JP2010189750A - High-strength aluminum alloy wire and rod material excellent in softening resistance and method of manufacturing the same - Google Patents

Abstract

[PROBLEMS] To provide a 6000 series high-strength aluminum alloy wire rod that is excellent in softening resistance and retains high mechanical properties even when exposed to high temperatures for a long time, and has excellent cold workability and corrosion resistance. And it aims at providing the manufacturing method.
An Al-Mg-Si aluminum alloy having a specific composition is hot-rolled by low-temperature strong working to produce a wire rod, and fine crystal precipitates in the structure of the aluminum alloy wire rod are refined. Even when exposed to a high temperature for a long time, it has excellent softening resistance and can maintain high mechanical properties, and also has excellent corrosion resistance.
[Selection figure] None

Description

  The present invention relates to a high-strength Al—Mg—Si-based aluminum alloy wire rod excellent in softening resistance. The wire rod of the present invention is a rolled wire rod that has been hot-rolled in the production process, and is a general term for a wire rod having a relatively small diameter and a rod material having a relatively large diameter. Hereinafter, aluminum is also referred to as Al, and Al—Mg—Si is also referred to as 6000.

  Conventionally, fasteners such as steel bolts and screws are usually used for fastening engine parts of automobiles that have been reduced in weight using light alloys such as aluminum alloys and magnesium alloys.

  On the other hand, in recent years, in connection with the weight reduction of automobile bodies, in order to reduce the weight of automobile engine parts, these bolts, screws and other fasteners are also used as wire rod materials such as aluminum alloy wires and rods. There is a demand to use a fastener made of an aluminum alloy produced by molding.

Conventionally, a high-strength 6000 series aluminum alloy screw (including bolts) used for assembling aluminum alloy structures such as window sashes and automobile bodies has been proposed in Patent Document 1 and the like. In this patent document 1, as the mechanical properties of the screw (hereinafter also referred to as mechanical properties), the proof stress is 300 N / mm ² or more, the elongation is 6% or more, and the torsion strength is AL3 (JIS-B-1057-1989). In order to obtain a value that is 10% or more higher than the screw strength of A6061-T6), a 6000 series aluminum alloy extruded material having a specific composition is used. That is, Mg: 0.5-1.5 wt%, Si: 0.5-1.5 wt%, Cu: 0.5-1.5 wt%, Mn: 0.2-0.5 wt%, Ti: 0. 005 to 0.1 wt%, B: 0.001 to 0.05 wt%, Zr: 0.05 to 0.25 wt%, and an Al-Mg-Si based aluminum alloy composition composed of the balance aluminum and inevitable impurities. .

  This Patent Document 1 is meaningful in that a 6000 series aluminum alloy is selected as an aluminum alloy for fasteners such as window sashes and automobile bodies. This aluminum alloy other than 6000 series has the following problems for practical use as an aluminum alloy for fasteners, as described in Patent Document 1.

5000 series aluminum alloys such as 5052 and 5056 have a large amount of alloys such as Mg, are inferior in recyclability and low in strength as compared to 6000 series. In addition, molding and workability such as header processing and screw rolling processing on fasteners are also inferior.
Although 7000 series aluminum alloys such as 7N01 and 7075 have high strength, they have a large amount of alloys such as Zn and Cu and are inferior in recyclability. Moreover, since there are many alloy quantities, such as Zn and Cu, it is easy to corrode and lacks reliability. And, molding and workability are inferior, and it is easy to break during header processing and screw rolling.

  Although 2000 series aluminum alloys, such as 2024, have high heat resistance, when there are many alloy quantities, such as Cu, there exists a problem which is inferior to recyclability and is easy to corrode. Moreover, it is inferior in molding and workability, and easily breaks during header processing and screw rolling. The same applies to AA2618 which is a typical heat-resistant aluminum alloy. This alloy has already been used for several decades, and examples of applications include the body of a supersonic aircraft Concorde. The heat-resistant temperature is about 120 ° C., which is the highest among practical aluminum alloys. However, the corrosion resistance is low, and it is necessary to take measures against corrosion resistance for its use. For this reason, the usage environment is limited, and the alloy is not easy to use.

  However, even in the case of a 6000 series aluminum alloy, the existing alloys such as A6061 and A6056 used as the fasteners are still inferior in molding and workability, and are easily broken during header processing and screw rolling, Even after artificial age hardening, the strength was low. Patent Document 1 also attempts to improve these problems of the 6000 series aluminum alloy.

Japanese Patent No. 3939414

  Here, the characteristics required for the fasteners of the above-mentioned automobile engine parts are the same as the normal fasteners intended by Patent Document 1, ensuring stable axial force at the time of fastening, and axial force during use after fastening. For example, there is no looseness due to a decrease in the height, or there is no breakage. And in order for the fasteners of automobile engine parts to exhibit these characteristics, the aluminum alloy wire rod material used as the material has various mechanical characteristics such as high strength, high proof stress, high elongation at break, and fasteners. It is necessary to have both cold workability such as header processing and thread rolling processing, and corrosion resistance.

  However, the fastener of this automobile engine part intended by the present invention has mechanical characteristics such as high strength, high yield strength and high elongation even when exposed to high temperature for a long time as an engine part. Maintaining softening resistance is required. This is a point different from the normal fastener used at room temperature as the object of Patent Document 1, and is a more strict point of the required characteristics of the automobile engine component fastener.

  On the other hand, including the said patent document 1, the conventional wire rod material of 6000 series aluminum alloy has a problem that softening resistance is inferior. In other words, even if the strength is high at room temperature, the mechanical properties such as strength and proof stress are remarkably lowered when heated (exposed) to a temperature of 100 ° C. or higher for a long time. is there. In recent years, in order to reduce the weight of automobile bodies, the softening resistance required for fasteners for automobile engine parts has become increasingly severe. However, even in the above-mentioned Patent Document 1, although there are data satisfying these characteristics at room temperature from the examples, when it is heated to such a temperature of 100 ° C. or higher for a long time, the strength, The proof stress is remarkably lowered, and the mechanical properties cannot be satisfied.

