JPH0660366B2 - Aluminum alloy sheet for zinc phosphate treatment and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an aluminum alloy sheet for forming, for example, an aluminum alloy sheet for use in a body sheet of an automobile, which is used for forming and coating baking. The present invention relates to an aluminum alloy plate used after being treated with zinc phosphate as a coating base treatment.

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been mainly used for automobile body sheets, but recently, aluminum alloy rolled sheets have been tried to be used mainly due to the demand for weight reduction of vehicle bodies.

Body sheets of automobiles are used after being press-molded, so they have excellent moldability, especially elongation,
It is required that it has excellent overhanging properties and that it does not generate Luders marks during molding, and that it also has high strength. Moreover, since the body sheet of an automobile is generally baked, it is baked. It is required that the subsequent strength is high. It is also necessary that the adhesion of the coating film at the time of coating is good, and that the corrosion resistance after coating is also good.

By the way, there have been various kinds of aluminum alloys used for forming work requiring high strength, and the main ones are roughly classified as follows depending on the alloy component system.

(B) O material of 5052 alloy which is a non-heat treatment type Al-Mg alloy or O material of 5182 alloy.

(B) 2036 alloy T4 treated material or T6 treated material which is a heat treatment type Al-Cu alloy.

(C) Heat treatment type Al-Mg-Zn-Cu alloy T4 treated material. Examples of aluminum alloys of this type include, for example, JP-A-52-141409, JP-A-53-103914,
Alternatively, there are alloys described in JP-A-57-98648. Al, which is introduced on pages 63 to 72, especially page 64 of “Nikkei New Material April 7, 1986”.
-4.5% Mg-0.38% Cu-1.46% Zn-0.18% Fe
There is also a -0.09% Si alloy.

(D) 6009 alloy T which is a heat treatment type Al-Mg-Si alloy
4 treated material, 6010 alloy T4 treated material (for example, JP-A-59-3
9499). Furthermore, AC120 alloy T4 processing material proposed in Japanese Examined Patent Publication No. 61-15148.

Problems to be Solved by the Invention Conventional aluminum alloys for high-strength forming as shown in (a) to (d) above all satisfy all of the above-mentioned characteristics required for a body sheet for an automatic operator. It was difficult to get it done. Further, even when an aluminum alloy is used for an automobile body, it is usual to use an aluminum alloy sheet together with a steel plate to assemble and manufacture the body. In that case, there are the following problems from the viewpoint of paint baking. It was

That is, when an automobile body is assembled and manufactured by using a steel plate and an aluminum alloy plate together, a body part made of a formed steel plate and a body part made of a formed aluminum alloy plate are assembled and spot-welded by resistance welding to form the body. After the preparation, the whole body is usually subjected to degreasing treatment, zinc phosphate treatment, and then electrodeposition coating or spray coating. Therefore, in this case, parts made of an aluminum alloy plate are also subjected to zinc phosphate treatment before coating. However, all of the conventional aluminum alloys for high-strength forming as described above have poor zinc phosphate treatability. However, there is a problem that a zinc phosphate film is not sufficiently formed on the surface. Since the zinc phosphate film is not sufficiently formed in this way, the adhesion of the coating film formed on it cannot be sufficiently obtained, and there is a problem that thread rust is likely to occur on the surface after coating. That is, when a conventional aluminum alloy for high-strength forming is used for an automobile body sheet, if the zinc phosphate treatment is taken into consideration, the adhesion of the coating film after coating cannot be sufficiently obtained, which leads to the thread rust resistance. There was an inferior problem.

The present invention has been made in view of the above circumstances. It has good moldability and high strength, and at the same time, has excellent zinc phosphate processability, good adhesion of coating film, and excellent yarn rust resistance. It is an object of the present invention to provide an aluminum alloy sheet for zinc phosphate treatment, which enables a baked coated sheet to be obtained.

Means for Solving the Problems The aluminum alloy plate for zinc phosphate treatment according to claim 1, wherein Mg is 0.1 to 1.5%, Si is 0.3 to 2.5%, and Z is Z.
n 0.3% or more and less than 0.5%, Cu 0.5% or less, further Fe 0.5% or less, Mn 0.8% or less, Cr
It is characterized by containing one or more of 0.3% or less, Zr 0.2% or less, and V0.2% or less, and the balance being Al and inevitable impurities.

