JPH06179996A - Aluminum material with excellent press formability - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides an aluminum material having excellent press formability. [Composition] Zn is 5 to 30 atomic%, Mg is 5 to 30 atomic%, and Zn + Mg is 20 to 60 on the surface of the aluminum material.
An alloy layer consisting of atomic% and residual Al is formed, and an Al-Mg-Z layer consisting of Zn and Mg having a lower concentration than that of the metal layer is formed below the alloy layer.
An aluminum material having an n-alloy layer and excellent in press formability. Furthermore, the thickness of the alloy layer on the surface is 0.05 to 3 μm.
And the thickness of the lower alloy layer is 1 to 300 μm, the aluminum material excellent in press formability as described above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum material, which is used after being subjected to processing such as press molding, in the field of automobiles, building materials, etc. The present invention relates to an aluminum material having excellent press formability such as scratch resistance.

[0002]

2. Description of the Related Art Aluminum materials have recently been investigated for application to automobile body panels by taking advantage of their light weight, but they have the following disadvantages, and their improvement is strongly desired. That is, the aluminum material is a material that is extremely difficult to form in press molding because it has a high sliding resistance on the surface and is easily plastically deformed so that it is easily cracked.
Although it is possible to improve it to some extent by applying a solid lubricant or the like to the surface, there is a drawback that it adversely affects adhesion and painting. Further, there is a drawback that surface scratches are likely to occur during press molding and subsequent assembling and handling, and there is a strong demand for improvement especially in automobile bodies and the like where aesthetics are important. There is a method of improving the scratch resistance by applying anodic oxidation treatment or chrome plating, but since an automobile body is generally painted, a phosphate film is not formed by the method,
As a result, the adhesion of the coating film becomes insufficient and the yarn rust resistance deteriorates.

In order to improve such phosphoric acid treatment property, JP-A-61-157693 and JP-A-4-17677 are used.
As disclosed in Japanese Patent Publication No. 2003-242242, etc., it is disclosed that the surface of an aluminum material is plated with Zn, but improvement in press formability can hardly be expected. Furthermore, Al-Zn-
Mg alloys are known as age hardening alloys and are characterized by high strength and relatively high hardness, but they are extremely inferior in press workability and are applicable to molded products with complicated shapes such as automobile bodies. Can not.

[0004]

In order to apply aluminum materials to automobile body panels and the like, it is important to improve lubricity (hereinafter referred to as "press formability") and scratch resistance in press forming. It is an issue. The present invention provides an aluminum material having excellent press formability that solves these problems by providing a layer having lubricity and scratch resistance on the surface of the aluminum material.

[0005]

The features of the present invention are as follows: (1) Zn is contained in an amount of 5 to 30 on the surface of an aluminum material.
Atomic%, Mg 5-30 at%, Mg + Zn 20-6
An alloy layer having 0 atomic% and the balance being Al is formed, and an Al-M layer containing Zn and Mg having a lower concentration than the metal layer is formed below the alloy layer.
An aluminum material which has a g-Zn alloy layer and is excellent in press formability. (2) The thickness of the alloy layer on the surface is 0.05
10 μm, and the thickness of the alloy layer thereunder is 1 to 300
The aluminum material is excellent in press formability according to the above (1), which is characterized by having a thickness of μm.

For example, when Zn-based plating is applied to an Al-Mg-based alloy plate and thermal diffusion treatment is performed at 200 ° C. for 10 hours to 550 ° C. for about 1 second, Al in the Zn-based plated layer is reduced.
And Mg diffuse, and at the same time Z in the Al-Mg alloy plate.
n diffuses. Depending on the heat treatment conditions, plated Zn
Is diffused in the Al—Mg alloy plate, and the penetration depth of Zn reaches several tens of μm. Further, Mg diffuses into the Zn-based plating layer preferentially over Al, and a concentrated layer is formed on the surface. An example of the distribution state of Zn, Mg and Al in the depth direction is shown in FIG. Thus, the feature of the present invention is that A
A concentrated layer of Zn and Mg composed of 1-Mg-Zn is formed, and an Al-Mg-Zn alloy layer composed of Zn and Mg having a lower concentration than the surface layer is formed below the concentrated layer.
Alternatively, an aluminum plate or an aluminum alloy plate having a Mg content not exceeding 10% is subjected to Zn-Mg vapor deposition plating and subjected to thermal diffusion treatment under conditions of 200 ° C, 10 hours to 550 ° C, and 1 second. , On the surface, Al-
A concentrated layer of Zn and Mg composed of Mg-Zn is formed, and an Al layer composed of Zn and Mg whose concentration is lower than that of the surface layer is formed below the concentrated layer.
-Mg-Zn alloy layer is formed.

