JP7768811B2 - Aluminum alloy extrusion billet, aluminum alloy extrusion profile, and manufacturing method thereof - Google Patents

Description

The present invention relates to a billet for aluminum alloy extrusion molding, an aluminum alloy extrusion profile, a method for manufacturing a billet for aluminum alloy extrusion molding, and a method for manufacturing an aluminum alloy extrusion profile.

The demand for lighter vehicles, such as automobiles, has led to an increased use of aluminum alloys in vehicle components. For example, Al-Mg-Si aluminum alloys, which combine high strength and good corrosion resistance, have been proposed (Patent Document 1).

International Publication No. 2019/167469

From the perspective of improving safety when a vehicle collides with an oncoming vehicle or an obstacle, vehicle components are required to have excellent energy absorption properties. To improve energy absorption properties, vehicle components need to have high strength as well as excellent bendability. If a vehicle component has excellent bendability, it will be crushed when the vehicle collides with an oncoming vehicle, etc., and the occurrence of cracks can be avoided. However, because there is a trade-off between strength and bendability, it is desirable to achieve both.

The present invention aims to provide an aluminum alloy extrusion profile that has high strength, good elongation, and excellent bendability suitable for energy absorption components, an aluminum alloy extrusion billet used to produce the extrusion profile, and a method for manufacturing the same.

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.
The term "excellent bendability" means that the result of a 180-degree bending test on a test piece having 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.

The gist and configuration of the present invention are as follows.
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,
An aluminum alloy billet for extrusion molding, having a composition containing Zn: 0.25% or less, Ti: 0.15% or less, and the balance consisting of Al and unavoidable impurities.
2. The aluminum alloy extrusion billet according to claim 1, having an electrical conductivity of 45.0% IACS or less.
3. The aluminum alloy extrusion billet according to 1 or 2 above, 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,
An aluminum alloy extrusion having a composition containing Zn: 0.25% or less, Ti: 0.15% or less, and the balance consisting of Al and unavoidable impurities.
5. The aluminum alloy extrusion profile according to 4 above, wherein the number density of [001]-oriented precipitates is 2000 particles/μm² ^{or more} .
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,
A raw material containing Zn: 0.25% or less, Ti: 0.15% or less, and the balance being Al and unavoidable impurities is melted and cast to produce 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. 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 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 shape, comprising hot extruding an aluminum alloy billet for extrusion molding according to any one of 1 to 3 above, cooling the extrusion billet to 100°C or less at an average cooling rate of 20°C/s or more, and then subjecting the extrusion billet to artificial aging treatment.

The present invention provides an aluminum alloy extrusion profile that has high strength, good elongation, and excellent bendability, making it suitable for energy absorption components, an aluminum alloy extrusion billet that can be used to produce the extrusion profile, and methods for producing the extrusion profile and the billet.

1 is a TEM photograph of an extruded profile of Example 11 of the Examples.

The present invention will now 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 chemical composition refers to "mass %" unless otherwise specified.

<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,
The composition contains Zn: 0.25% or less, Ti: 0.15% or less, and the balance being Al and unavoidable impurities.

[Si: 0.40% or more and 0.80% or less]
Si forms Mg ₂ Si (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 point of view that good elongation and formability can be easily ensured, the Si content is 0.80% or less, and preferably 0.60% or less.

[Mg: 0.80% or more and 1.20% or less]
Like Si, Mg forms Mg ₂ Si (β" phase, β' phase) and an Al-Mg-Si-Cu quaternary compound (Q' phase) in the metal structure, thereby 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 that good hot workability can be easily ensured, the Mg content is 1.20% or less, and preferably 1.00% or less.

[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, Q phase) in the metal structure. Furthermore, the inclusion of Cu reduces 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 can reduce these. From this perspective, the Cu content is 0.40% or more. If the Cu content is excessive, the strength improvement effect saturates, but corrosion resistance may be reduced. From this perspective, the Cu content is 0.70% or less.

[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 amount of crystallized material on the grain boundaries increases, resulting in a decrease in bendability. From this point of view, the Ni content is 0.40% or less.

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

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

[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 suppress a decrease in hardenability. For example, the Cr content can be preferably set to 0.04% or more and 0.08% or less.

[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 0.25% or less.

[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 lower end of the ingot due to settling during casting.

[Inevitable impurities]
The components other than those mentioned above are Al and inevitable 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 inevitable 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.

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.

The billet for extrusion molding preferably has a Vickers hardness of 60 HV or more. If the Vickers hardness is in this range, 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, which is advantageous because the strength of the extruded profile is improved. 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.

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

The extruded shape of the present invention has the same chemical composition as the aluminum alloy extrusion billet of the present invention.

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 result of 3R or less, resulting in excellent strength and bendability.