The aluminum alloy plate for zinc phosphate treatment according to claim 2 has Mg0.1 to 1.5%, Si0.3 to 2.5%,
Zn 0.3-2.5%, Cu less than 0.05%,
Further, Fe 0.5% or less, Mn 0.8% or less, Cr 0.
3% or less, 0.2% or less of Zr, 0.2% or less of V, one or more kinds are contained, and the balance consists of Al and unavoidable impurities.

On the other hand, the method for producing an aluminum alloy plate for zinc phosphate treatment according to claim 3 is: Mg 0.1-1.5%, Si 0.3-2.5%, Zn
Contains 0.3% or more and less than 0.5%, Cu 0.5% or less, further Fe 0.5% or less, Mn 0.8% or less, Cr
It was obtained by casting a molten aluminum alloy containing 0.3% or less, Zr 0.2% or less, and V0.2% or less, and one or more of which is the balance Al and unavoidable impurities. After rolling the ingot, the rolled plate is
The solution treatment is performed at a temperature within the range of 90 ° C, and the quenching is performed at a cooling rate of 5 ° C / sec or more.

Furthermore, the manufacturing method of the aluminum alloy plate for zinc phosphate treatment according to claim 4 is Mg 0.1 to 1.5%, Si 0.3
.About.2.5%, Zn 0.3 to 2.5%, Cu less than 0.05%, Fe 0.5% or less, Mn 0.8% or less,
Obtained by casting a molten aluminum alloy containing one or more of 0.3% or less of Cr, 0.2% or less of Zr, and 0.2% or less of V, and the balance of Al and unavoidable impurities. After rolling the ingot, the rolled plate is
The solution treatment is performed at a temperature within the range of 590 ° C, and the quenching is performed at a cooling rate of 5 ° C / sec or more.

First, the reasons for limiting the components of the aluminum alloy plate for zinc phosphate treatment of the present invention will be described.

Mg: Mg produces Mg ₂ Si by coexisting with Si,
Contributes to strength improvement. If the amount of Mg is less than 0.1%, the effect of improving the strength is insufficient, while if the amount of Mg exceeds 1.5%, the work hardening becomes remarkable and the moldability, especially the elongation decreases, and the body sheet for automobiles It becomes unsuitable for such uses.
Therefore, the amount of Mg is set within the range of 0.1 to 1.5%.

Si: Si is an element necessary for improving strength and formability, and especially M
Coexistence with g greatly contributes to the improvement of strength. S
If the amount of i is less than 0.3%, the effect of improving the strength is insufficient, while if the amount of Si exceeds 2.5%, the coarse particles of metallic Si increase and the formability, especially bendability, deteriorates. Therefore, the amount of Si is set within the range of 0.3 to 2.5%.

When the strength is particularly important, the Si content is 1.5% to
It is preferably within the range of 2.5%.

Zn, Cu: Both Zn and Cu improve the zinc phosphate treatment property so that a zinc phosphate film is sufficiently formed on the plate surface, and the zinc phosphate particles are uniformly miniaturized by the zinc phosphate treatment. As a result, the adhesion of the coating film formed on the zinc phosphate coating is improved, which contributes to good corrosion resistance after coating such as thread rust. If the amount of Zn is less than 0.3%, the above effect cannot be sufficiently obtained, so the lower limit of Zn was set to 0.3%.
On the other hand, if the amount of Zn is increased, the effect of improving the zinc phosphate processability is increased, but if the amount of Zn is excessively contained, the corrosion resistance of the alloy plate itself is deteriorated. Especially if the Zn content exceeds 2.5%,
Since the corrosion resistance of the alloy plate itself is remarkably reduced, the Zn content is limited to the range of 0.3 to 2.5% in the case of the invention of claim 2. Further, particularly when importance is attached to the corrosion resistance of the alloy plate itself, the amount of Zn is preferably less than 0.5. Therefore, in the case of the invention of claim 1, the range of Zn is 0.3% or more and less than 0.5%. Within Further, if a large amount of Cu is also contained, the corrosion resistance of the alloy plate itself is deteriorated, and as a result, the thread rusting property is deteriorated. Therefore, excessive Cu content must be avoided. In the case of the invention of claim 1, since the upper limit of the amount of Zn that adversely affects the corrosion resistance of the alloy plate itself is suppressed to a low level (less than 0.5%) like Cu, Cu is allowed up to 0.5%. Therefore, the Cu content of the invention of claim 1 is set to 0.5% or less. On the other hand, in the case of the invention of claim 2, Zn
Since the upper limit of the amount is set to be relatively high (2.5%), in order to ensure the corrosion resistance of the alloy plate itself, the amount of Cu is changed.
Limited to less than 0.05%.