[0007]

Next, the function of the present invention on press formability will be described. Since the aluminum material is soft and easily subjected to plastic deformation, it is extremely important to reduce the frictional resistance at the die shoulder and the bead portion to which the surface pressure is applied in order to flow the material into the mold. Even if a Zn plating layer is applied, Zn
Since it is a soft metal itself, it has no effect. Relatively hard Zn
Even if the Mg alloy plating layer is added, the effect of reducing the friction coefficient is slight. This is because the aluminum material is soft, and even if only a thin surface is hardened, the effect is not exhibited. In the present invention, the surface is an Al-Mg-Zn hardened alloy layer and, in addition, it is a concentrated layer of Zn and Mg, and the surface layer to which the maximum stress is applied during pressing is sufficiently hard. Wear can be effectively suppressed. Further, the lower layer of the surface layer has a lower concentration of Zn and Mg than the surface layer, but has a higher concentration of Zn and Mg as compared with the base material of the aluminum material, and therefore has an age hardening property depending on the metal concentration. Then
Supports the surface layer. Further, the Zn and Mg concentrations in the lower layer gradually decrease in the depth direction, and the workability gradually improves accordingly. Therefore, it is possible to reduce the friction coefficient at the time of press working, and at the same time, to prevent the generation of peeling pieces and peeling powder.

FIG. 2 shows the results of examining the change in hardness in the depth direction when press-fitting from the surface by changing the indenter load when measuring the Vickers hardness. Compared with a Zn-plated aluminum material, FIG. It is clear that the hardened layer of the aluminum material of the present invention reaches deep into the plate. Therefore, the friction coefficient is sufficiently reduced even under working conditions such as the flat plate pulling test in which the aluminum material undergoes plastic deformation. Thus, in press molding, the range of surface pressure that the aluminum material flows into the mold without breaking is expanded, the degree of freedom in panel design is expanded, and the stability of press work is enhanced.

The present invention is also very effective in preventing pressing scratches caused by foreign matter and scratches caused by tool contact in the steps of blanking, press molding and assembling aluminum materials.
Such surface scratches are caused by digging up the surface of the material with a tool or the like, but the Al-Mg-Zn alloy layer is composed of two layers, the surface layer and the lower layer, and is the hardest in the surface layer. The resistance to digging is high and scratches are hard to occur.

The surface layer of the present invention increases the surface hardness and the electric resistance, so that it has the effect of improving the continuous spotting property during spot welding. Further, by deeply penetrating Zn, the thread rust resistance after coating is improved. The effect of improving the property can be provided. The reason why the concentrations of Zn and Mg in the surface layer are limited to 5 to 30 atomic% is that the concentration of the metal is 5
If it is less than atomic%, the hardness is insufficient and the lower layer becomes softer, so that the substantial effect of improving lubricity and scratch resistance in press molding is not sufficient. When the concentration of the metal in the surface layer exceeds 30 atomic%, Al-Mg-Zn
This is not preferable because the alloy layer becomes brittle, and peeling pieces and peeling powder are remarkably generated during press molding, which rather increases the frequency of scratches. Since the hardness increases due to the concentration of Zn and Mg, when Zn + Mg is less than 20 atomic%, the effect of suppressing the adhesion with the mold is insufficient, and when it exceeds 60 atomic%, the surface workability is poor. When it is significantly reduced and becomes brittle, peeling pieces and peeling powder are generated as described above, and the frequency of scratches is increased.

The above-mentioned surface layer and lower layer Al, M
The changes in the g and Zn concentrations are as shown in FIG. 1, for example, by measurements such as glow discharge spectroscopy. The thickness of the alloy layer on the surface is preferably 0.05 μm or more and 10 μm or less. 0.
If it is less than 05 μm, the hardness is sufficient, but it is too thin to sufficiently suppress the adhesion to the mold, and if it exceeds 10 μm, it is not economical. The lower layer is for the purpose of supporting the stress applied to the surface layer and preventing peeling of the surface layer. For that purpose, it is preferable that the thickness of the lower layer is 1 μm or more, and there is no problem even if it reaches a depth of up to 300 μm. . However, if it exceeds 300 μm, the peeling prevention effect is saturated, but the heat treatment time becomes long, which is not economical.