The extruded profile of the present invention preferably has a number density of [001]-oriented precipitates of 2000 particles/μm² ^or more. If the number density is within this range, sufficiently high strength can be obtained. The upper limit of the number density is not particularly limited, and can be, for example, 3000 particles/μm² or ^less .
Here, the number density is a value measured by the method described in the examples.

<Method of manufacturing a billet 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.

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

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 segregated materials 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 precipitated materials.
The holding time is preferably 1 hour or more from the viewpoint of homogenizing segregated materials 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 precipitated materials.

The cast billet is held at a temperature of 500°C or higher and 590°C or lower, and then cooled. For example, the billet can be cooled to 100°C or lower, and the average cooling rate is preferably 0.25°C/s or higher. An average cooling rate of 0.25°C/s or higher can easily prevent precipitates from growing coarsely during cooling. This makes it easy to reduce the electrical conductivity of the billet for extrusion molding, easily controlling it to 45.0% IACS or lower, and also to increase the Vickers hardness, easily controlling it to 60 HV or higher. According to the method for producing a billet for extrusion molding of the present invention, even if the component composition is the same, by producing the billet for extrusion molding at an average cooling rate of 0.25°C/s or higher, the yield strength of the extruded shape obtained using the billet for extrusion molding can be improved compared to a billet for extrusion molding produced at a lower average cooling rate.
The upper limit of the average cooling rate is not particularly limited, and can be, 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.

<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.

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 in order to promote solid solution of the additive elements, and more preferably 580°C or lower in order 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.

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.

After cooling, the extruded profile is subjected to artificial aging treatment. The conditions for the artificial aging treatment are not particularly limited, but examples include holding the extruded profile at a temperature of 160°C or higher and 240°C or lower for 1 hour or longer and 18 hours or shorter. From the standpoint of productivity, holding the extruded profile at a temperature of 180°C or higher and 220°C or lower for 2 hours or longer and 6 hours or shorter is preferable. The natural aging time can be, for example, less than 3 hours, and is preferably less than 1 hour.

In the manufacturing method of the aluminum alloy extrusion profile of the present invention, after extrusion, processing such as drawing, cutting, bending, crushing, welding, and mechanical fastening may be performed as necessary.

<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.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

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 prepare a cast billet (diameter 8 inches, length 3000 mm). The prepared 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.

The extrusion billet was then preheated to 490°C and extruded at an extrusion speed of 4 mm/s until the temperature of the extruded section reached 570°C. It was then cooled to 20°C by water cooling (average cooling rate of 3000°C/min), and then artificially aged at 200°C for 2.5 hours to produce an extruded part (hollow rectangular bar, 99 mm wide x 33 mm long, 2 mm thick).

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.

<180 degree bending measurement>
Test pieces (20 mm wide x 60 mm long) were taken from the side (width direction) of the extruded member 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 piece 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.

<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.

<Vickers hardness measurement>
The Vickers hardness was measured at three central locations in 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.

<Number density of extruded shapes>
The number density of the extruded profile 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 profile. Specifically, the incident direction of the TEM was adjusted to the <100> orientation of the crystal grains, and images were taken at a magnification of 220,000 times. The captured image was enlarged approximately twice to observe a 200 nm x 200 nm field of view, and precipitates within the field of view were counted. The value converted to ^per 1 μm2 was used as the number density. In this case, the direction perpendicular to the observation plane was defined as [100], and precipitates with the [100] orientation within the field of view were counted. The lower limit of the particle size of the precipitates to be counted was 5 nm. Precipitates with the [010] orientation and [001] orientation that appear vertically and horizontally on the observation plane were not counted. Table 2 shows the measured values for Example 2 (Comparative Example) and Examples 5, 8, and 11 (Examples). A TEM photograph (magnification: 220,000 times) of Example 11 is shown in FIG.

As shown in Table 2, all of the extruded shapes in the examples had high yield strength and excellent bendability. Comparing Example 7 with Examples 8 and 9, and Example 10 with Examples 11 and 12, it can be seen that in the production of extrusion billets, a higher average cooling rate after holding at a specified temperature improves yield strength.

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 (8)

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,
An aluminum alloy billet for extrusion molding, having a composition containing Zn: 0.25% or less, Ti: 0.15% or less, and the balance consisting of Al and unavoidable impurities. The aluminum alloy extrusion billet according to claim 1, having an electrical conductivity of 45.0% IACS or less. The aluminum alloy extrusion billet according to claim 1 or 2, having a Vickers hardness of 60 HV or more. 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,
An aluminum alloy extrusion having a composition containing Zn: 0.25% or less, Ti: 0.15% or less, and the balance consisting of Al and unavoidable impurities. 5. The aluminum alloy extrusion according to claim 4, wherein the number density of the [001] oriented precipitates is 2000 pieces/μm ² or more. 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,
A raw material containing Zn: 0.25% or less, Ti: 0.15% or less, and the balance being Al and unavoidable impurities is melted and cast to produce 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. The method for producing a billet for 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. 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.