JP2983404B2 - Continuous annealing and acid cleaning same line processing method for Mg-containing aluminum alloy plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of performing acid cleaning on a Mg-containing aluminum alloy plate used as a material for a can or a body of an automobile for removing an oxide film mainly composed of MgO. Particularly, the present invention relates to a method of performing acid cleaning on the same line as continuous annealing.

[0002]

2. Description of the Related Art As is well known, alloys containing relatively large amounts of Mg include JIS No. 5000 series Al-Mg based alloys, JIS No. 6000 series Al-Mg-Si based alloys, and JIS No. 7000 series alloys. Al-Zn-Mg alloys and the like are available. By the way, since Mg is an element which is extremely easily oxidized, if the above-described Mg-containing aluminum alloy is subjected to a heat treatment in an atmosphere containing oxygen or moisture, the surface of the Mg-containing aluminum alloy becomes M
An oxide film mainly composed of gO is formed. On the other hand, in applications such as cans and automobile bodies, the surface of an aluminum alloy plate is often coated, and in that case, a chemical conversion treatment such as chromate treatment or zinc phosphate treatment is often performed before painting. However, in the case of an aluminum alloy plate having an oxide film mainly composed of MgO formed on the surface as described above, the adhesion of the coating film becomes poor, or the chemical conversion treatment becomes poor, so that the coating film or the chemical conversion film becomes uniform. And the corrosion resistance after coating is deteriorated. Therefore, conventionally, an Mg-containing aluminum alloy plate has been subjected to acid cleaning using a sulfuric acid solution or the like before coating or chemical conversion treatment to remove an oxide film on the surface.

Conventionally, in performing such acid cleaning, a dedicated acid cleaning line is provided, and the acid cleaning is performed in an independent process, or an acid cleaning apparatus is incorporated in the chemical conversion-coating line. Usually, acid cleaning is performed as a pretreatment of the chemical conversion treatment.

[0004]

As described above, in the case where a dedicated acid cleaning line is provided and acid cleaning is performed as an independent step for removing an oxide film from the Mg-containing aluminum alloy plate, the number of manufacturing steps increases. There is a problem that increases costs. In addition, when acid cleaning is performed as a pretreatment of a chemical conversion treatment by incorporating an acid cleaning device in the chemical conversion-coating line, the temperature of the acid cleaning cannot be made too high due to the relationship with the temperature of the chemical conversion treatment. There is a problem that the washing time becomes longer and the productivity is deteriorated.

[0005] In the recent production process of aluminum alloy sheets, annealing is performed for the purpose of recrystallization, solution treatment, softening, etc., and the sheet is continuously passed through the furnace while continuously feeding the sheet from the coil. In many cases, continuous annealing in which a coil is wound again is applied, and continuous annealing is often performed also on an Mg-containing aluminum alloy plate as described above.

Therefore, it is conceivable to incorporate an acid cleaning apparatus into such a continuous annealing line and perform continuous annealing and acid cleaning on the same line, thereby suppressing an increase in cost due to an increase in the number of manufacturing steps. However, in this case, a method for reliably removing an oxide film mainly composed of MgO under conditions suitable for a continuous annealing line and performing the method without significant modification of existing continuous annealing equipment is still established. The fact is that it was not done.

The present invention has been made in view of the above circumstances. For an Mg-containing aluminum alloy plate, acid cleaning for removing an oxide film mainly composed of MgO on the surface of the aluminum alloy plate is performed at a large cost and productivity. The basic purpose is to be able to perform at a high efficiency without inducing the decrease of, especially when the continuous annealing and the acid cleaning are processed in the same line, the oxide film can be reliably removed in a short time, Moreover, it is an object of the present invention to provide a method which can be carried out at low cost without significantly modifying the existing continuous annealing line.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted extensive experiments and studies, and as a result,
By setting the temperature of the pickling solution within an appropriate range according to the time during which the Mg-containing aluminum alloy plate to be treated is in contact with the pickling solution (the pickling time), MgO is surely mainly contained in a short time. It has been found that the oxide film can be removed. By applying the conditions, acid cleaning in the continuous annealing line can actually be performed, and it can be performed without significant modification of the existing continuous annealing equipment. The present inventors have found that the heat efficiency of the plate immediately after can be effectively utilized to improve the thermal efficiency, and have led to the present invention.

