JP2013036107A - Al-Zn-Mg ALLOY EXTRUDED MEMBER EXCELLENT IN TOUGHNESS AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Al-Zn-Mg alloy extruded member which is excellent in toughness and can be suitably used as a member of a motorcycle.SOLUTION: The Al-Zn-Mg alloy extruded member contains 7.0 to 9.5% Zn, 1.0 to 3.0% Mg, less than 0.5% Cu, and 0.05 to 0.30% Zr and also contains one or more of 0.70% or less Mn and 0.50% or less Cr, with the balance consisting of Al and inevitable impurities, wherein a Mn-containing compound or a Cr-containing compound having a grain size of 20 nm or more and 200 nm or less is dispersed in the matrix crystal grains in an amount of 7 pieces/μmor more.

Description

  The present invention relates to an Al—Zn—Mg alloy extruded material excellent in toughness and a method for producing the same.

  Since motorcycles are light in weight, high-strength 7000 series aluminum alloys are frequently used as materials. In particular, off-road race cars such as motocross and enduro perform jumps, so the materials are required to have high strength and toughness. Al-Zn- with more than 1.0% Cu added to handlebars and rims. Mg-Cu alloys are frequently used. These alloys have a high tensile strength exceeding 500 MPa, but on the other hand, the productivity is poor and the cost is high. Therefore, development of a high strength and high toughness alloy excellent in productivity is demanded.

  In general, it is known that an Al—Zn—Mg alloy having a Cu content of less than 0.5% is superior in extrudability compared to an Al—Zn—Mg—Cu alloy. 7N01 alloy is used for welded structures such as frames. However, the strength is about 430 MPa even in T6 tempering, and there is a problem that the strength is not sufficient for use in handlebars, rims and the like. In general, it is known that the greater the Zn content and the Mg content, the higher the strength. However, since the toughness is lowered, the compatibility of strength and toughness is a major issue.

  As an aluminum alloy extruded material for hydroform molding having high strength and excellent stress corrosion cracking resistance, Zn: 6.0 to 9.0%, Mg: 0.8 to 2.0%, Cu: 0.6 to 2 0.0%, Mn: 0.1-0.5%, Cr: 0.1-0.3%, Zr: 0.1-0.3%, consisting of the balance Al and unavoidable impurities, unavoidable Of the general impurities, Si is limited to 0.05% or less, preferably the total content of Mg and Cu is 3.6% or less, extruded by porthole extrusion, and the thickness of the surface recrystallized layer An aluminum alloy extruded tube with a thickness of 70 μm or less has been proposed. In this case, port hole extrusion is possible, but since Cu contains 0.6 to 2.0%, the melting point is low and extrusion processing is performed. It is inferior in toughness and no consideration is given to toughness (Patent Literature) ).

  As an aluminum alloy extruded material having excellent crushing properties, Mg: 0.5 to 1.8%, Zn: 4.0 to 8.0%, Ti: 0.005 to 0.3%, Cu: 0.05 to 0 0.6%, Mn: 0.1-0.7%, Cr: 0.03-0.3%, Zr: 0.05-0.25% of one or more It has a composition composed of the balance Al and inevitable impurities, has a fibrous structure, and has a characteristic that the thickness reduction rate of the fractured surface when a tensile test is performed with a JIS No. 5 tensile test piece is 20% or more. Although this also has been proposed, there is a problem that even in this case, the strength is not sufficient as a whole, and when the tensile strength exceeds 500 MPa, the extrudability and the SCC resistance are inferior (Patent Document 2).

JP 2010-196089 A JP 2008-274441 A

  In order to obtain an Al—Zn—Mg alloy extruded material having excellent productivity, high strength and high toughness, the present invention provides a composition of Al—Zn—Mg alloy and a compound dispersed in crystal grains of the alloy matrix. As a result of repeated tests and examinations on the relationship between the properties and impact properties of the steel, the purpose thereof is an extruded Al-Zn-Mg alloy that is excellent in toughness and can be suitably used as a motorcycle material, and its It is to provide a manufacturing method.

