Aluminum alloy extrusion billet, aluminum alloy extrusion profile, and manufacturing method thereof

Abstract

To provide an aluminum alloy billet for extrusion molding that yields an aluminum alloy extruded profile with high strength suitable for energy absorption members, excellent elongation and excellent bendability.SOLUTION: An aluminum alloy billet for extrusion molding consists of, in mass%, Si: 0.40% or more and 0.80% or less, Mg: 0.80% or more and 1.20% or less, Cu: 0.40% or more and 0.70% or less, Ni: 0.15% or more and 0.40% or less, Fe: 0.70% or less, Mn: 0.15% or less, Cr: 0.35% or less, Zn: 0.25% or less and Ti: 0.15% or less, with the balance being Al and inevitable impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a billet for extruding aluminum alloys, an aluminum alloy extrusion profile, a method for manufacturing a billet for extruding aluminum alloys, and a method for manufacturing an aluminum alloy extrusion profile. [Background technology]

[0002] Due to the demand for lighter vehicles such as automobiles, there has been an increasing trend to use aluminum alloys for vehicle components. For example, an Al-Mg-Si aluminum alloy material that combines high strength and good corrosion resistance has been proposed (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 167469 Summary of the Invention [Problem to be solved by the invention]

[0004] From the viewpoint of improving safety when a vehicle collides with an oncoming vehicle, an obstacle, or the like, vehicle components are required to have excellent energy absorption properties. In order to improve energy absorption properties, the vehicle components need to have high strength and excellent bendability at the same time. If a vehicle component has excellent bendability, it can be crushed when the vehicle collides with an oncoming vehicle, etc., and the occurrence of cracks can be avoided. However, since there is a trade-off between strength and bendability, it is desirable to achieve both.

[0005] An object of the present invention is to provide an aluminum alloy extrusion having high strength, good elongation, and excellent bendability suitable for energy absorbing members, an aluminum alloy extrusion billet used to produce the extrusion, and methods for producing the same.

[0006] Here, high strength means that the yield strength measured by the method described in the Examples is 325 MPa or more. Good elongation means that the tensile elongation at break measured by the method described in the Examples is 12.5% ​​or more. "Excellent bendability" means that the result of a 180-degree bending test on a test piece with a wall thickness of 2 mm, measured by the method described in the Examples, is an indenter radius of 3 mm or less. The 180-degree bending test in the Examples conforms to JIS Z 2248. [Means for solving the problem]

[0007] The gist and configuration of the present invention are as follows. 1. By mass%, Si: 0.40% or more and 0.80% or less, Mg: 0.80% or more and 1.20% or less, Cu: 0.40% or more and 0.70% or less, Ni: 0.15% or more and 0.40% or less, Fe: 0.70% or less, Mn: 0.15% or less, Cr: 0.35% or less, Zn: 0.25% or less and Ti: 0.15% or less and the balance consisting of Al and unavoidable impurities. 2. The aluminum alloy extrusion billet according to 1 above, having an electrical conductivity of 45.0% IACS or less. 3. An aluminum alloy extrusion billet according to 1 or 2 above, having a Vickers hardness of 60 HV or more. 4. By mass%, Si: 0.40% or more and 0.80% or less, Mg: 0.80% or more and 1.20% or less, Cu: 0.40% or more and 0.70% or less, Ni: 0.15% or more and 0.40% or less Fe: 0.70% or less, Mn: 0.15% or less, Cr: 0.35% or less, Zn: 0.25% or less and Ti: 0.15% or less and the remainder consisting of Al and unavoidable impurities. 5. The number density of precipitates with a

[0001] orientation is 2000 / μm 2 4. The aluminum alloy extrusion profile according to claim 4. 6. By mass%, Si: 0.40% or more and 0.80% or less, Mg: 0.80% or more and 1.20% or less, Cu: 0.40% or more and 0.70% or less, Ni: 0.15% or more and 0.40% or less Fe: 0.70% or less, Mn: 0.15% or less, Cr: 0.35% or less, Zn: 0.25% or less and Ti: 0.15% or less A raw material having a composition containing ZnO, with the remainder being Al and unavoidable impurities, is melted and cast to prepare a cast billet, The produced cast billet is held at a temperature of 500°C or more and 590°C or less, and then cooled. A method for manufacturing billets for aluminum alloy extrusion molding. 7. A method for producing a billet for use in extrusion molding of an aluminum alloy according to claim 6, comprising holding the cast billet at a temperature of 500°C or higher and 590°C or lower, and then cooling it to 100°C or lower at an average cooling rate of 0.25°C / s or higher. 8. A method for producing an aluminum alloy extrusion profile, comprising hot extruding an aluminum alloy extrusion billet according to any one of 1 to 3 above, cooling it to 100°C or less at an average cooling rate of 20°C / s or more, and then subjecting it to artificial aging treatment. [Effects of the Invention]