Specifically, the continuous annealing of the invention of claim 1
The acid cleaning same line processing method is to perform continuous annealing on an aluminum alloy plate containing 0.3 wt% or more of Mg, before winding the aluminum alloy plate after the continuous annealing,
The aluminum alloy plate after the continuous annealing is passed through an acid cleaning liquid or an acid cleaning liquid spray zone, and the contact time of the acid cleaning liquid during the passage is restricted to 20 seconds or less. Is regulated so as to satisfy the following equation (1): logt ≧ 3.6−3.5 × 10 ⁻² × T (1) .

Further, in the method for continuous annealing and pickling in the same line according to the second aspect of the present invention, in the method according to the first aspect, the acid cleaning solution may include sulfuric acid, nitric acid or phosphoric acid.
Those containing more than one species at a concentration of 1 to 20 wt% in total and having a pH of 2.0 or less are used.

According to a third aspect of the present invention, in the method of the first aspect, after the continuous annealing, the aluminum alloy plate is introduced into the acid cleaning solution or into the acid cleaning solution spray zone. Prior to this, alkali degreasing is continuously performed.

[0012]

According to the present invention, an aluminum alloy plate to be treated contains 0.3 wt% or more of Mg. Mg
In an aluminum alloy having a content of less than 0.3 wt%, an oxide film mainly composed of MgO is difficult to be formed, so that acid cleaning is rarely required. As described above, typical aluminum alloys containing 0.3 wt% or more of Mg include JIS No. 5000 series, 6000 series, and 7000 series as described above, but are not limited to these. is there.
Although the upper limit of the Mg content is not particularly specified, the aluminum alloy plate used industrially often has a Mg content of 10% by weight or less.

In the method of the present invention, the acid cleaning of the Mg-containing aluminum alloy plate as described above is performed in a continuous annealing line in the plate manufacturing process. That is, for example, as shown in FIG. 1, an acid cleaning device 2 is provided in a continuous annealing line 1 and acid cleaning is continuously performed after continuous annealing.

A specific example of the continuous annealing-acid cleaning will be described by taking the case of FIG. 1 as an example.
In the above, the aluminum alloy plate 4 fed from the uncoiler (coil feeding device) 3 is connected to an entry-side accumulator 5.
Through the continuous annealing furnace 6. This continuous annealing furnace 6
Usually, it is divided into a preheating zone 6A, a holding zone 6B, and a cooling zone 6C. In the case of a conventional general continuous annealing line, the aluminum alloy plate 4 that has exited from the cooling zone 6C of the continuous annealing furnace 6 is again wound into a coil shape by a recoiler (winding machine) 8 through an outlet accumulator 7 as it is. Taken. On the other hand, when carrying out the method of the present invention, the acid cleaning device 2 is installed between the discharge side of the continuous annealing furnace 6 and the discharge side accumulator 7, and the acid cleaning for the aluminum alloy plate 4 is performed after the continuous annealing and the winding. It will be done continuously before taking. Here, the pickling apparatus 2 is of a type in which the aluminum alloy plate is directly immersed in the pickling solution, that is, a pickling bath type, or a spray in which the pickling solution is sprayed on the aluminum alloy plate by a spray. A configuration having a band may be used.

As described above, in performing the pickling in the continuous annealing line, the relationship between the pickling time and the pickling temperature is extremely important.

