JP4830032B2 - Chemical conversion treatment liquid, method for producing the same, and method for forming chemical conversion film - Google Patents

Description

  The present invention relates to a chemical conversion treatment technique, and more particularly to a chemical conversion treatment technique for forming a chemical conversion film on the surface of zinc or a zinc alloy.

  The chromate treatment is a typical chemical conversion treatment for preventing the surface of zinc or zinc alloy from rusting. Chromate treatment has been widely used industrially because it is inexpensive and simple.

  However, since hexavalent chromium is a harmful substance, its use is being regulated. Therefore, researches on chemical conversion treatment using trivalent chromium instead of hexavalent chromium and chromium-free chemical conversion treatment are actively conducted.

  For example, Patent Document 1 describes a chemical conversion treatment solution containing aluminum, silicon, and one or more organic acids or inorganic acids. Patent Document 1 describes that a good appearance can be obtained when fluorine is added to the chemical conversion treatment liquid.

  Patent Document 2 discloses a chemical conversion treatment solution containing at least one of a water-soluble magnesium inorganic salt and a water-soluble lithium inorganic salt, another water-soluble inorganic salt or inorganic silicate or colloidal silica, and hydrogen peroxide. Are listed. Patent Document 2 describes that when this chemical conversion treatment solution is used, a chromium-free coating having sufficient corrosion resistance can be formed.

JP-A-11-181578 JP 2007-177304 A

  Fluorine compounds are corrosive and difficult to treat waste water. In addition, hydrogen peroxide requires low handling and has low stability. Therefore, a chromium-free chemical conversion treatment technique that does not use fluorine and hydrogen peroxide is desired.

  Further, the chemical conversion treatment liquid containing silicon is circulated in the form of two kinds of concentrated liquids, ie, a first concentrated liquid not containing silicon and a second concentrated liquid containing silicon, and these are mixed and necessary on site. May be prepared by diluting accordingly. When the silicon concentration in the second concentrated liquid is increased, the stability thereof is lowered. Therefore, the second concentrated liquid must be prepared to have a low silicon concentration. Therefore, the silicon concentration in the chemical conversion treatment liquid may be limited to a low value.

  An object of the present invention is to provide a chromium-free coating that can form a chemical conversion film having excellent corrosion resistance and appearance without using fluorine and hydrogen peroxide and without the stability problem caused by high silicon concentration. It is to provide chemical conversion treatment technology.

  According to the first aspect of the present invention, there is provided a chemical conversion treatment liquid for forming a chemical conversion film on zinc or a zinc alloy containing no chromium, hydrogen peroxide and fluorine, and containing 0.5 g / L to 38 g. / L of magnesium, 0.5 g / L to 2.5 g / L of silicon, and nitrate ions of 0.36 g / L or more, including the silicon as a water-soluble silicate, and optionally cobalt There is further provided a chemical conversion treatment solution further containing at a concentration of up to 3.25 g / L, and having an aluminum content of 0.08 g / L or less.

  According to a second aspect of the present invention, there is provided a chemical conversion treatment liquid production method comprising: mixing the first and second concentrated liquids and optionally water to obtain a chemical conversion treatment liquid according to the first aspect. The first concentrated liquid contains magnesium and nitrate ions at higher concentrations than the second concentrated liquid, and the second concentrated liquid contains water-soluble silicate compared to the first concentrated liquid. Methods are provided that contain higher concentrations.

  According to a third aspect of the present invention, there is provided a chemical conversion film forming method comprising subjecting zinc or a zinc alloy to chemical conversion treatment using the chemical conversion treatment liquid according to claim 1 or 2.

  According to the present invention, a chromium-free chemical conversion capable of forming a chemical conversion film excellent in corrosion resistance and appearance without using fluorine and hydrogen peroxide and without a stability problem due to a high silicon concentration. Processing techniques are provided.

A micrograph of a chemical conversion film. Photomicrograph of other chemical conversion films.

