JP2000313932A - Aluminum alloy sheet for coating excellent in filiform corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the filiform corrosion resistance as corrosion resistance after coating by incorporating Si, Mg and Cu in specified ranges into an Al alloy sheet and depositing the surface of the alloy sheet with zinc phosphate by the value equal to or above the specified one. SOLUTION: Into an Al alloy sheet for coating, by mass, 0.2 to 1.8% Si, 0.2 to 1.6% Mg and 0.3 to 1.5% Cu are incorporated. The surface of this Al alloy sheet is coated with zinc phosphate of >=1.5 g/m2 coating weight. The compsn. of the Al alloy can be incorporated with other elements such as Fe, Ni, V, Mn, Cr, Zr, Sc, Ag or the like in accordance with the use and the characteristics to be required. As a method for controlling the coating weight of zinc phosphate in the Al alloy sheet to >=1.5 g/m2, the one in which the amt. of free fluorine ions to be added to a zinc phosphate treating bath is increased for improving the etching properties of Al is given. This Al alloy sheet is excellent in filiform corrosion resistance although being incorporated with Cu.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a surface coated with zinc phosphate, which is excellent in corrosion resistance after coating, and has excellent rust resistance (fiber rust resistance). The present invention relates to an Al-Mg-Si-based aluminum alloy (hereinafter, aluminum is simply referred to as Al) plate suitable for use in panel materials and various members.

[0002]

2. Description of the Related Art Aluminum alloy plates have been used in place of steel materials for outer panels, structural materials or parts of transport vehicles such as automobiles, ships and vehicles in order to reduce weight. And, among the aluminum alloy sheets, AA from the viewpoint of material properties excellent in moldability and bake hardenability or recyclability
Al alloys of 6000 series to Al-Mg-Si series Al alloys (hereinafter simply referred to as 6000 series Al alloys) have begun to be used.

[0003] This 6000 series Al alloy is basically composed of Si: 0.2-1.
Al-M containing 8% (mass%, the same applies hereinafter), Mg: 0.2-1.6%
It is a g-Si based aluminum alloy. And this 6000 series Al
The alloy secures the formability with low proof stress during press forming, and improves the proof strength by age hardening during baking coating after press forming, thereby ensuring the required strength. Further, when the scrap is reused as a raw material for dissolving the Al alloy, the amount of alloy is relatively small and the original 6000 series Al alloy ingot is easily recyclable. Therefore, it is more advantageous than AA 5000 series Al alloys which have been conventionally used for transportation and have a large amount of alloy such as Mg.

[0004] This 6000 series Al alloy is used as a material for automobiles after forming (or without forming) a rolled sheet or extruded material of Al alloy by press forming or bending, etc. A phosphate treatment (chemical conversion treatment) of zinc or the like is applied, and then a cationic electrodeposition coating is applied, and then a coating such as an intermediate coating and a top coating is applied by spray coating and used.

On the other hand, the 6000 series Al alloy sheet has lower press formability and hemmability (180 ° bending workability) than the conventionally used 5000 series Al alloy sheet. Therefore, 60
In order for the 00 series Al alloy plate to be applied to members that are subjected to severe forming processing, such as outer panels of automobiles that are subjected to hem processing after press forming, it is necessary to improve these formability.

Conventionally, as a means for improving the formability of a 6000 series Al alloy sheet, the chemical composition of the 6000 series Al alloy sheet has been controlled. For example, JP-A-64-65243
No., JP-A-5-291834, JP-A-7-228939, etc., as disclosed in the basic composition Si (excess Si amount) and Mg
While controlling the amount, or the amount and form of the precipitate such as Mg ₂ Si, it is possible to improve the formability by adding Cu or the like.
JP-A-6-2064, JP-A-6-136478, JP-A-8-109428
And numerous proposals have been made in JP-A-9-209068 and JP-A-9-202933.

