JPH05311306A - Aluminum alloy for extrusion and forging - Google Patents

Abstract

PURPOSE:To provide an aluminum alloy having tensile strength comparable to that of an alloy for elongation, showing high elongation, and excellent in forgeability and wear resistance. CONSTITUTION:This aluminum alloy for extrusion and forging has a composition containing, by weight, 3.5-6.5% Si, 0.05-0.15% Sb, <=0.25% Fe, 0.5-3.5% Cu, 0.01-0.1% Ti, 0.2-0.6% Mg, and 0.0005-0.02% B. Further, this alloy can contain one or >=2 kinds selected from, by weight, 0.05-0.5% Mn, 0.05-0.3% Cr, 0.001-0.05% Sr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy having strength comparable to that of a wrought alloy and excellent in forgeability and wear resistance.

[0002]

2. Description of the Related Art Al-Mg-Si alloys in the 6000 series such as 6061, 6066, and 6082 have been conventionally used as aluminum alloys for hot forging. Among them, the 6061 alloy is most often used as a forging material. However, the 6061 alloy has a tensile strength of 27-
It is 33 kg / mm ² , which limits its use as a so-called medium-strength member.

Aluminum alloys in the 6000 series have been strengthened by hot forging and formed into a predetermined shape, and then subjected to heat treatment such as T ₆ . However, the heat treatment causes the recrystallized grains of the processed structure to become coarse, and mechanical properties such as strength and elongation deteriorate. The coarsening of the recrystallized grains due to the heat treatment remarkably occurs particularly in those forged with a high working rate of 50% or more.

Therefore, Japanese Patent Application Laid-Open No. 1-283337 proposes to suppress the coarsening of crystal grains by adding Mn, Cr, Zr or the like. Predetermined amount of M
It is said that when n, Cr and Zr are added to Al-Mg-Si based aluminum alloy in a composite manner, the growth of crystal grains is suppressed in the steps such as forging and heat treatment, and a material having a fine crystal structure can be obtained. .. Further, in Japanese Patent Laid-Open No. 3-6346, by adjusting the composition of Si, Cu, Mg, Mn, Be, etc., there is no discoloration in the forging process and the heat treatment process, and a forging alloy having the original color tone of the aluminum alloy is obtained. Has been introduced.

Aluminum alloys such as the 6010 series are
Although it is made into a material for forging through an extrusion process, it is inferior in wear resistance and has problems in fastening using bolts and joining with steel members. For example, during use, vibrations, shocks, sliding, etc. cause friction and wear between the aluminum member and the steel member, and loosening, falling out, and damage of the fastening portion are likely to occur. Therefore, there is room for improvement as an automobile part having many bolt fastening portions and the like. In order to improve wear resistance, the present inventors have found that it is effective to add Sb to an Al-Si alloy and extrude a solidified ingot by a semi-continuous casting method. It was introduced as Japanese Patent No. 268839.

[0006]

The aluminum alloy disclosed in Japanese Patent Laid-Open No. 1-268839, which has a finer structure due to the addition of Sb, has excellent wear resistance, but has a higher tensile strength, fatigue strength, etc. than the 6061 alloy. There are some problems in its use as a structural material that requires low strength.

On the other hand, the aluminum alloy disclosed in Japanese Patent Laid-Open No. 3-6346 aims to suppress discoloration of the surface of the forged product, which is presumed to be caused by the addition of Sb, by the addition of Be. The improvement in workability is not sufficient.

The present invention has been devised in order to solve such problems. Si, Sb, Fe, Ti, Mg,
By balancing the composition between B and Cu, 33 kg / mm for T ₆ treated material after forging that is comparable to wrought alloy
^An object of the present invention is to provide an aluminum alloy having a tensile strength of ² or more and an elongation of 13% or more, which is excellent in forgeability and wear resistance.

[0009]

The aluminum alloy for extrusion / forging according to the present invention has a Si:
3.5-6.5 wt%, Sb: 0.05-0.15 wt%, Fe: 0.25 wt% or less, Cu: 0.5-3.5
% By weight, Ti: 0.01 to 0.1% by weight, Mg: 0.2
~ 0.6 wt% and B: 0.0005-0.02 wt%
And the balance is substantially Al. This aluminum alloy further has Mn: 0.05-
0.5% by weight, Cr: 0.05 to 0.3% by weight and S
r: One or two or more selected from 0.001 to 0.05% by weight may be contained.