Hereinafter, embodiments of the present invention will be described.
We have 1g / L to 12g / L magnesium, 0.03g / L to 5g / L cobalt, 0.7g / L to 3.5g / L silicon, 3g / L to 15g. According to the chemical conversion solution containing / L nitrate ion, silicon as water-soluble silicate, and aluminum content of 0.01 g / L or less, fluorine and hydrogen peroxide are not used. Nevertheless, it has been found that a chemical conversion film excellent in corrosion resistance and appearance can be formed. The inventors changed the composition of the chemical conversion treatment liquid and examined its performance. As a result, it has been surprisingly found that lowering the silicon concentration broadens the acceptable concentration range for components other than silicon and cobalt. The technique described below is based on such knowledge.

  The chemical conversion treatment liquid according to one embodiment of the present invention is a chemical conversion treatment liquid for forming a chemical conversion film on zinc or a zinc alloy. This chemical conversion treatment liquid does not contain chromium, hydrogen peroxide, and fluorine, and typically does not contain aluminum. And this chemical conversion liquid contains magnesium, silicon, and nitrate ion in addition to aqueous solvents, such as water.

  This chemical conversion treatment liquid contains magnesium, for example, as magnesium ions. This chemical conversion treatment liquid may contain magnesium as a complex ion or polyatomic ion or as a combination thereof with magnesium ion.

  The magnesium concentration of the chemical conversion treatment liquid is in the range of 0.5 g / L to 38 g / L, and typically in the range of 2.5 g / L to 25 g / L. When the magnesium concentration is lowered, the corrosion resistance is lowered. When the magnesium concentration is increased, the corrosion resistance is lowered and the appearance is deteriorated.

  This chemical conversion treatment liquid contains silicon as a water-soluble silicate. When this chemical conversion treatment liquid contains silicon in a form other than water-soluble silicate, for example, as colloidal silica, the corrosion resistance and / or the better the chemical conversion treatment liquid contains silicon as water-soluble silicate. Appearance cannot be achieved.

  As a silicate, alkali metal salts, such as sodium silicate and potassium silicate, can be used, for example. As the silicate, a single compound may be used, or a plurality of compounds may be mixed and used.

  The silicon concentration of this chemical conversion solution is in the range of 0.5 g / L to 2.5 g / L, and typically in the range of 1 g / L to 1.6 g / L. When the silicon concentration is lowered, the corrosion resistance is lowered. When the silicon concentration is increased, the corrosion resistance is lowered and the appearance is deteriorated.

  The nitrate ion concentration of this chemical conversion treatment liquid is 0.36 g / L or more, and is typically in the range of 1.82 g / L to 51.06 g / L. When the nitrate ion concentration is lowered, the corrosion resistance is greatly reduced. When the nitrate ion concentration is increased, the corrosion resistance slightly decreases.

  This chemical conversion liquid can further contain cobalt. This chemical conversion treatment liquid may contain cobalt as cobalt ions. Or this chemical conversion liquid may contain cobalt as complex ion or polyatomic ion, or as a combination of them and cobalt ion.

  The cobalt concentration of this chemical conversion solution is 3.25 g / L or less, and is typically in the range of 0.05 g / L to 1.5 g / L. When the cobalt concentration is lowered, the corrosion resistance is slightly lowered. When the cobalt concentration is increased, the corrosion resistance is lowered and the appearance is deteriorated.

  The chemical conversion treatment liquid typically does not contain aluminum, but can contain aluminum at a concentration of 0.08 g / L or less. When the aluminum concentration is increased, the corrosion resistance is lowered and the appearance is deteriorated. The aluminum concentration of this chemical conversion liquid is, for example, 0.03 g / L or less, and typically 0.01 g / L or less.

  This chemical conversion treatment liquid typically contains only magnesium and cobalt as metal elements, or contains only magnesium, cobalt and aluminum as metal elements. This chemical conversion treatment liquid may further contain a metal element other than chromium, magnesium, cobalt and aluminum. For example, this chemical conversion treatment liquid may further contain a metal element such as sodium, potassium and calcium.

  This chemical conversion treatment liquid may further contain colloidal silica as long as sufficient performance is obtained. In this case, the colloidal silica concentration of the chemical conversion treatment liquid is such that the sum of the water-soluble silicate concentration converted to silicon and the colloidal silica concentration converted to silicon is within the range of the silicon concentration described above for the water-soluble silicate, for example. Set as follows.