[0007] Further, it is disclosed in Japanese Patent Application Laid-Open Nos. 61-46304 and 63-180331 that the surface of an Al alloy plate is roughened to improve lubricity during forming and improve formability. JP 8-
Many have been proposed in 168826, JP-A-9-78169 and the like. Among them, for example, in Japanese Patent Application Laid-Open No. 61-46304, the maximum roughness (Rmax) within 1 inch in the direction parallel and perpendicular to the rolling direction of the Al alloy sheet is 2 μm or more, and
The number of peaks or valleys with a height or depth of 25 inches or more in inches (PPI) is 30 or more, and the surface of the Al alloy plate is roughened to improve overhang and bending workability. Is disclosed.

However, in these 6000 series Al alloy sheets, the addition of Cu certainly improves the formability, but deteriorates the rust resistance, which is the corrosion resistance after painting. That is, more specifically, it is known that when 0.3% or more of Cu is added, the thread rust resistance is extremely deteriorated as compared with the case where Cu is not added.

The tendency of the rust resistance to deteriorate is 6000
In the system Al alloy plate, for improving the formability,
It is also promoted by roughening the surface of the Al alloy plate. Therefore, the problem of improving the formability and improving the rust resistance is a contradictory problem that if the formability is improved, the rust resistance is deteriorated. In a single plate, both are achieved at the same time. The fact is that there is no means yet.

Therefore, in order to solve this problem, in order to improve the rust resistance of a 6000 series Al alloy sheet containing 0.2 to 3.0% of Cu for improving the formability, a 6000 series Al alloy sheet containing Cu is added.
Using an Al alloy plate as the core material, and using an Al alloy plate with better thread rust resistance than the 6000 series Al alloy as a skin material, the thickness of this skin material is set to 2 to 20% of the total thickness on one side, An Al alloy clad plate for forming processing clad on one side or both sides has been proposed.

For example, JP-A-63-190131, JP-A-63-1
No. 95241 proposes a clad plate obtained by cladding a pure Al alloy plate having a purity of 99.0% or more as a skin material. Also,
JP-A-62-122744 and JP-A-63-262442 disclose AA.
A clad plate has been proposed in which an Al-Mn-based Al alloy plate containing 0.3 to 4% of Mn, such as 3000 series, is clad as a cladding material. Further, JP-A-62-122745 discloses Zn0.
A clad plate has been proposed in which an Al-Zn-based Al alloy plate containing 5 to 17% is clad as a cladding material. Also, JP-A-62-207
No. 642, JP-A-63-280626, etc.
A clad plate has been proposed in which an Al-Mg-based Al alloy plate containing 0.1 to 3.5% of Mg is clad as a cladding material.

[0012]

SUMMARY OF THE INVENTION These prior arts are:
In each case, it is assumed that properties such as moldability and bake hardenability of the 6000 series are not impaired. However, pure as skin material
When an Al alloy plate is used, scratches are likely to occur on the soft pure Al alloy plate during press forming, making it virtually impossible to press form, and dents and flaws also occur as structural materials such as automobiles Not easy to use and practical.

AA 3000 series, AA 5000 series
In the case of using an Al or AA 7000 series Al alloy plate, it is difficult to produce a clad plate itself having an adhesive property that can withstand press forming and bending. This is because the amount of alloy components of these skin materials is large, and the interface of the Al alloy plate is easily oxidized during rolling clad. Therefore, if the clad plate is manufactured while preventing these oxidations, the manufacturing cost will increase, which is not practical.

Further, as a skin material, pure Al type, AA 3000 type, AA
When a 5000 series or AA 7000 series Al alloy plate is used, no cladding (single)
Compared to the 000 series Al alloy sheet, the characteristics of the 6000 series Al alloy sheet, such as low yield strength at the time of forming and high yield strength due to bake hardening, are inevitably reduced. Therefore, Cu
In fact, there has been no effective technology for improving the rust resistance of 6000 series Al alloy sheets containing chromium.

The present invention has been made in view of such circumstances, and has as its object to improve yarn rust resistance.
An object of the present invention is to provide a 6000 series Al alloy sheet containing 0.3 to 1.5% of Cu.

