JPH10183287A - Aluminum alloy for cold forging and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy for cold forging, requiring no annealing treatment before cold forging and capable of producing a high strength even if solution hardening treatment is omitted after cold forging. SOLUTION: The aluminum alloy for cold forging has a composition consisting of, by weight, 0.4-0.8% Mg, 0.4-1.0% Si, 0.15-0.5% Cu, 0.005-0.2% Ti, and the balance Al with inevitable impurities and satisfying the relation of Y>=(1/1.73)X+0.15 when X and Y represent Mg content (wt.%) and Si content (wt.%), respectively. A cold forged product is produced by subjecting this alloy to extrusion at 440 -560'C and then to press quenching without delay and subjecting the resultant slug to cold forging and successively to aging treatment or short-time heating treatment at 190-250 deg.C for 5-30min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy for cold forging used as a material of a part to be subjected to cold forging, a method for producing the same, and a method for producing a cold forged product.

[0002]

2. Description of the Related Art Aluminum alloys have a specific gravity of about 1/3 that of iron and are lighter. Therefore, there are many examples of replacing aluminum with an aluminum alloy to reduce the weight. Forging methods include hot forging, in which the material is softened at a high temperature, and cold forging, in which the forging is performed at room temperature. In cold forging, it is necessary to soften the material at the time of working so that it is easy to forge. Therefore, a material that has been subjected to an annealing treatment in advance is used as the material. For example, in the case of JIS6061 alloy, which is a typical heat-treated aluminum alloy, the strength after extrusion (T1) is high and hard, so that it is 4% after extrusion.
After being subjected to annealing (O material treatment) at about 20 ° C. × 2 hours, it is subjected to cold forging (for example, Japanese Patent Application Laid-Open No. 3-170636).
Reference).

[0003]

As described above, since the conventional material is subjected to an annealing treatment before cold forging, in order to obtain high strength after cold forging, it is necessary to go through steps of solution quenching and aging. (See FIG. 2A). However, if the cold forging can be performed without performing the annealing step, not only the annealing step but also the subsequent quenching treatment is not required, and a significant cost reduction can be expected by omitting the step. Further, by not performing the quenching, the processing strain due to the cold forging can be used for increasing the strength.

[0004] On the other hand, in order to omit the annealing step and the solution quenching step, for example, so-called press quenching is performed by quenching an extruded material in a high-temperature state immediately after extrusion. It is conceivable to perform cold forging and then perform aging treatment. However, the above 60
Conventional Al-Mg-Si alloys such as alloy No. 61 have a large deformation resistance during cold working, making cold working difficult. In addition, even when cold forging is performed forcibly using a large-sized press, the cold forging property deteriorates, such as the deformation resistance gradually increasing and the dimensional accuracy varies. It is not realistic from the point of view.

The present invention has been made from such a viewpoint, and does not require annealing before cold forging, and can achieve high strength without solution quenching after cold forging.
Further, it is an object of the present invention to provide an aluminum alloy for cold forging in which the mechanical properties do not fluctuate and the cold forgeability does not decrease (that is, it has a delayed effect) even when left for a long time at room temperature after press quenching and before cold forging. Aim.

[0006]

The present inventors have conducted various studies to develop an aluminum alloy for cold forging having the above-mentioned characteristics, and as a result, have obtained the necessary cold forgeability. Is that it is necessary to limit the amount of addition of Mg and Si to a predetermined value or less, and that the Mg / Si ratio has a large effect on the delayed effect of preventing the cold forging property from changing over time;
Then, it has been found that the progress of room temperature aging is suppressed in a specific composition region on the Si-rich side from the stoichiometric ratio of Mg ₂ Si. Also, in order to improve the strength after cold forging,
It has been found that the addition of Cu, which has the effect of making the distribution of precipitates (Mg ₂ Si) after heat treatment uniform and fine, is effective.
The present invention has been completed.

The aluminum alloy for cold forging according to the present invention comprises 0.4 to 0.8% by weight of Mg, 0.4 to 1.0% by weight of Si, 0.15 to 0.5% by weight of Cu, and 0.005 to 0.5% by weight of Ti.
0.2% by weight, with the balance being Al and unavoidable impurities. Further, when the weight percentage of Mg is X and the weight percentage of Si is Y, the relationship of Y ≧ (1 / 1.73) X + 0.15 Is satisfied. This alloy contains 0.05 to 0.6% by weight of Mn and 0.05 to 0.
One or more of 3% by weight and Zr of 0.05 to 0.3% by weight are contained in a total of 0.9% by weight or less. Further, it is better that the inevitable impurities are small, but Fe 0.35% by weight or less,
Other impurities are allowed to be 0.05% by weight or less (0.15% or less in total) by itself.