  Moreover, these 6000 series aluminum alloy wire rod materials are also required to have cold workability such as header processing and screw rolling processing to fasteners such as bolts and screws for automobile engine parts. However, the conventional 6000 series aluminum alloy wire rods including Patent Document 1 cannot satisfy these cold workability and corrosion resistance while satisfying the softening resistance. It was. This is because, as a fastener for bolts and screws for automobile engine parts and the like, particularly when a wire rod having a circular cross section is manufactured, the heat as in Patent Document 1 is used. In the processing method by the inter-extrusion, as will be described later, there is a great limitation in improving the properties of the wire rod material.

  The present invention has been made in view of such problems, and an object thereof is to provide a 6000 series high-strength aluminum alloy wire rod excellent in softening resistance, cold workability, and corrosion resistance, and a method for producing the same. And

The gist of the high strength aluminum alloy wire rod excellent in softening resistance of the present invention for achieving the above object is an Al-Mg-Si aluminum alloy wire rod that has been hot-rolled, and is mass%. Mg: 0.65 to 1.75%, Si: 0.70 to 1.35%, Cu: 0.40 to 1.05%, Fe: 0.05 to 0.35%, Mn: 0.00. Each containing 05-0.95%, Cr: 0.05-0.25%, Ti: 0.01-0.10%, consisting of the balance Al and inevitable impurities, the maximum length in the structure being 200 nm or more, The average density of dispersed particles of 800 nm or less is 5 particles / μm ³ or more, and the average density of crystal precipitates having a maximum length of 10 μm or more is 500 particles / mm ² or less.

Moreover, the summary of the manufacturing method of the high intensity | strength aluminum alloy wire rod material excellent in the softening resistance of this invention for achieving the said objective is the mass%, Mg: 0.65-1.75%, Si: 0.8. 70 to 1.35%, Cu: 0.40 to 1.05%, Fe: 0.05 to 0.35%, Mn: 0.05 to 0.95%, Cr: 0.05 to 0.25% , Ti: 0.01 to 0.10% each, and the balance consisting of Al and inevitable impurities, and if necessary, Zr: 0.01 to 0.30%, V: 0.01 to 0.30% An Al—Mg—Si-based aluminum alloy ingot containing one or two of them is melted, and this ingot is subjected to homogenization heat treatment in the range of 470 to 565 ° C., and then the hot rolling start temperature is 320 to 520 ° C. Perform hot rolling with a processing rate of 95% or more in the range, and if necessary, further cold work to obtain aluminum with a predetermined diameter. Dispersed particles having a maximum length of 200 nm or more and 800 nm or less in the structure after being subjected to a tempering treatment in which the solution treatment and the rapid cooling treatment and the aging treatment at 150 to 200 ° C. are performed in the order of description. with an average density of the five / [mu] m ³ or more, the average density of the maximum length 10μm or more intermetallic compounds is to a 500 / mm ² or less.

  Here, the hot-rolled Al—Mg—Si-based aluminum alloy wire rod material referred to in the present invention is a wire rod material that has been hot-rolled in the manufacturing process as described above. Therefore, it may be a wire rod having a predetermined diameter or shape by hot rolling, and thereafter may be a wire rod that is not cold-worked, and is further cooled if necessary while appropriately annealing after hot rolling or during cold working. It may be a wire rod having a predetermined diameter or a predetermined shape by a desired cold working such as cold rolling, drawing, drawing, drawing, or forging. Moreover, the fastener which cold-worked the wire rod material also including the said selective annealing may be sufficient (In this invention, the fastener which cold-worked the wire rod material is also included as a wire rod material.). Furthermore, the present invention is intended for wire rods having a circular cross section, but the cross sectional shape is not limited to a perfect circle as long as it can be applied to a fastener, and other circular shapes such as an ellipse. The cross-sectional shape is also appropriately selected according to the application.

Here, the average density of crystal precipitates and the average density of dispersed particles in the structure defined in claim 1 or the machine in room temperature air after heat treatment at 150 ° C. defined in claim 2 for 500 hours. The physical properties are the structure and properties of the wire rod material and the cold-worked fastener after the tempering treatment in which the solution treatment and the rapid cooling treatment and the aging treatment at 150 to 200 ° C. are performed in the order of description. In other words, as long as the tempering treatment is performed, not only the state of the wire rod material but also the structure and properties measured in the state of the cold-worked fastener may be used.
If the average density of crystal precipitates in the wire rod material structure is the center portion (shaft center portion) of the wire rod material, as will be described later, depending on the cold working to the fastener and the tempering treatment, Almost no change, reflecting the structure of the original wire rod. On the other hand, the average density of the dispersed particles in the wire rod material structure is almost the same as the measurement site to be described later, if it is the central portion (axial center) of the wire rod material, but is hardly changed by cold working on the fastener, It varies depending on the tempering process. Therefore, the average density of crystal precipitates and the average density of dispersed particles, reflecting the structure and mechanical properties of the wire rod material with good reproducibility, or the mechanical properties in room temperature air after heat treatment at 150 ° C. for 500 hours In order to do this, at least the structure and properties of the wire rod material and the cold-worked fastener after the tempering treatment are measured.

  The crystal precipitates and the dispersed particles defined in the present invention can be confirmed as amorphous particles of any composition existing in the matrix by observation with an SEM or TEM of an aluminum alloy wire rod structure, and have a maximum length. The second phase particles that can be measured (discriminated).

  The present inventor considered that the crystal precipitates in the 6000 series aluminum alloy wire rod structure and cold workability, the dispersed particles and softening resistance (mechanical properties after heat treatment at a temperature of about 150 ° C. for a long time) And so on.

  First, if crystal precipitates in the 6000 series aluminum alloy wire rod structure can be refined, cold workability such as header processing and thread rolling processing to fasteners such as bolts and screws for automobile engine parts can be achieved. improves. This is because, when a substantial amount of coarse crystal precipitates is present, the cold workability of the 6000 series aluminum alloy wire rod such as the header processing and screw rolling processing is lowered. Therefore, in the present invention, in order to improve cold workability, the coarse crystal precipitates (average density) in the 6000 series aluminum alloy wire rod structure are reduced as much as possible.

  And this inventor started the refinement | miniaturization of the crystal precipitate of such a wire rod material structure | tissue only by the combination of the processing method by the 6000 series aluminum alloy of a specific composition, and the said low temperature and strong hot rolling, It was also found that it can be manufactured.