[0016]

In order to achieve this object, the gist of the present invention is that Si: 0.2 to 1.8%, Mg: 0.2 to 1.6%, C:
u: containing 0.3 to 1.5%, an Al-Mg-Si-based aluminum alloy plate to be coated after coating the surface with zinc phosphate, and the adhesion amount of the zinc phosphate was 1.5 g / m ² or more. That is.

As a result of repeated studies, the present inventors have found that if the amount of zinc phosphate deposited on an Al-Mg-Si-based Al alloy plate with a high Cu content is increased by a certain amount or more, the current phosphoric acid treatment and It has been found that when a coating is applied by applying a coating base treatment such as a cationic electrodeposition coating treatment, the rust resistance, which is the corrosion resistance after coating, is remarkably improved.

Of course, in the Al-Mg-Si-based Al alloy plate, the increase in the amount of zinc phosphate attached when Cu is contained is reported in the summary of the 93rd Autumn Meeting of the Japan Institute of Light Metals (1997), 31, 61-62. Chemical conversion treatment of 6000 series aluminum alloy sheet described on page
(Kada, Nomura, Nishimura, Kurata), pp. 139, pp. 61-62 of the 95th Annual Meeting of the Japan Institute of Light Metals (1998). Influence of trace added elements ”(Ueda, Ito) and others. Furthermore, Al
In alloy sheets, increasing the amount of zinc phosphate attached can improve the rust resistance.
(1997), pp. 161-168, "Zinc phosphate treatment technology for aluminum alloys for automobile bodies" (Usami, Su)
And the like.

[0019] However, the and documents, in Al-Mg-Si-based Al alloy plate containing Cu, best zinc phosphate coating weight of not only the data of up to 1.5 g / m ^2, moreover, these phosphorus There is no data or description on the thread rust resistance of the Al alloy sheet with increased zinc oxide adhesion.

In addition, the above-mentioned document does not show any Al alloy system based on data showing an increase in the amount of zinc phosphate attached and an improvement in yarn rust resistance, and it is unclear what Al alloy system is used. And Al
Even the data showing the relationship between the zinc phosphate treatment time and the zinc phosphate adhesion amount for the -Mg-Si-based Al alloy sheet is only data with the maximum zinc phosphate adhesion amount up to 1.5 g / m ² .

[0021] That is, in these documents, the correlation between the zinc rust resistance and the rust resistance when the zinc phosphate adhesion amount is as large as 1.5 g / m ² or more on the Al-Mg-Si-based Al alloy plate is unknown. is there. Generally, it is said that as the zinc phosphate adhesion increases, the rust resistance of the Al alloy plate also improves. But this is
If the chemical composition of the Al alloy plate and the zinc phosphate treatment conditions are different, the behavior will naturally be different, it is not a problem that can be said uniformly, it is necessary to confirm for each specific alloy, Technical common sense.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION (Zinc phosphate adhesion amount)
As described above, the adhesion amount of zinc phosphate is 1.5 g / m ² or more, preferably 2.0 g / m ² or more. The amount of zinc phosphate attached is 1.
If it is less than 5 g / m ^2, the high-Cu which contains Cu or 0.3% Al-Mg-Si
There is no effect of improving the rust resistance of the system Al alloy sheet.

And, in the present invention, high Cu Al-Mg-Si based Al
The excellent effect of improving the rust resistance of alloy sheets means that the maximum length L of rust generated under the following rust resistance test conditions is
We say that it is 3mm or less. The test conditions for yarn rust resistance were as follows: after a 7 cm cross-cut was made on the surface of the painted test piece, immersed in a 3% HCl aqueous solution at 35 ° C for 2 minutes, and then at a constant temperature of 40 ° C and 85% RH. It shall be left for 1500 hours in a constant humidity atmosphere, and the maximum length L (the distance in the vertical direction from the cross cut) of the thread rust generated at this time shall be measured.