  This chemical conversion treatment solution may contain only nitric acid as an acid, and may further contain other inorganic acids in addition to nitric acid. As an additional inorganic acid, for example, sulfuric acid, hydrochloric acid, or a combination thereof can be used. The density | concentration of inorganic acids other than nitric acid in this chemical conversion liquid shall be 10 g / L or less, for example.

  This chemical conversion treatment liquid is an acidic solution. The pH value of this chemical conversion solution is, for example, in the range of 1.0 to 5.0, and typically in the range of 1.5 to 3.0.

  When preparing this chemical conversion liquid, as a metal element source such as magnesium and cobalt, for example, nitrate, sulfate, chloride, or a combination of two or more thereof can be used. As the nitrate ion source, for example, nitrates of metals such as nitric acid, magnesium and cobalt, or combinations thereof can be used.

This chemical conversion liquid can be manufactured, for example, by the following method.
First, first and second concentrated liquids are prepared.

The first concentrated liquid contains magnesium. The magnesium concentration in the first concentrated liquid is higher than the magnesium concentration in the chemical conversion liquid. The ratio M _Mg 1 / M _Mg C between the magnesium concentration M _Mg 1 in the first concentrated liquid and the magnesium concentration M _Mg C in the chemical conversion liquid is, for example, in the range of 1.0 to 672.0. It is in the range of 2.0 to 134.0.

  The first concentrated liquid further contains nitrate ions. The nitrate ion concentration in the first concentrated liquid is higher than the nitrate ion concentration in the chemical conversion treatment liquid.

  The first concentrated liquid typically does not contain silicon. The first concentrated liquid may further contain a small amount of silicon as a water-soluble silicate. However, the silicon concentration in the first concentrated liquid is set to a lower value than the silicon concentration in the second concentrated liquid.

  The pH value of the first concentrated liquid is, for example, in the range of 0.5 to 3.0, and typically in the range of 1.0 to 2.0. The first concentrated liquid having a large pH value cannot be stably produced. Further, when the pH value of the first concentrated liquid is small, in order to achieve the optimum pH value in the chemical conversion treatment liquid, it is necessary to further add an alkali to the chemical conversion treatment liquid, and it takes time to prepare the chemical conversion treatment liquid.

The second concentrated liquid contains silicon as a water-soluble silicate. The silicon concentration in the second concentrated liquid is higher than the silicon concentration in the chemical conversion liquid. The ratio M _Si 2 / M _Si C between the silicon concentration M _Si 2 in the second concentrated liquid and the silicon concentration M _Si C in the chemical conversion liquid is, for example, in the range of 1.0 to 18.0, typically It is in the range of 2.0 to 9.0.

  The second concentrated liquid can further contain cobalt. When the second concentrated liquid contains cobalt, the cobalt concentration in the second concentrated liquid is higher than the cobalt concentration in the chemical conversion treatment liquid.

  The pH value of the second concentrated liquid is, for example, in the range of 0.5 to 3.0, and typically in the range of 1.0 to 2.0. The second concentrated liquid having a large pH value tends to have low stability. In addition, when the pH value of the second concentrated liquid is small, in order to achieve the optimum pH value in the chemical conversion treatment liquid, it is necessary to further add alkali to the chemical conversion treatment liquid, and it takes time to prepare the chemical conversion treatment liquid.

Next, the first and second concentrated liquids are mixed. A chemical conversion treatment liquid is obtained as described above.
At least one of the first and second concentrates may be diluted with water before mixing. Alternatively, after the first and second concentrated liquids are mixed, the mixed liquid may be diluted with water. Alternatively, the first and second concentrated liquids and water may be mixed at the same time. Alternatively, the first and second concentrated liquids and the mixed liquid may not be diluted with water.

  As described above, the first concentrated liquid does not contain silicon or contains it at a low concentration. Therefore, the first concentrated liquid is excellent in stability. Moreover, the silicon concentration in the second concentrated liquid is relatively low. Therefore, the second concentrated liquid is also excellent in stability. Therefore, the first and second concentrated liquids can be stored for a long time.

  Here, the production of the chemical conversion treatment liquid using the first and second concentrated liquids has been described, but the chemical conversion treatment liquid may be produced by diluting a single concentrated liquid. For example, you may manufacture by diluting the concentrate containing all the components mentioned above about the chemical conversion liquid with water.