When the material is manufactured, 0.1 is applied to the surface of the material.
An oxide film having a thickness of μm or less may be formed and remain on the surface of the material, but this oxide film does not adversely affect the present invention. That is, even if an oxide film is present on the outermost surface, good lubricity and scratch resistance in press molding can be obtained if the surface layer and the lower layer satisfy the present invention. Zn-M
In the case of performing g-based vapor deposition plating, pure aluminum, Cu, Cu,
Si, Mn, Mg, Cr, Zn, Fe, Zr, Ti, G
Alloy additives such as a and V may be used. These alloying elements diffuse more or less during the thermal diffusion treatment, but the effect thereof is incidental, and the basic effect of the present invention is maintained. However, the Mg content in the material is 10% by weight or less as described below.

When Zn-based plating is applied, Al--Mg
A system alloy plate is applied as the original plate. If the Mg content of the alloy plate is 0.5 wt% or more, M of the surface layer after heat treatment is
A g concentration of 5 atomic% or more can be secured. On the other hand, if the Mg content of the alloy sheet exceeds 10% by weight, the Mg concentration of the surface layer after heat treatment exceeds 30 atomic%, which is not preferable. In the original plate, in addition to Al and Mg, Cu, Si, Mn, Cr, Z
Alloys such as n, Fe, Zr, Ti, Ga and V may be added.

Zn or Zn-Mg plating amount is 1 to 1
0 g / m²Is preferred. 1 g / m ²Less than Zn and M
The surface layer concentration of g does not reach 5 atomic% after heat treatment. Also
10 g / m²Thick plating that exceeds the
For example, it is possible to control the concentration of the metal below 30 atom%.
However, it is not economical. The Zn-based plating layer is made of pure Zn.
In addition, there are 20 metals such as Fe, Mn, Cr, Al and Ni.
A combination of P, B, C, N, O, etc. with the metal in an amount of less than weight%
1% by weight or less, and 5 dispersoids such as alumina and silica
Even if the content is less than or equal to% by weight, the effect of the present invention is maintained.
It

A pure aluminum plate, an Al-Mg alloy plate or an aluminum alloy plate other than the above is alkali-cleaned and / or acid-cleaned, and Zn-based plating is subjected to displacement plating, electroplating, vapor deposition plating, or Zn-Mg.
It is preferable that the plating is deposited by a vapor deposition method so that the plating amount is in the range of 1 to 10 g / m ² . If it is less than 1 g / m ² , the effect of the present invention after the thermal diffusion treatment is practically insufficient. 10
Even if it exceeds g / m ² , the action and effect of the present invention are exhibited,
Not economical. Next, a thermal diffusion treatment is performed at 200 ° C. for 10 hours to 550 ° C. under a soaking and retaining condition for about 1 second.
Treatment in a reducing or non-oxidizing atmosphere is preferred, but treatment in air is also possible. In the latter case, it is preferable to remove the oxide film with an alkali or an acid after the heat treatment.

It is rational to incorporate the above-mentioned thermal diffusion treatment into the manufacturing process of the aluminum material.
That is, the heat diffusion is performed by utilizing strain relief annealing or solution treatment performed to improve the mechanical properties of the aluminum base material after cold rolling. There are the following methods. First, after cold rolling, the above-described alkali cleaning and / or acid cleaning before plating is performed, Zn-based plating or Zn-Mg plating is performed, and then the sample is introduced into a continuous annealing furnace and heated to 500 to 550 ° C. During air cooling and strain relief annealing, a surface metal layer composed of the above-mentioned Zn, Mg and the remaining Al, and a Z layer having a lower concentration than that of the metal layer are formed under the surface metal layer.
This is a method of forming a Zn-Mg-Al alloy layer composed of n and Mg. After continuous annealing, if necessary, leveling, cleaning, and then finish annealing at less than 200 ° C. may be added as usual. Second
Uses a solution heat treatment, and in a continuous annealing furnace
It is the same method as the above-mentioned conditions except holding at 550 degreeC for 1 to 20 seconds. Third, after cold rolling, alkali cleaning and / or acid cleaning before plating is performed, Zn-based plating or Zn-Mg plating is performed, and then in a batch annealing furnace at a temperature of 300 to 450 ° C for 30 minutes to 5 hours. This is a method of forming the above-mentioned surface metal layer and an alloy layer below the surface metal layer while holding and performing strain relief annealing or solution treatment.
In a batch annealing furnace, it is also recommended to adjust to a reducing atmosphere or a non-oxidizing atmosphere.

