JP2001123274A - High corrosion resistance surface treated magnesium alloy product and producing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high corrosion resistance surface treated magnesium alloy product using a nonchromate treating solution capable of attaining corrosion resistance equal to or above that by chemical convertion treatment using a chromate bath without being incorporated with hexavalent chromium and heavy metals and to provide such a high corrosion resistance surface treated magnesium alloy product. SOLUTION: As to this method for producing a high corrosion resistance surface treated magnesium alloy product, the surface of an aluminum-containing magnesium alloy is subjected to chemical convertion treatment for 0.3 to 10 min with a treating solution in which the concentration of the water soluble salt of permanganic acid or manganic acid is >=2 g/L expressed in terms of the content of KMnO4 and also less than the solubility thereof, the concentration of the water soluble salt of phosphoric acid is 0.05 to 100 g/L expressed in terms of the content of Na3PO4, the concentration of acetic acid is 0.05 to 100 ml/L, the concentration of sodium acetate is 0.05 to 50 g/L, pH is <=7, and solution temperature is 288 to 368K, and the high corrosion resistance surface treated magnesium alloy product is obtained by the producing method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly corrosion-resistant surface-treated magnesium alloy product obtained by subjecting a surface of an aluminum-containing magnesium alloy to a chemical conversion treatment, and more particularly to a method for producing the same. It is manufactured by chemical conversion treatment with a liquid.
The present invention relates to a highly corrosion-resistant surface-treated magnesium alloy having a corrosion resistance equal to or higher than that of a chromate-treated product chemically converted with a treatment solution containing valent chromium and having high recyclability, and a method for producing the same.

[0002]

2. Description of the Related Art As a chemical conversion bath for magnesium alloys, especially for magnesium alloys containing aluminum, JIS
Three types of H8651 standard and JP-A-8-225954
The chromate bath described in Japanese Patent Publication No.
11 types of the IS H8651 standard and JP-A-8-350
No. 73, Jan Ivar Skar, et al., SAE Technical P
aper Series, 970324, pp7-11, 1997, David Hawke, e
Chemical conversion baths containing a permanganic acid or a water-soluble salt of manganic acid are known from, for example, Japanese Patent Application Laid-Open No. 57-41.
A chemical conversion bath containing a water-soluble salt of permanganic acid and a titanium salt and / or a zirconium salt described in JP-A-376-376 and JP-A-11-36082 is known.

[0003]

A high corrosion-resistant surface-treated magnesium alloy product can be obtained by chemical conversion using a chromate bath, but hexavalent chromium contained in the chromate bath is a harmful substance. When a magnesium alloy is subjected to chemical conversion treatment using a chemical conversion bath containing heavy metal salts, the degree of corrosion resistance is insufficient, and when those heavy metals become impurities during recycling, it is difficult to adjust the alloy composition. Become.

Some magnesium alloys contain manganese, such as AZ alloys used in the field of electronic equipment and AM used in the field of automobile parts.
Manganese is contained in an aluminum-containing magnesium alloy such as a base alloy in an amount of about 0.1 to 0.5% by weight. Therefore, when a magnesium alloy is subjected to a chemical conversion treatment using a chemical conversion bath containing a water-soluble salt of permanganic acid or manganese acid, a highly recyclable corrosion-resistant surface-treated magnesium alloy can be obtained. Is not always satisfactory, and further improvement is required.

[0005] The present invention provides a non-volatile chemical compound capable of achieving corrosion resistance equivalent to or higher than that of a chemical conversion treatment using a chromate bath without containing hexavalent chromium which is a harmful substance or heavy metal which becomes an impurity at the time of recycling. An object of the present invention is to provide a method for producing a highly corrosion-resistant surface-treated magnesium alloy product by using a chromate treatment solution, and a highly corrosion-resistant surface-treated magnesium alloy product obtained by using such a treatment solution.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above-mentioned object, and as a result, have found that a treatment solution containing a water-soluble salt of permanganic acid or manganese acid and a water-soluble salt of phosphoric acid. Furthermore, by adding acetic acid and sodium acetate as pH adjusters and maintaining the pH of the treatment solution at 7 or less, the surface of the aluminum-containing magnesium alloy can be subjected to chemical conversion treatment at a relatively low treatment temperature and a relatively short treatment time. ,
A high corrosion resistant surface-treated magnesium alloy product was obtained, and the life of such a treatment solution was long (the area of the surface of the aluminum-containing magnesium alloy that can be treated per unit volume of treatment solution was large), and the present invention was completed. did.