Fe, Mn, Cr, Zr, V: Any of these contributes to refinement of crystal grains and stabilizes the structure, and also contributes to improvement of strength or formability. The above is included. However, if Fe exceeds 0.5%, the formability decreases, so Fe is made 0.5% or less. Further, Mn is 0.
If it exceeds 8%, Cr 0.3%, Zr 0.2%, and V 0.2%, a giant intermetallic compound is formed and the formability deteriorates. Therefore, Mn is 0.8% or less and Cr is 0.3%. Below, Zr
Was 0.2% or less and V was 0.2% or less.

In addition to the above elements, basically Al and inevitable impurities may be used.

In addition, in an ordinary aluminum alloy, a minute amount of Ti, or Ti and B may be added for refining the ingot, and the aluminum alloy plate of the present invention also contains Ti or Ti and B. Good.
In that case, if Ti exceeds 0.15%, primary TiAl ₃ crystallizes and impairs formability. Therefore, Ti is set to 0.15% or less, and when B is added together with Ti, TiB ₂ exceeds 500 ppm if TiB ₂ exceeds 500 ppm. It is preferable to set B to 500 ppm or less, since the coarse particles of (3) are mixed and impair the moldability.

Also, a small amount of Be may be added to these alloys.
Particularly when melting an alloy containing Mg, Be suppresses the oxidation of the molten metal and prevents the inclusion of impurities such as oxide particles in the material. However, Be exceeding 500 ppm Be
However, the amount of Be in the case of adding Be is preferably 500 ppm or less.

Next, a method for producing an aluminum alloy for zinc phosphate treatment having the above-described component composition, that is, the method of the invention of claim 2, will be described.

In order to fully exhibit the characteristics of the alloy having the above-described composition, basically, after solution rolling, solution treatment is performed at a temperature within the range of 450 to 590 ° C, and subsequent quenching is performed at 5 ° C. It is necessary to cool at a cooling rate of at least / sec. By this solution treatment, it is possible to finally obtain the amount of solid solution Mg and Si required to achieve the predetermined strength and formability. If the treatment temperature at this time is less than 450 ° C, solution treatment is insufficient, and the strength after cooling and the strength after baking are not sufficiently obtained.
If the temperature exceeds 90 ° C, eutectic melting may occur, so the solution treatment temperature must be in the range of 450 to 590 ° C. If the cooling rate after solution treatment is slower than 5 ° C / sec,
Not only sufficient strength cannot be obtained, but also corrosion resistance such as intergranular corrosion resistance deteriorates. Therefore, the cooling rate after solution treatment should be 5 ° C / sec or more.

Furthermore, in order to more fully bring out the characteristics of the aluminum alloy having the above-described composition, it is desirable to apply the following conditions and methods.

That is, first, a molten alloy having the above-described composition is melted according to a conventional method, and semi-continuous casting (DC
Casting). The casting speed at this time is not particularly limited, but generally casting may be performed at a casting speed of about 25 mm / min to 250 mm / min. Prior to hot rolling, the obtained ingot is homogenized by heating at 450 to 590 ° C for 1 to 48 hours. This homogenization treatment is intended to eliminate the unevenness of the ingot and improve the formability, and if the heating temperature is less than 450 ° C or the heating time is less than 1 hour, the degree of homogenization becomes insufficient. If the heating temperature exceeds 590 ° C, eutectic melting may occur, and if the heating time exceeds 48 hours, economic efficiency decreases. After this homogenization treatment, hot rolling may be performed according to a conventional method. The heating for hot rolling may be performed in combination with the above homogenization treatment,
It may also be done independently.

Instead of the above semi-continuous casting method, a thin plate continuous casting method (continuous casting and rolling method) may be applied. In this case, hot rolling can be omitted and cold rolling can be performed immediately,
Prior to cold rolling, preheating at 300 to 590 ° C for 1 to 48 hours is effective for the purpose of promoting homogenization and improving formability.

