JPH09165639A - Aluminum alloy sheet for fuel tank and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare an aluminum alloy sheet for fuel tank, reduced in weight and excellent in corrosion resistance, press formability, and weldability, and its production. SOLUTION: An Al alloy, having a composition consisting of, by weight, 2.2-6.0% Mg, 0.03-0.15% Cu, 0.03-0.50% Mn, 0.03-0.35% Cr, <=0.30% Fe, <=0.20% Si, and the balance Al with inevitable impurities, is used. By applying acid pickling or mechanical polishing to the surface of a sheet of the Al alloy, the thickness of a surface oxide film is regulated to <=500nm. By this method, the aluminum alloy sheet for fuel tank, excellent in corrosion resistance, press formability, and weldability, can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy sheet having excellent corrosion resistance, formability, and weldability, which is optimum as a container for containing a fuel tank material, particularly a fuel mainly containing gasoline, and a method for producing the same. is there.

[0002]

2. Description of the Related Art Conventional fuel tanks for automobiles have P
A so-called turn sheet plated with a b-Sn alloy is used, and favorable results have been obtained in terms of corrosion resistance, workability, economical efficiency and the like. However, recently, due to environmental problems, use restrictions on lead have become stricter, and Pb-free fuel tank materials have been demanded. On the other hand, for the purpose of reducing the weight of automobiles, application of aluminum alloys to automobiles has been studied and used for some members. Thus, as a material for a fuel tank for automobiles, a material that does not contain Pb, is lightweight, and has excellent corrosion resistance, workability, and weldability is required.

[0003]

The present invention has been made under the circumstances described above, and it is an object of the present invention to provide an aluminum alloy plate for a fuel tank having good corrosion resistance, press formability and weldability, and a method for producing the same. It is intended.

[0004]

Means for Solving the Problems As a result of various studies on the effects of alloy components on the corrosion resistance, press formability and weldability of aluminum alloys, the present inventor appropriately selected the component composition of this alloy, The inventors have found that the above object can be achieved by specifying the thickness of the oxide film on the plate surface, and have completed the present invention. That is, the present invention is (1) wt%, Mg: 2.2-6.0% Cu: 0.03-0.15% Mn: 0.03-0.50% Cr: 0.03-0 .35% Fe: 0.30% or less Si: 0.20% or less, the balance consisting of Al and unavoidable impurities,
An aluminum alloy plate for a fuel tank, wherein the oxide film on the plate surface has a thickness of 500 nm or less.

(2) The aluminum alloy according to the above (1) further comprises: Zn: 0.03 to 1.5% Zr: 0.03 to 0.4% V: 0.03 to 0.4% Ti: An aluminum alloy plate for a fuel tank containing one or more of 0.005 to 0.2%.

(3) The aluminum alloy described in (1) or (2) above is cast, hot-rolled and cold-rolled to a predetermined plate thickness, and after annealing, one or more of sulfuric acid, nitric acid or phosphoric acid is added in total. A method for producing an aluminum alloy plate for a fuel tank, which comprises dipping in a pickling solution set at a temperature of 50 to 90 ° C. for 2 to 60 seconds and containing at a concentration of 5 to 15%, ( 4) The aluminum alloy according to (1) or (2) above is cast, hot-rolled and cold-rolled to a predetermined plate thickness,
A method for producing an aluminum alloy plate for a fuel tank, which comprises mechanically grinding 1 to 100 μm each on both sides after annealing.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
First, the reasons for limiting the component composition will be described. Mg: Mg is an alloying element that is a basic element of the alloy of the system of the present invention, and contributes to the improvement of strength and press formability. When the amount of Mg is less than 2.2%, sufficient strength and formability cannot be obtained. On the other hand, when the amount of Mg exceeds 6.0%, not only the stress corrosion cracking resistance is lowered, but also oxidation and heat during melting are caused. The manufacturability is remarkably deteriorated such as the deterioration of the inter-workability. Therefore, the amount of Mg is set within the range of 2.2 to 6.0%.

Cu: Cu is an element effective for increasing the strength of the alloy plate, but if it is less than 0.03%, its effect is not sufficient, and if it exceeds 0.15%, the corrosion resistance decreases. Therefore, the content of Cu is set to 0.03 to 0.15%. Mn: Mn is an element that not only is effective in improving strength and refining crystal grains, but is also an element that improves resistance to stress corrosion cracking, but if it is less than 0.03%, its effect is not sufficient, and
If it exceeds 50%, the above effect is saturated, and a coarse intermetallic compound is formed to reduce the formability, so the content is made 0.03 to 0.50%.