Formation of the chemical conversion film using this chemical conversion liquid is performed, for example, by the following method.
First, an object to be processed made of zinc or a zinc alloy or an object to be processed provided with a layer made of zinc or a zinc alloy on the surface is prepared. As an object to be processed having a surface made of zinc or a zinc alloy, for example, a metal part having a surface provided with a plating layer made of zinc or a zinc alloy is used.

  Next, the surface which consists of zinc or zinc alloy of a to-be-processed object is used for an active process. This activation treatment is performed, for example, by bringing a nitric acid aqueous solution into contact with the surface of the object to be treated made of zinc or a zinc alloy. For example, the object to be treated is immersed in an aqueous nitric acid solution.

  After the activated treatment object is washed with water, the treatment object is subjected to chemical conversion treatment. That is, the chemical conversion liquid mentioned above is brought into contact with the object to be processed. For example, the object to be processed is immersed in the chemical conversion solution. At this time, the temperature of the chemical conversion solution is, for example, in the range of 10 ° C. to 80 ° C., and typically in the range of 30 ° C. to 50 ° C. Further, the time for which the chemical conversion treatment liquid is brought into contact with the object to be processed is, for example, in the range of 30 seconds to 600 seconds, and typically in the range of 60 seconds to 180 seconds.

After the chemical conversion treatment, the processed material is washed with water, and then subjected to a drying process. For example, the object to be treated is naturally dried or heated to a temperature higher than room temperature and dried. A drying temperature shall be 150 degrees C or less, for example.
As described above, a chemical conversion film is formed on the surface of the non-treated product.

  This method does not use chromium, fluorine or hydrogen peroxide. Nevertheless, according to this method, a chemical conversion film having excellent corrosion resistance and appearance can be formed.

  In particular, according to this method, excellent corrosion resistance can be achieved even when the workpiece has a complicated shape. That is, generally, when the workpiece has a concave portion and / or a convex portion on the surface like a bolt, it is difficult to achieve excellent corrosion resistance at the edge portion. On the other hand, according to the method described above, excellent corrosion resistance can be achieved even when the object to be processed has a concave portion and / or a convex portion on the surface like a bolt.

  Moreover, the chemical conversion treatment liquid used here has a low silicon concentration. Therefore, the silicon concentration in the concentrate used for the production of this chemical conversion treatment liquid can be made relatively low. A concentrated solution having a low silicon concentration is unlikely to gel even when stored for a long period of time.

  Moreover, the chemical conversion liquid used here has a wide allowable concentration range for components other than silicon and cobalt as described above. The wide concentration range that can be tolerated for nitrate ions is advantageous, for example, in the following respects.

  In the method described above, prior to bringing the chemical conversion treatment liquid into contact with the object to be treated, the object to be treated is subjected to an activation treatment using an aqueous nitric acid solution and a water washing treatment. When performing the activation treatment, the water washing treatment, and the chemical conversion treatment in the activation treatment tank containing the aqueous nitric acid solution, the water washing treatment tank containing the water, and the chemical treatment tank containing the chemical treatment liquid, respectively, the aqueous nitric acid solution in the active treatment tank A part of the water is mixed in the water in the water washing tank, and the water in the water washing tank containing nitric acid is mixed in the chemical conversion liquid in the chemical conversion tank. Therefore, as the treatment is repeated, the nitrate ion concentration in the chemical conversion treatment solution increases.

  If the water in the rinsing tank is frequently changed or the running water is always supplied to the rinsing tank, an increase in the nitrate ion concentration in the chemical conversion solution can be suppressed. However, doing this may require new equipment costs or increase operating costs.

  When the concentration range acceptable for nitrate ions is wide, an increase in the concentration of nitrate ions in the chemical conversion solution has a small effect on the performance of the conversion coating. Therefore, a chemical conversion film having excellent performance can be formed over a long period of time without frequently changing the water in the washing treatment tank.