That is, as will be described later by the present inventors in the embodiments described later, Mg 4.5 wt%, Cu 0.3
An acid cleaning solution consisting of a 10% H ₂ SO ₄ aqueous solution was used for an aluminum alloy plate containing wt%, the balance being substantially Al and having an oxide film mainly composed of MgO formed on the surface by ordinary continuous annealing. Mg on the surface when used
When the relationship between the time required for removing the oxide film mainly composed of O and the temperature of the acid cleaning solution was examined, the results shown in FIG. 2 were obtained. Here, the removal time of the oxide film mainly composed of MgO was determined by glow discharge emission spectroscopy (GDS) as the acid cleaning time until the Mg peak on the surface layer substantially disappeared. Representative examples of the GDS analysis results before and after the acid washing are shown in FIGS. FIG. 3A shows a state before the acid cleaning, in which a Mg peak appears near the surface, while FIG. 3B shows a state at 80 ° C. of 10% with an acid cleaning solution containing 10% H ₂ SO _4. It can be seen that the Mg peak has disappeared in the state after the acid washing for 2 seconds.

As shown in FIG. 2, the time required to remove the oxide film mainly composed of MgO on the surface formed by ordinary continuous annealing is greatly affected by the temperature of the acid cleaning solution, and is represented by a straight line L in FIG. It was found that the removal of the oxide film mainly composed of MgO was almost completely performed when the acid cleaning time and the acid cleaning solution temperature in the upper right region were set. Here, the acid cleaning time is t
(Seconds), if the temperature of the acid cleaning solution is T (° C.), the straight line L
Is expressed by the following equation (2). logt = 3.6-3.5 × 10 ⁻² × T (2)

Therefore, the pickling time (that is, the time during which the pickling solution is in contact with the pickling solution) is changed by the following equation (1) according to the temperature T of the pickling solution: logt ≧ 3.6−3.5 × 10 ⁻² × By setting the time to satisfy T 1 (1), it is possible to substantially completely remove the oxide film mainly composed of MgO.

In a continuous annealing line, the length of an acid cleaning device that can be installed in existing continuous annealing equipment is limited. On the other hand, even when a new line is installed, a compact design is required as much as possible. Line speed of continuous annealing of applied aluminum (30-200m /
min), acid cleaning for a long time is not suitable. In other words, when performing acid cleaning for a long time at a general continuous annealing line speed, the acid cleaning device becomes longer, and an acid cleaning device is provided between the continuous annealing furnace and the outlet accumulator in the existing continuous annealing line. Installation becomes difficult, and the line length becomes extremely long even for a newly installed line. Therefore, in the present invention, the passing length (length in contact with the acid cleaning liquid) described later is set to 10 m or less, and the lower limit (30 / min) of the line speed of the continuous annealing is set as follows.
The upper limit of the acid cleaning time (time in contact with the acid cleaning liquid) t was set to 20 seconds or less.

As described above, regarding the contact time t of the acid cleaning solution,
When the condition (1) is satisfied and the condition is 20 seconds or less,
It means that the contact time t and the temperature T of the acid cleaning liquid are determined in the shaded area in FIG. As can be seen from FIG. 2, the temperature T of the pickling solution is at least as high as about 65 ° C. or more. In the case of the method of the present invention, the heat given to the aluminum alloy plate during the continuous annealing is effectively used. Even in the acid cleaning at a high temperature of 65 ° C. or more as described above, less energy is required for heating the acid cleaning liquid. That is, in a continuous annealing furnace, although it varies depending on the purpose of annealing, the aluminum alloy plate usually has an ultimate temperature of 400 to 60.
Even when it is heated to about 0 ° C. and cooled in a cooling zone in a continuous annealing furnace, it usually has a temperature of about 100 to 250 ° C. at the outlet of the annealing furnace. Therefore, by immediately dipping or spraying the aluminum alloy plate after continuous annealing in an acid cleaning solution, the contact temperature of the acid cleaning solution also increases,
The heating of the acid cleaning solution itself is not required, or at least a slight heating is sufficient.