The Al—Zn—Mg alloy extruded material with excellent toughness according to claim 1 for achieving the above object is Zn: 7.0 to 9.5% (mass%, the same applies hereinafter), Mg: 1.0 to 3.0%, Cu: less than 0.5%, Zr: 0.05 to 0.30%, Mn: 0.70% or less and Cr: 0.50% or less contained, an extruded material of Al-Zn-Mg alloy and the balance Al and inevitable impurities, Mn-containing compound of the following size 200nm or 20nm in crystal grains of the matrix or Cr-containing compound is 7 / [mu] m ² It is characterized by being dispersed as described above.

  The extruded Al-Zn-Mg alloy material having excellent toughness according to claim 2 is the aluminum alloy extruded material according to claim 1, wherein the aluminum alloy extruded material is Ti: 0.15% or less and B: 50 ppm or less. It contains seeds.

The Al—Zn—Mg alloy extruded material with excellent toughness according to claim 3 has a Charpy impact value using a U-notch test piece having a depth of 2 mm as defined in JIS Z 2202 in (1) or (2). 2.3 × [Zn%] − 8.1 × [Mg%] + 42) (J / cm ² ) or more.

  The method for producing an Al-Zn-Mg alloy extruded material having excellent toughness according to claim 4 is a method for producing an Al-Zn-Mg alloy extruded material according to any one of claims 1 to 3, wherein The Al—Zn—Mg alloy having the composition described in 1 or 2 is melted, and the billet is manufactured by controlling the average cooling rate between the molten metal holding temperature and the 640 ° C. in the solidification process to be 0.10 ° C./second or more. It is characterized in that after the agglomeration is performed, the obtained billet is homogenized at a temperature of 420 ° C. or higher and 550 ° C. or lower for a period of 2 hours or more and 50 hours or less, and then subjected to hot extrusion and tempering.

According to the present invention, a Mn-containing compound or a Cr-containing compound having a size of 20 nm or more and 200 nm or less is dispersed in a crystal grain of the matrix by 7 pieces / μm ² or more, and a depth of 2 mm as defined in JIS Z 2202 is achieved. The Charpy impact value using the U-notch test piece was (−2.3 × [Zn%] − 8.1 × [Mg%] + 42) (J / cm ² ) or more, and Al—Zn— excellent in toughness A Mg alloy extruded material can be obtained. The Al—Zn—Mg alloy extruded material can be suitably used as a motorcycle material.

  Explaining the significance and reason for limitation of the alloy element of the Al-Zn-Mg alloy extrudate excellent in toughness according to the present invention, Zn is an element that functions to improve the strength by bonding with Mg atoms, and the preferred content Is in the range of 7.0 to 9.5%. If it is less than the lower limit, the strength becomes insufficient, and if it exceeds the upper limit, the SCC (stress corrosion cracking) resistance decreases. The more preferable content range of Zn is 7.5 to 9.5%, and the most preferable content range is 7.5 to 9.0%.

  Mg is an element that functions to combine with Zn to improve the strength, and the preferred content is in the range of 1.0 to 3.0%. If it is less than the lower limit, the strength becomes insufficient, and if it exceeds the upper limit, the SCC resistance decreases. The more preferable content range of Zn is 1.2 to 2.7%, and the most preferable content range is 1.4 to 2.4%.

  Cu is an element that functions to improve the SCC resistance, and the preferred content is less than 0.5%. If Cu is not contained, the SCC resistance is lowered. On the other hand, when the content exceeds the upper limit, the extrusion pressure is remarkably increased, the limit extrusion speed is lowered, clogging is likely to occur, and cracking is likely to occur during extrusion.

  Zr is an element that functions to improve strength and SCC resistance by making the microstructure of the extruded material into a fibrous form, and the preferred content is in the range of 0.05 to 0.30%. If it is less than the lower limit, the microstructure of the extruded material becomes a recrystallized structure, and the strength and the SCC resistance are lowered. If the content exceeds the upper limit, a coarse crystallized product is generated at the time of casting, resulting in a decrease in toughness. A more preferable content range of Zr is 0.10 to 0.20%.

