JPH02247349A - Aluminum alloy rolled sheet for cover of can vessel having excellent pitting corrosion resistance - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rolled aluminum alloy plate used as a material for the lid of a can container whose body is made of iron.

(Prior art) When combining metal cans as food containers, if the can body is made of aluminum alloy and the can lid is also made of aluminum alloy, the can body and can lid are made of iron such as tin or tin-free steel. Generally, steel is used for the can body and aluminum alloy is used for the can lid.

Aluminum alloys used for can lids have excellent tearability and formability, while iron used for can tubes has excellent can lid strength. However, because the iron lid has poor tearability, its use is limited, as it cannot be used for EOE cans. Therefore, Aρ-Mg alloy represented by JIS5052.5182 is generally used as a material for can lids.

(Problems to be Solved by the Invention) In the case of a metal can in which both the can body and the can lid are made of an aluminum alloy, there is no similar problem even if the can body and can lid contain corrosive components such as salt. However, due to cost and strength considerations, a combination of iron and aluminum alloy is sometimes used, and in this case pitting corrosion may occur. In other words, if the coating that is the protective film on the aluminum alloy can lid is insufficient or if the coating is damaged during molding, if the corrosion conditions are severe such as high Cρ- ion concentration or high dissolved oxygen concentration, Galvanic action due to the potential difference between Fe and Aρ causes local dissolution pitting corrosion, resulting in perforation.

(Means for Solving the Problems) In order to solve the above-described problems in using aluminum alloys, the inventors of the present invention have conducted extensive research to develop an aluminum alloy for food containers that has excellent corrosion resistance, particularly pitting corrosion resistance. The aluminum alloy for can container lids with excellent pitting corrosion resistance according to the present invention, which led to the development of the rolled plate, contains Ti: 0.05-1.0 wt%, the balance consists of aluminum and inevitable impurities, The first invention is an aluminum alloy rolled plate for can containers having a can body made of iron, which contains Ti: 0.05 to 1.0 wt%, and further contains Mn: 2.
．． A second invention provides an aluminum alloy rolled plate for can container lids containing one or more of Cu: 5wt% or less, Cu: 1.0wt% or less, the remainder consisting of aluminum and unavoidable impurities, and having a can body made of iron. .

Contains Ti: 0.05 to 1.0 wt%, and further contains Mn:
2.5 wt% or less, Cu: 1.0 wt% or less of one or more types, and Mg: 0.05 to 5.0 wt%, the remainder consisting of aluminum and inevitable impurities,
This invention consists of three inventions, with the third invention being an aluminum alloy rolled plate for can container lids whose can bodies are made of iron.

The reason for limiting each component of the aluminum alloy for food containers with excellent pitting corrosion resistance according to the present invention will be explained.

Ti: In all of the first to third inventions, Ti is a basic element for improving pitting corrosion resistance. Ti, which was conventionally considered to be a monomer component, forms T i B 2 together with B and is effective in refining the ingot crystal grains. However, in order to improve the pitting corrosion resistance, it is not necessary for B to be present in the aluminum alloy in addition to Ti; rather, if Ti is completely fixed as TiB2, the pitting corrosion resistance will not improve. Therefore, it is preferable that B is not added at all, or even if it is added for crystal 81H formation, it is preferably 50 ppm or less.

Ti forms a dense layer parallel to the rolled plate surface.

That is, when the surface of a rolled plate is measured using a minute portion determination device such as EPMA, it is observed that a high concentration segregation region with a content of more than twice the average content of the whole exists in parallel to the surface of the rolled plate. This is the Ti enriched layer.

The Ti-rich layer has the function of retarding the corrosion rate in the Cρ-containing liquid due to the Ti content, and also makes it difficult for pitting corrosion to occur by changing the direction of corrosion progression to a layered direction parallel to the rolled surface, so that corrosion does not occur in the rolled plate. It has the function of slowing the progress over the entire surface of the surface. As a natural result of Ti segregation in the Tifil1 layer, there is a layered region in contact with the Ti-concentrated layer where the Ti concentration is lower than the added content. In such a relatively low Ti concentration portion, the corrosion rate is high and reaches a level almost equal to that of an alloy without Ti. However, the Ti concentrated layer acts as a barrier against corrosive components such as salt, and as a result, the pitting corrosion resistance is dramatically improved.

