JPH06256879A - High specific strength al-li series alloy-extruded material excellent in hardenability and fatigue property - Google Patents

Abstract

PURPOSE:To combinedly impart high specific strength and excellent hardenability and fatigue properties to an extruded material, in an Al-Li series allay extruded material by incorporating specified amounts of Mg and Zr, Cr, Mn, V, Ti or the like. CONSTITUTION:The compsn. of an Al-Li series alloy-extruded material is constituted of a one contg., by weight, l.5 to 3.5% Li and 1.0 to 3.5% Mg and furthermore contg. one or >=two kinds selected from 0.05 to 0.3% Zr, 0.05 to 0.3% Cr, 0.05 to 1.5% Mn, 0.05 to 0.3% V and 0.005 to 0.1 Ti, and the balance Al with inevitable impurities. Li is an essential element for the reduction of the density of this alloy into a low one and the improvement of its strength. In this alloy-extruded material, ingot-making is performed so that its grain size can be refined as possible after melting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Al-Li-based alloy extruded material, and more particularly to an Al-Li-based alloy extruded material having excellent hardenability and fatigue characteristics and high specific strength.

[0002]

2. Description of the Related Art Aluminum and aluminum alloys are
Since it has extremely excellent extrudability as compared with other metal materials such as iron and copper, it has been widely used as a structural profile material. In particular, JIS6N with improved extrudability and hardenability
01 alloy (Al-Mg-Si system) is a medium-strength structural alloy, and JIS7N01 alloy (Al-Zn-Mg system) is a high-strength welded structural alloy. It was

However, in recent years, research for further speeding up and reducing the weight of railway vehicles has been underway at a rapid pace, and further higher strength and lower density are required for materials used. There is.

Further, when considering practical use as a railway vehicle body structure, for example, when operating on a route with many tunnels, repeated stress is applied when entering and leaving the tunnel, so that fatigue characteristics are also excellent. Is required.

Further, the extruded profile is often made into a product by omitting the solution treatment and quenching treatment after extrusion, performing press quenching, and then performing T5 tempering treatment only by tempering. Therefore, it is necessary that the extruded shape material has excellent hardenability.

As described above, as a material having excellent hardenability and high specific strength, there is an Al--Li alloy which has been put to practical use as a structural material for aerospace vehicles.
This Al-Li alloy includes AA2090 alloy (Al-Li
-Cu-based), AA2091 alloy and AA8090 alloy (both are Al-Li-Cu-Mg-based). The composition of each of these alloys is shown in Table 1 below.

[0007]

[Table 1]

In the present invention, the ratio (%) indicating the composition is% by weight.

[0009]

However, this conventional Al-Li alloy having high specific strength and high elasticity is
Research and development as structural materials for aerospace vehicles are being actively pursued, and practical application as a railway vehicle structure has not been substantially examined. In addition, there is no application of an Al-Li alloy as an alloy for extruded T5 material, and the alloy composition having the required material properties as extruded T5 material and the manufacturing conditions thereof are the same as those of conventional structural materials for aerospace vehicles. Different from the one. Therefore, even if an Al-Li alloy having a composition as a structural material for aerospace vehicles is simply applied to an extruded material for railway vehicles, sufficient characteristics cannot be obtained.

The present invention has been made in view of the above problems, and has high specific strength, excellent hardenability and excellent fatigue properties, and is excellent in hardenability and fatigue properties useful as a material for railway vehicle structures. It is an object of the present invention to provide a high specific strength Al-Li alloy extruded material.

[0011]

A high specific strength Al-li alloy extruded material having excellent hardenability and fatigue properties according to the present invention is Li; 1.5 to 3.5% by weight, Mg; 1.0 to 3.5% by weight.
In addition, Zr; 0.05 to 0.3% by weight, Cr; 0.0
5 to 0.3% by weight, Mn; 0.05 to 1.5% by weight, V; 0.05
To 0.3% by weight and Ti; 0.005 to 0.1% by weight, and one or more elements selected from the group consisting of 0.005 to 0.1% by weight, with the balance being Al and inevitable impurities.

[0012]

The reason for adding the components and the reason for limiting the composition of the Al-Li alloy material according to the present invention will be described below. Li 2 Li is an essential element for lowering the density and improving the strength of aluminum alloys. In the aging treatment process of the final heat treatment at the time of alloy production, Li combines with Al and precipitates as a δ'phase (Al ₃ Li), which contributes to age hardening.