  Moreover, in the chemical conversion treatment liquid used here, cobalt is an optional component. Nickel, chromium, cobalt, etc. are mentioned as an example of the metal which is easy to cause a metal allergy. Cobalt is a metal with a small environmental load compared to nickel and the like, and its use is hardly regulated at present. However, in Europe, where interest in environmental pollution is high, efforts are being made to reduce the amount of cobalt used. The absence of cobalt or the low cobalt concentration is also advantageous in this respect.

  In addition, although the organic acid free chemical conversion treatment liquid and the formation method of the chemical conversion film using the same have been described here, the chemical conversion treatment liquid may contain an organic acid.

  Moreover, you may perform the process which uses a finishing agent after the chemical conversion process mentioned above. For example, the object to be processed may be immersed in the finishing treatment liquid after the chemical conversion treatment and the water washing and before the drying treatment.

The tests conducted in connection with the present invention are described below.
<Test 1>
In this test, the effect of the concentration of water-soluble silicate on the stability of the concentrate was examined by the following method.

First, aqueous solutions 8A to 8K having different silicate concentrations were prepared. Here, anhydrous sodium metasilicate was used as the silicate. These solutions 8A to 8K were left at room temperature for 12 months. And the state of the liquid after 12 months passed was visually evaluated. Table 1 below shows the silicon concentrations and evaluation results of the solutions 8A to 8K used here.

  In Table 1, the symbol “◯” indicates that no sign of gelation, that is, no increase in viscosity was observed in the liquid. The symbol “Δ” represents that the viscosity of the liquid has slightly increased. The symbol “x” indicates that a part of the liquid is completely gelled.

  As shown in Table 1, no gelation occurred when the silicon concentration was 10 g / L or less, and no sign of gelation was observed when the silicon concentration was 9 g / L or less. Therefore, for example, when the silicate concentration in the chemical conversion liquid is 1/3 or less of the silicate concentration in the concentrate, the silicate concentration in the chemical conversion liquid is 3.3 g / L in consideration of the stability of the concentrate. Or less, more preferably 3 g / L or less.

<Test 2>
In this test, the effect of the magnesium concentration of the chemical conversion solution on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

  First, a plurality of steel parts were galvanized. As the steel part, an M8 bolt having a total length of 50 mm and a screw part length of 25 mm was used. As the plating bath, a zincate bath (Norcian / alkaline zinc plating process SurTec 704) was used. Barrel plating was used for galvanization. The thickness of these plating layers was in the range of 10 μm to 12 μm. Hereinafter, a steel part subjected to galvanization is referred to as a “galvanized part”.

Next, they were thoroughly washed with water and subsequently subjected to an activation treatment. This activation treatment was performed by immersing the galvanized part in a 1% nitric acid aqueous solution. These were sufficiently washed with water and further subjected to chemical conversion treatment using chemical conversion liquids 9A to 9Q. Table 2 below shows the compositions of the treatment liquids 9A to 9Q used here.

  Treatment liquid 9A was prepared by mixing sodium nitrate, anhydrous sodium metasilicate, cobalt chloride hexahydrate, and pure water. Treatment liquids 9B to 9Q were prepared by mixing magnesium chloride hexahydrate, sodium nitrate, anhydrous sodium metasilicate, cobalt chloride hexahydrate, and pure water.

  In addition, the chemical conversion treatment using the treatment liquids 9A to 9Q was performed at a treatment temperature of 40 ° C. and an immersion time of 120 seconds. The pH values of the treatment liquids 9A to 9Q were adjusted to about 2.0 using sulfuric acid.

  After finishing the chemical conversion treatment, the galvanized parts were sufficiently washed with water and dried at 100 ° C. for 5 minutes. As described above, a chemical conversion film was formed on the surface of the galvanized component.

  Next, the appearance of the chemical conversion film thus obtained was evaluated. Specifically, the evaluation regarding gloss and interference color was performed. Here, regarding the gloss and interference color, the evaluation when the gloss and interference color are recognized without any unevenness is “○”, and the evaluation when the image appears slightly cloudy or the interference color is slightly uneven is evaluated. The evaluation was “X” when “Δ” was observed as being cloudy in many parts or when the interference color was markedly uneven. The evaluation results are summarized in Table 2 above.