For this reason, the amount of zinc phosphate adhering to the Al alloy plate is reduced.
As a method for adjusting the amount to 1.5 g / m ² or more, preferably 2.0 g / m ² or more, in order to improve the etching property of Al, the amount of free fluorine (F) ions added to the zinc phosphate treatment bath is reduced. There is a method of increasing the amount, and if a high concentration of about 150 to 400 ppm is added, the amount of zinc phosphate deposited on the Al alloy plate can be secured.
However, the amount of zinc phosphate deposited differs depending on the chemical composition of the Al alloy plate and the zinc phosphate treatment conditions, so the amount of free fluorine (F) ions should be determined individually according to these specific conditions. It is.

(Applicable Al Alloy) Next, the Al alloy in the present invention
Alloy sheets have mechanical properties such as tensile strength and proof stress, workability,
6000 series Al alloy with weldability. In particular, in the case of transport applications, as described above, the 6000 series Al alloy ensures the formability at the time of press forming with low yield strength, and improves the yield strength by age hardening during baking coating after press forming, The required strength can be secured. Further, when scrap is reused as a raw material for dissolving an Al alloy, there are considerable advantages such as a relatively small amount of alloy and excellent recyclability such as easy acquisition of an original 6000 series Al alloy ingot.

The preferred properties of the 6000 series Al alloy sheet, for example, for an automobile panel, are that the Al alloy sheet has a relatively low proof stress at the time of forming and is excellent in formability, and is subjected to painting and baking hardening after forming. The proof stress after heating is, for example, a high proof stress of 100 N / mm ² or more as a proof stress after heating at 175 ° C. for 30 minutes after 2% stretching.

In order to satisfy these characteristics, the preferable range of the chemical component composition is the component standard of the Al-Mg-Si-based 6000 series Al alloy (6101, 6003, 6151, 6061, 6N01, 6063, etc.). Basically, Si: 0.2 to 1.6%, Mg:
It contains 0.2 to 1.6%, and also contains Fe, Mn, Cr, Zn, Ti, etc., in the order of AA to JIS. But 6000
Even if it does not conform to each component standard of the system Al alloy, as long as it has the basic characteristics of the 6000 system Al alloy, to improve the characteristics further or add other characteristics, change the component composition Is appropriately allowed.

In the present invention, the content of Cu is indispensable in order to improve the formability.
It may not be within the AA to JIS component standards. Therefore, the elements other than the basic components Si and Mg are from AA to
Even if it does not conform to each component standard of JIS, as long as it has the above-mentioned basic characteristics, it is permissible to change the component composition as needed to further improve the characteristics and add other characteristics. In this regard, depending on the specific application and required characteristics, Fe, N
It is permissible to appropriately include other elements such as i, V, Mn, Cr, Zr, Sc, and Ag.

Next, with regard to the content of each element of the Al alloy sheet of the present invention, critical significance and preferred ranges will be described.

Mg: 0.2-1.6%. Mg forms a compound phase with Si by artificial aging (paint baking, etc.)
Further, the Cu-containing composition is an essential element for further forming a compound phase with Cu and Al to impart high strength (proof stress) or bake hardenability during use. If the content of Mg is less than 0.2%, sufficient strength cannot be obtained even with artificial aging. On the other hand, when the content exceeds 1.6%, more desirably more than 1.0%, the proof stress becomes too high, and on the contrary, the formability such as bending is hindered. Therefore, the content of Mg is 0.2-1.6%, preferably
The range is 0.2 to 1.0%.

Si: 0.2-1.8%. Si also precipitates as Mg ₂ Si together with Mg by artificial aging, resulting in high strength during use
(Proof stress) is an essential element for imparting, but if the content is less than 0.2%, sufficient strength cannot be obtained by artificial aging,
If it is contained in excess of 1.8%, it precipitates as coarse particles during casting and quenching, and impairs formability, such as lower elongation. Therefore, the content of Si is set in the range of 0.2 to 1.8%. The precipitation state during baking heating was Mg and
It is greatly affected by the ratio of the Si content. When Mg / Si exceeds 1, the precipitation becomes coarse, and the effect of improving the strength is reduced. Therefore, Mg / Si is preferably set to 1 or less.