Fourth, after cold rolling, strain relief annealing or solution treatment is carried out in a continuous annealing furnace to create mechanical properties of the aluminum base material, and if necessary, leveling processing is performed, and then plating is performed. This is a method of performing Zn-based plating or Zn-Mg plating after the previous alkali cleaning and / or acid cleaning, and then using finish annealing to form the above-mentioned surface metal layer and the alloy layer thereunder. . In this case, the final annealing is 200 to 3 in the batch annealing furnace.
It is preferable to maintain the temperature of 00 ° C. for 1 to 10 hours.
The fifth is a method in which a batch annealing furnace is used instead of the continuous annealing furnace in the previous method, and the other is the same method as the fourth method.

[0018]

EXAMPLES The embodiments and effects of the present invention will be described in detail based on Examples and Comparative Examples. Table 1 shows the manufacturing process and heat treatment conditions of the aluminum material, Table 2 shows the plating conditions and the constitution of the surface metal layer and the alloy layer thereunder, and Table 3 shows the quality performance test results.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

After the aluminum material was cold-rolled to a plate thickness of 1 mm, it was plated and heat-diffused in the manufacturing process shown in Table 1. For Zn-based plating, alkali cleaning and acid cleaning were carried out by the usual method, and the following method was used. Displacement plating is N
aOH 75 g / l, ZnO 15 g / l, Rochelle salt 5
It was precipitated from a solution to which 0 g / l was added. For electroplating, ZnSO ₄ 150 g / l, if necessary, from sulfuric acid acid bath containing other metal ions or colloid, current density 20 A / dm ²
It was electrodeposited in. In the vapor deposition plating, Zn and Mg were heated and evaporated in a vacuum container of 10 ⁻³ Torr, and evaporated on an aluminum material.

The composition of the surface metal layer and the alloy layer thereunder was measured by glow discharge spectroscopy, and Zn and M in the surface metal layer were measured.
The concentration of g and the thickness of the alloy layer thereunder were determined. Flat plate pull-out test: Specimen size 1mm thick x 30mm width aluminum material with cleaning oil (Preton R303 manufactured by Sugimura Chemical)
P) and apply 200 mm / mm while pressing both sides with a tool (contact area 30 mm x 30 mm) with a load (N) of 450 kgf.
I pulled it out at the speed of a minute. When the pull-out load is F, the friction coefficient μ is obtained from F = 2 μN.

Evaluation of scratch resistance: The Vickers hardness with an indenter load of 25 g was evaluated. Continuous spot welding test: Cu-C with a tip diameter of 6 mm and 40R
Using r electrode, welding current 27kA, pressure 2950N,
Continuous spot welding was performed under the condition of a welding time of 8 cycles, and evaluation was made by the number of points where the nugget diameter was maintained at 5 mm or more. Thread rust resistance test: A 70 mm x 150 mm test piece was used to form a phosphate film in a fluoride-containing phosphate treatment bath, and cationic electrodeposition coating was performed at 200 µm, and intermediate coating and top coating were applied to give a total coating thickness of 80 µm. did. After making a knife cut to reach the aluminum material substrate, salt spray (5% NaCl, 3%
The maximum length of thread rust from the knife cut after 8 weeks of exposure to a cycle environment test consisting of 5 days at 5 ° C., 5 days at wet (85% relative humidity, 40 ° C.) and 1 day of standing in the room was evaluated.

[0025]

EFFECTS OF THE INVENTION According to the present invention, lubricity at the time of press forming, which is a drawback of aluminum material, scratch resistance, continuous spotting property at spot welding and thread rust resistance after coating are remarkably improved. It is possible to obtain an aluminum material that can be advantageously applied to applications such as automobile body panels, which are used for forming, joining and painting.

[Brief description of drawings]

FIG. 1 shows Zn, M in the depth direction from the surface of an aluminum material according to the present invention (Example 1) by glow discharge spectroscopy.
It is a figure which shows the distribution state of g and Al.

FIG. 2 is a diagram showing a change in hardness when the aluminum materials of Example 1, Comparative Example 1 and Comparative Example 2 are press-fitted from the surface by changing the indenter load in the Vickers hardness test.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masao Kikuchi 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd.

Claims (2)

[Claims] 1. Zn is added to the surface of an aluminum material in an amount of 5 to 3
0 atom%, Mg is 5 to 30 atom%, Zn + Mg is 20 to
An alloy layer consisting of 60 atomic% and the balance being Al is formed, and an Al-layer consisting of Zn and Mg having a lower concentration than that of the metal layer is formed below the alloy layer.
An aluminum material excellent in press formability, which is characterized by forming an Mg-Zn alloy layer. 2. The thickness of the alloy layer on the surface is 0.05 to 10.
μm, and the thickness of the lower alloy layer is 1 to 300 μm.
The aluminum material excellent in press formability according to claim 1.