That is, according to the method for producing a highly corrosion-resistant surface-treated magnesium alloy product of the present invention, the surface of an aluminum-containing magnesium alloy is treated with a permanganic acid or a water-soluble salt of manganic acid having a concentration of 2 g / km2 in terms of KMnO _4. 1 to less than the solubility, preferably 3 to 60 g / l, more preferably 5 to 55 g / l, and the concentration of the water-soluble salt of phosphoric acid is Na
₃ in terms of PO ₄ weight 0.05 to 100 g / l, preferably 0.05~30g / l, more preferably 0.1 to 1
0 g / l, and the concentration of acetic acid is 0.05 to 100 ml /
l, preferably 0.1 to 50 ml / l, more preferably 1 to 20 ml / l, and the concentration of sodium acetate is 0.1 ml.
The pH is from 0.5 to 50 g / l, preferably from 0.1 to 50 g / l, more preferably from 1 to 20 g / l, and the pH is 7 or less, preferably from 2.3 to 6, more preferably from 3 to 5, Temperature is 288-368K, preferably 293-353K,
More preferably, the treatment liquid having a temperature of 303 to 333 K is 0.3
The chemical conversion treatment is performed for 10 to 10 minutes, preferably 0.4 to 7 minutes, more preferably 0.5 to 3 minutes.

Further, the high corrosion resistant surface treated magnesium of the present invention is also provided.
Alloy product is obtained by the above manufacturing method,
100-600mg / m^TwoAnd the amount of P attached is
200mg / m^TwoAnd CH_ThreeCOO^-Adhesion amount
0.01 to 1000 mg / m ^TwoIs characterized by
You.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As the aluminum-containing magnesium alloy subjected to the chemical conversion treatment in the production method of the present invention, all aluminum-containing magnesium alloys practically used in various technical fields, for example, AZ-based, AM-based, AM (Ca
) -Based and AS-based magnesium alloys, so that the aluminum content is generally about 2 to 12% by weight. Further, the form of the aluminum-containing magnesium alloy product to be subjected to the chemical conversion treatment in the present invention includes a mold casting,
Sand casting, die casting, wrought material and the like can be exemplified.

Before the surface of the aluminum-containing magnesium alloy is subjected to the chemical conversion treatment, it is preferable that the surface of the aluminum-containing magnesium alloy is solvent-degreased, pre-treated, and then dried after the chemical conversion treatment. The solvent degreasing can be performed, for example, by performing ultrasonic cleaning in acetone for 15 minutes.

In the pretreatment, for example, the substrate is immersed in an aqueous solution of potassium pyrophosphate at a concentration of 35 g / l at 60 ° C. for 1 minute,
Thereafter, washing with pure water and washing with pure water are performed, and then immersion for 3 minutes in an aqueous solution of caustic soda concentration of 50 g / l at 60 ° C., followed by washing with pure water and washing with pure water. The above solvent degreasing conditions and pretreatment conditions are merely examples of solvent degreasing and pretreatment, and any other solvent degreasing and pretreatment conditions can be employed.

The chemical conversion treatment solution used in the production method of the present invention contains a water-soluble salt of permanganic acid or manganic acid, preferably an alkali metal salt such as a potassium salt, a sodium salt or a lithium salt, or a magnesium salt or the like. May be contained, and in addition, an ammonium salt may be contained. The concentration of the permanganic acid or the water-soluble salt of manganic acid in the chemical conversion treatment solution is 2 in terms of the amount of KMnO _4.
g / l or more and solubility or less, preferably 3 to 60 g / l,
More preferably 5-55 g / l, even more preferably 15-55 g / l.
45 g / l. The concentration of the permanganic acid or the water-soluble salt of manganic acid in the chemical conversion treatment solution is 2 in terms of KMnO ₄ amount.
If it is less than g / l, the corrosion resistance of the magnesium alloy surface after the chemical conversion treatment tends to be insufficient. Further, the water-soluble salt of permanganic acid or manganese acid can exist up to the solubility in the chemical conversion treatment solution, but the concentration of the water-soluble salt of permanganic acid or manganese acid in the chemical conversion treatment solution becomes higher than a certain level. since not seen improvement in the corrosion resistance commensurate with it, in terms of KMnO ₄ amount, preferably 60 g /
1 or less, more preferably 55 g / l or less, and even more preferably 45 g / l or less.