Cu: 0.3-1.5%. Cu is Mg when baking and heating,
It forms a compound phase with Al and precipitates, imparts bake hardenability, and improves moldability in a solid solution state during T4 refining. If the Cu content is less than 0.3%, these effects will not be obtained, and if it exceeds 1.5%, the effects will be saturated. On the other hand, if the Cu content exceeds 1.5%, the corrosion resistance after coating, particularly the yarn rust resistance, is rather deteriorated. Therefore, the content of Cu is
0.01 to 1.5%.

Next, Zn, Ti, B, Be, Mn, Cr, Zr, V
Is an element selectively contained depending on the purpose.

Zn: 0.005 to 2.0%. Zn has an effect of improving yarn rust resistance. However, if the content of Zn is less than 0.005%, a sufficient effect cannot be obtained. On the other hand, if the content exceeds 2.0%, the corrosion resistance is significantly reduced. Therefore, the content of Zn is preferably in the range of 0.005 to 2.0%.

Ti: 0.001 to 0.1%. Ti is an element added to refine the crystal grains of the ingot and improve press formability. However, if the content of Ti is less than 0.001%, this effect cannot be obtained. On the other hand, if the content of Ti exceeds 0.1%, coarse crystals are formed and the formability is reduced. Therefore, Ti
Is preferably in the range of 0.001 to 0.1%.

B: 1 to 300 ppm. B, like Ti, is an element added to refine the crystal grains of the ingot and improve press formability. However, if the content of B is less than 1 ppm, this effect cannot be obtained, while if the content is more than 300 ppm,
Again, coarse crystals are formed and formability is reduced. Therefore, the content of B is preferably in the range of 1 to 300 ppm.

Be: 0.1 to 100 ppm. Be is an element contained to prevent re-oxidation of the Al melt in the air. However, if the content is less than 0.1 ppm, this effect cannot be obtained, while if the content exceeds 100 ppm, the material hardness increases,
Decreases moldability. Therefore, the content of Be is 0.1 to
It is preferable to be in the range of 100 ppm.

Mn: 1.0% or less, Cr: 0.3% or less, Zr: 0.15% or less, V: 0.15% or less. These elements are used during the homogenizing heat treatment and during the subsequent hot rolling, Al ₂₀ Cu ₂ Mn ₃ , Al ₁₂ Mg ₂ Cr, Al
₃ Zr, and generates dispersed particles such as Al ₂ Mg ₃ Zn _3. Since these dispersed particles have an effect of hindering the movement of the grain boundary after recrystallization, fine crystal grains can be obtained. However, an excessive content tends to generate a coarse intermetallic compound at the time of melting and casting, becomes a starting point of destruction at the time of molding, and causes a decrease in moldability. Further, an excessive content of Zr tends to make the microstructure needle-like, deteriorating fracture toughness and fatigue properties in a specific direction, and further deteriorating formability. Therefore, the content of these elements, respectively, Mn: 1.0% or less, Cr: 0.3% or less, Zr: 0.15% or less,
V: 0.15% or less.

Fe: Fe contained as an impurity is Al ₇ Cu ₂ F
e, Crystallized substances such as Al ₁₂ (Fe, Mn) ₃ Cu ₂ and (Fe, Mn) Al ₆ are generated. These precipitates degrade fracture toughness and fatigue properties, as well as formability. In particular, when the content of Fe exceeds 0.5%, these characteristics are significantly deteriorated.
Preferably, it is 0.5% or less. In addition, crystallized substances generated during casting are, in addition to the above-mentioned Fe system, Al ₂ Cu ₂ Mg, Al ₂ Cu ₂ , Mg ₂ Si
It is preferable that these are dissolved sufficiently in the Al matrix by solution treatment and quenching. In addition, Ni is preferably set to 0.05% or less.

Further, the surface of the plate is roughened by, for example, cold rolling or light pressure (skin pass) rolling with a roll roughened by a shot dull or a laser dull, and is adhered to the Al alloy plate surface. Improving the lubricity of lubricating oil to further improve press formability is also included in the scope of the present invention.