Cr: Cr, like Mn, is also added as an element effective for improving strength, refining crystal grains, and improving stress corrosion cracking resistance. If it is less than 0.03%, the effect is not sufficient, and if it exceeds 0.35%, the above-mentioned effect is saturated as well as in the case of Mn, and the formability is lowered. It was set to 0.35%. Fe, Si: Fe and Si are originally present in the aluminum alloy as unavoidable impurities, but when the content of Fe exceeds 0.30% and Si 0.2%, the formability is significantly deteriorated. Therefore, Fe and Si
Content of 0.30% or less and 0.20% or less, respectively.

In addition to the above basic composition, Zn, Zr, V,
It is also effective to contain one or more of Ti.
Of these, Zn is an element that contributes to the improvement of the strength of the alloy. If the content of Zn is less than 0.03%, the above effects are insufficient, while if it exceeds 1.5%, the formability and corrosion resistance are improved. Therefore, when Zn is added, the content is made 0.03 to 1.5%.

Further, Zr and V are effective elements for improving strength and refining crystal grains, but their contents are both 0.0.
If it is less than 3%, the above effect is not sufficiently obtained, and if it exceeds 0.4%, the above effect is not only saturated, but also a huge intermetallic compound is formed, which may adversely affect the formability and corrosion resistance. Therefore, the contents of Zr and V are both within the range of 0.03 to 0.4%. Further, Ti is generally added alone or in combination with a slight amount of B in order to refine the crystal grains of the ingot. In this case, the Ti content is 0.
If it is less than 005%, the above effect cannot be obtained, and if it exceeds 0.2%, the effect is saturated. Therefore, the Ti content is set within the range of 0.005 to 0.2%. The amount of B added is preferably 0.0005 to 0.03%.

Next, the thickness of the oxide film on the plate surface in the present invention will be described. Generally, resistance welding, arc welding, or the like is used for manufacturing the fuel tank. In resistance welding, if an oxide film with a high melting point and high insulation resistance is present on the plate surface, not only will electrode wear be severe and the electrode life will be shortened, but also the joint strength will vary greatly and continuous spotting performance will decrease. The problem arises. The present inventors investigated the effect of the surface oxide film thickness on the resistance weldability of aluminum alloys, and found that when the oxide film thickness was 500 nm or less, the electrode life was significantly improved and the variation in joint strength was reduced. It was Further, in arc welding, the oxide film on the surface of the aluminum alloy not only serves as a hydrogen supply source that causes blowholes, but also remains as inclusions in the weld metal to deteriorate the joint characteristics. Therefore, it is desirable that the surface oxide film thickness be as thin as possible, but 500 nm
At the film thicknesses below, the above defects hardly appear. Therefore, the thickness of the surface oxide film is set to 500 nm or less.

Next, the manufacturing method of the present invention will be described. The plate material may be manufactured by a conventional general method. For example, after making a billet by DC casting etc.,
A predetermined plate thickness is obtained by hot rolling and cold rolling. Next, after annealing, pickling or mechanical grinding is performed.
A sulfuric acid solution is preferable as the pickling solution from the viewpoint of economy and environmental problems, but it is not limited to the sulfuric acid solution as long as it is an inorganic acid capable of removing the oxide film in a short time. The mixed acid and the like can be used.
Further, the total concentration of such inorganic acids is suitably 5 to 15%. If the temperature of the pickling solution is less than 50 ° C., the time required for removing the oxide film is long, and conversely, if the temperature is 90 ° C. or more, the reaction is too fast to control the amount of fusing. Therefore,
The temperature of the pickling solution was 50 to 90 ° C. If the immersion time is less than 2 seconds, the oxide film is not sufficiently removed.
If it is more than a second, productivity will be reduced. Therefore, the immersion time in the pickling solution was set to 2 to 60 seconds.

Mechanical grinding may be performed by using a commonly used method. Grinding depth of 0.1 on both sides of plate
If the thickness is at least μm, the oxide film can be completely removed, but 1 μm
If it is less than 100 μm, the grinding accuracy is insufficient, and if it exceeds 100 μm, the yield of the plate is reduced, which is not economical. Therefore, the grinding depth was set to 1 to 100 μm on both sides of the plate. By these treatments, the thickness of the oxide film can be reduced to 500 nm or less. The acid cleaning and mechanical grinding may be performed continuously with a coil or may be performed with a cut plate.