Further, the method for producing an aluminum alloy for cold forging according to the present invention comprises:
It is characterized by extruding at 40 to 560 ° C and press hardening immediately after extrusion. Then, the extruded material that has been press-quenched is used as a material for cold forging, and this is cold forged,
Subsequently, a high-strength cold forged product can be obtained by performing normal aging treatment or short-time heating treatment.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for adding components and limiting the composition of the aluminum alloy for cold forging according to the present invention will be described below.

Mg, Si As mentioned above, the stoichiometric ratio of Mg ₂ Si to S
When i is added in an excessively large amount, aging at room temperature is suppressed and a delayed effect is exhibited. The ratio of Mg and Si is represented by Y ≧ (1/1.
73) It is a range satisfying X + 0.15. From this Mg
Rich side, that is, Y <(1 / 1.73) X + 0.15
In the range, the effect of suppressing the aging at room temperature by Si is insufficient, and the aging at room temperature proceeds.

On the other hand, Mg combines with Si to form Mg ₂ Si, thereby improving alloy strength. In order to exhibit this effect, the amount of Mg needs to be 0.4% by weight or more. However, if the content of Mg exceeds 0.8% by weight, even if the above range is satisfied, aging at room temperature proceeds due to the diffusion of Mg, and deformation resistance at room temperature increases, resulting in cold forging. Reduce the nature. Therefore, the content of Mg is set to 0.4% by weight or more and 0.8% by weight or less. In addition, Si has the effect of forming Mg ₂ Si and improving the alloy strength as described above. However, if the added amount of Si is less than 0.4% by weight, the strength of the material cannot be improved, and if it is 1.0% by weight or more, the ductility of the material is hindered, and the deformation resistance at room temperature increases and the coldness increases. The forgeability decreases. Further, Si acts as a nucleus for Mg ₂ Si precipitation. When the amount of Si increases, the number of nuclei of the precipitation increases. As a result, the precipitation proceeds easily, and the slow effect is lost. Therefore, the content of Si is set to 0.4% by weight or more and 1.0% by weight or less.

[0012] In the above range, a region having a lower content of Mg provides a better delayed effect, and a cold forgeability is improved, whereby a member having a complicated shape can be formed. The range of application expands. Accordingly, the Mg content is preferably not more than 0.65% by weight, and within this range, it exhibits a remarkably excellent retarding effect. More preferably, the Mg content is 0.6% by weight or less, and at the same time, the content of Si is in the range of 0.5 to 0.7% by weight. Can be obtained. FIG. 1 illustrates the composition ranges of Mg and Si of the present invention. Note that Y = (1 /
1.73) The line of X is a line of the stoichiometric ratio of Mg ₂ Si.

Cu Cu improves the alloy strength by precipitation hardening and improves the ductility of the material. Further, by adding Cu, there is an effect of uniformly and finely distributing the precipitate Mg ₂ Si generated by Mg and Si. However, if the added amount of Cu is less than 0.15% by weight, the above effect cannot be exhibited. On the other hand, if it exceeds 0.5% by weight, press hardenability is reduced and deformation resistance is increased. Therefore, C
The content of u is 0.15% by weight or more and 0.5% by weight or less.

Mn, Cr, Zr Mn, Cr, Zr precipitate as fine intermetallic compounds during the billet homogenization treatment and refine the crystal grains to improve the strength and ductility. However, these elements have the effect of increasing the quenching sensitivity and increasing the press quenching property as the added amount increases. Mn, C
If the amount of each of r and Zr is less than 0.05% by weight, the above effect cannot be exerted. On the other hand, if the addition amounts of Mn, Cr, and Zr exceed 0.6% by weight, 0.3% by weight, and 0.3% by weight, respectively, or if the total of these exceeds 0.9% by weight, coarse metal The compound is crystallized and the quenching sensitivity is sharpened, and the improvement of the predetermined alloy strength cannot be achieved.
Therefore, the content of Mn, Cr, and Zr is from Mn 0.05 to
0.6% by weight, Cr 0.05 to 0.3% by weight, Zr0.
At least 0.9% by weight in total of at least one of 0.05 to 0.3% by weight
The following is assumed.

Ti Ti improves alloy strength by refining crystal grains during casting. In order to exhibit this effect, the amount of Ti added must be 0.005% by weight or more.
On the other hand, if the added amount of Ti exceeds 0.2% by weight, the above effect is saturated, and a coarse intermetallic compound is crystallized and a predetermined alloy strength cannot be obtained. Therefore, the content of Ti is 0.0
0.5 to 0.2% by weight.

Inevitable impurities Fe Fe is the most abundant impurity in aluminum ingots.
If present in the alloy in an amount exceeding 0.35% by weight, coarse intermetallic compounds are crystallized during casting, which impairs the mechanical properties of the alloy. Therefore, the content of Fe is set to 0.35% by weight or less.

