriculture, the shipbuilding, the construction sector or white goods. Find a way to use it in the manufacture of.

The present invention will be described with reference to the following non-limiting examples and comparative examples.

An aqueous zinc phosphate treatment solution was prepared. Each has a point number of free acids with 1.1 points of KCl added, 19.5 points of Fisher total acid, an A value of 0.056, and a pH in the range 2.5-3.5. Was there. The phosphate-treated solutions do not contain nickel, and each is _{calculated as P 2} O ₅ , 15 g / l phosphate ion, 0.8 g / l zinc ion, 1.0 g / l manganese ion, and so on. It contained an amount of free fluoride (see Table 1), _{1.0 g / l boron calculated as BF 4 in} the form of BF ₄ , and 34 mg / l hydrogen peroxide accelerator. The phosphate treatment solution was brought to a temperature of 45 ° C.

Each washed aluminum test sheet (AA6016) was uniformly sprayed with one phosphate treatment solution, rinsed and acidic aqueous passivation composition containing _{150 mg / l H 2} ZrF _{6 calculated as Zr.} The object was immersed in the object at room temperature for 30 seconds. The seats were previously electrodeposited without being oven dried and finally wet coated (standard automotive coating structure).

The test sheets were subjected to a 144 hour CASS test with DIN EN ISO 9227, 2017-07 and a 1008 hour filamentous test with DIN EN 3665, 1997-08. The corrosion results are summarized in the table below (F _free = free fluoride content).

As shown in Table 1, reducing the free fluoride content in the phosphating solution clearly reduces corrosion on aluminum in both the CASS and filamentous tests.

Applicants sampled with varying free fluoride contents from a zinc phosphate treatment bath in customer operation for a period of 2.2 years and contained free fluoride (F _free ) and zirconium (Zr). The amount was determined. For this purpose, fluoride selective potentiometric titration measurement combination electrodes were used or ICP (inductively coupled plasma) analysis was performed.

As is clear from Table 2, the decrease in free fluoride content (with some time delays (see 10-26 months)) was accompanied by a decrease in zirconium content in the bath. Conversely, an increase in free fluoride content (with some time delays (see 4.5-14.5 months)) was accompanied by an increase in zirconium content in the bath. Therefore, low free fluoride content reduced bath poisoning with zirconium.

An aqueous zinc phosphate treatment solution (ZPS No. 1 to 8) was prepared. Each had a point number of free acids supplemented with 1.5 points of KCl. The phosphating solution is free of nickel, phosphate ions 15 g / l, calculated as _P 2 _{O 5,} respectively, zinc ions 0.8 g / l, manganese ions 1.0 g / l, of 100 mg / l It contained free fluoride and various amounts of sodium and potassium ions, and either tetrafluoroborate or hexafluorosilicate. The phosphate treatment solution was brought to a temperature of 45 ° C. and stirred in a beaker at medium speed using a stir bar. The dissolution concentrations of aluminum, silicon and boron were determined by ICP analysis at the start (0 hours) and after 24 hours. When the concentration of molten aluminum decreased, this was due to precipitation in the form of cryolite. In contrast, when the concentration of dissolved silicon is lowered, which it was based on the precipitation in the form of K ₂ SiF _6.

As is clear from Table 3, the content of 5.0 g / l sodium ion resulted in a decrease in the concentration of dissolved aluminum, i.e. precipitation of cryolites (ZPS2 and 6). Cliolite precipitation in the presence of tetrafluoroborate (ZPS2) was slightly less pronounced than in the case of hexafluorosilicate (ZPS6). The same applies to the content of 2.5 g / l sodium ion and 2.5 g / l potassium ion (comparison between ZPS4 and ZPS8). In contrast, with a content of 2.5 g / l sodium ions (ZPS 1 and 5) or 5.0 g / l potassium ions (ZPS 3 and 7), there was no cryolite precipitation.

For hexafluorosilicate, in the presence of potassium ions, decrease in the concentration of dissolved silicon, i.e. there is _K 2 _SiF of 6 (ZPS7 and 8) precipitation. The formation of the corresponding precipitate of tetrafluoroborate could not be detected. Correspondingly, there was no reduction in the concentration of dissolved boron here (ZPS 3 and 4).

Claims (15)