Although the mechanism for improving the hardenability by Li as described above has not been clarified yet, the findings of the research so far have revealed that Li has a large effect of trapping frozen atomic vacancies at the time of quenching. It is considered that the diffusion of other solute atoms is hindered, the progress of precipitation during the quenching treatment is suppressed, and the quenchability is improved. Also, Li
It is considered that the δ ′ phase containing γ does not easily become a stable phase, which also contributes to the improvement of hardenability.

When the content of Li is less than 1.5% by weight,
The effect of lowering the density and increasing the strength of the aluminum alloy is small, and when the Li content exceeds 3.5% by weight, the ductility and toughness of the aluminum alloy are significantly reduced. Mg Mg is an element that improves the strength of the Al alloy. That is, the Mg element forms a solid solution in the matrix and so-called solute strengthening improves the strength of the aluminum alloy. Also, Mg is L
By reducing the solid solution limit of i, it also has the function of promoting the precipitation of the δ'phase and improving the strength of the Al alloy.
When the Mg content is less than 1.0% by weight, the effect of improving the strength and reducing the density is small, and when the Mg content exceeds 3.5% by weight, the hot deformation resistance is remarkably increased and the extrudability is extremely lowered. To do. Zr Zr has an effect of suppressing recrystallization in the microstructure after the final heat treatment. Therefore, Zr is an element that contributes to the improvement of strength and ductility of the aluminum alloy. Z
When the r content is less than 0.05% by weight, recrystallization occurs and the microstructure becomes large, so that the ductility is remarkably reduced although the reduction in strength is not so noticeable. Zr content is
If it exceeds 0.3% by weight, the effect of addition is saturated, and a huge crystallized product containing Zr is produced, resulting in deterioration of strength and toughness. Cr, Mn, V Cr, Mn, and V, like Zr, are elements that contribute to the improvement of strength and ductility by suppressing recrystallization in the microstructure after the final heat treatment. When the content of each of Cr, Mn, and V is less than 0.05% by weight, recrystallization occurs and the microstructure becomes large, so that the ductility of the aluminum alloy decreases. On the other hand, when Cr is contained in an amount exceeding 0.3% by weight, Mn is contained in an amount exceeding 1.5% by weight, and V is contained in an amount exceeding 0.3% by weight, the effect of the addition is saturated, and any further addition is useless. Ti Ti is an element that contributes to the refinement of the microstructure of the ingot. However, if the Ti content is less than 0.005% by weight, a sufficient refining effect cannot be obtained, and if it exceeds 0.1% by weight, crystallized substances increase and the ductility and toughness of the alloy decrease.

Further, F contained as an impurity in the ingot
If the contents of e and Si exceed 0.25% by weight, respectively, Al
-Fe-Si system crystallized substances increase, and the ductility and toughness of the final product significantly decrease. Therefore, impurities Fe or Si
It is necessary to regulate the content to 0.25% by weight or less.

Next, a high specific strength Al- having the above composition
A method for manufacturing a Li-based alloy extruded material will be described. An Al-Li-based alloy having the above-mentioned composition is melted, and an Al-Li-based alloy ingot is cast so that the crystal grain size becomes as fine as possible. When the crystal grain size of this ingot is 3 mm or more, the size and distribution of the crystallized substances existing at the grain boundaries become coarse and non-uniform, so that the ductility and toughness of the final product deteriorate.

Next, the ingot is subjected to a homogenizing heat treatment at a temperature of 400 to 550 ° C. By this homogenizing heat treatment, elements such as Li and Mg can be sufficiently solid-dissolved, and crystallized substances can be partially solid-dissolved to reduce the size.

Then, the ingot after the homogenization treatment is heated to 350 to 500 ° C.
Extrude at the temperature of. The extrusion ratio is preferably 10 or more in order to break the solidified structure of the ingot and make it uniform.

To give the final desired product strength,
Perform refining. Since the alloy of the present invention has excellent hardenability, it can be hardened during the cooling process during extrusion.

Thereafter, cold working is carried out if necessary,
Perform artificial aging treatment. In addition, prior to the aging treatment, by performing solution treatment and quenching treatment in separate steps,
It goes without saying that high strength products can be obtained.