  Next, when the density of fine dispersed particles in a specific range in the 6000 series aluminum alloy wire rod structure is increased, the mechanical properties in room temperature atmosphere even after being heated to the high temperature for a long time (heat treated) It was found that the mechanical properties such as the original high strength, high yield strength and high elongation at break were maintained. It was also found that the crystal grain size and fiber structure of the aluminum alloy wire rod structure can be made finer, and the corrosion resistance such as intergranular corrosion resistance can be improved. It was also found that such a density of fine dispersed particles in a specific range of the wire rod material structure can be produced by a 6000 series aluminum alloy having a specific composition and a homogenization heat treatment in the specific range.

If the crystal precipitates in this aluminum alloy wire rod structure can be refined and the number of fine dispersed particles can be increased, the crystal grain size of this aluminum alloy wire rod structure can also be refined. Is possible. For this reason, even after the heat treatment at the high temperature for a long time, the effect of not lowering the mechanical properties in the air at room temperature is promoted, and the corrosion resistance such as intergranular corrosion resistance can be improved. In the present invention, as will be described later, these structures are obtained by hot rolling at the low temperature and strong processing combined with the homogenization heat treatment in the specific range.
As a result, the present invention is an automotive engine part that has excellent softening resistance and can maintain high mechanical characteristics, is excellent in header processing and screw rolling processing on fasteners, and also has corrosion resistance. 6000 series high-strength aluminum alloy wire rod suitable for use as a fastener and a method for producing the same can be provided.

  Hereinafter, embodiments of the present invention will be specifically described in order from the composition of the present invention 6000 series aluminum alloy sheet.

Composition-6000 series:
The chemical component composition of the 6000 series aluminum alloy wire rod in the present invention will be described below. As described above, the fastener of an automobile engine part as the main object of the present invention is to secure a stable axial force at the time of tightening even when heated to a temperature of 100 ° C. or higher for a long time (heat treated). Softening resistance is required, such as no loosening due to a decrease in axial force during use after tightening, or no breakage. In order to guarantee this, the aluminum alloy wire rod that is the material of the fastener has high strength and high mechanical properties in room temperature air after being heated (heat treated) to about 150 ° C for a long time. It is necessary to have proof stress and high elongation at break. At the same time, it is also necessary to have excellent corrosion resistance such as intergranular corrosion resistance.

  In order to satisfy such a requirement, the aluminum alloy rolled wire rod of the present invention that has been hot-rolled in the production process thereof has a mass% of Mg: 0.65 to 1.75%, Si: 0. 70 to 1.35%, Cu: 0.40 to 1.05%, Fe: 0.05 to 0.35%, Mn: 0.05 to 0.95%, Cr: 0.05 to 0.25 %, Ti: 0.01 to 0.10%, respectively, and an Al—Mg—Si based aluminum alloy composition composed of the balance Al and inevitable impurities. In addition,% display of content of each element means the mass% altogether.

The chemical composition of the aluminum alloy rolled wire rod of the present invention is the same as that of the 6000 series aluminum alloy. Many. Normally, if the kind and content of the alloy elements are relatively large, coarse crystal precipitates are inevitably formed in the ingot. For this reason, when a wire rod material is manufactured by hot extrusion or the like, seizure with a die is likely to occur during hot extrusion. In order to prevent such seizure, it is necessary to reduce the extrusion speed, which reduces productivity. Further, if the extrusion speed is increased excessively, the surface of the extruded material is damaged, which is likely to cause broken lines and surface cracks during wire processing. Furthermore, in the extrusion process, coarse crystal precipitates are likely to remain from the surface layer of the extruded material toward the center, and the high-strength material has a structure condition defined by the present invention (the crystal having a maximum length of 5 μm or more). The average density of precipitates is inevitably not more than 500 pieces / mm ² ), and coarse crystal precipitates cannot be eliminated. Accordingly, the cold workability is lowered, and the workability to the wire or screw is remarkably lowered.

  On the other hand, in the aluminum alloy rolled wire rod material of the present invention, the selected alloy element and the amount of the alloy element, as in the chemical composition described above, although the type and content of the alloy element are relatively large. Balance with the combination. In addition, in the manufacturing process of the aluminum alloy wire rod material, the wire rod material structure as described above or described later by the combination with the low temperature, strong hot rolling or synergistic effect The crystal precipitate inside is refined. Further, the dispersed particles are finely densified by a combination or balance of alloy elements, alloy element amounts, and soaking temperatures. That is, the aluminum alloy wire rod of the present invention has high cold workability during wire processing and screw processing, and even after being heated to the high temperature for a long time (heat treated), the high strength, high yield strength, Various mechanical properties such as high breaking elongation can be maintained.

  At the same time, if the balance is made by the combination of the selected alloy element and the amount of the alloy element, as in the chemical component composition described above, the type and content of the alloy element is not enough for the chemical component composition of the 6000 series aluminum alloy. Despite being relatively large, the corrosion resistance can also be improved.

  Here, it may further contain one or two of Zr: 0.01 to 0.30% and V: 0.01 to 0.30%.

  Other elements other than these are basically impurities, and the content (allowable amount) at each element level in accordance with AA to JIA standards and the like. However, from the viewpoint of recycling, not only high-purity Al bullion but also 6000 series alloys, other aluminum alloy scrap materials, low-purity Al bullion, etc. are used as melting materials. There is a high possibility that other elements other than the above will also be mixed. And reducing these impurity elements itself increases the manufacturing cost, and it is necessary to allow the inclusion to some extent. On the other hand, there is an element whose content is better regulated within a range not hindering the object and effect of the present invention described above.

  For example, B, which is included in the mother alloy for Ti addition, and is inevitably included when Ti is added, has the same effect as Ti, as described later, and allows inclusion of 0.05% or less. . Further, Ag is allowed to be 0.2% or less, and Sn is allowed to be 0.2% or less. On the other hand, Zn is particularly harmful to corrosion resistance, and it is preferable to regulate the content as low as possible to 0.05% or less.

  The preferable content range and significance of each element in the 6000 series aluminum alloy, or the allowable amount will be described below for each element.