The hot-rolled sheet or continuously cast thin sheet obtained as described above is cold-rolled according to a conventional method to obtain a sheet pressure of 0.
The plate should be about 5 to 3 mm. Intermediate annealing may be performed during the cold rolling or between the cold rolling and the hot rolling before the cold rolling in order to improve formability. That is, when coarse crystal grains are generated during hot rolling, if they are cold rolled as they are, defects called ridging or flow line may occur during the molding process, which may impair the appearance of the molded product. The problem can be solved by performing the above step and recrystallizing. When performing this intermediate annealing in a batch type annealing furnace, the intermediate annealing conditions are 250 to 4
50 ° C x 1 to 48 hours is suitable. Intermediate annealing temperature is 250 ℃
If less than 450 ° C, recrystallization does not occur, while if it exceeds 450 ° C, coarsening of crystal grains tends to occur. Also, even if the intermediate annealing time is less than 1 hour, the recrystallization becomes insufficient, while the annealing for a long time exceeding 48 hours only deteriorates the economical efficiency. The intermediate annealing may be carried out in a continuous annealing furnace. In this case, the intermediate annealing temperature is suitably 400 to 580 ° C, and the holding time at the intermediate annealing temperature is zero or 5 minutes or less.

After cold rolling to the required plate thickness,
Perform solution treatment within the range of 450-590 ℃. This solution treatment is preferably performed in a continuous annealing furnace in consideration of mass productivity. In this case, the holding time at the above temperature may be zero, but is usually preferably 10 seconds or more. In the solution heat treatment using a continuous annealing furnace, quenching is performed immediately after the solution heat treatment at a cooling rate of 5 ° C / sec or more, so that the crystal grains are refined and the formability is improved.

As described above, by producing an alloy having a predetermined composition by the above method, it is possible to obtain an aluminum alloy plate having excellent strength and formability and zinc phosphate treatment property.

Example [Example 1] The aluminum alloys shown in Sample Nos. 1 to 6 in Table 1 were melted by a conventional method and cast by a semi-continuous casting method. Casting size is 500 × 1200 × 300mm and casting speed is 65mm
/ Min. After homogenizing the obtained ingot at 520 ℃ for 12 hours, start hot rolling at 500 ℃.
A hot rolled sheet with a thickness of 5 mm was used. Then the hot-rolled sheet is 1 mm thick
Cold rolled until. For the obtained cold rolled sheet,
Immediately after the solution treatment for minutes, it was cooled by water quenching (cooling rate 10 ² to 10 ³ ° C / sec).

The plate after quenching was left for 2 weeks, and the mechanical properties and formability were examined. The results are shown in Table 2. In Table 2, the Erichsen value indicates the result of the Erichsen test according to JIS-B method, and the ball-head overhang test value is the ball-head stick-out with a PVC film stuck, using a ball-head punch of 100 mmφ. The test results are shown.

Similarly, with respect to a plate that had been left for two weeks, the strength of the plate after cold rolling at a 5% or 10% working rate was examined assuming the forming process, and the cold rolled plate and the cold rolled plate were not used. For baking, assuming baking coating 1
The strength after heating at 75 ° C for 1 hr was examined. The results are shown in Table 3.

Further, a plate that had been left to stand for 2 weeks in the same manner as above was examined for zinc phosphate treatment property, and was subjected to baking coating after zinc phosphate treatment to examine thread rust property. The results are shown in Table 4. Here, zinc phosphate treatment and thread rust were examined as follows.

That is, first, in a 2% sodium silicate-based degreasing solution, 45 ° C ×
Soak for 2 minutes to degrease, rinse with water, then soak in 15% HNO ₃ aqueous solution for 1 minute at room temperature to desmut, wash with water, and soak for 1 minute in a commercially available titanium-containing surface conditioning solution to adjust the surface. Then, the zinc phosphate treatment is performed by immersing it in a commercially available fluorine-containing zinc phosphate-based chemical conversion treatment solution, and 1 g
/ M ² of zinc phosphate film was formed, then washed with water and dried. And the generation state (adhesion state) of the zinc phosphate film on the surface
Was observed with a scanning electron microscope.

In addition, after forming a zinc phosphate film in this way, electrodeposition coating, intermediate coating, and topcoating are applied, and after artificially adding a mark X mark to the coating film on the surface of the obtained coated plate, JIS Z2371 Perform a compliant salt spray test for 24 hours, then at 80
Wet test soaking at 85% humidity for 250 hours,
The length of the generated thread rust was examined to evaluate the thread rust property.

The tests whose results are shown in Tables 2 to 4 were also carried out on a commercially available galvanized steel sheet (Sample No. 7) for reference.