By a method of chemical pretreatment and selective phosphate treatment of composite metal structures containing at least a portion made of aluminum, at least a portion made of zinc, and any additional portion made of iron. There,
(I) In the first step, a surface-covering crystalline zinc phosphate having a coating mass in the range of ^{0.5 to 5 g / m 2} on the iron-made portion and the zinc-made portion. Treatment of the composite metal structure with an aqueous zinc phosphate treatment composition, which results in layer formation but does not form a zinc phosphate layer having a coating mass of at least 0.5 g / m ^{2 on the aluminum moiety.} And then perform an intermediate water rinse operation,
(II) In the second step, the acidic passivation composition comprises the application of an aqueous acidic passivation composition having a pH in the range of 2.0 to 5.5 to the composite metal structure. , The aluminum portion that removes 50% or less of the crystalline zinc phosphate on the zinc-made portion and the iron-made portion, but does not constitute a crystalline phosphate layer covering the surface. Form a passivation layer on top,
The zinc phosphate treatment composition in step (I) comprises a content of sodium and / or potassium ions, and aluminum ions.
The zinc phosphate treated composition in step (I) had a temperature in the range of 20-65 ° C. and contained a free fluoride content of at least 5 mg / l but not more than 200 mg / l.
Boron in the form of a water-soluble inorganic compound, calculated as _{BF 4} , which is at least 0.04 g / l but not more than 3.2 g / l, is present in the zinc phosphate treatment composition and said zinc phosphate treatment. A method in which the number of points of the free acid to which KCl is added in the composition is at least 0.6 points. The zinc phosphate treatment composition in step (I) is 10 to 200 mg / l, preferably 20 to 150 mg / l, more preferably 20 to 120 mg / l, particularly preferably 50 to 120 mg / l, and very particularly preferably. The method of claim 1, wherein has a free fluoride content in the range of 70-120 mg / l. The zinc phosphate treatment composition in step (I) contains 0.08 to 2.5 g / l, more preferably 0.08 to 2 g / l, of boron in the form of a water-soluble inorganic compound calculated as _{BF 4.} Claim 1 or claim 1 or which has a concentration in the range of 0.25 to 2 g / l, particularly preferably 0.5 to 1.5 g / l, and very particularly preferably 0.8 to 1.2 g / l. The method according to 2. The content of sodium ions and / or potassium ions (calculated as sodium) in the zinc phosphate treatment composition in step (I) is in the range of 1 to 4 g / l, particularly 2 to 3 g / l, and is free. The method according to any one of claims 1 to 3, wherein the fluoride content is in the range of 50 to 150 mg / l, particularly 70 to 120 mg / l. _{The content of the inorganic compound containing silicon (calculated as SiF 6} ) in the zinc phosphate treatment composition in step (I) is less than 25 mg / l, preferably less than 15 mg / l, more preferably less than 5 mg / l. , And most preferably less than 1 mg / l, according to any one of claims 1 to 4. The zinc phosphate treatment composition in step (I) was 0.6 to 3.0 points, preferably 0.8 to 3.0 points, more preferably 1.0 to 3.0 points, and most preferably 1. The method according to any one of claims 1 to 5, which has a number of points of free acid added with KCl in the range of 0 to 2.5 points. Regarding the zinc phosphate-treated composition in the step (I), the dimensionless quotient (A value × T) / (F _tot. × [B] × 1000)
However, the method according to any one of claims 1 to 6, wherein the method is in the range of 0.13 to 22.5, preferably 0.2 to 15. The zinc phosphate treatment composition in step (I) is one or more of the following cations −0.3 to 2 g / l, preferably 0.5 to 1.5 g / l of manganese (II),
− 0.3 to 2 g / l, preferably 0.8 to 1.2 g / l of nickel (II),
− 0.001 to 0.2 g / l, preferably 0.005 to 0.1 g / l of iron (III)
The method according to any one of claims 1 to 7, further comprising. Claimed that the pH of the passivation composition in step (II) is in the range of 2.5 to 5.5, more preferably 3.0 to 5.5, and most preferably 3.5 to 5.5. Item 8. The method according to any one of Items 1 to 8. The passivation composition in step (II) is in the form of a complex of Ti, Zr and / or Hf, preferably 20 to 500 mg / l, more preferably 50 to 300 mg / l, and more preferably 50 to. 6. One of claims 1-9, comprising a concentration in the range of 150 mg / l (calculated as Ti, Zr and / or Hf) and any additional metal ion in the form of a water soluble compound. the method of. The passivation composition in step (II) comprises at least one organosilane and / or at least one hydrolysis product thereof, and / or at least one condensation product thereof, preferably 5 to 200 mg. The method according to any one of claims 1 to 10, further comprising a concentration in the range of / l, more preferably 10 to 100 mg / l, and particularly preferably 20 to 80 mg / l (calculated as Si). .. The invention according to any one of claims 1 to 8, for selective phosphating of steel, zinc-plated steel and / or alloy zinc-plated steel surfaces in composite metal structures comprising a portion made of aluminum. Zinc phosphate treated composition
The number of points of at least 0.6 points of the free acid to which KCl was added, and preferably a pH in the range of 2.5 to 3.5, and (a) ₅ to 50 g / l calculated as _{P 2} O 5. Phosphate ion,
(B) 0.3 to 3 g / l of zinc ion,
(C) Free fluoride of at least 5 mg / l but less than 200 mg / l, and (d) Water-soluble inorganic compounds calculated as _{BF 4 of at least 0.04 g / l but less than 3.2 g / l.} Has a form of boron,
A zinc phosphate-treated composition, wherein the zinc phosphate-treated composition further comprises a content of sodium ion and / or potassium ion and aluminum ion. The zinc phosphate-treated composition according to claim 12, which can be obtained by diluting with a suitable solvent and / or dispersion medium, preferably with water, and optionally adjusting the pH. The method according to any one of claims 1 to 11, comprising at least a portion made of aluminum, at least a portion made of zinc, and any additional portion made of iron. Can be a composite metal structure. The method of use of the composite metal structure according to claim 14 in the automobile supplier industry, in the body structure of automobile manufacturing, in the agricultural mechanical structure, in shipbuilding, in the construction sector or in the manufacture of white goods.