The time during which the aluminum alloy plate is in contact with the pickling solution, that is, the passage time in the pickling solution or the passing time in the pickling solution spray zone, is the length of the plate passing in the pickling bath or spray zone (contact with the pickling solution). Length) and the line speed of the continuous annealing, but when an acid washing device is added to the existing continuous annealing equipment, it is possible to estimate the threading length at a maximum of about 10 m as described above. Therefore, if the threading length is set to 10 m and the relation of the above equation (1) is rewritten to the relation between the acid cleaning temperature T (° C.) and the line speed R (m · sec ⁻¹ ), the equation (3) is obtained. become. log (10 / R) ≧ 3.6−3.5 × 10 ⁻² × T (3) From the expression (3), the expression (4) is obtained. log (R ⁻¹ ) ≧ 2.6−3.5 × 10 ⁻² × T (4) When the expression (4) is satisfied, the ^value ( ¹ ) is always required when the pickling plate length is 10 m. ) Expression is also satisfied.
When the threading length L (m) is 10 m or less, t = L
By determining the temperature T of the acid cleaning liquid and the line speed R so as to satisfy the expression (1) as / R, it is possible to reliably remove the oxide film mainly composed of MgO.

The solution used for acid cleaning in the method of the present invention is preferably a sulfuric acid solution from the viewpoint of economy and environmental problems. However, a sulfuric acid solution is preferable if it is an inorganic acid capable of removing an oxide film mainly composed of MgO in a short time. However, the present invention is not limited thereto, and for example, nitric acid, phosphoric acid, a mixed acid thereof, or the like can be used in addition to sulfuric acid. It is appropriate that the concentration of the inorganic acid is 1 to 20 wt% in total and the pH of the inorganic acid solution is 2 or less. If sufficient environmental measures are taken, the reaction can be promoted by adding a fluorine compound to these inorganic acid solutions, in which case the acid cleaning apparatus can be made more compact.

Further, the aluminum alloy sheet after the continuous annealing may be immediately subjected to acid cleaning. However, if an oil or fat such as rolling oil remains on the surface of the alloy sheet, uniform acid cleaning is hindered. For this reason, it is preferable to perform alkali degreasing using sodium phosphate, sodium hydroxide, sodium orthosilicate, or the like after continuous annealing and before acid cleaning. For this purpose, for example, an alkaline degreasing tank (not shown) may be provided between the continuous annealing furnace 6 and the acid cleaning device 2 in FIG.

In the method of the present invention, the treatment after the acid washing is not particularly limited. Usually, the acid solution remaining on the surface after the acid washing is removed by washing with water, followed by drying and further drying. It is usual to apply a lubricating oil or a rust-preventive oil to prevent scratching and rust prevention.

The sheet manufacturing process before the continuous annealing and the specific conditions of the continuous annealing can be arbitrarily set according to the material, the use of the product sheet, and the like. In general, DC casting—soaking—hot rolling— A continuous annealing furnace after degreasing a rolled sheet having a predetermined thickness by cold rolling or a rolled sheet having a predetermined thickness by continuous casting and cold rolling using an alkaline solution, an organic solvent, hot water, or the like. In a continuous annealing furnace, the temperature is usually raised to about 400 to 550 ° C., and is usually not held or held for a short time of about 20 seconds or less. In a continuous annealing furnace, it is usual to use a combustion gas or heated air as a heating atmosphere.

[0026]

[Example 1] An aluminum alloy containing 4.5 wt% of Mg and 0.3 wt% of Cu, and the balance substantially consisting of Al was converted to a normal DC.
Casting, soaking, hot rolling, cold rolling
m rolled plate. After degreased with an organic solvent (MEK), the rolled plate was heated at 500 ° C. × 10 by a continuous annealing furnace.
Heat for 2 seconds and air-cool to 200 ° C.
Aqueous solution of sulfuric acid at ~ 90 ° C (sulfuric acid concentration 10wt%, pH <
It was immersed in 1) for 2 to 60 seconds. After acid cleaning, the substrate was washed with pure water and dried. GDS analysis was performed on the surface layer of the dried plate to determine the concentration distribution of Mg, Al, and O in the depth direction.
The existence state of the oxide film mainly composed of O was examined.

FIG. 2 shows the relationship between the removal state of the oxide film mainly composed of MgO (the presence state of the Mg concentration peak), the acid cleaning time (contact time with the acid cleaning liquid), and the temperature of the acid cleaning liquid.