[0021]

EXAMPLES Next, examples of the high specific strength Al-Li alloy extruded material according to the present invention will be described in comparison with comparative examples.

Aluminum alloys having the components shown in Table 2 below were melted and cast to produce an ingot having a diameter of 150 mm. The homogenization treatment of the ingot was performed in two stages of 450 ° C and 540 ° C. Then, hot extrusion was performed at 420 ° C. to produce an extruded material having a thickness of 4 mm. This extruded material is 520 ℃ × 3
After solution treatment for 0 minutes, 1) water cooling, 2) air cooling (2 ° C / sec)
Quenching was performed under the following two quenching cooling conditions. The cooling rate of this air cooling is an approximate cooling rate from the solution heat treatment temperature.

[0023]

[Table 2]

After that, as a cold working, a stretch of 1.5% was performed, and finally, an artificial aging treatment was performed under a peak aging condition.

Then, the influence of the contained components and the quenching and cooling conditions was examined by a tensile test. Table 3 below shows the tensile properties and densities of the alloys. To evaluate hardenability, the ratio of tensile strength of air-cooled material to that of water-cooled material {σB (air-cooled material)
/ ΣB (water-cooled material)} × 100 (%) is also shown in Table 3.

[0026]

[Table 3]

As is apparent from Table 3, the air-cooled material has lower strength and ductility than the water-cooled material. However, in the example
The No. 1 to 11 alloys have a high strength with a tensile strength of about 470 MPa even in an air-cooled material and a density as low as 2.55 g / cm ³ or less, and thus have an extremely high specific strength. On the other hand, the No. 12 alloy of the comparative example has a small amount of Li and thus has a large density and has poor hardenability. Further, since the alloy of Comparative Example No. 13 has a large amount of Li, the ductility decreases. Furthermore, Comparative Example No. 14 alloy is M
Since the amount of g is small, the strength is not sufficient. Further, the alloy of Comparative Example No. 15 had a large amount of Mg, so that the extrudability was remarkably deteriorated and it was impossible to manufacture. Furthermore, in Comparative Example No. 16 alloy, giant crystallized products were formed.

On the other hand, the aluminum alloys shown in the columns of Example Nos. 2, 3, 9 and 10 of Table 2 were melted and cast to have a diameter of 230 mm.
The ingot of was produced. The homogenization treatment of these ingots is 450 ℃
And 540 ° C in two steps. Then, hot extrusion was performed at 440 ° C. to produce an extruded material having a thickness of 4 mm. The cooling at the time of extrusion was air cooling with a fan, and was accompanied by quenching. After that, 1.5% stretch was performed as cold working, and finally artificial aging treatment was performed under peak aging conditions.
As the comparative alloy, JIS 6N01 alloy (tempered T5), which is a conventional aluminum alloy for vehicle structure, was used.

Then, the characteristic evaluation was conducted by a tensile test and a fatigue test. The fatigue test is an axial fatigue test, and the stress ratio is 0.1.

Table 4 below shows the tensile properties and cycles of each alloy.
Fatigue strength after 10 ⁷ cycles is shown. As is clear from Table 4, the strengths of the alloy Nos. 2, 3, 9 and 10 of the examples are J
It was much higher than that of the IS6N01 alloy and also had a high fatigue strength.

[0031]

[Table 4]

[0032]

As described above, the high specific strength Al-Li alloy extruded material having excellent hardenability and fatigue characteristics according to the present invention has the composition described in the claims. Therefore, it has a high specific strength, as well as excellent hardenability and fatigue characteristics, and is extremely useful as a material for a railway vehicle structure, making a great contribution to weight reduction and the like.

Claims (1)

[Claims] 1. Li: 1.5 to 3.5% by weight, Mg: 1.0 to 3.5% by weight, further Zr: 0.05 to 0.3% by weight, Cr: 0.05 to 0.3% by weight, Mn: 0.05 to 1.5% by weight, V: 0.05 to 0.3% by weight and Ti: 0.005 to 0.1% by weight, containing one or more elements selected from the group, and the balance being Al and inevitable impurities, hardenability And high specific strength Al with excellent fatigue characteristics
-Li-based alloy extruded material.