The treatment after pickling or mechanical grinding is not particularly limited, but it is usually after removing by pickling solution or cutting oil or the like remaining on the surface after pickling or mechanical grinding. It is usual to dry and then apply a lubricating oil or rust preventive oil to prevent scratches on the surface and prevent rust. As described above, in the present invention, by appropriately adjusting the component composition of the alloy and by prescribing the thickness of the oxide film on the plate surface, excellent corrosion resistance, press formability and weldability are secured for a fuel tank. It is possible to

[0016]

EXAMPLES Next, the present invention will be described with reference to Examples. Example 1 Each alloy having the chemical composition shown in Table 1 was melted, cast, chamfered, homogenized, and then hot-rolled, cold-rolled and annealed by a conventional method to obtain a sheet having a thickness of 1.5 mm. A cold rolled annealed plate was produced. The obtained alloy plate was immersed in an aqueous solution of sulfuric acid at 50 to 90 ° C (sulfuric acid concentration: 10 wt%, pH <1) for 2 to 60
It was soaked in the second for acid cleaning. After acid cleaning, it was washed with pure water and dried. GDS analysis was performed on the dried plate surface layer to determine the thickness of the oxide film from the concentration distribution of Mg, Al, and O in the depth direction. The obtained pickled plate was evaluated for mechanical properties, corrosion resistance, press workability and weldability.

[0017]

[Table 1]

For the corrosion resistance, the corrosion resistance on the outer surface of the fuel tank was tested by salt spray test (from the rust generation state after spraying for 500 hours, ◯: no rust,
△: small rust, ×: evaluated in three stages of large rust), and the inner surface corrosion resistance was evaluated by the SAE method (corrosion condition after 26 weeks immersion in methanol mixed fuel ◯: no corrosion, Δ: small corrosion, ×: corrosion It was evaluated in three levels). The press formability was evaluated by the limit drawing ratio (LDR) and the Erichsen value in the cylindrical deep drawing test. Resistance weldability is 1,500 points or more in continuous welding points by spot welding (the number of welding points in which the tensile shear strength of the welded part has decreased to 60% or less of the tensile strength of the base metal in light of JIS Z 3140). The following was evaluated in two stages of x. In addition, the arc weldability was evaluated by performing two-stage evaluation of ◯ (good) and × (poor) based on the presence or absence of blowholes and cracks in the cross section of the welded portion by performing automatic MIG welding using an A5356 electrode wire.

The thickness of the oxide film is 5 in any alloy.
The thickness was less than 00 nm, which was less than the thickness specified in the present invention. Table 2 shows the evaluation results of mechanical properties, formability, corrosion resistance and weldability. Alloy No. Since the alloys 1 to 20 are within the composition range of the present invention, they show excellent properties in terms of formability, corrosion resistance and weldability. On the other hand, platinum No. No. 21 has a low strength because the amount of Mg is less than the component range of the present invention. No. 22 is excellent in strength and formability because the amount of Mg is more than the component range of the present invention, but inferior in corrosion resistance and weldability.

No. 23, 24, 26, 27, 29, 3
0 and 31 are Si, Fe, Mn, Cr and Z, respectively.
Since r and V are out of the component range of the present invention, the weldability is good, but the corrosion resistance is slightly inferior and the formability is remarkably inferior.
In addition, No. No. 25 is inferior in corrosion resistance and weldability because the amount of Cu is added in the component range of the present invention or more.
Nos. 28 and 32 are inferior in corrosion resistance because the Zn amount is also above the range of the components of the present invention. No. 32, Z
Since the contents of r, V and Ti are also above the range of the components of the present invention, the moldability is also poor. As described above, the alloys within the composition range defined in the present invention have the oxide film thickness of 5 by pickling.
When the thickness is not more than 00 nm, it is excellent in all of the characteristics of formability, corrosion resistance and weldability, and can be said to be a material suitable for a fuel tank.

