JP5279119B2 - Partially modified aluminum alloy member and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy member which, when quality characteristics required for a product are different per part, is partially modified in accordance with the parts to be required, and to provide a method for producing the same, particularly, when the quality characteristics to be required are mutually contrary per part, which is effective in making both the characteristics consistent. <P>SOLUTION: In a precipitation hardening type aluminum alloy in which, by relatively controlling a rapidly cooled part and a gradually cooled part partially after the whole is heated to a solid solution temperature, a strength difference is formed between the rapidly cooled part and the gradually cooled part after the subsequent artificial aging treatment. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an aluminum alloy member partially modified in properties such as strength and stress corrosion cracking resistance according to a site required for a product, and a method for manufacturing the same.

In order to reduce the weight of the vehicle, the use of aluminum alloys has been widely studied in place of conventional iron parts.
For vehicle aluminum parts and machine structural aluminum parts, high strength is not always required for the whole part. For example, in the case of a part that is partially stressed, it is a connecting part with other iron parts. In other words, a portion to which stress is applied although high strength is required may require stress corrosion cracking resistance higher than that of high strength.
In particular, when the aluminum alloy is an Al—Zn—Mg JIS 7000 series alloy, the alloy is designed for precipitation hardening rather than solid solution hardening. There are also material properties with a strong negative correlation such as reduced corrosion cracking.

Therefore, it is expected that the material characteristics can be adjusted for each required part.
A partial heat treatment method has been proposed as a partial reforming method for adjusting material properties for each part, but what has been proposed so far is partially induced for iron-based parts as shown in Patent Documents 1 and 2. Those that are heated and those that are partially immersed in a high-temperature liquid.
However, when these methods are applied to an aluminum alloy, since the aluminum alloy has good thermal conductivity, it is difficult to control the partial heating, and as shown in FIG. 6, the boundary between the heating part and the general part has a large hardness. There is a problem that a V-shaped heat-affected zone occurs.

JP 2005-330504 A JP 2003-129131 A

  An object of the present invention is to provide an aluminum alloy member that is partially modified according to a required part when the quality characteristics required for a product differ from part to part, and in particular, the quality required for each part. When the characteristics are contrary to each other, it is effective to make both the characteristics compatible.

  The partially modified aluminum alloy member according to the present invention is a precipitation hardening type aluminum alloy, and after the whole is heated to the solution temperature, the quenching portion and the slow cooling portion are partially controlled relatively thereafter. In the artificial aging treatment, there is a difference in strength between the rapid cooling portion and the slow cooling portion.

Here, precipitation hardening type aluminum alloy refers to an aluminum alloy that can improve the hardness and strength by precipitating a crystallized substance in an alloy matrix by artificial aging after liquefaction treatment, and includes a solid solution hardening component in the alloy component. This is also included.
Moreover, as long as it has a precipitation hardening characteristic by heat processing, it can apply to various aluminum alloys.

The solution temperature is a temperature suitable for the components added in the aluminum alloy to be sufficiently dissolved in the matrix, and depending on the amount of the added component, depending on the alloy system such as JIS 4000, JIS 6000, and JIS 7000. Is also different.
Controlling the rapid cooling portion and the slow cooling portion refers to partially varying the cooling rate until the entire aluminum alloy member is heated to the solution treatment temperature and then becomes 200 ° C. to 100 ° C. or less. It is selected according to the required cooling rate, such as cooling or forced air cooling.
Such a heat treatment method according to the present invention includes a step of heating the entire precipitation hardening type aluminum alloy member to a solution temperature, a step of partially liquid cooling, and a step of artificially aging the whole. It is characterized by being.

The precipitation hardening type aluminum alloy is heated to the solution temperature and then rapidly cooled, and then subjected to artificial aging treatment, whereby fine precipitates are uniformly crystallized in the alloy matrix to improve the tensile strength.
At this time, if the cooling rate after the solution temperature is low, precipitates gradually grow in the cooling process, and the effect of increasing the tensile strength is reduced by the subsequent artificial aging treatment, but the stress corrosion cracking resistance is improved. The

In particular, an Al—Zn—Mg alloy is an aluminum alloy in which high strength is easily obtained, but stress corrosion cracking is likely to occur, and the application effect of the present invention is great.
Therefore, in consideration of the influence of components on strength and stress corrosion cracking resistance in an Al—Zn—Mg alloy, the following ranges are preferable.
(Zn and Mg components)
Zn and Mg components are effective in improving the strength.
The Zn component can contribute to improvement of strength while suppressing deterioration of extrudability. When added in an amount of 6% by mass (hereinafter simply referred to as “%”), high strength is obtained, but when it exceeds 8%, stress corrosion cracking resistance [SCC resistance] Since the strength (SCC: stress corrosion cracking) decreases rapidly, the range of 6 to 8% is preferable, and ideally the range is 7 to 8%.
Mg component is easily added at the same time as Zn, but high strength is likely to be obtained, but it is easy to cause a decrease in extrudability, and when the amount added is high, quenching sensitivity becomes high and quenching (cooling after heating to solution temperature) ) Cooling rate management becomes difficult.
Therefore, it is preferable to set it in the range of 0.9 to 2.5%, and ideally in the range of 1.6 to 2.0%.
(Cu component)
When added simultaneously with Mg, the Cu component is effective in improving the strength, and has the effect of relaxing the potential difference within the crystal grain boundaries and improving the SCC resistance.
However, when the addition amount is increased, the general corrosion resistance is lowered, the quenching sensitivity is increased, and the management of the cooling rate becomes difficult, so the range of 0.1 to 0.4% is preferable.
(Mn, Cr and Zr)
Since Mn, Cr and Zr components can be added alone or in combination to suppress the growth of recrystallization, the SCC resistance is improved. However, if these components are added in large amounts, the quenching sensitivity increases. Is preferably 0.5% or less, and in the range of 0.2 to 0.8% in total.