  Mn and Cr function to produce a compound in the crystal grains of the extruded material matrix and improve toughness by a combination of casting conditions and homogenization conditions described later. Preferable content is the range of Mn: 0.70% or less and Cr: 0.50% or less. When even one of Mn and Cr is not contained, the Mn-containing compound or Cr-containing compound having a size of 20 nm or more and 200 nm or less does not exist in the crystal grains inside the extruded material, and the toughness is lowered. When each content exceeds the upper limit, a coarse crystallized product is generated at the time of casting, resulting in a decrease in toughness. More preferable content ranges of Mn and Cr are Mn: 0.50% or less and Cr: 0.30% or less.

  Ti and B function to refine the cast structure and suppress cracking during casting in the manufacturing process of the aluminum alloy extruded material. Preferable content is the range of Ti: 0.15% or less, B: 50 ppm or less. When it contains exceeding each upper limit, a coarse intermetallic compound will increase and toughness will fall. More preferable content ranges of Ti and B are Ti: 0.10% or less and B: 20 ppm or less. In addition, Cu: less than 0.5%, Mn: 0.70% or less, Cr: 0.50% or less, Ti: 0.15% or less, B: 50 ppm or less, the content does not include 0% Of course.

  Fe and Si are contained as inevitable impurities. Fe and Si, as the content increases, produce Al-Fe-Si-based crystallized product during casting and reduce the toughness of the final product. Then, since the cost increases, considering the balance between cost and toughness, the allowable Fe and Si contents are in the range of Fe: 0.4% or less and Si: 0.3% or less.

In the Al-Zn-Mg alloy extruded material having excellent toughness according to the present invention, Mn-containing compounds or Cr-containing compounds having a size of 20 nm or more and 200 nm or less are dispersed in the crystal grains of the matrix at 7 particles / μm ² or more. It is preferable. Dispersion of the Mn-containing compound or the Cr-containing compound suppresses crack propagation during impact deformation and improves toughness. When the number of Mn-containing compounds or Cr-containing compounds having a size of 20 nm or more and 200 nm or less is less than 7 / μm ² , the effect of suppressing crack propagation is reduced and the toughness is reduced.

In the present invention, the toughness is evaluated by a Charpy impact test. The Al-Zn-Mg alloy extruded material according to the present invention is a Charpy impact using a U-notch test piece having a depth of 2 mm as defined in JIS Z2202. The value is preferably (−2.3 × [Zn%] − 8.1 × [Mg%] + 42) (J / cm ² ) or more. In this case, the direction of the Charpy impact test is performed in the direction with the lowest toughness. For example, in the case of an extruded material with a rectangular cross section, if the test is performed so that the length direction of the test piece is parallel to the width direction of the extruded material, and the crack propagation direction of the impact test is the thickness direction of the extruded material The Charpy impact value is the lowest. When the Charpy impact value is less than the lower limit, the toughness may be insufficient when used for motorcycle parts.

The manufacturing method of the Al-Zn-Mg alloy extrusion material excellent in toughness by this invention is demonstrated.
First, an Al—Zn—Mg alloy having the above composition is melted, and the billet is agglomerated by controlling the average cooling rate between the molten metal holding temperature and the 640 ° C. in the solidification process to be 0.10 ° C./second or more. To do. When the average cooling rate between the molten metal holding temperature and 640 ° C. is less than the lower limit, a coarse crystallized product may be generated, resulting in a decrease in toughness of the extruded material. Furthermore, the Mn-containing compound or Cr-containing compound dispersed in the crystal grains inside the extruded material may be less than 7 / μm ² , leading to a decrease in toughness. The more preferable average cooling rate between the molten metal holding temperature and 640 ° C. is 0.15 ° C./second or more, and the most preferable average cooling rate is 0.20 ° C./second or more.

  Next, after the obtained billet is homogenized at a temperature of 420 ° C. or higher and 550 ° C. or lower for 2 hours or longer and 50 hours or shorter, hot extrusion and tempering are performed. When the holding temperature or holding time of the homogenization treatment is less than the lower limit, the size of the Mn-containing compound or the Cr-containing compound dispersed in the crystal grains inside the extruded material becomes less than 20 nm, leading to a decrease in toughness. When the holding temperature or holding time exceeds the upper limit, the size of the Mn-containing compound or Cr-containing compound dispersed in the crystal grains inside the extruded material exceeds 200 nm, leading to a decrease in toughness.