Si: 0.70 to 1.35%
Si, together with Mg, partly dissolves in the matrix and strengthens the aluminum alloy wire rod. Moreover, it is necessary to satisfy the characteristics required for the fasteners of automobile engine parts by demonstrating the age hardening ability to form aging precipitates that contribute to strength improvement during the artificial aging treatment at the relatively high temperature, It is an essential element for obtaining the high strength and high yield strength. In addition, in order to exhibit the excellent age-hardening ability in the artificial aging treatment at the relatively high temperature, excess Si containing Mg / Si at a mass ratio of 1.73 or less and containing Si excessively with respect to Mg. It is preferable to use a type 6000 series aluminum alloy composition.

  If the Si content is too small, the absolute amount is insufficient, so that the solid solution strengthening and age hardening ability are insufficient. As a result, the required high strength and high yield strength cannot be obtained. On the other hand, if the Si content is too large, coarse crystals and precipitates are formed, and on the contrary, the necessary high strength, high yield strength and high elongation at break cannot be obtained. Moreover, the hot workability and cold workability to a wire rod material, and the moldability to a fastener are remarkably inhibited. Accordingly, Si is set in the range of 0.70 to 1.35%.

Mg: 0.65 to 1.75%
Mg forms an aging precipitate that contributes to strength improvement with Si during solid solution strengthening and artificial aging treatment, exhibits age hardening ability, and satisfies the characteristics required for fasteners of automobile engine parts. It is an essential element for obtaining the high strength, high yield strength, and high elongation at break necessary for the above.

  If the Mg content is too small, the absolute amount is insufficient, so that the solid solution strengthening and age hardening ability are insufficient. As a result, the required high strength and high yield strength cannot be obtained. On the other hand, if the Mg content is too large, coarse crystals and precipitates are formed, and on the contrary, the necessary high strength, high yield strength and high elongation at break cannot be obtained. Therefore, the Mg content is in the range of 0.65 to 1.75%.

Cu: 0.40 to 1.05%
Cu, together with Mg and Si, contributes to improvement in strength, proof stress, and elongation at break. If the Cu content is too small, the effect cannot be sufficiently obtained, and the high strength, high proof stress, and high elongation at break required for satisfying the characteristics required for a fastener for automobile engine parts cannot be obtained. . On the other hand, when there is too much Cu content, strength, yield strength, and elongation at break decrease. In addition, the formability and workability of the fastener and the corrosion resistance are greatly reduced. Therefore, the Cu content is in the range of 0.40 to 1.05%.

Fe: 0.05 to 0.35%
Fe also forms dispersed particles in the same manner as Mn, Cr, Zr, and V, and thus contributes to improvement in elongation at break, heat resistance, etc., such as refining of crystal grains. If the Fe content is too small, the crystal grains are likely to be coarsened, and the high elongation at break required to satisfy the characteristics required for fasteners for automobile engine parts cannot be obtained. On the other hand, when there is too much Fe content, a coarse crystallization thing will be formed and rejected, and elongation at break will fall. In addition, the formability and workability of the fastener are greatly reduced. Therefore, the Fe content is in the range of 0.05 to 0.35%.

Mn: 0.05-0.95%
Mn partially dissolves in the matrix and strengthens the aluminum alloy wire rod. Also, during the homogenization heat treatment, Al-Mn-based dispersed particles are formed, and even when heated to the high temperature for a long time, softening does not easily occur. The mechanical properties such as high strength, high yield strength and high elongation at break are maintained. Moreover, it becomes possible to make the crystal grains of the aluminum alloy wire rod material structure finer and to form a fiber structure, thereby improving the strength, formability and corrosion resistance.

  If the Mn content is too small, the effect cannot be sufficiently obtained, and the high strength, high yield strength, and high elongation at break required for satisfying the characteristics required for fasteners for automobile engine parts cannot be obtained. . On the other hand, when there is too much Mn content, strength, yield strength, and elongation at break decrease. Moreover, the moldability and workability to a fastener are large, and corrosion resistance falls. Therefore, the Mn content is in the range of 0.05 to 0.95%.

Cr: 0.05 to 0.25%,
Cr, Zr, and V form dispersed particles containing the respective elements in the same manner as Mn and Fe, and contribute to improvement in softening resistance and workability to fasteners. Moreover, it has the effect | action which prevents the coarsening of the crystal grain at the time of heat processing of an aluminum alloy wire rod, and refines | miniaturizes a crystal grain. This contributes to improvement in strength, proof stress, and elongation at break, and also improves workability to the fastener. However, in the hot extrusion process, it becomes easy to form an intermetallic compound that causes a pickup (a defective defect that occurs in the extrusion direction of the surface of the extruded material). For this reason, it is difficult to increase the extrusion speed, and the productivity is significantly reduced. On the other hand, in this case, since hot rolling is applied to hot working, there is no pickup and Cr can be positively added.
However, if this Cr content is too small, even if it contains Zr, V, the effect is not sufficiently obtained, and it is necessary to satisfy the characteristics required for fasteners for automobile engine parts, High strength, high yield strength and high elongation at break cannot be obtained. On the other hand, when there is too much Cr content, strength, yield strength, and elongation at break decrease. Moreover, the workability to a fastener falls significantly. Therefore, the Cr content is in the range of 0.05 to 0.25%.

  Zr and V may be selectively contained in addition to Cr for the purpose of assisting the effect of Cr. When Zr and V are used supplementarily in this way, one or two of Zr: 0.01 to 0.30% and V: 0.01 to 0.30% are contained. If these contents are too small, the effect cannot be obtained sufficiently, and if these contents are too large, coarse crystals are formed and strength, proof stress, elongation at break are lowered, and molding into a fastener is performed. The workability and workability are also greatly reduced.

Ti: 0.01-0.10%
Ti has the effect of refining the crystal grains of the ingot together with B contained in the mother alloy for Ti addition. This improves casting and rolling cracks in the production process of the aluminum alloy wire rod. If the Ti content is too small, the effect cannot be obtained sufficiently, cracking is likely to occur, and productivity is significantly inhibited. On the other hand, when there is too much Ti content, a coarse intermetallic compound will be formed and strength, yield strength, and elongation at break will fall. In addition, the formability and workability of the fastener are greatly reduced. Therefore, the Ti content is in the range of 0.01 to 0.10%. Moreover, B permits 0.05% or less of inclusion for the same reason as Ti.

Refinement of structure-crystal precipitates:
As described above, in the present invention, first, crystal precipitates in the 6000 series aluminum alloy wire rod structure are refined to reduce coarse crystal precipitates (average density) as much as possible. This improves cold workability such as header processing and screw rolling processing on fasteners such as bolts and screws for automobile engine parts.