As shown in FIG. 2, the temperature T of the pickling solution is
When the contact time t with the acid cleaning liquid was in the upper right region of the straight line L, that is, when the formula (1) was satisfied, the oxide film mainly composed of MgO could be almost completely removed. In the upper right area of the straight line L in FIG.
Even when the time exceeds 0 second, the oxide film mainly composed of MgO is completely removed. However, as described above, the pickling time exceeding 20 seconds causes inconvenience in an actual continuous annealing line.

Example 2 In performing acid cleaning after continuous annealing in the same manner as in the above example, the contact length of the rolled plate with the acid cleaning liquid was kept constant at 10 m, and the continuous annealing line speed was 0.3 m / sec or more. The temperature was changed within a range of 1.0 m / sec, and the temperature of the pickling solution was changed within a range of 50 to 90 ° C. In this case, when the relationship between the temperature T of the pickling solution and the line speed R satisfies the expression (4),
The oxide film mainly composed of MgO was completely removed.

[0030]

As is apparent from the above description, according to the method of the present invention, the acid cleaning for removing the oxide film mainly composed of MgO on the surface of the aluminum alloy plate containing Mg is performed by continuous annealing. It can be carried out efficiently and continuously in the same line as the line, without any decrease in productivity especially by applying acid cleaning, and reliably removing oxide films while applying the normal line speed of the continuous annealing line It can be carried out without significant modification of existing continuous annealing equipment, and it is possible to carry out acid cleaning at high temperature by effectively utilizing the heating energy in continuous annealing. Not only is it excellent, it can also reduce the energy for heating the acid cleaning solution, thus increasing the total heat utilization efficiency and reducing the total running cost. It is possible to achieve.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of equipment for performing continuous annealing and acid cleaning on the same line according to the method of the present invention.

FIG. 2 is a correlation diagram showing a relationship between an acid cleaning liquid temperature and an acid cleaning time (an acid cleaning liquid contact time) and an oxide film removal state when an acid cleaning is performed on an Mg-containing aluminum alloy plate after continuous annealing.

3 is a graph showing a typical example of a concentration distribution of Mg, Al, and O in a depth direction in a surface layer of an Mg-containing aluminum alloy plate by GDS analysis for obtaining data shown in FIG. FIG. 3 is a graph showing a sheet after annealing and before acid cleaning, and FIG. 3B is a graph showing a sheet after continuous annealing and acid cleaning.

[Explanation of symbols]

 Reference Signs List 1 continuous annealing line 2 acid cleaning device 6 continuous annealing furnace

Continued on the front page (72) Inventor Kimitaka Hayashi 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Headquarters (72) Inventor Yoshihiko Takeoka 2-6-3 Otemachi, Chiyoda-ku, Tokyo New Nippon Steel Corporation (58) Field surveyed (Int.Cl. ⁶ , DB name) C23G 3/02

Claims (3)

(57) [Claims] 1. In performing continuous annealing on an aluminum alloy sheet containing 0.3 wt% or more of Mg, before winding the aluminum alloy sheet after continuous annealing, the aluminum alloy sheet after continuous annealing is placed in an acid cleaning solution. Alternatively, the solution is passed through an acid cleaning solution spray zone, and the acid cleaning solution contact time during the passage is regulated to 20 seconds or less, and the relationship between the contact time t (second) and the temperature T (° C.) of the acid cleaning solution is as follows. (1) Formula logt ≧ 3.6−3.5 × 10 ⁻² × T (1) A method for continuous annealing and acid cleaning of Mg-containing aluminum alloy sheets on the same line, characterized by regulation. . 2. The method according to claim 1, wherein the acid washing solution contains one or more of sulfuric acid, nitric acid and phosphoric acid at a total concentration of 1 to 20% by weight and has a pH of 2.0 or less. The same line processing method for continuous annealing and acid cleaning of the Mg-containing aluminum alloy plate used. 3. The method according to claim 1, wherein the alkali-degreasing is continuously performed after the continuous annealing before introducing the aluminum alloy plate into the pickling solution or into the pickling solution spray zone. Continuous annealing and acid cleaning same line processing method.