  After homogenization, hot extrusion and tempering are performed. The tempering process refers to appropriately tempering according to the quality such as T5, T6, T7, etc. according to the application. The tempering treatment is basically a heat treatment composed of solution treatment, quenching, and artificial aging treatment, and the solution treatment temperature is preferably 400 ° C or higher, and the quenching is performed up to 100 ° C or less. The average cooling rate is preferably 1 ° C./second or more. Further, by performing press quenching in the extrusion process, solution treatment and quenching can be omitted, and press quenching is also included in the tempering process. The artificial aging treatment is preferably performed at a temperature of 100 ° C. or more and 170 ° C. or less, and the holding time is appropriately set so that the peak aging is performed at each artificial aging treatment temperature at T5 and T6, and the overaging is performed at T7. Is done.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects. In addition, these Examples show one Embodiment of this invention, and this invention is not limited to these.

Example 1
Aluminum alloys (alloys A to M) having the compositions shown in Table 1 were melted and formed into billets (diameter 400 mm) by a semi-continuous casting method. At this time, the melt holding temperature at the time of casting was set to 700 ° C., and the casting speed was set to 1 mm / s, whereby the average cooling rate up to 640 ° C. at the billet center was controlled to 0.20 ° C./sec.

  Each billet was homogenized for 10 hours at a temperature of 450 ° C., then cooled to room temperature, heated again to a temperature of 400 ° C., and hot extruded into a rectangular cross section having a thickness of 20 mm and a width of 80 mm. And cooled to room temperature. The obtained extruded material was subjected to a solution treatment for 1 hour at a temperature of 450 ° C., then quenched in water at room temperature, and further subjected to an artificial aging treatment for 6 hours at a temperature of 150 ° C. Got.

  About the test materials 1-13, the number of compounds in a crystal grain, the Charpy impact value, the tensile strength, and the presence or absence of the crack in a SCC test were investigated on the conditions shown below. The results are shown in Table 2.

  Number of compounds in crystal grains: Test pieces with a thickness of about 1 mm, a width of about 5 mm, and a length of about 5 mm are cut from the center of the width and thickness of the test material, collected, and polished to a thickness of about 40 μm with water-resistant abrasive paper. Then, a transmission electron microscope (TEM) structure observation specimen was obtained by a twin jet polishing method. For each test piece, the structure was observed 20000 times with a TEM, and after confirming the Mn-containing compound or the Cr-containing compound with EDX, five structure photographs were taken, and the size of the crystal grains was 20 nm or more and 200 nm or less. The number of Mn-containing compounds or Cr-containing compounds was measured and divided by the observation visual field area.

  Charpy impact value: A Charpy impact test piece having a thickness of 10 mm, a width of 10 mm, and a length of 55 mm having a U-notch of 2 mm in depth according to JIS Z 2202 is molded, and a Charpy impact test at room temperature in accordance with JIS Z 2242. The impact value was measured. At this time, from the central part of the extruded material, the length direction (55 mm) of the Charpy impact test piece is parallel to the width direction of the extruded material, and the depth direction of the U notch is parallel to the thickness direction of the extruded material. Charpy impact test specimens were collected.

  Tensile strength: No. 14A test piece described in JIS Z 2201 is prepared from the width and thickness center of the test material so that the tensile test direction is parallel to the extrusion direction, and at room temperature in accordance with JIS Z 2241. A tensile test was performed to measure the tensile strength at a nominal strain of 0.2%. At this time, the diameter of the parallel part of the tensile test piece was 6 mm. A tensile strength of 500 MPa or more was used as a criterion for acceptance.

