JPH108264A - Production of magnesium-containing aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of sludge in a phosphate chromating treating stage and to reduce its coating weight to a treating tank, a nozzle, piping or the like, at the time of subjecting an Mg-contg. Al alloy to alkali etching and phosphate chromating treatment, by removing Mg in the surface layer part of the alloy with an acidic soln. of specified pH before the treatment so as to regulate its content to specified value or below. SOLUTION: The surface of an Mg-contg. Al alloy is subjected to etching with an alkali degreasing soln., thereafter, Mg in the surface layer part of the alloy is removed with an acidic soln. of pH0.5 to 3 to regulate its content to <=1mg/m<2> , and next, phosphate chromating treatment is executed. In the Mg-contg. Al alloy, the content of Mg in the surface layer part is increased by the heat treatment in the process of the production, and, in the case such alloy is subjected to phosphate chromating treatment, the surface layer part is etched, and Mg in the surface layer part is also eluted in the treating soln. to form sludge. Thus, by the above treating with the acidic soln., the generation of sludge can be suppressed to a small amt., and the problems of the unevenness in the treatment and the stop of the line caused by the clogging of a nozzle and piping in the process of continuous treatment, cleaning and the stop of the line for removing sludge or the like can be solved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum alloy containing Mg.
Controls the generation of sludge in the phosphate chromate treatment solution,
The present invention relates to a method for reducing maintenance of an apparatus.

[0002]

2. Description of the Related Art Mg-containing aluminum alloys are used for metal containers such as cans because of their excellent strength and formability. Conventionally, when manufacturing such alloys for metal containers, corrosion resistance and
A coating process is performed to impart decorativeness.In this case, before the coating process, in order to enhance the adhesion between the aluminum alloy and the coating film, a coating base process by a phosphoric acid chromate process is performed. Is commonly done. In this phosphoric acid chromate treatment step, an oxidation reaction (dissolution reaction) of aluminum and a reduction reaction of Cr ⁶⁺ occur to form a phosphoric acid chromate film.

[0003] Generally, the above-mentioned undercoating treatment is performed by preliminary degreasing →
Rinsing → Degreasing → Rinsing → Chemical conversion treatment (phosphoric acid chromate treatment)
→ Washing → Drying procedure. Here, alkali etching is generally performed as degreasing. The color tone and roughness of the surface are adjusted by the alkali etching.

[0004]

[SUMMARY OF THE INVENTION When subjected successively painting surface treatment as described above, sludge chemical conversion treatment step _{(MgAlF 5 · 1.5 H 2 O} ) that is generated is generally known . The generated sludge is treated tank, nozzle,
If it adheres to pipes, etc. and the amount of adhesion increases due to long-term
This can cause nozzle clogging and pipe clogging, causing troubles such as line stoppages and poor film formation.
Periodical sludge collection and cleaning of the processing equipment are required,
This is a problem in terms of productivity and cost.

The cause of sludge generation is M
g, Al, F, etc. Among them, Mg is an element that does not contribute to the formation reaction of the phosphoric acid chromate film, and the amount of Mg brought into the chemical conversion treatment tank greatly affects the generation of sludge. . Therefore, when the amount of Mg eluted in the chemical conversion treatment liquid is reduced, the amount of sludge generated can be suppressed even if the amount of Al and F in the chemical conversion treatment liquid is large.

However, in a Mg-containing aluminum alloy, Mg diffuses into the surface layer of the material due to heat treatment in the manufacturing process, and the amount of Mg in the surface layer increases. Therefore, even if the area subjected to the phosphoric acid chromate treatment is small, the amount of Mg eluted into the phosphoric acid chromate treatment solution has increased, and a large amount of sludge has been generated in a short period of time.

[0007] As a pretreatment for the phosphoric acid chromate treatment, a method of etching the surface with an alkali degreasing solution or the like is generally performed. However, since the Mg diffusion layer formed by the heat treatment has low solubility in the alkali degreasing solution, it is hardly removed by the alkali etching treatment and is brought into the phosphate chromate treatment solution. That is, in the case of the conventional alkali etching, Al elutes, but Mg in the surface layer does not elute in the alkaline solution, so that it is carried into the phosphoric acid chromate treatment solution, and the amount of eluted Mg increases.

[0008]

Means for Solving the Problems The present invention has made intensive studies to solve these problems, and as a result, by preventing Mg from being introduced into the phosphoric acid chromate treatment solution, the present invention has been developed in the phosphoric acid chromate treatment step. And found a method of suppressing the generation of sludge.

That is, according to the present invention, the surface of the Mg-containing aluminum alloy is removed by etching the surface of the Mg-containing aluminum alloy with an alkaline degreasing solution, and then removing the Mg from the surface layer of the Mg-containing aluminum alloy with an acidic solution having a pH of 0.5 to 3. A Mg-containing aluminum alloy, which is not more than 1 mg / m ² and then subjected to a phosphoric acid chromate treatment.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In a Mg-containing aluminum alloy, Mg diffuses into the surface layer of the material due to heat treatment during the manufacturing process, and the amount of Mg in the surface layer increases. When treated with a chromate solution, the surface layer is etched, so that Mg in the surface layer as well as Al elutes into the phosphate chromate treatment solution. Therefore, more Mg is eluted into the processing liquid than the average Mg content of the entire material. Eluted Mg and Al is reacted with F phosphate-chromate treatment solution to generate a sludge composition of the MgAlF ₅ · 1.5 H ₂ O.