[0008] According to the present invention, there are provided an aluminum alloy extrusion profile having high strength, good elongation and excellent bendability suitable for an energy absorbing member, an aluminum alloy extrusion billet that can be used to produce the same, and methods for producing the same. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a TEM photograph of an extruded profile of Example 11 of the embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail. Hereinafter, "aluminum alloy extrusion billet" will also be referred to simply as "extrusion billet." Furthermore, "aluminum alloy extrusion profile" will also be referred to simply as "extrusion profile." "%" in the component composition means "mass %" unless otherwise specified.

[0011] <Aluminum alloy extrusion billet> An aluminum alloy extrusion billet according to one embodiment of the present invention will be described. The extrusion billet of the present invention comprises, in mass %, Si: 0.40% or more and 0.80% or less, Mg: 0.80% or more and 1.20% or less, Cu: 0.40% or more and 0.70% or less, Ni: 0.15% or more and 0.40% or less, Fe: 0.70% or less, Mn: 0.15% or less, Cr: 0.35% or less, Zn: 0.25% or less and Ti: 0.15% or less and the balance is Al and unavoidable impurities.

[0012] [Si: 0.40% or more and 0.80% or less] Si forms MgSi (β" phase, β' phase) and an Al-Mg-Si-Cu quaternary compound (Q' phase) in the metal structure, contributing to precipitation strengthening. From this point of view, the Si content is 0.40% or more, and preferably 0.50% or more. From the viewpoint of easily ensuring good elongation and formability, the Si content is 0.80% or less, and preferably 0.60% or less.

[0013] [Mg: 0.80% or more and 1.20% or less] Like Si, Mg forms MgSi (β" phase, β' phase) and an Al-Mg-Si-Cu quaternary compound (Q' phase) in the metal structure, contributing to precipitation strengthening. From this point of view, the Mg content is 0.80% or more, and preferably 0.90% or more. From the point of view of easily ensuring good hot workability, the Mg content is 1.20% or less, and preferably 1.00% or less.

[0014] [Cu:0.40% or more and 0.70% or less] Cu not only strengthens the Al layer through solid solution but also contributes to precipitation strengthening by forming Al-Mg-Si-Cu quaternary compounds (Q' phase and Q phase) in the metal structure. Furthermore, the inclusion of Cu reduces the size of the precipitate-free zone (PFZ) and the amount of grain boundary precipitates. The PFZ and grain boundary precipitates can be the starting points for fracture during a collision, but the inclusion of Cu reduces these. For this reason, the Cu content is set to 0.40% or more. Excessive Cu content saturates the strength improvement effect, but may also reduce corrosion resistance. For this reason, the Cu content is set to 0.70% or less.

[0015] [Ni: 0.15% or more and 0.40% or less] Ni contributes to improving strength by refining Mg2Si precipitates in the metal structure. From this point of view, the Ni content is 0.15% or more. On the other hand, if the Ni content is excessive, the increase in crystallized material on the grain boundaries reduces bendability. From this point of view, the Ni content is 0.40% or less.

[0016] [Fe:0.7% or less] Fe contributes to suppressing seizure during casting and improving strength, but the Fe content is set to 0.70% or less in order to suppress the formation of large amounts of coarse or large-sized crystallized particles and the resulting decrease in ductility.

[0017] [Mn:0.15% or less] Mn contributes to the refinement of crystal grains and the suppression of stress corrosion cracking, but in order to prevent a decrease in hardenability, the Mn content is set to 0.15% or less.

[0018] [Cr:0.35% or less] Cr contributes to grain refinement and the suppression of stress corrosion cracking, but the Cr content is set to 0.35% or less in order to prevent a decrease in hardenability. For example, the Cr content can be preferably set to 0.04% or more and 0.08% or less.

[0019] [Zn:0.25% or less] Zn is an element that can be contained for various purposes, but in order to prevent a decrease in stress corrosion cracking resistance, the Zn content is set to 0.25% or less.

[0020] [Ti:0.15% or less] Ti refines crystal grains and contributes to preventing casting cracks, but the amount of Ti is set to 0.15% or less in order to prevent segregation at the bottom end of the ingot due to settling during casting.