As shown in Tables 2 and 3, the aluminum alloy sheet for zinc phosphate treatment of the present invention according to Example 1 has mechanical properties,
Although the bake hardenability and formability are at the same level as the comparative alloy, it is clear that zinc phosphate treatment and thread rusting have excellent performance comparable to galvanized steel sheets as shown in Table 4. Is.

[Example 2] Casting in the same manner as in Example 1 for aluminum alloys within the composition range of the components of the present invention shown in sample numbers 8 to 10 in Table 5,
It was rolled to obtain a cold-rolled plate with a plate thickness of 1 mm. For this cold rolled sheet,
Using a continuous annealing furnace, heating to 540 ° C at a heating rate of about 30 ° C / sec, holding at that temperature for 10 seconds, and then forced cooling at a cooling rate of about 30 ° C / sec for solution treatment-quenching .
Various tests were performed on the quenched plate in the same manner as in Example 1. The results are shown in Tables 6 to 8 corresponding to Tables 2 to 4 for Example 1.

As shown in Tables 6 to 8, the aluminum alloy sheet of the present invention according to Example 2 also has good mechanical properties, bake hardenability and formability, and at the same time has excellent zinc phosphate processability and thread rust. It is clear that they have sex.

EFFECTS OF THE INVENTION The aluminum alloy sheet for zinc phosphate treatment of the present invention has not only good strength, particularly strength after baking coating and moldability, but also excellent zinc phosphate treatment property. The resulting coating film has excellent adhesion and corrosion resistance after coating, in particular, thread rust resistance, and is therefore most suitable for an automobile body sheet used after being treated with zinc phosphate.

Further, according to the manufacturing method of the present invention, it is possible to easily manufacture an aluminum alloy plate for zinc phosphate treatment having the above-mentioned excellent performance on a mass-production scale.

The aluminum alloy sheet of the present invention is most suitable for an automobile body sheet, but it is needless to say that it can be used for other applications where it is treated with zinc phosphate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yohka Takada 4-3-18 Nihonbashi Muromachi, Chuo-ku, Tokyo Sky Aluminum Co., Ltd. (56) References Japanese Patent Laid-Open No. 3-6348 (JP, A)

Claims (4)

[Claims] 1. Mg 0.1-1.5% (weight%, the same hereinafter), Si 0.3-2.5%, Zn 0.3% or more 0.1.
Less than 5%, Cu 0.5% or less, and Fe0.
5% or less, Mn 0.8% or less, Cr 0.3% or less, Zr
An aluminum alloy plate for zinc phosphate treatment, containing one or more of 0.2% or less and V0.2% or less, and the balance being Al and inevitable impurities. 2. Mg 0.1-1.5%, Si 0.3-2.
5%, Zn 0.3-2.5%, Cu less than 0.05%, Fe 0.5% or less, Mn 0.8% or less, C
Aluminum alloy for zinc phosphate treatment, characterized by containing one or more of 0.3% or less of r, 0.2% or less of Zr, and 0.2% or less of V, and the balance consisting of Al and inevitable impurities. Board. 3. Mg 0.1-1.5%, Si 0.3-2.
5%, Zn 0.3% or more and less than 0.5%, Cu 0.5% or less, and further Fe 0.5% or less, Mn 0.8% or less, Cr 0.3% or less, Zr 0.2% or less, V0. 2%
Contains one or more of the following, with the balance being Al
After casting a molten aluminum alloy consisting of unavoidable impurities and rolling the obtained ingot, the rolled plate was
Solution treatment at a temperature in the range of 50 to 590 ℃, 5 ℃ / s
A method for producing an aluminum alloy sheet for zinc phosphate treatment, which comprises quenching at a cooling rate of ec or more. 4. Mg 0.1-1.5%, Si 0.3-2.
5%, Zn 0.3 to 2.5%, Cu less than 0.05%, Fe 0.5% or less, Mn 0.8% or less, Cr
It was obtained by casting a molten aluminum alloy containing 0.3% or less, Zr 0.2% or less, and V0.2% or less, and one or more of which is the balance Al and unavoidable impurities. After rolling the ingot, the rolled plate is
A method for producing an aluminum alloy sheet for zinc phosphate treatment, which comprises performing solution treatment at a temperature within a range of 90 ° C and quenching at a cooling rate of 5 ° C / sec or more.