According to the present invention, the generation of the sludge is suppressed to a small amount by removing Mg from the surface layer of the Mg-containing aluminum alloy plate before performing the phosphoric acid chromate treatment. That is, even if the Al concentration in the phosphoric acid chromate treatment liquid exceeds the general control concentration of 1500 ppm, or the F concentration exceeds the control concentration, the sludge formation reaction does not occur unless Mg is present, so the sludge is No longer occurs. According to this method, the phosphoric acid chromate treatment can be continuously performed for a long time.

The degree of removal of the Mg diffusion layer is preferably such that the amount of Mg in the surface layer is 1 mg / m ² or less. Since the amount of Mg eluted is small, the generation of sludge can be suppressed to a low level. Further, even if the treated area becomes large and the amount of eluted Al increases, the M
Since g has been removed and the amount of Mg eluted has been reduced, the amount of sludge generated does not increase as in the prior art.

Further, the p of the acidic liquid after the alkali etching is changed.
The reason for limiting H to 0.5 to 3 is that if the pH is less than 0.5, not only does the Mg removal effect saturate, but also the amount of sulfuric acid and the like increases, which is not economical and the handling of the apparatus is difficult. When the pH exceeds 3, M of the surface layer
This is because the effect of removing g is small, and Mg is brought into the phosphoric acid chromate treatment solution, and the generation of sludge cannot be sufficiently suppressed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments.

After melting and casting the aluminum alloys shown in Table 1, various treatments such as homogenization, hot rolling, cold rolling, intermediate annealing, and cold rolling were performed to obtain an aluminum alloy plate having a thickness of 0.30 mm. .

[0016]

[Table 1]

The aluminum alloy plate obtained by the above process is subjected to alkaline etching treatment under various conditions shown in Table 2.
An acidic solution treatment was performed to vary the amount of Mg in the surface layer of the aluminum alloy plate as shown in Table 2. The pH of the acidic treatment liquid is a value measured at 25 ° C. Thereafter, phosphoric acid chromate treatment was performed so that the amount of Cr attached was 20 to 30 mg / m ² . The phosphoric acid chromate treatment was performed on an aluminum alloy plate having a total treatment area of 300 m ² using 10 liters of a treatment liquid having the components shown in Table 3. After the treatment, the deposits in the apparatus and the precipitate in the phosphoric acid chromate treatment solution were filtered through a 0.1 μm membrane filter, and the recovered amount was defined as the amount of sludge generated. The results are also shown in Table 2.

[0018]

[Table 2]

[0019]

[Table 3]

The phosphoric acid chromate used in this example
The processing liquid was Alsurf 401 manufactured by Nippon Paint Co., Ltd.
(2.5%) and Alsurf 45 (0.5%)
And 1m ^Three 10,000m per processing solution^TwoSurface area
The aluminum plate was treated. 45 ℃
And heat the aluminum alloy plate to this treatment solution for about 1 hour.
Dipped for 0 seconds. Maintain Cr deposition during continuous processing
20m for^TwoCheck the amount of Cr adhering for each treatment.
(Alsurf 401 and / or Alsurf 45)
Was performed.

The amount of Mg in the surface layer was measured at 500 ml.
10% of a 100 mm x 100 mm aluminum alloy plate was immersed in 30% nitric acid at 30 ° C for 1 minute, the Mg concentration in the nitric acid was analyzed, and the Mg amount calculated from the obtained value was calculated for the following reason. Of Mg. That is, as a preliminary experiment, Table 4 shows the results of measuring the Mg concentration of the aluminum alloy plate having the composition shown in Table 1 before alkali etching as a sample every minute up to the immersion time of 5 minutes by the above measurement method. As is clear from Table 4, M after 2 minutes
Since the amount of eluted g was extremely small, the amount of Mg calculated from the measurement result after immersion for one minute was defined as the amount of Mg in the surface layer.

[0022]

[Table 4]

As is clear from Table 2, Example No. 1 of the present invention
In Nos. To 4, the amount of sludge generated after the phosphoric acid chromate treatment was significantly smaller than in Comparative Examples Nos. 5, 6, and 8, indicating that sludge generation was sufficiently suppressed. In Comparative Example No. 7, although the generation of sludge was sufficiently suppressed, the pH was as small as 0.5, so that about ten times or more sulfuric acid was used as compared with the Example of the present invention. In addition, problems such as melting of a part of the device occurred.

[0024]

As described in detail above, according to the present invention,
When phosphoric acid chromate treatment of Mg-containing aluminum alloy, sludge generation can be suppressed, so processing unevenness due to nozzle clogging during continuous processing, line stoppage due to pipe clogging, cleaning / line stoppage for sludge removal,
It has industrially remarkable effects, such as solving the problem of sludge disposal.

Claims (1)

[Claims] 1. After etching the surface of an aluminum alloy containing Mg with an alkaline degreasing solution, the pH of the aluminum alloy is adjusted to 0.5.
3. A method for producing a Mg-containing aluminum alloy, comprising removing Mg in the surface layer of the Mg-containing aluminum alloy to 1 mg / m ² or less with an acidic solution of (1) to (3), and then subjecting the Mg-containing aluminum alloy to phosphoric acid chromate treatment.