[0021] [Inevitable impurities] Components other than those mentioned above are Al and unavoidable impurities. Inevitable impurities include impurities that are inevitably mixed in due to raw materials or manufacturing processes. Examples include elements such as Ga, V, B, Zr, Co, Ag, Bi, Pb, and Sn. The allowable amount of each element as an unavoidable impurity is 0.05% or less, preferably 0.01% or less. The allowable amount of the total of these elements is 0.15% or less, preferably 0.10% or less.

[0022] The extrusion billet of the present invention preferably has an electrical conductivity of 45.0% IACS or less. A conductivity within this range is advantageous because Mg, Si, Cu, and Ni, which contribute to strength, are sufficiently dissolved in the Al matrix, and the precipitates become finer during aging treatment in the production of the extruded profile, improving the strength of the extruded profile. The electrical conductivity can be 40.0% IACS or more, and from the viewpoint of extrudability, it is preferably 41.0% IACS or more. Here, the electrical conductivity is a value measured by the method described in the examples.

[0023] The extrusion billet preferably has a Vickers hardness of 60 HV or more. A Vickers hardness in this range is advantageous because Mg, Si, Cu, and Ni, which contribute to strength, are sufficiently dissolved in the Al matrix, and the precipitates become finer during aging treatment in the production of the extruded profile, improving the strength of the extruded profile. The Vickers hardness can be 80 HV or less, and from the viewpoint of extrudability, it is preferably 75 HV or less. Here, the Vickers hardness is a value measured by the method described in the examples.

[0024] <Aluminum alloy extrusions> An aluminum alloy extrusion according to one embodiment of the present invention will be described.

[0025] The extruded shape of the present invention has the same component composition as the aluminum alloy extrusion billet of the present invention.

[0026] The extruded profile of the present invention contains specified amounts of Cu and Ni, and by controlling precipitates, it is possible to achieve a yield strength of 325 MPa or more, an elongation of 12.5% ​​or more, and a 180-degree bending test of 3R or less, thereby providing excellent strength and bendability.

[0027] The extruded profile of the present invention has a number density of precipitates with a

[0001] orientation of 2000 particles / μm 2 If the number density is in this range, a sufficiently high strength can be obtained. There is no particular upper limit to the number density, and it is preferably 3000 particles / μm 2 It can be as follows: Here, the number density is a value measured by the method described in the examples.

[0028] <Method of manufacturing billets for aluminum alloy extrusion molding> A method for producing an aluminum alloy extrusion billet according to one embodiment of the present invention will now be described. By this method, the extrusion billet of the present invention can be obtained.

[0029] The method for producing an extrusion billet of the present invention includes melting a raw material having the component composition of the extrusion billet to prepare a molten aluminum alloy, and casting the prepared molten aluminum alloy to produce a cast billet. The casting method is not particularly limited, and examples thereof include continuous casting and rolling, semi-continuous casting (DC casting), and hot-top casting.

[0030] The produced cast billet is subjected to homogenization treatment by holding it at a temperature of 500° C. to 590° C. The temperature is preferably 550° C. or higher in order to homogenize segregates and promote solid solution of added elements, and is preferably 580° C. or lower in order to avoid a decrease in strength due to coarsening of crystal grains and precipitates. The holding time is preferably 1 hour or more from the viewpoint of homogenizing segregates and promoting solid dissolution of added elements, and is preferably 5 hours or less from the viewpoint of reducing strength due to coarsening of crystal grains and precipitates.

[0031] The cast billet is held at a temperature of 500°C to 590°C and then cooled. For example, it can be cooled to 100°C or less, preferably at an average cooling rate of 0.25°C / s or more. An average cooling rate of 0.25°C / s or more can easily prevent precipitates from growing coarsely during cooling. This makes it easy to reduce the electrical conductivity of the extrusion billet and control it to 45.0% IACS or less. It also makes it easy to increase the Vickers hardness and control it to 60 HV or more. According to the method for producing an extrusion billet of the present invention, even if the component composition is the same, by producing an extrusion billet at an average cooling rate of 0.25°C / s or more, the yield strength of the extrusion profile obtained using the extrusion billet can be improved compared to a billet produced at a lower average cooling rate. The upper limit of the average cooling rate is not particularly limited, and can be set to, for example, 400° C. / s or less, and can be sufficiently controlled even at an average cooling rate of 0.5° C. / s or less. The cooling method can be selected depending on the average cooling rate, and examples thereof include fan cooling, mist cooling, shower cooling, liquid nitrogen cooling, water cooling, etc. These methods may also be combined.

