JP2001294963A - Aluminum alloy sheet excellent in corrosion resistance and coating substrate treatability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aluminum alloy sheet excellent in chemical convertibility, corrosion resistance, adhesive strength of coating film or the like by adopting an alloy design in which the concentration of Mg in the surface layer part is controlled to <=20%. SOLUTION: This aluminum alloy has a composition containing, by weight 2.5 to 5.5% Mg, 0.05 to 0.4% Cu, 0.005 to 0.2% Mn, 0.005 to 0.1% Cr, 0.01 to 0.05% Ti, <=0.08% Si, <=0.1% Fe and 0.0001 to 0.01% Be and further containing, at need, one or more kinds selected from 0.001 to 0.1% Zr, 0.001 to 0.1% V and 0.0001 to 0.01% B, and the residue is substantially Al. A substrate high in affinity with a coating film can be formed by a chemical treatment using zinc phosphate, and the coated sheet is applied to such as an automotive outside sheet excellent in corrosion resistance and adhesion for a coating film.

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 and coating undercoating properties, which is suitable as a coated sheet material for an automobile outer panel or the like.

[0002]

2. Description of the Related Art An aluminum alloy sheet used for an automobile outer panel is generally used after being applied with a coating. Therefore, an excellent coating base treatment property is required. In addition, corrosion resistance after coating, particularly yarn rust resistance, is required. The undercoating property was given by chromate treatment using chromic acid. However, due to the environmental impact of using chromic acid and the requirement for simultaneous undercoat treatment of cold-rolled steel sheets and aluminum alloy sheets, zinc phosphate treatment is often used at present as in the case of cold-rolled steel sheets. ing. In the case of simultaneous zinc phosphate treatment with a cold-rolled steel sheet, the properties of the aluminum alloy surface are problematic in order for the surface of the aluminum alloy plate to be sufficiently subjected to a base treatment.

[0003] Al-Mg widely used for automobile outer panels
A system alloy plate is manufactured by DC casting, homogenizing heat treatment, hot rolling, cold rolling, intermediate annealing, cold rolling, and final annealing as in the usual case. Further, in consideration of formability, measures against stretcher strain, etc., final annealing has been performed at a high temperature. However, in the final annealing, Mg accumulates on the surface to form MgO, which hinders the undercoating property, and adversely affects the corrosion resistance, especially the rust resistance.
In particular, when the Mg concentration on the surface exceeds 20%, the corrosion resistance is significantly deteriorated.

[0004]

In order to suppress an increase in the Mg concentration in the surface layer, a method of incorporating a washing step with an acid or an alkali in the manufacturing process is disclosed in Japanese Patent Laid-Open No. 3-111.
No. 532. Even in this case, it is difficult to reduce MgO near the surface by diffusing Mg on the surface of the aluminum alloy plate by heat treatment and oxidizing near the surface.
Further, if cleaning is performed with an acid or an alkali after completion of the final heat treatment, there is a problem that scratches occur on the product plate surface. In addition, an extra cleaning step is required, which causes an increase in manufacturing cost. Therefore, it is desired to be able to manufacture an aluminum alloy plate having excellent undercoating properties at a lower cost, if possible, without a cleaning step.
For this purpose, it is necessary to effectively prevent the segregation of Mg on the surface of the aluminum plate.

Japanese Patent Application Laid-Open No. 3-287779 discloses an aluminum alloy in which the crystal structure of an Al-Mg-Cu-Cr system is refined to be equiaxed to improve the undercoating property and corrosion resistance. I have. However, even in this aluminum alloy, Mg tends to be concentrated in the surface layer portion, and good base treatment property may not be obtained in some cases. In the case where Mg is extremely concentrated, the corrosion resistance is significantly deteriorated. The present invention has been devised to solve such a problem, and the concentration of Mg on the surface is suppressed by finely adjusting the contained components, the amount of Mg in the surface layer is controlled, and cooling is performed. It is an object of the present invention to provide an aluminum alloy sheet having excellent corrosion resistance and coating undercoating property while a solution-treated strip is provided.