The Ti-concentrated layer and the low-Ti concentration layer are caused by the difference in the amount of Ti solid solution in Ag. On the other hand, if Ti crystallizes as a primary crystal during casting, a giant intermetallic compound with A1 is generated, and if a large amount of primary crystals are generated, the amount of solid solution Ti in the AI state will decrease, and the difference in the amount of Ti solid solution. becomes less. Therefore, in order to actively generate a Ti enriched layer, it is preferable to employ a casting method with a fast cooling rate, such as a continuous casting method. Pitting corrosion resistance improves with the amount of Ti added.

If the Ti content is less than 0.05 wt%, the effect of improving pitting corrosion resistance is weak. On the other hand, if Ti is contained in excess of 1.0 wt%, the rollability and workability will be impaired, so the upper limit is set at 1.0 wt%.
And so. Preferably, 0°15 to 0.80 wt% T1
The content range is excellent in pitting corrosion resistance and workability.

Cu, Mn+ Pitting corrosion resistance is further improved by further adding Cu and Mn in addition to TI. Since the potential of the Cu (At) alloy matrix itself is responsible, the can lid approaches the natural electrode potential of the tin plate of the can body, improving pitting corrosion resistance.

When Cu is added, the amount of Ti added can be reduced, and the rollability of the plate and the formability of the can lid can be improved. If 1.0 wt% or more of Cu is added, cracks will easily occur during casting, which is not favorable for operation.
The upper limit of the amount of Cu added is 1.0 wt%. If the amount of Cu added is less than 0.05 wt%, the effect of improving pitting corrosion resistance will not appear, so the lower limit of the amount of Cu added is preferably 0.05 wt%.

Mn prevents the generation of Fe-based crystallized substances or precipitates that promote pitting corrosion, and since the potential of Mn-based crystallized substances is very close to that of the aluminum alloy matrix, Mn improves the corrosion resistance. effective. Addition amount of Mn is 0.05w
If the amount of Fe is less than t%, the negative effects cannot be eliminated if the amount of Fe is large, and if it is more than 2.5wt%, although there is an effect, the rollability of the plate and the workability of the can lid will deteriorate, so the preferable lower limit is set to 0.05wt%. %, with an upper limit of 2.5 wt%.

Note that, like Cu, Mn is also effective in reducing the amount of T1 added and improving rolling properties and workability. Therefore, Ti, Cu of the present invention.

Within the range of the amount of Mn added, it is necessary to determine the amount of these elements added so that pitting corrosion resistance and rollability/workability are balanced. Note that Cu and Mn are elements that are also effective in improving strength.

In the second and third inventions in which Mn and Cu are added, a rolled plate with a Ti content of 0.5% or less and a good balance between pitting corrosion resistance and rolling workability can be obtained.

Mg: Unlike -B, Mg rarely deteriorates rolling properties and improves strength, but deteriorates pitting corrosion resistance. However, Ti
By adding Mg together with , Cu, and Mn, it is possible to improve the strength without realizing the adverse effects caused by the addition of Mg. The amount of Mg added is 0.05, which shows the effect of improving strength.
The preferable lower limit was 5.0 wt%, and the upper limit was 5.0 wt%, which was the operational limit for rolling properties.

Cr may be added to improve heat resistance by retarding softening during baking, but when added at the same time as Ti, it promotes the generation of primary crystals, so it is necessary to keep it at 0.2 wt% or less. In addition to the above elements, Fe and Si are contained as unavoidable impurities, similar to ordinary aluminum alloys. All of these impurities degrade the pitting corrosion resistance, so the smaller the better, but the rolled sheets of the second and third inventions to which Mn is added are allowed to contain impurities up to a total amount of 0.5 wt%.

Next, an example of an aluminum alloy rolled plate for food containers with excellent pitting corrosion resistance according to the present invention will be described.