[0010]

[Operation] As shown in Fig. 1, the Al-Si-Mg alloy changes in tensile properties such as tensile strength σ _B and elongation δ depending on the Si content. That is, when the Si content exceeds 7% by weight, the strength is improved but the elongation is reduced.
On the contrary, if the Si content is less than 4% by weight, the wear resistance is reduced. Further, the elongation tends to increase as the eutectic Si becomes smaller as shown in Table 1, and is improved by the addition of Sb.

[Table 1]

In the present invention, in order to maintain strength, elongation and wear resistance in the Si content range of 4 to 7% by weight,
It has been found that the addition of Cu is most effective. The added Cu is solid-soluted in the matrix in the as-cast state, but it becomes fine Al ₂ Cu precipitates in the matrix by subsequent processing, heat treatment, etc. And improve hardness.

In this respect, M used for similar reinforcement
Since g is an element for solid-solution hardening the matrix, unlike Cu, even if the strength is improved, the elongation and the workability are significantly reduced. Therefore, a large amount of Mg cannot be added to an aluminum alloy that requires workability. Further, the added Cu has the effect of promoting the refinement hardening by Al-Ti-B even in the ingot state and suppressing the coarsening of the recrystallized grains after the heat treatment even in the extrusion round bar. As a result, the strength is increased and elongation is prevented from decreasing.

As the strength and hardness of the matrix increase, the force for fixing the eutectic Si particles, which has a great influence on the wear resistance, in the matrix increases. Therefore, peeling of the eutectic Si particles due to sliding with the mating material is prevented, and higher wear resistance can be obtained. Moreover, the cooling rate of the ingot shifts to the slow cooling side with the addition of Cu, and the time from crystallization of eutectic Si to solidification becomes longer. As a result, eutectic Si
The particles have a rounded shape and also have a uniform distribution in the ingot. This also improves wear resistance.

The addition of Cu brings good results in terms of forgeability, and particularly contributes to the reduction of rough skin which is one index of deformability. This is not only due to the effect of refining the macro-grains due to the addition of Cu, but also due to the addition of Sb in combination
This is due to the synergistic effect of (Cu + Sb), which is a combination of the grain refining actions. In addition, elongation can be improved by the combined addition of Sb.

The alloy components and their contents of the aluminum alloy of the present invention will be described below. Si: An alloying element that is effective in imparting good castability and improving wear resistance. 3.5 to 3.5
The aluminum alloy of the present invention containing 6.5% by weight is advantageous as an automobile part having many bolt fastening portions. Si
If the content is less than 3.5% by weight, not only the castability deteriorates, but also the strength and wear resistance decrease. On the other hand, 6.5
When a large amount of Si in excess of weight% is contained, elongation, toughness, etc. deteriorate, and forgeability deteriorates.

Sb: A function of refining eutectic Si, and particularly improving the elongation of aluminum alloys used for casting and forging. Also, in extrusion and forging processing,
The solution treatment time can be shortened by adding Sb.
Such an action of Sb is remarkable when it is contained in an amount of 0.05% by weight or more. However, the addition of a large amount exceeding 0.15% by weight accelerates the generation of brittle intermetallic compounds such as Sb ₂ Mg ₃ and deteriorates the workability of the aluminum alloy. Therefore, the Sb content is set in the range of 0.05 to 0.15% by weight.

Fe: Fe, which is an element mixed in the aluminum alloy as an impurity, becomes an Al—Fe—Si compound and disperses in the matrix, adversely affecting elongation, toughness, corrosion resistance and the like. Therefore, the smaller the Fe content, the more preferable. However, excessive reduction of the Fe content makes it difficult to melt the alloy. So Fe
The content is 0.25% by weight without any substantial adverse effect
Set the upper limit to.

Cu: An alloying element that plays an important role in the aluminum alloy of the present invention, and improves mechanical strength, wear resistance and the like without reducing elongation. The improvement of strength by adding Cu is due to the precipitation of Cu by heat treatment such as T _6.
This is due to Al ₂ . In order to obtain a tensile strength of 33 kg / mm ² or more, it is necessary to contain 0.5% by weight or more of Cu. The strength of the aluminum alloy increases in proportion to the Cu content. However, when the Cu content exceeds 3.5% by weight, the strength improving effect is saturated,
On the contrary, it causes deterioration of corrosion resistance and toughness. Therefore, the Cu content is set in the range of 0.5 to 3.5% by weight.

Ti: The structure of the ingot is made finer to prevent cracking of the ingot, and also to prevent roughening of the surface of the forged product due to plastic working such as orange peel. Such an effect becomes remarkable when the content of Ti is 0.01% by weight or more. But 0.1
When adding a large amount of Ti in excess of wt%, TiB ₂ ,
Huge crystallized substances such as TiAl ₃ are likely to be generated, which causes cracks during forging and surface defects during cutting. Also,
Degradation of toughness is also observed due to the inclusion of a large amount of Ti. Therefore, the Ti content is set in the range of 0.01 to 0.1% by weight.