Therefore, in the present invention, the average density of the crystal precipitates having a maximum length of 10 μm or more in the aluminum alloy wire rod structure is specified to be 500 pieces / mm ² or less, and the coarse crystal precipitates are eliminated. The crystal precipitates are refined and the cold workability is improved by a synergistic effect with the component composition. When a substantial amount of coarse crystal precipitates is present in the 6000 series aluminum alloy wire rod structure, the average density of the crystal precipitates having a maximum length of 10 μm or more is not 500 pieces / mm ² or less, Reduces cold workability such as header processing and thread rolling.

  Here, as described above, the crystal precipitates defined in the present invention are, as described above, as amorphous particles of any composition existing in the matrix by observation with an SEM having a magnification of about 400 times the aluminum alloy wire rod structure. This refers to second phase particles that can be confirmed (can be determined whether the maximum length defined in the present invention is 10 μm or more). These crystal precipitates are mainly Mg, Si-based compounds, Si, Fe-based compounds, etc. (however, when a large amount of transition elements such as Cu and Mn, Cr, Zr, V are contained, These elements may be included). These consist of crystallized substances mainly produced during ingot casting, ingot soaking, and precipitates produced mainly during hot rolling, solution treatment / quenching treatment, tempering treatment, and the like. However, in the present invention, as described above, since the composition of the second phase particles is not limited, elemental analysis (elements) of each crystal precipitate using EDX (energy dispersive spectroscopy) or the like at the time of observation by the SEM (Quantitative analysis) is not necessary. That is, the second phase particles that can be observed as described above by SEM are handled as crystal precipitates that prescribe all.

As is well known, these crystal precipitates are likely to be coarsened during cooling after the homogenization heat treatment, during heating to the hot working temperature, and during holding without being an aluminum alloy wire rod. In the present invention, the aluminum alloy wire rod is manufactured by hot rolling, and the crystal precipitates that are likely to be coarsened are coarsened by lowering the temperature of the hot rolling and increasing the processing rate. Without making it finer. That is, as described above, the coarse crystal precipitates are eliminated so that the average density of the crystal precipitates having a maximum length of 10 μm or more in the aluminum alloy wire rod structure is 500 pieces / mm ² or less. The precipitate is refined and the cold workability is improved by a synergistic effect with the component composition.

  Further, when the crystal precipitates are refined, there is an effect that the crystal grains of the aluminum alloy wire rod structure can be also refined. For this reason, there exists an effect which can improve corrosion resistance, such as an intergranular corrosion resistance as a fastener of a motor vehicle engine component.

As described above, these crystal precipitates are likely to become coarse during cooling after the homogenization heat treatment and during heating and holding to the hot working temperature. Therefore, under the extrusion processing conditions and hot rolling conditions at a high temperature exceeding 520 ° C., the crystal precipitates of the wire rod material structure cannot be refined as much as the hot rolling of the present invention, and the maximum length specified in the present invention is The average density of the crystal precipitates of 10 μm or more inevitably becomes larger than 500 / mm ² . For this reason, the cold workability is necessarily inferior.

  Moreover, when these crystal precipitates are coarsened, the corrosion resistance as a fastener for automobile engine parts is also lowered. This is the reason why the conventional 6000 series aluminum alloy wire rod material has poor corrosion resistance.

Measurement of average density of crystal precipitates:
The measurement surface of the average density of crystal precipitates defined in the present invention is relative to the longitudinal direction (axial direction) of the tempered aluminum alloy wire rod material and the fasteners of bolts and screws formed and processed. The central part of any parallel cross section. Measurement and calculation are performed from observation of the tissue at the central portion of these parallel cross sections at a magnification of 1000 times with a scanning electron microscope (SEM).

That is, by the image analysis of the observation visual field by this SEM, the maximum length (of the amorphous part) of each crystal precipitate observed in the observation visual field as the second phase particle of any composition is measured. In addition, the number of crystal precipitates having a maximum length of 10 μm or more is measured. Then, the density (number / mm ² ) per 1 mm ^{2 of the} crystal precipitate having the maximum length of 10 μm or more is calculated. The measurement is carried out at five arbitrary cross sections of each test wire rod for 25 visual fields (total 125 visual fields), and these are averaged to obtain the average density of crystal precipitates defined in the present invention.

Tissue-density of dispersed particles:
As described above, in the present invention, by increasing the density of fine dispersed particles in a specific range in the 6000 series aluminum alloy wire rod structure, it is difficult to soften even when heated to the high temperature for a long time, and even after heating to room temperature atmosphere. The mechanical properties in the inside are small and the original mechanical properties such as high strength, high yield strength and high elongation at break are retained.

Therefore, in the present invention, the average density of dispersed particles having a maximum length in the structure of 6000 series aluminum alloy wire rod material of 200 nm or more and 800 nm or less is 5 particles / μm ³ or more. When the average density is less than 5 particles / μm ³ , the softening resistance cannot be improved even if there are many dispersed particles having a maximum length of less than 200 nm or dispersed particles having a maximum length exceeding 800 nm.

  The dispersed particles defined in the present invention are mainly compounds of transition elements such as Cu, Mn, Cr, Zr, and V, and Al and other alloy elements. These are mainly generated at the time of ingot casting, at the time of ingot soaking, and the like. However, unlike the crystal precipitates, since the maximum length level is greatly different (small), the dispersed particles defined in the present invention are observed and measured at a magnification of 5000 times using a TEM (transmission electron microscope). To do. For this reason, it is not necessary to identify by elemental analysis (element amount analysis) using EDX or the like.

Measurement of average density of dispersed particles As with the crystal precipitates, the average density measurement surface of the dispersed particles defined in the present invention is an aluminum alloy wire rod after tempering treatment, and bolts and screws formed and processed. The central portion of any cross section parallel to the longitudinal direction (axial direction), such as the fastener of the above. A thin film sample is prepared from the central portion of these parallel cross sections, and five fields of view are observed at a magnification of 5000 using a TEM (transmission electron microscope) attached to the component analyzer. The thin film sample has a thickness of 200 to 300 nm. In image processing, the maximum length is 200nm or more, and Kauinto number of less dispersed particles 800 nm, calculate the number per 1 [mu] m ^3, they were averaged, and the average density of the dispersed particles specified in the present invention.