  Next, the corrosion resistance of the galvanized parts after the surface treatment was evaluated according to the salt spray test method specified in Japanese Industrial Standard JIS Z 2371 (2000). Here, when the salt spray test was continued for 72 hours, the area ratio of the corrosion products generated in the galvanized parts to the entire parts (hereinafter referred to as corrosion product generation rate) was measured.

  The evaluation when the corrosion product is not generated is “A”, the evaluation when the corrosion product generation rate is larger than 0% and 5% or less is “B”, and the corrosion product generation rate is 5%. The evaluation when the value was 10% or less was “C”, the evaluation when the corrosion product generation rate was greater than 10% and 50% or less was “D”, and the corrosion product generation rate was greater than 50%. In this case, the evaluation was “E”. The evaluation results are summarized in Table 2 above.

  As shown in Table 2 above, when the magnesium concentration was in the range of 0.2 g / L to 40.0 g / L, sufficient performance with respect to gloss and interference color could be achieved. When the magnesium concentration is in the range of 5.0 g / L to 38.0 g / L, excellent performance with respect to gloss and interference color can be achieved. The chemical conversion film obtained using the treatment liquids 9B to 9F was lightly colored. Moreover, the color unevenness was conspicuous in the chemical conversion film obtained using the treatment liquid 9P.

  Further, as shown in Table 2, sufficient corrosion resistance could be achieved when the magnesium concentration was in the range of 0.5 g / L to 38.0 g / L. And when magnesium concentration exists in the range of 2.5 g / L thru | or 25.0 g / L, the outstanding corrosion resistance was able to be achieved.

<Test 3>
In this test, the influence of the nitrate ion concentration of the chemical conversion treatment liquid on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

  First, a chemical conversion film was formed on the surface of the galvanized component by the same method as described in Test 2 except that chemical conversion liquids 10A to 10V were used instead of chemical conversion liquids 9A to 9Q. The treatment liquid 10A was prepared by mixing magnesium chloride hexahydrate, anhydrous sodium metasilicate, cobalt chloride hexahydrate, and pure water. The treatment liquids 10B to 10V were prepared by mixing magnesium chloride hexahydrate, sodium nitrate, anhydrous sodium metasilicate, cobalt chloride hexahydrate, and pure water.

Next, the appearance and corrosion resistance of the chemical conversion film thus obtained were evaluated by the same method as described in Test 2. Table 3 below summarizes the compositions and evaluation results of the treatment liquids 10A to 10V.

  As shown in Table 3 above, when the nitrate ion concentration was 0.15 g / L or more, sufficient performance with respect to gloss and interference color could be achieved. When the nitrate ion concentration is in the range of 0.73 g / L to 218.82 g / L, excellent performance with respect to gloss and interference color can be achieved. The chemical conversion film obtained using the treatment liquids 10B to 10D was slightly lightly colored. In addition, some color unevenness was observed in the chemical conversion film obtained using the treatment liquid 10V.

  Further, as shown in Table 3 above, when the nitrate ion concentration was 0.36 g / L or more, sufficient corrosion resistance could be achieved. And when the nitrate ion concentration was in the range of 1.82 g / L to 51.06 g / L, excellent corrosion resistance could be achieved.

<Test 4>
In this test, the effect of the silicon concentration of the chemical conversion solution on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

  First, a chemical conversion film was formed on the surface of the galvanized component by the same method as described in Test 2 except that chemical conversion liquids 11A to 11R were used instead of chemical conversion liquids 9A to 9Q. The treatment liquid 11A was prepared by mixing magnesium chloride hexahydrate, sodium nitrate, cobalt chloride hexahydrate, and pure water. The treatment liquids 11B to 11R were prepared by mixing magnesium chloride hexahydrate, sodium nitrate, anhydrous sodium metasilicate, cobalt chloride hexahydrate, and pure water.

Next, the appearance and corrosion resistance of the chemical conversion film thus obtained were evaluated by the same method as described in Test 2. Table 4 below summarizes the compositions and evaluation results of the treatment liquids 11A to 11R.

  As shown in Table 4 above, when the silicon concentration was in the range of 0.4 g / L to 3.5 g / L, sufficient performance with respect to gloss and interference color could be achieved. When the silicon concentration is in the range of 0.6 g / L to 3.0 g / L, excellent performance with respect to gloss and interference color can be achieved.