[0006]

The aluminum alloy sheet of the present invention, which is excellent in corrosion resistance and coating undercoating property, has a content of 2.5 to 5.5% by weight of Mg and a content of 0.1% of Cu in order to achieve the object.
0.05 to 0.4% by weight, Mn: 0.005 to 0.2% by weight, Cr: 0.005 to 0.1% by weight, Ti: 0.01
-0.05% by weight, Si: 0.08% by weight or less, Fe:
0.1% by weight or less and Be: 0.0001 to 0.01
A cold-rolled solution-treated plate having an oxide layer on the surface, the balance being substantially Al, containing Mg,
A = Mg% -10 × Cu% -10 between Cu and Be
At the position where the A value defined by 00Be% [% by weight] is 4 or less, and where the Mg concentration peaks in the depth direction of the plate surface, B = Mg% / (Al% + O%) [atomic% ]
The B value defined by is regulated to 0.3 or less. This aluminum alloy plate further comprises Zr:
0.001 to 0.1% by weight, V: 0.001 to 0.1% by weight, and B: 0.0001 to 0.01% by weight.

[0007] Such an aluminum alloy sheet is subjected to a homogenizing treatment of an ingot, and is rolled into a cold rolled sheet having a predetermined thickness by hot rolling and cold rolling. 100 ° C for this cold rolled sheet
/ Second or more, induction heating at a temperature rising rate of not less than 450 ° C./sec, holding for 3 seconds or less in a temperature range of 450 ° C./sec. The Mg concentration is reliably suppressed to 20% by weight or less. Subsequent to the solution treatment, it is preferable to perform a stabilization treatment of heating to 110 to 160 ° C for 1 to 3 hours. The cold-rolled aluminum alloy sheet is, for example, 430 to 450 ° C. and 1 to 24
First-stage homogenization treatment for heating for 1 hour, second-stage homogenization treatment for heating at 480 to 550 ° C for 1 to 12 hours, hot rolling at a hot rolling start temperature of 500 ° C or less and a hot rolling end temperature of 370 to 420 ° C It is manufactured through cold rolling at a working ratio of 70 to 90%. Intermediate annealing may be performed as needed during the cold rolling.

[0008]

The aluminum alloy plate according to the present invention basically has M
It is a material whose strength is improved by using solid solution strengthening by g, and achieves precipitation hardening by Cu and refinement of crystal grains by Mn, Cr and the like. Hereinafter, the alloy elements and their contents will be described. Mg: 2.5 to 5.5% by weight Mg is an alloy element necessary for imparting strength and formability. However, when the Mg content is less than 2.5% by weight, the strength is not sufficiently improved. Conversely, when a large amount of Mg is contained in excess of 5.5% by weight, the strength is increased, but the effect of improving the formability is reduced. As a result, casting cracks during DC casting and edge cracks during hot rolling are likely to occur, and are also sensitive to stress corrosion cracking. For this reason, in the present invention, the content of Mg is set in the range of 2.5 to 5.5% by weight.

Cu: 0.05 to 0.4% by weight Cu is an alloying element that imparts strength similarly to Mg.
In particular, the effect of improving the proof stress by the precipitation of the Al-Cu-based compound in the paint baking step is great. In addition, it has an effect of effectively improving the stress corrosion cracking resistance and also has an effect of suppressing the diffusion of Mg to the material surface during solution treatment. Such an effect is remarkably observed when the Cu content is 0.05% by weight or more. However, when a large amount of Cu exceeding 0.4% by weight is contained, there is a tendency that the rust resistance is deteriorated. Therefore, in the present invention, the Cu content is 0.0
It was set in the range of 5 to 0.4% by weight.