  The partially-modified aluminum alloy member according to the present invention controls a portion where the cooling rate at the time of quenching, which is cooled from the state heated to the solution temperature, is relatively rapidly cooled between the portions, and a portion which is gradually cooled. As a result, an aluminum alloy member optimized for each quality characteristic (material characteristic) such as strength, hardness, elongation, and SCC resistance can be obtained for each part of the product.

An example of the production process of the partially modified aluminum alloy according to the present invention is schematically shown in FIG.
The aluminum alloy member may be processed by any method such as extruded material, drawn material, rolled material, forged material, and cast material.
The alloy component is heated and held to a solution temperature at which the alloy component is sufficiently dissolved in the metal matrix (step S1).
The solution temperature is set to an optimum temperature depending on the alloy system, and generally ranges from 450 ° C to 580 ° C.
Next, quenching is performed by partially varying the cooling rate (step S2).
In the embodiment shown in FIG. 1, one end (a) of the aluminum alloy member 1 is partially immersed in water or oil for partial liquid quenching, and the other part (b) is cooled by fan air cooling. A controlled example is shown.
In this way, if the quenching part and the quenching part can be controlled within the quenchable range, such as the part that is relatively rapidly cooled by liquid quenching and the part that is relatively slowly cooled by fan air cooling, means for cooling method Does not matter.
For example, the shower liquid may be partially cooled.
Next, an artificial aging process is performed (step S3).
The purpose of the artificial aging treatment is to precipitate precipitates in the metal matrix, and the optimum conditions differ depending on the alloy system. In the JIS6000 series, the one-stage aging is good at 160 to 190 ° C. × 4 to 6 hours, and in the JIS7000 series alloys, It is preferable to perform a two-stage aging of 140 to 160 ° C. × 4 to 12 hours after a one-stage aging of 85 to 95 ° C. × 3 to 6 hours.

As preliminary evaluation, Zn: 7.9%, Mg: 1.95%, Mn: 0.35%, Cu: 0.35%, Cr: 0.13%, Zr: 0.2%, Ti: 0 .02%, JIS7000 series extruded round bar (φ = 25 mm × length 300 mm) consisting of Al and impurities in the balance, heated at 450 to 550 ° C. × 1 hour, then cooled with a = 50 mm, b = A 250 mm fan was air-cooled.
Next, an artificial aging treatment of 90 ° C. × 4 hours + 145 ° C. × 8 hours was performed.
The hardness (Hv: Vickers hardness) distribution of this test piece is shown in FIG.
As a result, in the partial quenching method according to the present invention, it has been clarified that the V-shaped softened region generated by the conventional partial heating does not occur.

Next, examples of the present invention will be described.
Examples 1 and 2 shown in FIG. 3 are examples of JIS6000-based Al—Mg—Si-based alloys, and Example 3 is an example of JIS4000-based Al—Si-based alloys.
Using a round bar (extruded material) of φ = 25 mm and length of 300 mm made of this chemical component, a = 50 mm was water-cooled.
In Examples 1 to 3, the cooling rate indicates an average cooling rate from the solution temperature to 100 ° C. or less, and the artificial aging treatment was performed at 180 ° C. for 3 hours.
From this result, it can be seen that a partially modified aluminum alloy member having partially different hardness can be obtained by partially changing the cooling rate during quenching.

Examples 4 to 12 and Comparative Examples 1 and 2 shown in FIG. 4 are examples of JIS7000-based Al—Zn—Mg alloys.
Here, Si and Fe components are impurities, Si is preferably 0.15% or less, and Fe is preferably 0.3% or less.
The Ti component is effective for refining the crystal and is preferably in the range of 0.001 to 0.05%.
Using a round bar (extruded material) having a diameter of φ = 25 mm and a length of 300 mm, a = 50 mm was water-cooled.
The artificial aging treatment is performed in the range of 90 ° C. × 4 to 6 hours + 140 to 150 ° C. × 6 to 12 hours, and the SCC resistance is JIS H8711, No. 2 test piece as shown in FIG. The test was carried out by the alternate dipping method shown in JIS H8711 under a stress of about 70%, and the target was that no cracks would occur in the fan air-cooled part for 90 days.
Further, the hardness was targeted to be HV = 120 or more in order to maintain a predetermined tensile strength.
As shown in FIG. 4, Examples 4 to 12 have a hardness difference of 10 or more between the water cooling part and the air cooling part (fan cooling part), and both the target hardness and the target SCC resistance are clear. I understand.

The manufacturing process example which concerns on this invention is shown. The relationship between partial water cooling and hardness distribution is shown. Examples of JIS 6000 and JIS 4000 alloys used for the evaluation are shown. An example of a JIS7000 series alloy used for the evaluation will be shown. The test shape for SCC resistance evaluation is shown. The relationship between the conventional partial heating and hardness distribution is shown.

Claims (2)

An Al—Zn—Mg based precipitation hardening type aluminum alloy,
After the whole is heated to the solution temperature, the quenching part and the slow cooling part are partially controlled relatively, so that there is a difference in strength between the rapid cooling part and the slow cooling part in the subsequent artificial aging treatment. A partially modified aluminum alloy member characterized by the above. Heating the entire Al—Zn—Mg precipitation hardening aluminum alloy member to a solution temperature;
A method for producing a partially modified aluminum alloy member, comprising a step of partially liquid cooling and a step of artificially aging the whole.

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