(Example) An aluminum alloy having the ingredients shown in Table 1 was prepared in a laboratory scale using a 4h+a copper mold, 20IIIi or 40I
It was cast using an Ilffi iron mold, a unidirectional solidification device, and a small continuous caster. Solidification speed is 3!1 for small size! Casting machine〉
The order was unidirectional solidification (15 mm from the solidification end) > 4hm iron mold > 2ha iron mold. After casting, -rate 55
After soaking at 0°C for 1 hour, it was cold rolled to 0.28m.
An aluminum alloy plate with a thickness of m was produced. In the pitting corrosion test, paint baking, which is usually done on can lids, is performed under conditions that are more severe than the later tests.
The test was carried out with only 200°C x 20 minutes or 270°C x 20 seconds). A test gold plate was connected to one electrode and a tin plate was connected to the opposite electrode with a conductive wire, and the pitting depth of the test gold plate was measured after immersion in the test solution at 40° C. for 24 hours to compare pitting corrosion resistance.

The test solution is citric acid sodium citrate NaCj2 CuCffz type component and has a pH of 2.94 to 3.
．． 02. CI2 concentration is 525-625 ppm.

The Cu2+ concentration is 1.04 to 1.13 ppm.

In the table, "Workability J" was evaluated in three stages: ◎Very easy, ○Easy, and ×Difficult by integrating the rollability and the formability of the product rolled sheet.In addition, the number of Ti enriched layers was determined by EPMA This is the measured value of the number of layers per 100 μm depth on the surface of the rolled plate. Fig. 1 shows an EPMA photograph (1000x magnification) showing the Ti-concentrated layer.

Among the alloy rolled sheets Nos. 1 to 8 of the present invention, Nos. 1 to 3 are Mn, Cu, Mg, Cr, and FeSi are impurities.
Examples of the invention, No. 4 to 5 are Mg, Cr, Fe
, is an embodiment of the second invention in which SL is an impurity, and N01
Examples 6 to 8 are examples of the third invention in which Cr, Fe, and Si are impurities.

(Left below) As is clear from Table 1, the rolled alloy sheet according to the present invention has superior pitting corrosion resistance compared to the 1100.5052.5082 alloy, and its workability is equivalent to that of the 1100.5052 alloy. .

Furthermore, looking at the relationship between the pitting depth, the number of Ti enriched layers, and the composition of the rolled alloy sheet according to the present invention, the pitting depth becomes shallower when the Ti content and the number of Ti enriched layers are larger. (Alloy 1~
B): It can be seen that the depth of pitting corrosion becomes even shallower due to the addition of Mn and Cu (alloy 5).

In addition, when the Ti enriched layer was changed by changing the amount of Ti added, the amount of the third element that affects the amount of solid solution of Ti, the casting speed, etc., the TiJ condensation number was changed at least on one side (solution containing salt and Good pitting corrosion resistance was obtained when there were 8 or more layers at 100 μm from the contacting surface.

Even if the process of Alloy 6 to Gold alloy in Table 1 is adjusted within the conventional range, the yield strength after baking can be increased from 20 kgf/mm2 to 37 kgf/mm2, and can lids with extremely high strength can be obtained.

(Effects of the Invention) As described above, the rolled aluminum alloy plate for food containers with excellent pitting corrosion resistance of the present invention has extremely good pitting corrosion resistance and does not cause deep pitting corrosion, so it is particularly suitable for beverages and foods containing salt. Suitable for steel can lids.

[Brief explanation of drawings]

FIG. 1 shows the Ti enriched layer of the rolled alloy sheet according to the present invention.
This is a photograph of PMA metallographic structure (1000x magnification). Patent applicant Sky Aluminum Co., Ltd. Agent
Patent attorney Takuo Murai 1st technique VA side No. I

Claims (1)

[Claims] 1. An aluminum alloy rolled plate for a can lid, containing 0.05-1.0 wt% Ti, the remainder consisting of aluminum and unavoidable impurities, and having a can body made of iron. 2. Contains Ti: 0.05 to 1.0 wt%, further Mn: 2.5 wt% or less, Cu: 1.0 wt%
An aluminum alloy rolled plate for can container lids containing one or more of the following, the remainder consisting of aluminum and unavoidable impurities, and having a can body made of iron. 3. Contains Ti: 0.05 to 1.0 wt%, further Mn: 2.5 wt% or less, Cu: 1.0 wt%
One or more of the following, and Mg: 0.05 to 5.
An aluminum alloy rolled plate for can container lids, containing 0 wt%, the remainder consisting of aluminum and unavoidable impurities, and having a can body made of iron.