  Further, as shown in Table 4 above, sufficient corrosion resistance could be achieved when the silicon concentration was in the range of 0.5 g / L to 2.5 g / L. And when the silicon concentration was in the range of 1.0 g / L to 1.6 g / L, excellent corrosion resistance could be achieved.

<Test 5>
In this test, the effect of the silicon concentration of the chemical conversion solution on the structure of the chemical conversion film was examined by the following method.

  First, a chemical conversion treatment liquid similar to the treatment liquid 9J was prepared except that the silicon concentration was 3 g / L. Hereinafter, this chemical conversion treatment liquid is referred to as “chemical conversion treatment liquid 9R”. Next, a chemical conversion film was formed on the surface of the galvanized component by the same method as described above except that this chemical conversion treatment liquid 9R was used. Each of the chemical conversion film thus obtained and the chemical conversion film obtained using the treatment liquid 9J was photographed with a scanning electron microscope.

  FIG. 1 is a photomicrograph of the chemical conversion film obtained using the treatment liquid 9R. FIG. 2 is a photomicrograph of the chemical conversion film obtained using the treatment liquid 9J.

  When the magnesium concentration in the chemical conversion treatment liquid is relatively high, if the silicon concentration in the chemical conversion treatment liquid is increased, a chemical conversion film having cracks tends to be obtained as shown in FIG. On the other hand, even if the magnesium concentration in the chemical conversion solution is relatively high, a dense chemical conversion film can be obtained as shown in FIG. 2 if the silicon concentration in the chemical conversion solution is lowered.

<Test 6>
In this test, the effect of the cobalt concentration of the chemical conversion solution on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

  First, a chemical conversion film was formed on the surface of the galvanized component by the same method as described in Test 2 except that chemical conversion liquids 12A to 12P were used instead of chemical conversion liquids 9A to 9Q. The treatment liquid 12A was prepared by mixing magnesium chloride hexahydrate, sodium nitrate, anhydrous sodium metasilicate, and pure water. The treatment liquids 12B to 12P were prepared by mixing magnesium chloride hexahydrate, sodium nitrate, anhydrous sodium metasilicate, cobalt chloride hexahydrate, and pure water.

Next, the appearance and corrosion resistance of the chemical conversion film thus obtained were evaluated by the same method as described in Test 2. Table 5 below summarizes the compositions and evaluation results of the treatment liquids 12A to 12P.

  As shown in Table 5 above, when the cobalt concentration was 3.75 g / L or less, sufficient performance with respect to gloss and interference color could be achieved. And when cobalt concentration was 3.25 g / L or less, the outstanding performance regarding glossiness and interference color was able to be achieved.

  Moreover, as shown in the said Table 5, when the cobalt concentration was 3.25 g / L or less, sufficient corrosion resistance was able to be achieved. And when the cobalt concentration was in the range of 0.05 g / L to 1.5 g / L, excellent corrosion resistance could be achieved.

<Test 7>
In this test, the effect of the aluminum concentration of the chemical conversion treatment liquid on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

  First, a chemical conversion film was formed on the surface of the galvanized component by the same method as described in Test 2 except that chemical conversion liquids 13A to 13P were used instead of chemical conversion liquids 9A to 9Q. The chemical conversion liquids 13A to 13P all contain aluminum as shown in Table 6 below. Here, aluminum nitrate nonahydrate was used as the aluminum source.

  Next, the appearance and corrosion resistance of the chemical conversion film thus obtained were evaluated by the same method as described in Test 2 except that the duration of the salt spray test was 24 hours. In addition, regarding the occurrence of white powder, the evaluation when the white powder was not observed on the surface was “◯”, and the area ratio of the white powder generated on the galvanized part to the whole part was greater than 0% and 50% or less Was evaluated as “Δ”, and when this area ratio was larger than 50%, the evaluation was “x”.

Table 6 below summarizes the compositions and evaluation results of the treatment liquids 13A to 13P.

  As shown in Table 6 above, when the aluminum concentration was 0.50 g / L or more, sufficient performance with respect to gloss and interference color could not be achieved. And when aluminum concentration was 0.10 g / L or more, sufficient performance was not able to be achieved regarding corrosion resistance, and generation | occurrence | production of white powder was recognized.