  Presence / absence of crack in SCC test: A C-ring test piece described in Appendix 5 of JIS H 8711 was prepared from the width and thickness of the test material. At this time, the outer diameter is 19.05 mm, the thickness is 1.50 mm, the length direction of the C-ring test piece is parallel to the length direction of the extruded material, and the slit position of the C-ring test piece is JIS H 8711. Appendix 5 A C-ring test piece was prepared in a direction consistent with the plan view of the plank of FIG. C-ring test piece is tightened with screws so that 90% of tensile strength of the yield strength obtained in the tensile test is applied, and the contact part between C-ring test piece and screw is vinyl resin so that no electric corrosion occurs. The SCC test was performed by coating with paint and alternating immersion with 3.5% salt water. The SCC test was based on JIS H 8711, and after a 30-day test, the presence or absence of cracks was examined with a magnifying glass.

As seen in Table 2, all of the test materials 1 to 13 according to the present invention have a compound number of 7 / μm ² or more in crystal grains and a Charpy impact value of (−2.3 × [Zn%] − 8. 0.1 × [Mg%] + 42) (J / cm ² ) or more, and no cracks were observed in the SCC test. Moreover, the tensile yield strength showed a high value of 500 MPa or more.

Example 2
Aluminum alloy D shown in Table 1 was melted and formed into billets (diameter 400 mm) by a semi-continuous casting method. At this time, the molten metal holding temperature at the time of casting was set to 700 ° C., and the casting rate and the average cooling rate up to 640 ° C. at the billet center were set as the conditions shown in Table 3.

  For each billet, after homogenization treatment was performed under the conditions shown in Table 3, it was cooled to room temperature, heated again to a temperature of 400 ° C., and subjected to hot extrusion into a rectangular cross section having a thickness of 20 mm and a width of 80 mm. Cooled to room temperature. The obtained extruded material was subjected to a solution treatment at a temperature of 450 ° C. for 1 hour, then quenched in water at room temperature, and further subjected to an artificial aging treatment at a temperature of 150 ° C. for 6 hours to obtain test materials 14 to 17 Got.

  About the test materials 14-17, the number of compounds in a crystal grain, the Charpy impact value, the tensile strength, and the presence or absence of the crack in a SCC test were investigated on the same conditions as Example 1. The results are shown in Table 4.

As can be seen from Table 4, in each of the test materials 14 to 17, the number of compounds in crystal grains was 7 / μm ² or more, and the Charpy impact value was (−2.3 × [Zn%] − 8.1 ×. [Mg%] + 42) (J / cm ² ) or more, and no cracks were observed in the SCC test. Moreover, the tensile yield strength showed a high value of 500 MPa or more.

Comparative Example 1
Aluminum alloys (alloys N to Y) having the compositions shown in Table 5 were melted and formed into billets (diameter 400 mm) by a semi-continuous casting method. At this time, the melt holding temperature at the time of casting was set to 700 ° C., and the casting speed was set to 1 mm / s, whereby the average cooling rate up to 640 ° C. at the billet center was controlled to 0.20 ° C./sec. In Table 5, those outside the conditions of the present invention are underlined.

  Each billet was homogenized for 10 hours at a temperature of 450 ° C., then cooled to room temperature, heated again to a temperature of 400 ° C., and hot extruded into a rectangular cross section having a thickness of 20 mm and a width of 80 mm. And cooled to room temperature. The obtained extruded material was subjected to a solution treatment for 1 hour at a temperature of 450 ° C., then quenched in water at room temperature, and further subjected to an artificial aging treatment at a temperature of 150 ° C. for 6 hours. Got.

  About the test materials 18-29, the number of compounds in a crystal grain, the Charpy impact value, the tensile strength, and the presence or absence of the crack in a SCC test were investigated on the same conditions as Example 1. The results are shown in Table 6. In Table 6, those outside the conditions of the present invention are underlined.

  As seen in Table 6, the strength of the test material 18 was low because the Zn content was less than the lower limit. Since the amount of Zn exceeded the upper limit, the test material 19 was cracked in the SCC test. The test material 20 had low strength because the Mg content was less than the lower limit. Since the amount of Mg exceeded the upper limit, the test material 21 was cracked in the SCC test. Since the test material 22 did not add Cu, cracks occurred in the SCC test. Since the amount of Cu exceeded the upper limit, the test material 23 was cracked by extrusion, and a test piece could not be produced.