[0032] <Method of manufacturing aluminum alloy extrusions> A method for producing an aluminum alloy extrusion according to one embodiment of the present invention will now be described. By this method, the extrusion of the present invention can be obtained.

[0033] The method for producing an extruded profile of the present invention includes hot extruding the extrusion billet of the present invention. The conditions for the hot extrusion are not particularly limited, but the temperature of the extruded profile is preferably 500°C or higher and 590°C or lower, more preferably 550°C or higher to promote solid solution of the additive elements, and more preferably 580°C or lower to suppress surface defects such as tearing. The preheating temperature and extrusion speed of the billet are not particularly limited, and for example, known conditions can be adopted.

[0034] After hot extrusion, the extruded shape is quenched to 100°C or less at an average cooling rate of 20°C / s or more. It is preferable to start quenching immediately after extrusion, and for example, quenching can be started within 10 seconds after the end of extrusion. From the viewpoint of hardenability, the average cooling rate is preferably 40°C / s or more. There is no particular upper limit to the average cooling rate, and it can be, for example, 100°C / s or less. The method of rapid cooling can be selected depending on the average cooling rate, and examples thereof include fan cooling, mist cooling, shower cooling, liquid nitrogen cooling, water cooling, etc. These methods may also be combined.

[0035] The cooled extruded shape is subjected to artificial aging treatment. The conditions for the artificial aging treatment are not particularly limited, and examples include holding the extruded shape at a temperature of 160°C to 240°C for 1 hour to 18 hours. From the viewpoint of productivity, holding the extruded shape at a temperature of 180°C to 220°C for 2 hours to 6 hours is preferred. The natural aging time can be, for example, less than 3 hours, and preferably less than 1 hour.

[0036] In the method for producing an aluminum alloy extrusion of the present invention, after extrusion, drawing, cutting, bending, crushing, welding, mechanical fastening, etc. may be carried out as necessary.

[0037] <Application> The obtained extruded profile has high strength, good elongation, and excellent bendability suitable for energy absorbing members, and can be used, for example, as vehicle members for automobiles, motorcycles, etc. Examples of vehicle members include structural materials such as battery cases, bumper beams, door beams, side sill reinforcements, and floor cross members, as well as structural materials for undercarriage such as suspension arms. [Example]

[0038] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0039] The extrusion billets and extruded shapes of the examples and comparative examples were produced as follows. A raw material having the composition shown in Table 1 (the balance being Al and unavoidable impurities) was melted and cast by hot-top casting to produce a cast billet (diameter 8 inches, length 3000 mm). The produced cast billet was held at 570°C for 3.7 hours for homogenization, and then cooled to 100°C at the average cooling rate shown in Table 2 to obtain a billet for extrusion molding.

[0040] Next, the extrusion billet was preheated to 490°C and extruded at an extrusion speed of 4 mm / s until the temperature of the extruded profile reached 570°C. It was then cooled to 20°C by water cooling (average cooling rate of 3000°C / min), and then subjected to artificial aging treatment at 200°C for 2.5 hours to produce an extruded part (hollow rectangular bar, width 99 mm x length 33 mm, thickness 2 mm).

[0041] The following measurements were carried out on the extruded profile, and the results are shown in Table 2. <Measurement of yield strength, tensile strength, and tensile elongation at break> JIS No. 5 test pieces were taken from the extrusion direction of the side (width direction) of the extruded profile and subjected to a tensile test in accordance with JIS Z 2241:2011 to measure the yield strength (0.2% yield strength), tensile strength, and tensile elongation at break. The tensile speed was 2 mm / min. The measured values ​​for each example are shown in Table 2.

[0042] <180 degree bend measurement> Test pieces (20 mm wide x 60 mm long) were taken from the side (width direction) of the extruded part so that the extrusion direction was the bending axis, and a bending test was performed using the indentation bending method described in JIS Z 2248 at an indentation speed of 100 m / min. The indenter radius of the indenter used was R (unit: mm), the thickness of the test piece was t (2 mm), and the support distance (mm) was (2 x R + 3 x t). The test was evaluated based on the minimum indenter radius R at which no cracks occurred. The smaller the value, the better the bendability. The measured values ​​for each example are shown in Table 2.

[0043] <Conductivity measurement> The electrical conductivity was measured in accordance with JIS H4100 using an eddy current electrical conductivity meter at the center of the cross section of the billet in the extrusion direction at room temperature of 20° C. The measured values ​​for Examples 1 to 3 (Comparative Examples) and Examples 10 to 12 (Examples) are shown in Table 1.