Others When casting an aluminum alloy, impurities are mixed through various routes such as a base metal and an intermediate alloy of an additional element. Although various elements are mixed, impurities other than Fe alone have little effect on the properties of the alloy as long as the content of each element is 0.05% by weight or less and the total amount is 0.15% or less. Therefore, these impurities alone are set to 0.05% by weight or less (0.15% or less in total).

The aluminum alloy ingot having the above composition is
A homogenization treatment is carried out at a temperature of 00 to 600 ° C. × 2 to 10 hours, followed by extrusion at 440 to 560 ° C., and immediately after extrusion, for example, press quenching by water cooling or fan air cooling to obtain a material for cold forging. it can. When the homogenization temperature is set as described above, if it is less than 500 ° C., it is insufficient to diffuse the segregation generated during casting into the matrix, and if it exceeds 600 ° C., local melting occurs, and This is because it sometimes becomes a defect. When the temperature of the extrusion process is set as described above, if the temperature is lower than 440 ° C., it is not sufficient to decompose the precipitates generated in the cooling process after the homogenization treatment into a solid solution state, and exceeds 560 ° C. This is because local melting occurs due to heat generated during processing during extrusion.

This material is cut to a predetermined length and subjected to cold forging. After cold forging, the material is subjected to ordinary conditions (for example, 180 to 19).
Aging treatment is performed at 0 ° C. × 3 to 8 hours (FIG. 2B).
reference). It should be noted that the aluminum alloy for cold forging can obtain a high strength of about 90% or more after the above-mentioned aging treatment only by heating for a very short time after cold forging. This is because precipitation is promoted due to the addition of working strain due to cold forging, and aging proceeds in a short time.
Therefore, instead of the above aging treatment, 190-250 ° C. ×
This short-time heating may be performed under the condition of 5 to 30 minutes.

Next, the fact that the extruded aluminum alloy having the composition specified in the present invention has an excellent retardation effect will be specifically described by way of examples. First, 16 of the composition shown in Table 1
580 ℃ for aluminum alloy billet of 0φ × 150h
A homogenization treatment of × 2 hr was performed. The billet was reheated and extruded at a billet temperature of 500 ° C. and an extrusion speed of 5 m / min. At this time, the press hardening was performed for No. 18 (J
IS6061) was performed using water cooling, and the others were performed using fan air cooling. The cross-sectional shape of the extruded material is 40 × 40 × 2
It was extruded with a square pipe of t.

[0021]

[Table 1]

A JIS No. 5 tensile test piece was sampled from the extruded material and subjected to a tensile test immediately after extrusion (within 3 days) and after 120 days at room temperature to examine the mechanical properties of the test material. Table 2 shows the results. In addition, Table 3 shows the results of similarly examining the mechanical properties of the extruded material immediately after extrusion by subjecting the extruded material to artificial aging at 190 ° C. for 3 hours (T5 tempering), using a JIS No. 5 tensile test piece.

[0023]

[Table 2]

[0024]

[Table 3]

According to the alloy No. 1 of the present invention, Nos. 1 to 7 are conventional product Nos.
Compared with No. 18, the change in mechanical properties was small even after prolonged standing at room temperature, and No. Except for 7, the strength in the T5 state is equal to that of the conventional product. On the other hand, Comparative Alloy No. Looking at the results of 8 and 9, the Ti content was 0.00
No. less than 5% by weight. No. 9 has low strength in the T5 state, and conversely exceeds 0.20% by weight. 8 has low strength and low elongation due to a coarse intermetallic compound.

The comparative alloy No. having a content of Mn, Cr and Zr exceeding 0.90% by weight. According to the results of Example No. 10, it was found that T5
Both strength and elongation in the state are low. Comparative alloy No. 11,
Looking at the results of No. 12, No. 12 containing less than 0.40% by weight of Mg was used. 12 has low strength in T5 state, and conversely 0.8
No. exceeding 0% by weight. No. 11 shows that the change in mechanical properties is large after 120 days, and that the aging at room temperature is progressing.

Comparative alloy No. Looking at the results of Nos. 13 and 14, No. 13 containing less than 0.15% by weight of Cu was used. No. 14 has low strength in the T5 state, and conversely, No. 14 exceeds 0.50% by weight. 13 has low strength and low elongation, and aging at room temperature is also progressing. Comparative alloy No. Looking at the results of 15 and 16, S
No. i having a content of less than 0.40% by weight. 16 is T
5 Strength in low state, conversely more than 0.80 wt% N
o. 15 has low elongation. Comparative alloy No. 17 is Y ≧
(1 / 1.73) X + 0.15
It can be seen that the change in mechanical properties after a lapse of days is large, and the effect of suppressing the aging by room temperature with Si is insufficient, and the aging at room temperature is progressing.