The chemical conversion solution used in the production method of the present invention is
A water-soluble salt of an acid, preferably Na_ThreePO_Four, Na
_TwoHPO_Four, NaH_TwoPO_Four, NH_FourH_TwoPO_Four, Mn
(H _TwoPO_Four)_Two, Zn (H_TwoPO_Four)_TwoContains etc.
be able to. Concentration of water-soluble salt of phosphoric acid in chemical conversion solution
Is Na_ThreePO_Four0.05-100g /
l, preferably 0.05 to 30 g / l, more preferably
0.1 to 10 g / l. Water of phosphoric acid in chemical conversion solution
When the soluble salt is Na_ThreePO_Four0.05 g / l in terms of quantity
If it is full, the magnesium alloy surface after chemical conversion
Eating habits tend to be inadequate. In addition, chemical conversion treatment
Even if the concentration of the water-soluble salt of phosphoric acid becomes higher than a certain level
There is no corresponding improvement in corrosion resistance._Three
PO_FourGenerally, 100 g / l or less in terms of amount is preferable.
30 g / l or less, more preferably 10 g / l or less
To

The chemical conversion solution used in the production method of the present invention is p
Acetic acid and sodium acetate are contained as H regulators. The concentration of acetic acid in the chemical conversion treatment solution is 0.05 to 100 ml / l,
Preferably 0.1 to 50 ml / l, more preferably 1 to 50 ml / l
20 ml / l and a concentration of sodium acetate of 0.05
５０50 g / l, preferably 0.1-50 g / l, more preferably 1-20 g / l. When the concentration of acetic acid in the chemical conversion treatment liquid is less than 0.05 ml / l and / or the concentration of sodium acetate is less than 0.05 g / l, the corrosion resistance of the magnesium alloy surface after the chemical conversion treatment tends to be insufficient. is there. Further, even if the concentrations of acetic acid and sodium acetate in the chemical conversion treatment solution are higher than a certain level, no corresponding improvement in corrosion resistance is observed.
ml / l or less, preferably 50 ml / l or less, more preferably 20 ml / l or less, and the concentration of sodium acetate is 50 g / l or less, preferably 50 g / l or less.
More preferably, it is 20 g / l or less.

[0015] The p of the chemical conversion treatment solution used in the production method of the present invention.
H is maintained at 7 or less. PH of chemical conversion solution is 7
If higher, the chemical conversion reaction becomes extremely slow,
The required processing time becomes extremely long and impractical.
On the other hand, if the pH of the chemical conversion treatment solution is too low, smut tends to be easily formed, and if only acetic acid and sodium acetate are used as pH adjusters, the minimum achievable pH value is about 2.3. The pH of the chemical conversion treatment liquid is preferably 2.3 to 6, more preferably 3 to 5. In addition, when lowering the pH of the chemical conversion treatment solution to 2.3 or less, a mineral acid or the like can be added as an auxiliary component.

The temperature of the chemical conversion treatment solution used in the production method of the present invention is maintained at 288 to 368K. When the temperature of the chemical conversion treatment liquid is lower than 288 K, the chemical conversion treatment reaction becomes slow, and the required treatment time becomes long, which is not practical.
On the other hand, even when the temperature of the chemical conversion treatment solution is higher than 368K, the corrosion resistance of the magnesium alloy surface after the chemical conversion treatment is not improved, and even the tendency of deterioration is recognized, which is disadvantageous in terms of production cost. . In the production method of the present invention, the temperature of the chemical conversion treatment solution is preferably 293 to 353.
K, more preferably 303-333K.