[0044] <Vickers hardness measurement> The Vickers hardness was measured at three central locations on the cross section of the billet in the extrusion direction under a load of 5 kgf and a test time of 15 seconds in accordance with JIS Z 2244, and the average value was taken as the hardness. The measured values ​​for Examples 1 to 3 (Comparative Examples) and Examples 10 to 12 (Examples) are shown in Table 2.

[0045] <Number density of extruded shapes> The number density of the extruded shape was measured using a transmission electron microscope (hereinafter also referred to as "TEM") with the observation plane perpendicular to the extrusion direction of the extruded shape. <100> The image was then magnified approximately twice to observe a 200nm x 200nm field of view, and the precipitates within the field were counted and measured at a magnification of 1μm. 2 The value converted to per 1000 was taken as the number density. In this case, the direction perpendicular to the observation surface was defined as

[0100] , and precipitates with

[0100] orientation within the field of view were counted. The lower limit of the particle size of the precipitates to be counted was set to 5 nm. Precipitates with

[0010] orientation and

[0001] orientation that appeared vertically and horizontally on the observation surface were not counted. The measured values ​​for Example 2 (Comparative Example) and Examples 5, 8, and 11 (Examples) are shown in Table 2. A TEM photograph (magnification 220,000 times) of Example 11 is shown in Figure 1.

[0046] [Table 1]

[0047] [Table 2]

[0048] As shown in Table 2, all of the extruded shapes of the Examples had high yield strength and excellent bendability. A comparison of Example 7 with Examples 8 and 9, and a comparison of Example 10 with Examples 11 and 12 shows that in the production of extrusion billets, a higher average cooling rate after holding at a predetermined temperature improves yield strength. [Industrial Applicability]

[0049] The aluminum alloy extrusion of the present invention has high strength, good elongation, and excellent bendability suitable for energy absorbing members, and can therefore be suitably used, for example, for vehicle members such as automobiles and motorcycles (structural members such as battery cases, bumper beams, door beams, side sill reinforcements, and floor cross members, and structural members for undercarriage such as suspension arms).

Claims

1. In mass%, Si: 0.40% or more and 0.80% or less, Mg: 0.80% or more and 1.20% or less, Cu: 0.40% or more and 0.70% or less, Ni: 0.15% or more and 0.40% or less Fe: 0.70% or less, Mn: 0.15% or less, Cr: 0.35% or less, Zn: 0.25% or less and Ti: 0.15% or less and the balance consisting of Al and unavoidable impurities.

2. 2. The aluminum alloy extrusion billet according to claim 1, which has an electrical conductivity of 45.0% IACS or less.

3. 3. The aluminum alloy extrusion billet according to claim 1, having a Vickers hardness of 60 HV or more.

4. In mass%, Si: 0.40% or more and 0.80% or less, Mg: 0.80% or more and 1.20% or less, Cu: 0.40% or more and 0.70% or less, Ni: 0.15% or more and 0.40% or less Fe: 0.70% or less, Mn: 0.15% or less, Cr: 0.35% or less, Zn: 0.25% or less and Ti: 0.15% or less and the remainder consisting of Al and unavoidable impurities.

5. The number density of precipitates with [001] orientation is 2000 pieces / μm ２ The aluminum alloy extrusion according to claim 4, wherein

6. In mass%, Si: 0.40% or more and 0.80% or less, Mg: 0.80% or more and 1.20% or less, Cu: 0.40% or more and 0.70% or less, Ni: 0.15% or more and 0.40% or less, Fe: 0.70% or less, Mn: 0.15% or less, Cr: 0.35% or less, Zn: 0.25% or less and Ti: 0.15% or less a raw material having a composition containing the above-mentioned aluminum alloy and the remainder consisting of aluminum and unavoidable impurities is melted and cast to prepare a cast billet; The produced cast billet is held at a temperature of 500°C or higher and 590°C or lower, and then cooled. A method for manufacturing billets for aluminum alloy extrusion molding.

7. 7. The method for producing a billet for use in extrusion molding of an aluminum alloy according to claim 6, comprising holding the cast billet at a temperature of 500°C or higher and 590°C or lower, and then cooling the billet to 100°C or lower at an average cooling rate of 0.25°C / s or higher.

8. A method for producing an aluminum alloy extrusion shape, comprising hot extruding the aluminum alloy billet for extrusion molding according to any one of claims 1 to 3, cooling the extruded billet to 100°C or less at an average cooling rate of 20°C / s or more, and then subjecting the extruded billet to artificial aging treatment.

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