As described above, the extruded material of the alloy of the present invention which has been subjected to press quenching has excellent long-acting properties. The present invention is to use the extruded material of this composition as a material for cold forging,
The advantage of this cold forging material is that it does not have a large deformation resistance, and its mechanical properties do not fluctuate even after being left at room temperature for a long period of time. Therefore, it is excellent in cold forgeability and can obtain high strength by subsequent aging treatment. Have.

[0029]

EXAMPLES Hereinafter, examples of the present invention will be described in accordance with JIS60.
61 is described as a comparative example.

An aluminum alloy billet having a composition shown in Table 4 and having a diameter of 160φ × 150 hours was cast and homogenized at 580 ° C. × 2 hours. The billet was reheated and extruded at a billet temperature of 500 ° C. and an extrusion speed of 5 m / min. At this time, press hardening was performed with water cooling. The cross-sectional shape of the extruded material was extruded with a φ20 round bar. The extruded round bar was removed from bending by tensile straightening. JIS606
After straightening one alloy, 420 ° C in an air furnace
After holding for 2 hours, the furnace was cooled to 100 ° C. and an annealing treatment was performed.

[0031]

[Table 4]

Thirty days after the press annealing, the test material was cut into 20 mm, the deformation resistance was measured by a normal temperature hammer test, and the working ratio was 65% with a 30 ton compression tester.
Upset forging was performed, and it was visually determined whether or not cracks occurred on the surface, and those without cracks were evaluated as ○. Next, some of the specimens subjected to the upsetting forging were subjected to aging treatment at 180 ° C. for 8 hours in an air furnace, and
Short-time heating at 20 ° C. × 15 min was performed, and the Vickers hardness was measured for each. A part of the JIS 6061 alloy subjected to the upsetting forging was subjected to 530 ° C. × 2 hr in an air furnace before aging treatment or heating for a short time.
Was immediately immersed in a water tank and water-quenched. Table 5 shows the above manufacturing conditions, and Table 6 shows the test results.

[0033]

[Table 5]

[0034]

[Table 6]

As shown in Table 6, if JIS6061 alloy was not annealed, the deformation resistance was too high to exceed the capacity of the compression tester, and upset forging could be performed only 40%. From this, it can be seen that the aging of the JIS6061 alloy has progressed at room temperature, and the forgeability is extremely poor unless annealing is performed. On the other hand, the example of the present invention is JIS even without an annealing step.
It turns out that it has the same deformation resistance and cold forgeability as the 6061 annealed material.

In the case of the JIS6061 alloy, if the solution quenching is not performed, the predetermined strength is not exhibited even if the subsequent aging treatment is performed. On the other hand, in the present invention example, even if only the aging treatment without the quenching process, the JIS6061 alloy T6 is equivalent. It can be seen that it exerts the strength of. Furthermore, in the example of the present invention, 22
It can be seen that even with the short-time heating at 0 ° C. × 15 min, it has 90% or more strength after the aging treatment.

[0037]

According to the present invention, a high-strength cold forged material can be obtained using an aluminum alloy having a predetermined composition. In addition, by using the aluminum alloy for cold forging, it is possible to omit the annealing process before forging and the quenching process after forging, and the cost of the manufacturing process can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a conventional process of cold forging and a process of the present invention.

FIG. 2 is a diagram showing a range of Mg and Si of the alloy of the present invention.

──────────────────────────────────────────────────の Continuation of front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 691 C22F 1/00 691B 691A 694 694B

Claims (6)

[Claims] 1. 0.4 to 0.8% by weight of Mg, 0.4% of Si
To 1.0% by weight, Cu 0.15 to 0.5% by weight, Ti
0.005 to 0.2% by weight, the balance consisting of Al and unavoidable impurities.
When the content weight% is Y, Y ≧ (1 / 1.73) X +
An aluminum alloy for cold forging, characterized by satisfying a relationship of 0.15. 2. Mn 0.05-0.6% by weight, Cr0.
2. The aluminum for cold forging according to claim 1, wherein a total of 0.9% by weight or less of at least one of 0.05 to 0.3% by weight and 0.05 to 0.3% by weight of Zr is contained. alloy. 3. The aluminum alloy for cold forging according to claim 1, wherein the extruded material is press-quenched. 4. A method for producing an aluminum alloy for cold forging, comprising extruding an aluminum alloy having the composition according to claim 1 or 2 at 440 to 560 ° C., and press hardening immediately after the extrusion. 5. An aluminum alloy having the composition described in claim 1 or 2 is extruded at 440 to 560 ° C., press-quenched immediately after extrusion, and cold forged as a material.
Subsequently, an aging treatment is performed. 6. An aluminum alloy having the composition described in claim 1 or 2 is extruded at 440 to 560 ° C., press-quenched immediately after extrusion, and cold forged as a material.
Subsequently, a short-time heat treatment at 190 to 250 ° C. × 5 to 30 minutes is performed.