(Manufacturing method of Al alloy plate) The base plate of the Al alloy itself is manufactured as a plate by a conventional method such as rolling, extrusion, forging, casting or the like. That is, the molten aluminum alloy melt-adjusted within the component standard range is cast by appropriately selecting a normal melting casting method such as a continuous casting rolling method and a semi-continuous casting method (DC casting method). Next, the Al alloy ingot is subjected to a homogenizing heat treatment, and is subjected to hot rolling, cold rolling and roughening or intermediate annealing, if necessary, by a tempering treatment (solution treatment and quenching treatment, aging treatment, overaging treatment). A plate product having the following characteristics:

At this time, the roll in the final pass of the cold rolling or the roll in the skin pass rolling after the cold rolling is rolled as a roll roughened by shot dull or laser dull finish, and rolled on the surface of the Al alloy plate. The maximum roughness (R _Z ) within 1 inch in the direction parallel and perpendicular to the rolling direction can be roughened to 2 μm or more, preferably 5 μm or more by transferring it can.

The method of roughening the surface of the Al alloy plate is as follows.
Mechanically, such as shot blasting directly on the surface of the Al alloy plate,
Alternatively, the surface may be chemically roughened by alkali etching or the like.
The method of controlling Rmax (μm) is preferable because it is easy to control and efficient.

After the tempering treatment, the surface of the Al alloy plate is appropriately cleaned. These washings are performed by appropriately combining an acid solution such as nitric acid and sulfuric acid, an alkaline solution such as caustic soda, or a commercially available detergent.

In order to prevent the Al alloy plate from being oxidized when the manufactured Al alloy plate is stored until press-formed, a rust-preventive oil is applied to the surface of the Al alloy plate or the zinc-based plating is applied. Applying is also effective.

[0046]

Embodiment 1 Next, an embodiment of the present invention will be described. Al alloy ingots (No. 2, 3) with compositions corresponding to AA 6151, 6061, and 6N01 standards and with an adjusted amount of Cu from No. 1 to No. 4 shown in Table 1.
, 4 actively contain Cu and No. 1 does not actively contain Cu) by DC casting method, and then ingot was subjected to a homogenizing heat treatment at 540 ° C for 8 hours, Hot rolled to 3.5mm. Next, cold-rolled to a thickness of 1.0 mm without intermediate annealing,
Solution cooling treatment at 550 ° C for 1 hour using a nitrite furnace followed by water cooling
(Water quenching) was performed to prepare an Al-Mg-Si-based Al alloy plate. In the final pass of cold rolling, the maximum roughness Rmax of the surface of the Al alloy plate was all controlled to 3.0 μm by cold rolling using a roll having a predetermined surface roughened by shot dull. The bake hardenability of the Al alloy plate was evaluated by measuring the proof stress before and after baking. Also this
The formability of the Al alloy plate was evaluated by measuring elongation. Table 2 shows the results.

(Zinc Phosphate Treatment Conditions) These Al alloy sheets U
The bent part (R part) of the bent molded material was sampled as a corrosion resistance test piece after painting, the lubricant on the surface was degreased and completely removed, and then, in both the invention examples and the comparative examples, the colloid of titanium phosphate Dispersion colloidal liquid (colloidal titanium solution:
The product was treated with PBL3020 (trade name, manufactured by Nippon Parker Rising Co., Ltd., temperature 25 ° C, immersion for 1 minute) and treated with zinc phosphate (temperature 42 ° C, immersion for 2 minutes). At this time, the amount of free fluorine (F) ions added to the zinc phosphate treatment bath is 50 to 400.
Adjustment was made in the range of ppm to control the amount of zinc phosphate attached to each test piece. Table 2 shows the zinc phosphate coating weight of each test piece, Nanba2～4 in Table 2 are invention examples in which the amount of zinc phosphate deposition and 1.5 g / m ² or more, No.1 Table 1 6016 system without Cu
Reference examples in which the amount of zinc phosphate attached to the Al alloy plate was less than 1.5 g / m ² , and Nos. 5 to 7 are comparative examples in which the amount of zinc phosphate attached was less than 1.5 g / m ² . In addition, in the case of Invention Example No. 3 and Comparative Example No. 7 only, the surface of the test piece was subjected to Zn plating at ² g / m ² by displacement plating before zinc phosphate treatment.