Production method:
The refinement of crystal precipitates as described above can be produced only by the combination or synergistic effect of the above-mentioned 6000 series aluminum alloy with the above specific composition and the above-mentioned processing into a wire rod material by high-temperature hot rolling at low temperatures. is there. That is, it can be manufactured by melting a 6000 series aluminum alloy billet (ingot) having the above specific composition and performing hot rolling at a processing rate of 90% or more after homogenizing heat treatment of the billet.

  After this hot rolling, if necessary, desired cold working such as cold rolling, drawing, drawing, drawing, rolling, forging, etc. may be performed to obtain a wire rod having a predetermined diameter or shape. Further, as described above, a wire rod having a predetermined diameter or a predetermined shape is formed by hot rolling, and thereafter, a wire rod that has been hot-rolled and is not cold worked may be used. These aluminum alloy wire rods having a predetermined diameter are then subjected to a tempering treatment in which the solution treatment and quenching treatment and the aging treatment at 150 to 200 ° C. are performed in the order described. These wire rods are, for example, materials for applications such as bolts and screws, which are fasteners for the automobile engine parts, and depending on the application, molding or processing to a predetermined diameter or a predetermined shape, if necessary. Surface treatment is performed.

The manufacturing method of the aluminum alloy rolled wire rod of the present invention will be described below in the order of steps.
(Dissolution, casting cooling rate)
First, in the melting and casting process, a molten aluminum alloy melt-adjusted within the above-mentioned 6000 series component composition range is cast by appropriately selecting a normal melting casting method such as a semi-continuous casting method (DC casting method).

(Homogenization heat treatment)
Prior to hot rolling, the cast aluminum alloy billet (ingot) is subjected to homogenization heat treatment (soaking) in the range of 470 to 565 ° C. to homogenize the structure (segregation within the crystal grains in the ingot structure). Etc.). The soaking temperature is selected from the range of 470 to 565 ° C., and the homogenization time is selected from the range of 2 hours or more.

If the soaking temperature is too high, the dispersed particles are coarsened, the number of dispersed particles having a maximum length exceeding 800 nm increases, and the density of dispersed particles having a maximum length of 200 nm or more and 800 nm or less decreases. For this reason, the average density of the dispersed particles cannot be made 5 particles / μm ³ or more, and the softening resistance cannot be improved. On the other hand, if the soaking temperature is too low, the dispersed particles become finer, the number of dispersed particles having a maximum length of less than 200 nm increases, and the density of dispersed particles having a maximum length of 200 nm to 800 nm also decreases. For this reason, the average density of the dispersed particles cannot be made 5 particles / μm ³ or more, and the softening resistance cannot be improved. Further, even if this soaking temperature is too low, the crystal precipitates in the 6000 series aluminum alloy wire rod structure do not become small, and even if this soaking temperature is too high, the crystal precipitates become coarse and the maximum length is 10 μm. the average density of the intermetallic compounds described above is more likely to not be a 500 / mm ² or less. Furthermore, if the soaking temperature is too high, the risk of ingot burning increases.

  After this soaking, it is preferable to forcibly quench the billet (ingot) with a fan or the like to increase the cooling rate. If the cooling rate is slow, such as allowing the billet (ingot) to cool, there is a risk that the MgSi compound (crystallized product) will become coarse during the cooling process. The standard of the average cooling rate in such rapid cooling is preferably 80 ° C./hr or higher up to a temperature of 300 ° C. or lower including room temperature.

(Hot rolling)
In order to refine the crystal precipitates of the wire rod material structure, the billet after the homogenization treatment is subjected to hot rolling at low temperature and strong processing. For this reason, the hot rolling start temperature (hot rolling start temperature) is in the range of 320 to 520 ° C., preferably in the range of 320 to 485 ° C., depending on the composition of the aluminum alloy and the size of the ingot. It is preferably selected from the lowest possible temperature in the range of 320 to 470 ° C. When the hot rolling start temperature is too high, rolling at a low temperature is not performed, the crystal precipitates are not pulverized to a small size, and coarse crystal precipitates remain. There is a high risk that it cannot be miniaturized. On the other hand, if the hot rolling start temperature is too low as less than 320 ° C., the rolling load is particularly excessive in the hot rolling in the strong working, and the rolling of the wire rod itself becomes difficult. In the present invention, the hot rolling start temperature is inevitably lower than the soaking temperature. Therefore, after the soaking, cooling is performed from the homogenizing heat treatment temperature, and hot rolling is started as the hot rolling start temperature. To do. Further, after the homogenization heat treatment, it may be once cooled to room temperature, reheated to the hot rolling start temperature, and hot rolling may be started at this reheating temperature.

  The hot rolling processing rate is also selected from the range of 90% or higher processing rate as high as possible depending on the composition of the aluminum alloy and the relationship between the ingot size and the wire rod diameter. If the processing rate is too small, the crystal precipitates are not pulverized small, and coarse crystal precipitates remain, and the crystal precipitates cannot be refined as defined in the present invention.

  Here, hot rolling is a hot extrusion method in which a wire rod having a circular cross section (round) can be produced without causing new problems or other problems with the structure and characteristics of the present invention. It is much better than

  For example, in the case of a wire rod having a round cross-section as the object of the present invention, the shape is simple in extrusion, unlike the case of a shape having a complicated shape. For this reason, the shape of the die is also simplified, and the center portion of the billet (ingot) is extruded as it is as the center portion of the wire rod material without being processed by the die, and the center portion of the wire rod material is The cast structure of the billet tends to remain as it is. In other words, in the central portion of the wire rod material manufactured by hot extrusion, the coarse crystallized material existing in the cast structure of the billet is not pulverized to a small size and remains coarse. The crystal precipitate cannot be refined as specified. Contrary to this central portion, the billet surface is more strongly processed and easily heated, and the crystallized material having a relatively low melting point present on the billet surface is locally melted and easily adhered to a die or the like. For this reason, the surface of the wire rod material during extrusion is peeled off, causing a phenomenon called mushy, and the surface failure of the wire rod material called pickup tends to occur. In order to prevent such defects of the extruded material, it is necessary to increase the soaking temperature or reduce the amount of transition elements in order to reduce the crystallized matter on the surface. However, as described above, when the soaking temperature is increased, the dispersed particles become coarse, and when the amount of the transition element is decreased, the dispersed particles are reduced and the density is decreased, and the dispersed particle density specified in the present invention cannot be achieved. Thus, in the hot extrusion process, it is difficult to produce a wire rod having a structure and characteristics as in the present invention. When manufacturing a wire rod material having a circular cross section as a fastener for bolts and screws for automobile engine parts, etc., there is a great limit to the improvement in characteristics in the conventional manufacturing by extrusion as in Patent Document 1. That is why.