Mg: It is an essential alloy component for improving the strength of an aluminum alloy like Cu. In the aluminum alloy of the present invention to which Mg is added, fine Mg ₂ Si is precipitated in the matrix by heat treatment such as T ₆ and the strength is improved. When the Mg content is less than 0.2% by weight, the effect of improving strength by adding Mg is hardly seen. However, when a large amount of Mg exceeding 0.6% by weight is contained, not only the strength improving effect due to precipitation hardening is saturated, but also cracking susceptibility, toughness, etc. are deteriorated and workability such as extrusion and forging is deteriorated. Therefore, the Mg content is 0.2 to
The range was set to 0.6% by weight.

B: Similar to Ti, it is an alloy element effective for refining crystal grains, and its effect can be seen at a content of 0.0005% by weight or more. However, if B is contained in an amount of more than 0.02% by weight, a huge crystallized substance such as TiB ₂ is likely to be generated and workability such as forging and cutting is deteriorated. Therefore, the B content is set in the range of 0.0005 to 0.02% by weight.

Cr, Mn and Sr added as selective components have the following effects. Cr: An alloying element effective in suppressing the growth of crystal grains during extrusion, forging and subsequent heat treatment, and making the structure after heat treatment fine. This ensures high strength, elongation and toughness. The effect is that 0.05% by weight or more of Cr
It is remarkably seen when it contains. However, when a large amount of Cr is contained in excess of 0.3% by weight, Al-Si-F
The precipitation amount of hard and brittle intermetallic compounds such as e-Cr system increases, and the elongation and toughness, which adversely affect the workability, are reduced. Therefore, when Cr is contained, its content is set in the range of 0.05 to 0.3% by weight.

Mn: Similar to Cr, it is an alloying element that suppresses coarsening of crystal grains and improves strength, elongation, toughness and the like.
The effect of adding Mn becomes significant at 0.05% by weight or more.
However, if Mn is contained in excess of 0.5% by weight, A
The precipitation amount of hard and brittle intermetallic compounds such as 1-Si-Fe-Mn system increases, and elongation, toughness, etc., which adversely affect workability, are reduced. Therefore, when Mn is contained, its content is set in the range of 0.05 to 0.5% by weight.

Sr: Similar to Sb, it is an alloying element effective in refining eutectic Si and improving impact value and elongation. Further, it also effectively works for shortening the solution treatment time and improving forgeability. Such an action of Sr has a content of 0.
It appears remarkably when it is 001% by weight or more. But 0.0
When Sr is contained in an amount of more than 5% by weight, workability is deteriorated due to the generation of intermetallic compounds, and gas, inclusions and the like are mixed in the molten aluminum. Therefore,
When Sr is contained, its content is 0.001-
It is set in the range of 0.05% by weight.

[0025]

Example: Various aluminum alloys having the components and plasticity shown in Table 2 were melted and semi-continuously cast to have an outer diameter of 325 m.
A billet having a length of m and a length of 600 mm was manufactured. In addition, Table 1
Inventive Examples 1 and 2 in Claims 1 and 2 respectively
Corresponds to the aluminum alloy specified in. After the obtained billet was kept at 510 ° C. for 4 hours, it was further heated to 400-4
It was heated to 50 ° C. and a round bar having a diameter of 45 mm was extruded.

[0026]

[Table 2]

Next, the extruded material was hot forged at a temperature of 450 ° C. and a working rate of 75% and subjected to T ₆ heat treatment. As the T ₆ heat treatment after forging, a heat history was employed in which the temperature was kept at 510 ° C. for 4 hours, then water-cooled, allowed to stand at room temperature for 48 hours, and tempered at 170 ° C. for 10 hours. The crystal structure of each heat-treated test piece was observed and the grain size was measured. In addition, tensile strength, yield strength and elongation were investigated. The survey results are shown in Table 3.

Further, cold forging performed at room temperature and 350 ° C.
A roughening phenomenon was observed on the surface of the forged product by an upsetting test by hot forging performed at each temperature of 400 ° C. and 450 ° C., and the forgeability of the extruded round bar was evaluated based on its quality. As the test piece used at this time, an extruded round bar was held at 410 ° C. for 1 hour for a cold forging test and then annealed, and an extruded round bar was used for a hot forging test. It was used. In each test, a cylindrical test piece having a diameter of 14 mm and a height of 26 mm cut out from an extruded round bar was used. These test pieces were compressed to a thickness of 5 mm at a speed of 100 mm / sec using a 25-ton hydraulic electric servo pulsar tester, and the roughened state of the measurement surface was observed at a processing rate (upsetting rate) of 80%. .. Recrystallization was promoted by upset forging, and some of them produced coarse recrystallized grains of 400 to 500 μm, but in the alloys of the present invention, fine recrystallized grains of 150 to 350 μm were all used to prevent rough skin during forging. It was effectively suppressed.