[0021]

[Table 2]

Example 2 Among the alloys shown in Table 1, alloy No. 3 was melted, cast, chamfered and homogenized by a conventional method, and then hot-rolled and cold-rolled to produce a cold-rolled sheet having a sheet thickness of 1.5 mm. Part of the obtained cold-rolled sheet was annealed in the atmosphere and partly in an inert gas at 520 ° C. for 1 minute to obtain a cold-rolled annealed sheet. Some of the sheets annealed in the atmosphere are 70
Acid cleaning was carried out by immersing in a sulfuric acid aqueous solution (sulfuric acid concentration: 10 wt%, pH <1) at 1 ° C. for 1 second and 30 seconds. After acid cleaning, it was washed with pure water and dried. Further, with respect to a part, both sides of the plate were mechanically ground by 10 μm. The surface layer of the alloy plate thus obtained was subjected to GDS analysis to obtain M in the depth direction.
The thickness of the oxide film was determined from the concentration distribution of g, Al and O. Thereafter, each alloy plate was evaluated for formability, corrosion resistance and weldability.

Corrosion resistance was determined by salt spray test (corresponding to rust generation after spraying for 500 hours, ◯: no rust,
△: small rust, ×: evaluated in three stages of large rust), and the inner surface corrosion resistance was evaluated by the SAE method (corrosion condition after 26 weeks immersion in methanol mixed fuel ◯: no corrosion, Δ: small corrosion, ×: corrosion It was evaluated in three levels). The press formability was evaluated by the limit drawing ratio (LDR) and the Erichsen value in the cylindrical deep drawing test. Resistance weldability is 1,500 points or more in continuous welding points by spot welding (the number of welding points in which the tensile shear strength of the welded part has decreased to 60% or less of the tensile strength of the base metal in light of JIS Z 3140). The following was evaluated in two stages of x. In addition, the arc weldability was evaluated by performing two-stage evaluation of ◯ (good) and × (poor) based on the presence or absence of blowholes and cracks in the cross section of the welded portion by performing automatic MIG welding using an A5356 electrode wire. Table 3 shows the evaluation results.

[0024]

[Table 3]

The thickness of the surface oxide film is defined in the present invention both in the case where the oxide film is removed by pickling or mechanical grinding at 70 ° C. for 30 seconds after annealing in air and the case where annealing is performed in an inert gas. Since it is less than the thickness, it is excellent in all characteristics such as formability, corrosion resistance and weldability,
It can be seen that the alloy plate is suitable for a fuel tank. In contrast, as-annealed in air or pickling time is 1
In the case of the second, the thickness of the surface oxide film is 50 specified by the present invention.
Since it exceeds 0 nm, the formability is satisfactory, but the weldability is remarkably inferior and the corrosion resistance is somewhat inferior.

[0026]

As is apparent from the above description, according to the present invention, the thickness of the oxide film on the surface of the aluminum alloy plate is 500.
When the thickness is not more than nm, excellent properties can be obtained in any of mechanical properties, formability, corrosion resistance, and weldability, and an aluminum alloy plate suitable for a fuel tank can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyasu Ukiana 2-6-3 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Steel Corporation

Claims (4)

[Claims] 1. By weight%, Mg: 2.2-6.0% Cu: 0.03-0.15% Mn: 0.03-0.50% Cr: 0.03-0.35% Fe : 0.30% or less Si: 0.20% or less, with the balance being Al and inevitable impurities,
An aluminum alloy plate for a fuel tank, wherein the oxide film on the plate surface has a thickness of 500 nm or less. 2. The aluminum alloy according to claim 1, further comprising: Zn: 0.03 to 1.5% Zr: 0.03 to 0.4% V: 0.03 to 0.4% Ti: 0. An aluminum alloy plate for a fuel tank containing one or more of 005 to 0.2%. 3. The aluminum alloy according to claim 1 or 2 is cast, hot-rolled and cold-rolled to a predetermined plate thickness, and after annealing, one or more of sulfuric acid, nitric acid or phosphoric acid is added in a total amount of 5 to 5.
A method for producing an aluminum alloy plate for a fuel tank, comprising dipping for 2 to 60 seconds in a pickling solution which is contained at a concentration of 15% and is set to a temperature of 50 to 90 ° C. 4. The aluminum alloy according to claim 1 or 2 is cast, hot-rolled and cold-rolled to a predetermined plate thickness, and after annealing, both sides of the plate are mechanically ground by 1 to 100 μm. And a method for manufacturing an aluminum alloy plate for a fuel tank.