(Coating conditions) Then, under the same coating conditions, a cationic electrodeposition coating (baking at 170 ° C. for 20 minutes) was performed on these test pieces, and then a 30 μm thick polyester melamine-based coating film was provided as an intermediate coating. Then, baking was performed at 140 ° C. for 20 minutes, and a polyester melamine-based coating film having a thickness of 30 μm was provided as an overcoat, and baking was performed at 140 ° C. for 20 minutes. A polyester melamine-based coating was provided.

(Corrosion Resistance Test after Coating) The coated test pieces of the invention examples and comparative examples were all subjected to a yarn rust evaluation test under the same conditions. Table 2 also shows the results of these evaluations. The rust resistance test was performed by cutting a 7 cm cross-cut on the surface of the painted test piece, immersing it in a 3% HCl aqueous solution at 35 ° C for 2 minutes, and then in a constant temperature and humidity condition of 40 ° C and 85% RH. Atmosphere 15
After leaving for 00 hours, the maximum length L (the distance in the vertical direction from the cross cut) of the generated thread rust was measured. Then, the maximum length L (mm) of the thread rust generated on the test piece is represented by ○: L ≦ 2.0,
Δ: 2.0 <L <3.0, ×: L ≧ 3.0.

As is evident from the results in Table 2, invention examples within the scope of the present invention when the zinc phosphate adhesion amount is 1.5 g / m ² or more.
Nos. 2 to 4 have the maximum length of the thread rust of about 2.0 mm, similar to the reference example No. 1 of the 6016-based Al alloy plate containing no Cu, despite containing Cu. Excellent in rust resistance.

On the other hand, the amount of zinc phosphate deposited was 1.5 g / m ²
Comparative Examples Nos. 5 to 7 in which the maximum length of the thread rust was 4.0
mm, which indicates that the rust resistance is extremely poor as compared with the invention examples. From these results, it can be seen that as the zinc phosphate attachment amount increases in the region of 1.5 g / m ² or more, the rust resistance improves as the amount increases. In addition, the tensile properties of the invention examples in Table 2 show that the bake hardenability and workability are not inferior to or superior to that of Reference Example No. 1 of the 6016 Al alloy sheet containing no Cu.

Therefore, the above facts support the critical significance of the zinc phosphate deposition amount of 1.5 g / m ² of the present invention and the significance of preferable conditions for achieving excellent corrosion resistance.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

Example 2 Further, an Al alloy plate having the chemical components No. 1, 3 and 4 shown in Table 1 was manufactured under the same conditions as in Example 1, and a test piece was obtained. Also, 5082 (5000 series) Were prepared under the same conditions as in Example 1 and the amount of free fluorine ions added to the zinc phosphate treatment bath was adjusted to 50%. Adjustment was made in the range of 400400 ppm to change the amount of zinc phosphate attached to each test piece. The test pieces were not subjected to zinc plating before the zinc phosphate treatment. Then, a coating film was formed on each of the test pieces in which the amount of zinc phosphate attached was changed under the same conditions as in Example 1, and a rust resistance evaluation test was performed.

Each of the test pieces obtained from the test results
Figure 1 shows the relationship between the maximum length L of thread rust and the amount of zinc phosphate attached
(a) to (d). Fig. 1 (a) is an example of No. 1 that does not actively contain Cu in Table 1 (Cu: 0.02%), and Figs. 1 (b) and 1 (c) are examples that actively contain Cu. 1 (b) is No.3 (Cu: 0.4%), Fig.1 (c) is No.4
(Cu: 0.7%). FIG. 1D corresponds to the 5082 alloy (Cu: 0.1%).