In the production method of the present invention, the chemical conversion treatment time is 0.3 to 10 minutes. When the chemical conversion treatment time is less than 0.3 minutes, the corrosion resistance of the magnesium alloy surface after the chemical conversion treatment tends to be insufficient, and even when the chemical conversion treatment time exceeds 10 minutes, the corrosion resistance corresponding to the chemical conversion treatment time exceeds 10 minutes. Since no improvement is seen, production costs will increase. In the production method of the present invention, the chemical conversion treatment time is preferably 0.4 to 7 minutes, more preferably 0.5 to 3 minutes.

After the chemical conversion treatment under the above conditions, the product is washed with water and pure water, and then dried. Drying is generally carried out at 10 to 80 ° C. for 10 to 120 minutes. The chemical conversion treatment liquid used in the present invention has an extremely long life when used in the chemical conversion treatment under the above conditions, that is, the area of the surface of the aluminum-containing magnesium alloy that can be treated per unit volume of the treatment liquid is extremely large.

The amount of Mn deposited on the surface of the surface-treated magnesium alloy product obtained by the production method of the present invention is 100 to 60.
0 mg / m ² , the P adhesion amount is 200 mg / m ² or less, and the CH ₃ COO ⁻ adhesion amount is 0.01 to 1000 m.
g / m ^2, which is believed to result in improved corrosion resistance of the alloy product.

Further, the surface of the surface-treated magnesium alloy product obtained by the production method of the present invention has improved coating adhesion at the time of coating, and has the same coating adhesion as a chromate-treated product. Since there is a high possibility that the adhered Mn is adhered as manganese dioxide, the film resistance is expected to be low, and it is considered that the effect is also obtained with respect to the electromagnetic shielding required for electronic devices and the like.

[0021]

The present invention will be specifically described below based on examples and comparative examples. Examples 1 to 9 Many test pieces made of a magnesium alloy (AZ91) were subjected to ultrasonic cleaning in acetone at room temperature for 15 minutes, and dried at room temperature for 5 minutes. Next, it was immersed in an aqueous potassium pyrophosphate solution (35 g / l, 60 ° C.) for 1 minute, and then washed with tap water at room temperature for 30 seconds and with pure water at room temperature for 30 minutes.
Seconds. Next, a sodium hydroxide aqueous solution (50 g / l, 6
(0 ° C.) for 3 minutes, followed by washing with tap water at room temperature for 30 seconds and pure water at room temperature for 30 seconds.

Each of the test pieces treated as described above was then subjected to KMnO ₄ , Na ₃ PO ₄ , CH ₃ COOH and C
Each containing H ₃ COONa at the concentrations shown in Table 1,
It was immersed in a chemical conversion treatment solution having the pH value and the treatment temperature shown in Table 1 for the treatment time shown in Table 1, and then washed with tap water at room temperature for 30 seconds and pure water at room temperature for 30 seconds. Finally, drying was performed at room temperature for 2 hours.

Each of the test pieces which had been subjected to the chemical conversion treatment and dried as described above was subjected to a corrosion resistance test according to JIS Z 2371, and the state after 24 hours was evaluated by the rating number method. The results were as shown in Table 1.

An acrylic baking paint is applied to the surface of each of the test pieces which have been subjected to the chemical conversion treatment and dried as described above by a dip coating method, and is left to stand for 10 minutes, followed by heating and drying at 150 ° C. for 20 minutes. Carried out. After that, JIS K5
Cross cut tape method (1 mm
(Interval) to carry out a coating adhesion test. The results were as shown in Table 1.

COMPARATIVE EXAMPLE 1 A test piece made of a magnesium alloy (AZ91) was degreased with a solvent, pretreated and washed with water in the same manner as in the above example.
A chemical conversion treatment was carried out in accordance with the three types of JIS H8651 standards, that is, under the treatment conditions shown in Table 1, followed by rinsing with hot water, rinsing with water and drying as in the above Examples. The test piece obtained in Comparative Example 1 was also subjected to a corrosion resistance test and a paint adhesion test in the same manner as in the above-described example. The results are as shown in Table 1.

Comparative Example 2 A test piece made of a magnesium alloy (AZ91) was degreased with a solvent, pretreated and washed with water in the same manner as in the above example.
According to the method described in JP-A-8-225954,
That is, they were subjected to chemical conversion treatment under the treatment conditions shown in Table 1, and then washed and dried in the same manner as in the above Examples. The test piece obtained in Comparative Example 2 was also subjected to a corrosion resistance test and a paint adhesion test in the same manner as in the above-described example. The results are as shown in Table 1.