Mn: 0.005 to 0.2% by weight Mn has an effect of refining the grain structure after annealing and controlling the recrystallization texture. When the Mn content is 0.01% by weight or less, this effect usually does not significantly appear. However, when performing rapid cooling at 100 ° C./sec or more, the effect of Mn is sufficiently exerted even when the Mn content is 0.005% by weight or more. On the other hand, when a large amount of Mn exceeding 0.2% by weight is contained, a coarse intermetallic compound is easily generated, and the moldability is reduced. Therefore, in the present invention, Mn
The content was set in the range of 0.005 to 0.2% by weight.

Cr: 0.005 to 0.1% by weight Cr is effective in refining the grain structure similarly to Mn, but its effect is small when it is less than 0.005% by weight. On the other hand, when a large amount of Cr exceeding 0.1% by weight is contained, the formability decreases. Therefore, in the present invention, Cr
The range of the content was set in the range of 0.005 to 0.1% by weight. Ti: 0.01 to 0.05% by weight Ti is an alloying element that, together with B, reduces the crystal grain size of the ingot to prevent casting cracks. However, 0.
If the Ti content is less than 01% by weight, the effect is small.
Conversely, if the Ti content exceeds 0.05% by weight, Al ₃ T
It tends to generate coarse particles of i and degrade the moldability. Therefore, in the present invention, 0.01 to
The Ti content was set in the range of 0.05% by weight.

Fe: 0.1% by weight or less Fe is a harmful impurity which causes a decrease in ductility and deteriorates the formability such as bending property and overhang property. Therefore, in consideration of applications requiring particularly high formability, such as automobile outer panels, the upper limit of the Fe content is set to 0.1% by weight in the present invention.
Stipulated. Si: 0.08% by weight or less Si is also an impurity element that inhibits formability depending on the amount of Si added.
08% by weight. Further, in the present invention, since the hardening in the paint baking step is expected not to be due to the precipitation of Al—Cu-based compounds but to Mg ₂ Si, the Si content is set to 0.08.
The required strength is ensured even if it is reduced to not more than weight%.

Be: 0.0001 to 0.01% by weight Be prevents Mg from oxidizing and disappearing during melting of the aluminum alloy, and prevents oxidation of Mg diffused from the inside of the material to the surface. It is an effective alloying element for The oxidative consumption of Mg is effectively prevented at a Be content of 0.0001% by weight or more. Further, by adding 0.0001% by weight or more of Be, improvement in the rust resistance is also observed. However, Be content exceeding 0.01% by weight tends to degrade molding workability such as overhanging property.

The aluminum alloy of the present invention may contain B, V and Zr as optional components.
The effects of these alloy elements are as follows. B: 0.0001 to 0.01% by weight B is an alloying element which, like Ti, reduces the crystal grain size of the ingot and prevents casting cracks. But,
If the content of B is less than 0.0001% by weight, the effect is small. Conversely, when the B content exceeds 0.01% by weight,
Coarse particles such as B ₂ and TiB ₂ are generated to reduce ductility and impair moldability. Therefore, when B is contained, its content is set in the range of 0.0001 to 0.01% by weight.

V: 0.001 to 0.1% by weight V has the effect of controlling the processed structure similarly to Mn and Cr and improving the formability of the final sheet. This effect is small when the V content is less than 0.001% by weight, and decreases the moldability when the V content exceeds 0.1% by weight. Therefore, when V is contained, its content is set in the range of 0.001 to 0.1% by weight. Zr: 0.001 to 0.1% by weight Zr exerts an effect of controlling the work structure during hot rolling and improving the formability of the final sheet. This effect is small when the Zr content is less than 0.001% by weight, and when the Zr content is more than 0.1% by weight, coarse particles are generated to lower the elongation. Therefore, when Zr is contained, the content is 0.00
It is set in the range of 1 to 0.1% by weight.

In the present invention, the following relationship is further maintained between the above alloy elements. This relationship has been empirically determined from numerous experiments by the present inventors,
This is an effective index for preventing Mg from being concentrated on the surface layer. First, A = (Mg%) − 10 × (Cu%) −
The components among Mg, Cu and Be are adjusted so that the A value defined by 1000 × (Be%) becomes 4 or less. Here, (Mg%), (Cu%) and (Be%)
Is a numerical value indicating each content in% by weight. C
u and Be are elements that suppress the diffusion of Mg to the surface in the material. When the relationship of A ≦ 4 is maintained, the diffusion of Mg to the surface of the material during solution treatment is suppressed in the alloy of the present system, and MgO Growth is suppressed.