<Test 8>
In this test, the effect of the type of metal in the chemical conversion solution on the appearance and corrosion resistance of the chemical conversion film was examined by the following method.

  First, a chemical conversion film was formed on the surface of the galvanized component by the same method as described in Test 2 except that chemical conversion liquids 14A to 14E were used instead of chemical conversion liquids 9A to 9Q. In addition, as shown in Table 7 below, each of the chemical conversion liquids 14A to 14E contains another metal instead of magnesium. In preparing the chemical conversion liquids 14A to 14E, sodium molybdate, sodium tungstate, dipotassium hexafluorozirconate, aluminum nitrate, and titanium chloride were used as metal sources instead of the magnesium source.

Next, the appearance and corrosion resistance of the chemical conversion film thus obtained were evaluated by the same method as described in Test 2 except that the duration of the salt spray test was set to 50 hours. Table 7 below summarizes the compositions and evaluation results of the treatment liquids 14A to 14E.

  When magnesium was replaced with molybdenum, zirconium or titanium, excellent performance with respect to gloss and interference color could be achieved as shown in Table 7 above, and sufficient performance could be achieved with respect to the occurrence of white powder. . However, in this case, sufficient performance with respect to corrosion resistance could not be achieved.

  Further, when magnesium was replaced with tungsten, as shown in Table 7 above, sufficient performance with respect to gloss and interference color could be achieved. However, in this case, sufficient performance with respect to corrosion resistance could not be achieved. In this case, sufficient performance could not be achieved with respect to the occurrence of white powder.

  When magnesium was replaced with aluminum, as shown in Table 7 above, sufficient performance with respect to gloss and interference color and corrosion resistance could not be achieved. In this case, sufficient performance could not be achieved with respect to the occurrence of white powder.

Claims (4)

A chemical conversion treatment liquid for forming a chemical conversion film on zinc or a zinc alloy containing no chromium, hydrogen peroxide and fluorine, and containing 0.5 g / L to 38 g / L of magnesium and 0.5 g / L to 2.5 g / L of silicon and 0.36 g / L or more of nitrate ions, including the silicon as a water-soluble silicate, and optionally cobalt up to a concentration of 3.25 g / L Further, a chemical conversion treatment liquid containing aluminum and having an aluminum content of 0.08 g / L or less (however, for forming a chemical conversion film on zinc or a zinc alloy not containing chromium, hydrogen peroxide and fluorine) A chemical conversion treatment solution comprising 1 g / L to 12 g / L magnesium, 0.03 g / L to 5 g / L cobalt, 0.7 g / L to 3.5 g / L silicon, and 3 g / L to Containing 15 g / L of nitrate ions, Include hydrogen as a water-soluble silicate, the content of aluminum except for chemical conversion treatment liquid is not more than 0.01 g / L).   The concentration of magnesium is in the range of 2.5 g / L to 25 g / L, the concentration of cobalt is in the range of 0.05 g / L to 1.5 g / L, and the concentration of silicon is 1 g / L to 1. The chemical conversion solution according to claim 1, wherein the concentration of nitrate ions is in the range of 6 g / L and the concentration of nitrate ions is in the range of 1.8 g / L to 51 g / L. A chemical conversion treatment liquid for mixing a first and second concentrated liquid and optionally water to form a chemical conversion film on zinc or a zinc alloy which does not contain chromium, hydrogen peroxide and fluorine. 0.5 g / L to 38 g / L of magnesium, 0.5 g / L to 2.5 g / L of silicon, and 0.36 g / L or more of nitrate ions. A method for producing a chemical conversion treatment solution comprising obtaining a chemical conversion treatment solution containing a salt, optionally further containing cobalt at a concentration of up to 3.25 g / L, and an aluminum content of 0.08 g / L or less. The first concentrated liquid contains magnesium and nitrate ions at a higher concentration than the second concentrated liquid, and the second concentrated liquid contains a water-soluble silicate in the first concentrated liquid. Contained at a higher concentration compared to   A method for forming a chemical conversion film, comprising subjecting zinc or a zinc alloy to chemical conversion treatment using the chemical conversion treatment solution according to claim 1.

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