(Tempering treatment)
In the case of cold working such as cold rolling after hot rolling, annealing may be performed as appropriate after hot rolling and before cold working, or may be performed by sandwiching annealing during the cold working.
After hot rolling or after cold working such as cold rolling, as a tempering treatment for the wire rod material, first, solution treatment and rapid cooling (quenching) treatment are performed. This solution treatment is preferably performed at 500 ° C. or more in order to sufficiently precipitate aging precipitates that contribute to strength improvement by the relationship with the component composition of the aluminum alloy and the subsequent artificial age hardening treatment at high temperatures. 570 is performed under the condition of holding for a predetermined time. Immediately after the solution treatment, rapid cooling (quenching) is performed at a cooling rate of 10 ° C./second or more. When the cooling rate of the rapid cooling treatment after the solution treatment is slow, Si, MgSi compounds and the like are likely to precipitate on the grain boundaries, and mechanical properties and formability are deteriorated.

  Next, after this solution quenching treatment, a high temperature aging treatment at 150 to 200 ° C. is preferably performed immediately in order to improve mechanical properties such as strength of the wire rod. When such high-temperature aging treatment is not performed, the mechanical properties of the aluminum alloy wire rod at room temperature are set to tensile strength: 410 MPa or more, 0.2% proof stress: 350 MPa or more, and elongation: 6% or more. It is difficult. Therefore, these mechanical properties cannot necessarily be satisfied as the mechanical properties in the air at room temperature after the heat treatment at 150 ° C. for 500 hours.

(Molding)
These wire rod materials are further subjected to cold working and molding such as header processing and screw rolling processing to a predetermined diameter and shape according to the use of fasteners such as fasteners for automobile engine parts. Here, a known surface treatment may be appropriately performed on these fasteners.
In addition, when the aluminum alloy wire rod is formed and processed for fasteners such as bolts and screws of automobile engine parts, the tempering treatment may be performed before the forming and processing, or the bolt The tempering treatment may be performed after molding and processing for fasteners such as screws and screws.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

  Next, examples of the present invention will be described. After casting the 6000 series aluminum alloy shown in Table 1, hot rolling at a soaking temperature, a hot rolling start temperature and a hot rolling process rate shown in Table 2 is performed to produce a wire rod with a circular cross section. Various properties such as cold workability, softening resistance and corrosion resistance were evaluated.

  More specific production conditions for the aluminum alloy wire rod are as follows. A 6000 series aluminum alloy having each composition shown in Table 1 was cast into a billet (ingot) by a semi-continuous casting method. These billets were changed in diameter in order to change the hot rolling rate, and were soaked for 4 hours (hr) in common at the soaking temperature shown in Table 2. And after cooling to room temperature once after that, it reheated to each hot rolling start temperature shown in Table 2, and it hot-rolled with the processing rate shown in Table 2, and manufactured the wire rod material of (phi) 13mm in common. Here, the billet after the soaking was forcibly quenched by a fan, and the average cooling rate up to 300 ° C. or less was set to 150 ° C./hr.

  Further, this hot-rolled wire rod was cold drawn to Φ3.5 mm. Next, the wire rod material reduced in diameter was cut into a predetermined length and subjected to header processing and screw rolling processing in a cold state to produce a large number of M4 bolts. Next, the prepared bolt was subjected to a solution treatment at 570 ° C. for 3 hours, followed by water quenching, followed by a high temperature aging treatment at 180 ° C. for 9 hours. At this time, with respect to the order of the M4 bolt preparation and the tempering process, the process of performing the tempering process after the bolt is manufactured in the cold working after the tempering process is performed after the tempering process. A process for producing a bolt by inter-processing was designated as a B process.

Processability:
In this bolt processing, the header processability and rolling processability (M4) were evaluated, and the example that the entire amount could be processed into bolts without defects such as cracks occurred, defects such as cracks occurred, The example judged that workability was bad was evaluated as x.

  Sample materials were cut out from these bolts, and the structure and characteristics were measured and evaluated as the structure and characteristics of the aluminum alloy wire rod as described below. These results are also shown in Table 2.

Organization:
The average density of crystal precipitates and dispersed particles in the bolt specimen was measured by the method described above.

mechanical nature:
From the bolt specimen, Fed. A 4 type small tensile test piece was prepared, and a tensile test was performed until breakage at room temperature at a crosshead speed of 5 mm / min. From the stress-strain rate, tensile strength (MPa) and 0.2% yield strength (MPa) were measured. The elongation (%) was calculated from the spacing between the marking lines before and after the tensile test of the parallel part of the small tensile test piece (interval 10 mm before the tensile test). In addition, these measured values were made into the average value of each measured value of five bolt test materials.

Mechanical properties after prolonged exposure to high temperatures:
Tensile properties after heating as softening resistance were obtained by heat-treating a bolt at 150 ° C. for 500 hours, then preparing a tensile test piece, and performing a tensile test at normal temperature in the same manner as the normal temperature tensile test, Yield strength and elongation were measured.

Corrosion resistance:
In order to evaluate the corrosion resistance, a corrosion test was carried out in accordance with the method described in Section 4.4.3 of the JIS-W1103 method for each of the bolt specimens (before being exposed to a high temperature for a long time). That is, the corrosion test conditions were as follows. First, after immersion in an etching solution at 93 ° C. (composition of 70% concentrated nitric acid 50 ml, 48%, hydrofluoric acid 5 ml, distilled water 945 ml), washed with distilled water and dried. It was. Thereafter, it was immersed in a corrosion accelerating solution at 30 ° C. (57 g of NaCl, 10 ml of 30% hydrogen peroxide solution diluted to 1 liter with distilled water) for 6 hours. Then, the test specimen parallel section was immersed in an etching solution (composition of 70% concentrated nitric acid 2.5 ml, concentrated hydrochloric acid 1.5 ml, 48% hydrofluoric acid 1.0 ml, distilled water 95.0 ml) for 10 seconds, followed by distillation. Washed with water and dried. The corrosion state of this test piece parallel cross section was observed with a 200-fold metal microscope. In the observation of the corrosion, the degree of corrosion was determined using 6061-T6 as a comparative material in the microscope field of view, distinguishing it from other pitting corrosion and overall corrosion. These results were evaluated as “x” when the degree of corrosion was large, and “o” as the same or equivalent.