At the position where the Mg concentration peaks in the depth direction of the material surface after the solution treatment, B = [Mg%]
B value defined by / ([Al%] + [O%]) is 0.3
It is necessary to maintain: [Mg%],
[Al%] and [O%] are numerical values in which each content is represented by atomic%. M so that B ≦ 0.3 holds
By balancing g, Al and O, the Mg content becomes 20% by weight or less at the position where the Mg concentration is maximum in the depth direction, and the coating material has improved yarn rust resistance and coating film adhesion. You. For example, in Test No. 1 used in Examples described later, Al, Mg and O are distributed in the concentration distribution shown in FIG. As a result of examining similar concentration distribution curves for alloys having various compositions, when A ≦ 4 and B ≦ 0.3 are satisfied, oxidation of Mg is prevented, and the maximum Mg concentration in the depth direction is 20%. It was clarified that it could be suppressed to less than% by weight.

Since the aluminum alloy sheet of the present invention has been subjected to the solution treatment after cold rolling, the oxide layer is still formed on the surface. Therefore, the surface layer is mainly composed of Al, Mg and O. Mg on surface layer
Although the diffusion of Cu is suppressed and the Mg concentration is set to 20% by weight or less, the amount of the oxide should be reduced as much as possible. Assuming that there is no oxide in an ideal state, 20% by weight
The following Mg content is [20 / (atomic weight of Mg)] /
[80 (atomic weight of Al)] = [20 / 24.3] / [8
0 / 27.0] = 0.28 = about 0.3. Actually, an oxide is formed and O is added to the denominator. Therefore, if the B value becomes 0.3 or less, the corrosion resistance can be improved.

The aluminum alloy sheet of the present invention is made into an ingot by, for example, ordinary DC casting. After the ingot is homogenized, it undergoes a final heat treatment in a continuous annealing furnace through the steps of hot rolling, cold rolling, intermediate annealing, and cold rolling. The homogenization treatment improves the strength of a product plate, formability, and the like by homogenizing the distribution of elements such as Mg segregated during casting and controlling the shape of a crystallized substance generated during casting. For this homogenization treatment, it is preferable to employ first-stage heating on the low-temperature side and second-stage heating on the high-temperature side. In the first-stage heating, Mg ₂ Al ₃ formed at the time of casting is dissolved in the matrix as much as possible under the condition that local melting (burning) of the β phase does not occur at the time of raising the temperature. Therefore, in the first stage,
The condition of heating to 430 to 450 ° C. for 1 to 24 hours is employed. In the second stage heating, Mg is completely dissolved and Al ₆
Formability is improved by controlling the shape of the intermetallic compound such as Fe. In this regard, in the second stage, 4
The condition of heating to 80 to 550 ° C. for 1 to 12 hours is adopted.

The homogenized ingot is hot-rolled in a usual manner to a desired thickness. In the hot rolling, in order to prevent hot cracking, the hot rolling start temperature is preferably 500 ° C or lower, and the hot rolling end temperature is preferably 370 to 420 ° C. After hot rolling, cold rolling is performed by a usual method to a desired thickness. At this time, the rate of cold working affects the recrystallized grains during final annealing. In order to make the recrystallized grains fine, it is preferable to set the working ratio in all the steps of cold rolling to 70 to 90%. In cold rolling at a working ratio of less than 70%, recrystallized grains may become coarse. On the other hand, the working ratio of cold rolling is 90%
If it exceeds, the recrystallized grains become too fine, and stretcher strain marks are likely to occur.