Comparative Example 3 A test piece made of a magnesium alloy (AZ91) was degreased with a solvent, pretreated and washed with water in the same manner as in the above example.
A chemical conversion treatment was carried out according to the method described in JP-A-8-35073, that is, under the treatment conditions shown in Table 1, and then washed and dried in the same manner as in the above Examples. The test piece obtained in Comparative Example 3 was also subjected to a corrosion resistance test and a paint adhesion test in the same manner as in the above example. The results are as shown in Table 1.

Comparative Example 4 A test piece made of a magnesium alloy (AZ91) was degreased with a solvent, pretreated and washed with water in the same manner as in the above example.
Jan Ivar Skar, et al., SAE Technical PaperSeries,
970324, pp7-11, 1997, that is, they were subjected to chemical conversion treatment under the treatment conditions shown in Table 1, and then washed with water and dried as in the above Examples. The test piece obtained in Comparative Example 4 was also subjected to a corrosion resistance test and a paint adhesion test in the same manner as in the above example. The results are as shown in Table 1.

Comparative Examples 5 to 6 A test piece made of a magnesium alloy (AZ91) was degreased with a solvent, pretreated, and washed with water in the same manner as in the above-described example.
David Hawke, et al., Metal Finishing 93, 10, pp34-
Chemical conversion treatment was carried out according to the method described in No. 38, 1995, that is, under the treatment conditions shown in Table 1, followed by washing with water and drying as in the above examples. The test pieces obtained in Comparative Examples 5 and 6 were also subjected to a corrosion resistance test and a paint adhesion test in the same manner as in the above Examples. The results are as shown in Table 1.

Example 10 A number of test pieces made of a magnesium alloy (AZ91) were subjected to ultrasonic cleaning in acetone at room temperature for 15 minutes and dried at room temperature for 5 minutes. Next, it was immersed in an aqueous potassium pyrophosphate solution (35 g / l, 60 ° C.) for 1 minute, and then washed with tap water at room temperature for 30 seconds and with pure water at room temperature for 30 minutes.
Seconds. Next, a sodium hydroxide aqueous solution (50 g / l, 6
(0 ° C.) for 3 minutes, followed by washing with tap water at room temperature for 30 seconds and pure water at room temperature for 30 seconds.

Each of the test pieces treated as described above was then immersed in the chemical conversion treatment solution used in Example 1 for one minute, and then washed with tap water at room temperature for 30 seconds and at room temperature. For 30 seconds. Finally, drying was performed at room temperature for 2 hours. The total surface area of the chemical conversion test specimens was 0, 25, 50, 75, 100, 125, 150, 1 respectively.
The corrosion resistance test was performed on the test pieces at 75 and 200 dm ² / l in the same manner as in the above example. The results were as shown in Table 2.

Further, Mn, P and CH ₃ adhering to the surface of each of the test pieces subjected to the chemical conversion treatment and dried as described above.
COO ^- adhesion amount was determined by the following methods. That is, each test piece was immersed in 200 ml of a 3 mass% sulfuric acid aqueous solution at room temperature for 3 minutes, and the amount of Mn and P
The amount was analyzed, and the amount of Mn and P attached was calculated. The results were as shown in Table 2.

Each test piece was mixed with an aqueous alkaline solution (Na ₂ CO ₃ 2.7 mM + NaHCO ₃ 0.3 mM).
Immersed in water at 30 ° C for 1 hour
The amount of H ₃ COO ⁻ was analyzed, and the attached amount of CH ₃ COO ⁻ was calculated. The results were as shown in Table 2.

Comparative Example 7 A number of test pieces made of a magnesium alloy (AZ91) were subjected to ultrasonic cleaning in acetone at room temperature for 15 minutes and dried at room temperature for 5 minutes. Next, it was immersed in an aqueous potassium pyrophosphate solution (35 g / l, 60 ° C.) for 1 minute, and then washed with tap water at room temperature for 30 seconds and with pure water at room temperature for 30 minutes.
Seconds. Next, a sodium hydroxide aqueous solution (50 g / l, 6
(0 ° C.) for 3 minutes, followed by washing with tap water at room temperature for 30 seconds and pure water at room temperature for 30 seconds.