  Since the test material 24 had a Zr amount less than the lower limit, the extruded material had a recrystallized structure, the strength was low, and cracks occurred in the SCC test. In the test material 25, the amount of Zr exceeded the upper limit, so a coarse crystallized product was generated, and the toughness was lowered. Since the test material 26 contained neither Mn nor Cr, the number of compounds in the crystal grains became less than the lower limit, and the toughness was lowered. Since the test material 27 exceeded the upper limit in the amount of Mn, the test material 28 exceeded the upper limit in the amount of Cr, and the test material 29 exceeded the upper limits in the amounts of Ti and B, both produced coarse crystallized products and decreased toughness. .

Comparative Example 2
Aluminum alloy D shown in Table 1 was melted and formed into billets (diameter 400 mm) by a semi-continuous casting method. At this time, the molten metal holding temperature at the time of casting was set to 700 ° C., and the casting rate and the average cooling rate up to 640 ° C. at the billet center were set as the conditions shown in Table 7.

  For each billet, after homogenizing under the conditions shown in Table 7, cooled to room temperature, heated again to a temperature of 400 ° C., hot extruded into a cross-sectional rectangular shape with a thickness of 20 mm and a width of 80 mm, Cooled to room temperature. The obtained extruded material was subjected to a solution treatment for 1 hour at a temperature of 450 ° C., then quenched in water at room temperature, and further subjected to an artificial aging treatment for 6 hours at a temperature of 150 ° C. Got. In Table 7, those outside the conditions of the present invention are underlined.

  For the test materials 30 to 34, the number of compounds in crystal grains, the Charpy impact value, the tensile strength, and the presence or absence of cracks in the SCC test were examined under the same conditions as in Example 1. The results are shown in Table 8. In Table 8, those outside the conditions of the present invention are underlined.

  As shown in Table 8, since the average cooling rate between the molten metal holding temperature and 640 ° C. is less than the lower limit, the test material 30 produces coarse crystals, and the number of compounds in the crystal grains is less than the lower limit, and the toughness is reduced. It was low. Since the test material 31 has a homogenization treatment temperature below the lower limit and the test material 32 has an upper homogenization temperature, the test material 33 has a homogenization treatment time less than the lower limit, so the test material 34 has a homogenization treatment time. As a result, the number of compounds containing Mn or Cr having a size of 20 nm or more and 200 nm or less in the crystal grains became less than the lower limit, and the toughness decreased.

Claims (4)

Zn: 7.0 to 9.5% (mass%, the same shall apply hereinafter), Mg: 1.0 to 3.0%, Cu: less than 0.5%, Zr: 0.05 to 0.30% Further, an extruded material of an Al—Zn—Mg alloy containing one or two of Mn: 0.70% or less and Cr: 0.50% or less, the balance being Al and inevitable impurities, An Al-Zn-Mg alloy extruded material with excellent toughness, characterized in that Mn-containing compounds or Cr-containing compounds having a size of 20 nm or more and 200 nm or less are dispersed in grains within 7 grains / μm ² or more. 2. The Al—Zn—Mg excellent in toughness according to claim 1, wherein the aluminum alloy extruded material further contains one or two of Ti: 0.15% or less and B: 50 ppm or less. Alloy extruded material. The Charpy impact value using a U-notch specimen having a depth of 2 mm as defined in JIS Z 2202 is (−2.3 × [Zn%] − 8.1 × [Mg%] + 42) (J / cm ² ) It is the above, The Al-Zn-Mg alloy extrusion material excellent in toughness of Claim 1 or 2 characterized by the above-mentioned. A method for producing the extruded material of Al-Zn-Mg alloy according to any one of claims 1 to 3, wherein the Al-Zn-Mg alloy having the composition according to claim 1 or 2 is melted and in a solidification process. The billet is agglomerated by controlling the average cooling rate between the molten metal holding temperature and 640 ° C. to be 0.10 ° C./second or more, and the obtained billet is at a temperature of 420 ° C. or higher and 550 ° C. or lower for 2 hours or more 50 A method for producing an extruded material of Al-Zn-Mg alloy excellent in toughness, characterized by performing hot extrusion and tempering treatment after homogenization treatment for a time equal to or less than the time.