Further, the aluminum alloy sheet work-hardened by cold rolling causes the work structure to recrystallize and soften,
Intermediate annealing is performed as needed to control the formability of the final sheet. For the intermediate annealing, either a batch type annealing furnace or a continuous type annealing furnace can be used. For the intermediate annealing, annealing conditions in consideration of the balance between the r value and the elongation are adopted so that the required deep drawability is obtained. When performing intermediate annealing in a batch type annealing furnace, a condition of heating to 320 to 350 ° C. for 1 to 10 hours is adopted. If the annealing temperature is lower than 320 ° C., the segregation of Mg tends to be promoted.
If it exceeds, oxidation of the plate surface becomes active. When performing intermediate annealing in a continuous annealing furnace, 400 to 520 ° C in a short time within 3 seconds
Heating conditions are adopted. If the heating temperature during continuous annealing exceeds 520 ° C., segregation of Mg is promoted, and if it is less than 400 ° C., sufficient recrystallization is not performed. When the intermediate annealing is performed, cold rolling is further performed to obtain a predetermined thickness.

In order to improve the undercoating property and corrosion resistance of the Al-Mg alloy, it is important to prevent the segregation of Mg generated in the solution treatment of the cold-rolled aluminum alloy sheet. The solution treatment also has an effect of recrystallizing a worked structure generated during cold working. By sufficiently shortening the heating time so as not to allow time for Mg to diffuse over a long distance during the solution treatment, the concentration of Mg in the surface layer can be suppressed. Although the concentration of Mg in the surface layer portion also occurs in the hot rolling step, the Mg-enriched layer containing MgO or the like on the surface is destroyed by the hot rolling, and does not adversely affect the product characteristics. However, Mg concentrated in the surface layer during solution treatment
Has an adverse effect on the paint base treatment properties, corrosion resistance, and the like. In order to perform sufficient solution formation by heating for a short time, it is effective to heat to a high temperature in a short time by performing heating from the inside with an eddy current using an induction heater, and then cool sufficiently quickly. When using other heating methods such as heat transfer, infrared rays, heating from the surface such as blowing hot air, the heating time for solution becomes longer, Mg concentration on the surface is unavoidable, and short time is not enough. In many cases, the solution effect cannot be obtained.

In order to recrystallize and form a solution without concentrating Mg on the plate surface, the plate is rapidly heated to a temperature range of 450 to 520 ° C. at a rate of 100 ° C./sec or more. If the heating rate is slower than 100 ° C./sec, Mg that is easily diffused is accumulated on the surface layer of the aluminum alloy plate, so
Deterioration of corrosion resistance. If the solution temperature is lower than 450 ° C., sufficient recrystallization and solution cannot be achieved in a practical processing time. Conversely, long-term solution treatment exceeding 3 seconds or 5
At a solution temperature exceeding 20 ° C., defects such as Mg concentration and surface oxidation are likely to appear. The solution-treated aluminum alloy plate is cooled at a rate of 1 ° C./sec or more because Mg diffuses even in the process of cooling. For example, an aluminum alloy plate is rapidly cooled by spraying or dipping cold water, hot water, cold air, or the like, and becomes a quenched state.

The solution-treated aluminum alloy plate is:
For example, by applying a tensile deformation of about 0.2 to 1% using a tension leveler, thermal strain generated in the solution treatment is removed. However, the straightening may reduce the ductility of the aluminum alloy sheet and deteriorate the formability. Therefore, the corrected aluminum alloy plate is
It is preferable to perform a stabilization treatment of heating to ~ 160 ° C for 1 to 3 hours. By the stabilization process, the distortion is removed, and the original elongation is restored. To this end, the stabilization process must be performed at 110
It is necessary to heat to a temperature of not less than 1 ° C. for not less than 1 hour.
However, when the heating temperature exceeds 160 ° C. or the heating time exceeds 3 hours, precipitation of S ′ phase, S phase, etc. is observed, and although the strength is improved, the workability tends to be deteriorated. The aluminum alloy plate adjusted in this way is 16
Paint baking is performed by heating to 0 to 180 ° C for 20 to 30 minutes. During this heating, an S phase or an S ′ phase composed of an Al—Cu—Mg intermetallic compound or the like is precipitated, and a coated plate having the required strength and hardness is obtained.