As can be seen from FIGS. 1 (a) to 1 (d), the 6000 series which is a target of the present invention and contains 0.4% and 0.7% of Cu positively.
In the case of the Al alloy, the maximum length L of the thread rust changes rapidly (decreases) at the boundary of the zinc phosphate adhesion of 1.5%. Zinc oxide adhesion
At 2.0% or more, the maximum length L of the thread rust can be suppressed to 3.0 mm or less. And this 6000 series Al containing Cu
The tendency in the alloy is shown in Fig. 1 (a) for the 6000 series Al alloy without Cu.
And the behavior or tendency of the 5082 alloy in FIG. 1 (d). That is, in the 6000 series Al alloy and 5082 alloy that do not contain Cu, even if the zinc phosphate adhesion amount increases, the maximum length L of the thread rust does not decrease so much. There is no clear correlation as much as the 6000 series Al alloy containing.

Therefore, based on these facts, the behavior of the rust resistance of the 6000 series (Al-Mg-Si series) Al alloy sheet containing a large amount of Cu is different from that of the 6000 series Al alloy sheet containing no Cu and the other 5000 series. It can be seen that the behavior is significantly different from that of the Al alloy plate. And, as described above, in the 6000 series Al alloy plate containing Cu, even if the relationship with the zinc rust resistance when the zinc phosphate adhesion amount is less than 1.5 g / m ² is known, the zinc phosphate adhesion amount However, the correlation with the rust resistance when 1.5 g / m ² or more is adhered has not been known so far, and if the chemical composition of the Al alloy plate and the zinc phosphate treatment conditions are different, the behavior will naturally differ. Is supported.

[0059]

According to the present invention, Cu is contained in an amount of 0.3 to 1.5%,
It is possible to improve the rust resistance of an Al-Mg-Si-based aluminum alloy sheet with improved formability, and to provide a 6000-series Al alloy sheet with both contradictory formability and excellent rust resistance. . Accordingly, the use of the Al alloy plate for transportation equipment such as automobiles, vehicles, ships, etc., has a great industrial value in that it can be expanded.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of the present invention and showing a relationship between a maximum length of thread rust and an attached amount of zinc phosphate.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 22/12 C23C 22/12 (72) Inventor Mariko Sakata 1-5-5 Takatsudai, Nishi-ku, Kobe City Stock Company Kobe Steel, Kobe Research Institute F-term (reference) 4D075 BB26Z BB75X BB89Z CA33 DA03 DB07 DC13 4F100 AA02A AA04B AB09A AB10A AB11A AB17A AB31A BA02 BA03 BA04 BA07 BA10A BA10C BA10D CC00C CC00DEJBEJC JL01 YY00 YY00A YY00B 4K026 AA09 AA22 BA04 BB07 BB08 CA16 CA23 CA28 DA16 EA11

Claims (9)

[Claims] 1. Si: 0.2-1.8% (mass%, the same applies hereinafter), M
g: 0.2-1.6%, Cu: containing 0.3-1.5%, coated Al-Mg-Si based aluminum alloy plate coated with zinc phosphate, the adhesion amount of the zinc phosphate is 1.5 g / m ² or more, an aluminum alloy plate for coating with excellent thread rust resistance. 2. The aluminum alloy plate for coating excellent in thread rust resistance according to claim 1, wherein the adhesion amount of the zinc phosphate is 2.0 g / m ² or more. 3. The aluminum alloy sheet for coating excellent in yarn rust resistance according to claim 1, wherein a base treatment for cationic electrodeposition coating is performed after coating with the zinc phosphate. 4. The aluminum alloy sheet for coating excellent in yarn rust resistance according to claim 1, wherein the cationic electrodeposition coating does not contain lead. 5. The aluminum alloy sheet for coating excellent in yarn rust resistance according to claim 1, wherein the cationic electrodeposition coating does not contain tin. 6. The aluminum alloy sheet for coating excellent in thread rust resistance according to claim 1, wherein the aluminum alloy material is used after being coated after forming. 7. The proof stress of the aluminum alloy material after baking hardening treatment is 100 N / mm ² or more.
7. The aluminum alloy sheet for coating according to any one of the above, which is excellent in yarn rust resistance. 8. The aluminum alloy sheet for coating excellent in thread rust resistance according to claim 1, wherein the aluminum alloy sheet is for a transport machine. 9. The aluminum alloy sheet for coating excellent in thread rust resistance according to claim 1, wherein the aluminum alloy material is used for automobile materials.