Next, each of the test pieces treated as described above was immersed in the chemical conversion treatment solution used in Comparative Example 2 for one minute, and then washed with tap water at room temperature for 30 seconds and at room temperature. For 30 seconds. Finally, drying was performed at room temperature for 2 hours. The total surface area of the chemical conversion test specimens was 0, 25, 50, 75, 100, 125, 150, 1 respectively.
The corrosion resistance test was performed on the test pieces at 75 and 200 dm ² / l in the same manner as in the above example. The results were as shown in Table 2.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

According to the production method of the present invention, a non-chromate treatment liquid which does not contain hexavalent chromium which is a harmful substance or heavy metal which becomes an impurity at the time of recycling and which has a long life of the treatment liquid is used. It is possible to provide a high corrosion-resistant surface-treated magnesium alloy product that can achieve corrosion resistance equal to or higher than that of a chemical conversion treatment using, and has high recyclability. In addition, the highly corrosion-resistant surface-treated magnesium alloy product obtained by the production method of the present invention has improved coating adhesion at the time of coating, and it is possible to achieve the same coating adhesion as a chromate-treated product.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Nobunori Kasahara 1333-2, Hara-shi, Ageo-shi, Saitama Mitsui Kinzoku Mining Co., Ltd. (72) Mitsuo Suzuki 1333-2, Hara-shi, Ageo-shi, Saitama Mitsui Mining & Smelting (72) Inventor Makoto Dobashi 1333-2, Hara-shi, Ageo-shi, Saitama Mitsui Mining & Mining Co., Ltd. F-term (reference) 4K026 AA01 BA01 BA03 BB08 BB10 CA13 CA18 CA23 CA35 CA37 CA38 DA13 DA15

Claims (4)

[Claims] 1. The method of claim 1, wherein the surface of the aluminum-containing magnesium alloy has a concentration of KMn of permanganic acid or a water-soluble salt of manganic acid.
O ₄ amount converted to 2 g / l or more and less than the solubility is 0.05 to 100 g / l concentration of the water-soluble salt of phosphoric acid in terms of Na ₃ PO ₄ content, the concentration of acetic acid 0 0.5 to 100 ml / l, a sodium acetate concentration of 0.05 to 50 g / l, a pH of 7 or less, and a chemical treatment with a liquid temperature of 288 to 368 K for 0.3 to 10 minutes. A method for producing a highly corrosion-resistant surface-treated magnesium alloy product, comprising: 2. The method according to claim 1, wherein the surface of the aluminum-containing magnesium alloy has a concentration of permanganic acid or a water-soluble salt of manganic acid of KMn.
The concentration of the water-soluble salt of phosphoric acid is 0.05 to 30 g / l in terms of the amount of Na ₃ PO ₄ , and the concentration of acetic acid is 0.1 to 0.1 in terms of O _4. The concentration of sodium acetate is 0.1 to 50 g / l, the pH is 2.3 to 6, and the liquid temperature is 293 to 353K. The method for producing a highly corrosion-resistant surface-treated magnesium alloy product according to claim 1, wherein the product is treated. 3. The surface of an aluminum-containing magnesium alloy, wherein the concentration of permanganate or a water-soluble salt of manganate is KMn.
In terms of O ₄ amount was 5~55g / l, the concentration of the water-soluble salts of phosphoric acid in terms of Na ₃ PO ₄ content is 0.1 to 10 g / l, the concentration of acetic acid 1~20ml / L, a sodium acetate concentration of 1 to 20 g / l, a pH of 3 to 5, and a chemical treatment with a liquid temperature of 303 to 333K for 0.5 to 3 minutes. The method for producing a highly corrosion-resistant surface-treated magnesium alloy product according to claim 2. 4. A method according to claim 1, wherein the Mn deposition amount is 100 to 600 mg / m ^2.
And the amount of P attached is 200 mg / m ² or less, and CH
₃ COO ^- high corrosion resistance surface treated magnesium alloy product adhesion amount is equal to or is 0.01 to 1000 / m ^2.