[0025]

EXAMPLES Example 1: Various aluminum alloys having the compositions shown in Table 1 were melted, and DC was applied to a 400 mm thick slab.
Cast. This slab is subjected to 440 ° C. × 10 hours and 52
After performing a two-stage soaking process at 5 ° C. × 1 hour, hot rolling was performed at a hot rolling start temperature of 450 ° C. to obtain a hot-rolled sheet having a thickness of 7 mm.
The hot rolling end temperature was set to 400 ° C. After cold rolling the obtained hot rolled sheet to a sheet thickness of 1.3 mm, the sheet was heated to 340 ° C. for 1 hour in a batch annealing furnace, and further, a sheet thickness of 1.0 mm
Until cold-rolled.

[0026]

The temperature of the cold rolled sheet is raised at 150 ° C. in the atmosphere.
/ Sec, and hold at 480 ° C for 3 seconds. Then, cooling water is sprayed on the surface of the cold rolled sheet to lower the temperature at 400 ° C.
Per second to room temperature. When the Mg concentration in the surface layer portion of the solution-treated plate material was measured by Auger analysis, the Mg concentration in the surface layer was found between Table A and Table B values.
Had the relationship shown in Further, the Al, Mg, and O concentrations in the plate material of Test No. 1 fluctuated from the surface toward the inside as seen from the Auger analysis results in FIG. The abscissa in FIG. 1 indicates a sputtering time (minute) and corresponds to the depth of the sample at a rate of {170} per minute. On the other hand, the vertical axis indicates the concentration of each element expressed in atomic%.

A test piece of 70 mm × 150 mm was cut out from each plate and subjected to chemical conversion treatment, electrodeposition coating, intermediate coating and top coating under the conditions shown in Table 2. 40 ° C for each specimen after painting
Was immersed in pure water for 24 hours, and the adhesion of the coating film was determined by counting the number of the remaining coating films in a test using a grid in which 100 2 mm squares were formed.
When the judgment results were arranged by the Mg concentration of the surface layer, as shown in Table 3, the adhesion was largely different at the boundary of the Mg concentration of 20% of the surface layer. That is, when the Mg concentration was maintained at 20% or less, there was no square where the coating film was peeled off, whereas when the Mg concentration exceeded 20%, at least 5 squares were observed.
The squares from which the individual coating films were peeled were counted. The excellent adhesion of the coating film obtained in the examples of the present invention is due to the formation of a base having high affinity with the coating film by the chemical conversion treatment.

[0029]

Example 2 The aluminum alloy of Test No. 1 shown in Table 1 was hot-rolled and cold-rolled in the same manner as in Example 1 to form a 1.0 mm-thick cold-rolled sheet. The solution treatment was carried out under the conditions shown in (1). In Examples of the present invention and Comparative Examples 6 and 7, the temperature was raised to the solution treatment temperature at a rate of 150 ° C./sec, and after the solution treatment, the temperature was lowered to room temperature at a rate of 400 ° C./sec. In Comparative Example 8, the heating rate was 10 ° C. /
The temperature was raised to the solution heat treatment temperature in seconds, and after the solution heat treatment, the solution was cooled to room temperature at a temperature decreasing rate of 150 ° C./sec.

Each test piece subjected to the solution treatment was coated through the same steps as in Example 1, and the chemical conversion property, corrosion resistance, coating film adhesion, etc. were examined. The chemical conversion property was evaluated by observing the surface of the test piece after zinc phosphate treatment with a scanning electron microscope, examining the precipitation state and density of zinc phosphate crystals, and evaluating the weight of the zinc phosphate film. Those with 5 g / m ² or more were judged to be acceptable. Corrosion resistance was determined by forming a cross cut that reached the substrate by scratching the specimen that had been coated to the top coat with a cutter.
The salt spray test was conducted as specified in SZ2371. To continue the salt spray for 24 hours, and then expose to a thermo-hygrostat maintained at a temperature of 40 ° C. and a relative humidity of 80% for 1500 hours, and measure the length from the cross-cut of the thread corrosion generated on the test piece. Was used to determine the corrosion resistance.