  Inventive Examples 1 to 10 in Table 2 using Alloy Nos. 1 to 9 in Table 1 are subjected to hot rolling at low temperature and strong working within the composition range of the present invention and within the above-described preferable condition range. ing. For this reason, as shown in Table 2, it has the structure | tissue which becomes the average density of the crystal precipitate prescribed | regulated by this invention, and a dispersed particle. As a result, the mechanical properties in the air at room temperature after heat treatment at 150 ° C. for 500 hours for a long time are as follows: tensile strength: 410 MPa or more, 0.2% proof stress: 350 MPa or more, elongation: 6% or more. Has softening resistance. It also has excellent corrosion resistance.

On the other hand, the comparative examples 11-21 of Table 2 are the alloys of the alloy numbers 10-20 shown in Table 1, and a component composition is outside the range of this invention.
The comparative example 10 has too little Mn content (it does not contain Mn).
The comparative example 11 has too little Cu content (it does not contain Cu).
The comparative example 12 has too little Cr content (it does not contain Cr).
The comparative example 13 has too much Mn content.
Comparative Example 14 has too much Cu content.
Comparative Example 15 has too much Cr content and Comparative Example 16 has too much Zn content.
The comparative example 17 has too much Si content.
Comparative Example 18 has too much Mg content.
The comparative example 19 has too little Mg content.
The comparative example 20 has too little Si content.

Moreover, although the comparative examples 22-25 of Table 2 use the alloy of the alloy number 1 which is in this invention component composition range shown in Table 1, it is the above-mentioned preferable condition range, and is hot-rolling of low temperature and strong work. Is not done.
Although the comparative example 22 has a high hot rolling reduction, the soaking temperature is too high.
In Comparative Example 23, the hot rolling start temperature is low, but the soaking temperature is too low.
In Comparative Example 24, the hot rolling reduction temperature is high, but the hot rolling start temperature is too high.
In Comparative Example 25, the hot rolling start temperature is low, but the hot rolling reduction is too low.

  For this reason, as shown in Table 2, each comparative example does not have or has the structure defined in the present invention, but the mechanical properties after being exposed to a high temperature for a long time are inferior. Moreover, corrosion resistance is also inferior.

  Therefore, the results of the above examples support the critical significance or effects on the cold workability, softening resistance, corrosion resistance, and the like of the bolts of the requirements of the components and structures in the present invention. Moreover, the critical significance or effect for obtaining the structure of the present invention under preferable production conditions is supported.

  According to the present invention, even when exposed to a high temperature for a long time (heated for a long time), it has excellent softening resistance and can maintain high mechanical properties, and also has excellent cold workability and corrosion resistance. In addition, a 6000 series high-strength aluminum alloy wire rod and a method for producing the same can be provided. For this reason, it can be used suitably for aluminum alloy fasteners such as bolts and screws of automobile engine parts.

Claims (6)

1. A hot-rolled Al—Mg—Si-based aluminum alloy wire rod in mass%, Mg: 0.65 to 1.75%, Si: 0.70 to 1.35%, Cu: 0.40 to 1.05%, Fe: 0.05 to 0.35%, Mn: 0.05 to 0.95%, Cr: 0.05 to 0.25%, Ti: 0.01 to 0. A crystal comprising 10% each, comprising the balance Al and inevitable impurities, the average length of dispersed particles having a maximum length of 200 nm or more and 800 nm or less in the structure of 5 / μm ³ or more, and a maximum length of 10 μm or more A high-strength aluminum alloy wire rod excellent in softening resistance, wherein the average density of precipitates is 500 pieces / mm ² or less.
2.   The mechanical properties in air at room temperature after heat-treating the aluminum alloy wire rod at 150 ° C. for 500 hours are tensile strength: 410 MPa or more, 0.2% proof stress: 350 MPa or more, elongation: 6% or more. Item 2. A high-strength aluminum alloy wire rod excellent in softening resistance according to Item 1.
3.   3. The aluminum alloy wire rod according to claim 1 or 2, wherein the aluminum alloy wire rod further contains one or two of Zr: 0.01 to 0.30% and V: 0.01 to 0.30% by mass%. A high-strength aluminum alloy wire rod excellent in softening resistance described in 1.
4.   The high-strength aluminum alloy wire rod material excellent in softening resistance according to any one of claims 1 to 3, wherein the aluminum alloy wire rod material is used as a fastener for automobile engine parts.
5. In mass%, Mg: 0.65 to 1.75%, Si: 0.70 to 1.35%, Cu: 0.40 to 1.05%, Fe: 0.05 to 0.35%, Mn: 0.05 to 0.95%, Cr: 0.05 to 0.25%, Ti: 0.01 to 0.10%, respectively, the balance consisting of Al and inevitable impurities, and if necessary, Zr: 0 0.01 to 0.30%, V: 0.01 to 0.30% of Al-Mg-Si-based aluminum alloy ingot containing one or two of them was melted, and this ingot was 470 to 565 After homogenization heat treatment in the range of ℃, hot rolling with a working rate of 95% or more at a hot rolling start temperature in the range of 320 to 520 ℃, further cold working as necessary, aluminum alloy wire rod with a predetermined diameter After that, a tempering treatment is performed in which the solution treatment and quenching treatment and the aging treatment at 150 to 200 ° C. are performed in the order described. The in tissue after applying, the maximum length is 200nm or more, with an average density of less dispersed particles 800nm is 5 pieces / [mu] m ³ or more, the average density of the maximum length 10μm or more intermetallic compounds is 500 / A method for producing a high-strength aluminum alloy wire rod excellent in softening resistance, characterized by being made to be ² mm ² or less.
6.   The method for producing a high-strength aluminum alloy wire rod excellent in softening resistance according to claim 5, wherein the aluminum alloy wire rod is processed into a fastener for an automobile engine part before or after the tempering treatment.