Table 3 also shows the observation results of the surface condition.
In Table 3, the measured surface of the forged product is smooth and has a metallic luster, ⊚, the one having a slight unevenness but having the metallic luster is ○, and the entire circumference is uneven. The sample was evaluated as Δ, the sample with a large depth of concavities and convexities that lost the metallic luster was evaluated as X, and the sample with a large number of concavities and convexities and a large level difference and some cracks was evaluated as XX.

[0030]

[Table 3]

As is apparent from Table 3, the aluminum alloys of Examples 1 and 2 of the present invention each have a high tensile strength of 33 kgf / mm ² or more, and have a fine crystal structure after forging, and have a rough appearance. There was nothing to present. It is speculated that this is due to the synergistic effect of Sb and Cu. That is, eutectic Si is refined by the addition of Sb, and the refining effect of the Al-Ti-B based intermetallic compound is promoted by the addition of Cu, which synergistically exhibit excellent mechanical properties and workability. Be done. Moreover, the decrease in elongation δ is small and the yield strength σ _0.2 is significantly improved.

In contrast, in Comparative Alloys 7 and 9, Cu
No strength was obtained due to no addition.
-Since the Ti-B and Cu are not added, the roughening of the forged product becomes severe. Further, in Comparative Alloy 10, Sb and C
Since u was not added, both the eutectic Si and the recrystallized macroparticles were coarse and inferior to the alloy of the present invention in all points of strength, elongation and rough skin.

For the abrasion resistance evaluation test, a dry type Ogoshi type tester was used, and a rotating disk of FC28 was used as a mating material. And load 2.1kg, friction speed 1.21m /
The test piece was rubbed against the mating material at the second, 2.24 m / second and 3,88 m / second, and the amount of the test piece scraped off by the rotating disk of FC28 was calculated. The calculation results are shown in Table 4.

[Table 4]

As is clear from Table 4, in the alloy of the present invention of Test No. 2, the amount of wear was small and the wear resistance was 6 in any speed region as compared with the alloy of Test No. 9 containing no Cu. It can be seen that it has improved by 22%. The two main reasons why the wear resistance is improved are as follows. The addition of Cu increases the hardness and strength of the matrix, and as a result, the force for fixing eutectic Si, which has the greatest effect on the wear resistance, is increased, and peeling by friction is prevented. Since the solidification rate becomes slower and the material is gradually cooled by the addition of Cu, the effect of Al-Ti-B is more prominently expressed, and the crystal grains of the ingot are made finer and uniform, The eutectic Si itself that solidifies at the boundary should be rounded and have a uniform distribution.

[0035]

As described above, in the present invention, the crystal grain refining action due to Sb, Ti, B, etc. and C
Utilizing matrix strengthening with u, Mg, etc., and adopting an alloy design that balances these alloy components makes it excellent in extrudability and forgeability, as well as having good resistance to surface roughening and mechanical properties. We have obtained aluminum alloys for extrusion and forging. Since this aluminum alloy has greatly improved tensile strength, proof stress, etc., as compared with the conventional forging aluminum alloy, it is suitable as a structural material for automobiles having many bolt fastening portions and the like.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of Si content on the tensile strength and elongation of Al-Si-Mg alloys.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kenji Tsuchiya 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture

Claims (2)

[Claims] 1. Si: 3.5 to 6.5% by weight, Sb:
0.05-0.15 wt%, Fe: 0.25 wt% or less, Cu: 0.5-3.5 wt%, Ti: 0.01-
0.1 wt%, Mg: 0.2-0.6 wt% and B:
An aluminum alloy for extrusion / forging, containing 0.0005 to 0.02% by weight, and the balance being substantially Al. 2. Si: 3.5 to 6.5% by weight, Sb:
0.05-0.15 wt%, Fe: 0.25 wt% or less, Cu: 0.5-3.5 wt%, Ti: 0.01-
0.1% by weight, Mg: 0.2 to 0.6% by weight, B: 0.
0005-0.02% by weight, further Mn: 0.05
~ 0.5 wt%, Cr: 0.05-0.3 wt% and S
r: An aluminum alloy for extrusion / forging containing one or more selected from 0.001 to 0.05% by weight, and the balance being substantially Al.