The adhesion of the coating film was examined by a grid test in the same manner as in Example 1, and was expressed as the number of grids on which the coating film remained out of 100 grids. As is clear from Table 3 showing the investigation results, in the example of the present invention in which the solution treatment in which the solution was heated to 450 to 520 ° C. for a short time within 3 seconds, the Mg concentration of the surface layer was 20
% Or less, and exhibited excellent properties in all of the chemical conversion treatment properties, corrosion resistance and coating film adhesion. On the other hand, in Comparative Example 6 heated for a long time, Comparative Example 7 heated at a high temperature, and Comparative Example 8 heated at a relatively low heating rate, a large amount of Mg exceeding 20% was concentrated in the surface layer. All of the processability, corrosion resistance and coating film adhesion were inferior.

[0033]

[0034]

As described above, in the present invention, Mg, which is easily concentrated on the surface of an aluminum alloy plate which has been subjected to a solution treatment after cold rolling, has a concentration of 20% or less by balancing alloy components. Is suppressed. Further, the Mg concentration of the surface layer is surely suppressed to 20% or less even by the solution treatment conditions including the rate of temperature rise and the rate of temperature decrease.
Aluminum alloy sheets with suppressed Mg concentration show excellent properties such as chemical conversion treatment, corrosion resistance and coating film adhesion, have the necessary strength and hardness after baking, and are suitable sheet materials for automobile outer panels and the like. .

[Brief description of the drawings]

FIG. 1 shows the concentration distribution of Mg, Al and O from the surface to the inside of a solution-treated material.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Moriyama 1-11-1 Koike, Inazawa-shi, Aichi Japan Nippon Light Metal Co., Ltd. Nagoya Plant (72) Inventor Toshiaki Suzuki 1-11-1 Koike, Inazawa-shi, Aichi No. Nippon Light Metal Co., Ltd. Nagoya Factory

Claims (2)

[Claims] 1. Mg: 2.5-5.5% by weight, Cu:
0.05 to 0.4% by weight, Mn: 0.005 to 0.2% by weight, Cr: 0.005 to 0.1% by weight, Ti: 0.0
1 to 0.05% by weight, Si: 0.08% by weight or less, F
e: 0.1% by weight or less and Be: 0.0001-0.
A cold-rolled solution-treated plate having an oxide layer on the surface containing 0.01% by weight, with the balance being substantially Al, containing M
A = Mg% −10 × Cu% − between g, Cu and Be
At the position where the A value defined by 1000 Be% [wt%] is 4 or less, and where the Mg concentration peaks in the depth direction of the plate surface, B = Mg% / (Al% + O%) [atomic% An aluminum alloy sheet having excellent corrosion resistance and coating undercoating property, wherein the B value defined in [1] is regulated to 0.3 or less. 2. Mg: 2.5-5.5% by weight, Cu:
0.05 to 0.4% by weight, Mn: 0.005 to 0.2% by weight, Cr: 0.005 to 0.1% by weight, Ti: 0.0
1 to 0.05% by weight, Si: 0.08% by weight or less, F
e: 0.1% by weight or less and Be: 0.0001-0.
01% by weight, Zr: 0.001 to 0.1% by weight, V: 0.001 to 0.1% by weight, and B: 0.01% by weight.
001 to 0.01% by weight of one or more kinds,
A cold-rolled solution-treated plate having an oxide layer on the surface where the balance is substantially Al, containing Mg, Cu and Be.
A = Mg% −10 × Cu% −1000Be% [wt%] has a relationship of not more than 4 and B is the position where the Mg concentration peaks in the depth direction of the plate surface.
= B defined as: Mg% / (Al% + O%) [atomic%]
An aluminum alloy sheet excellent in corrosion resistance and coating undercoating property, whose value is regulated to 0.3 or less.