JPH1068037A - Aluminum-lithium alloy excellent in extrudability and hardenability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide excellent extrudability and hardenability by removing Cu from the composition of an Al-Li alloy having specific chemical composition. SOLUTION: An Al-Li alloy, having a composition containing, by weight, 1.5-3.0% Li and 0.3-1.0% Mg as essential components, also containing one or >=2 kinds among 0.05-0.3% Zr, 0.05-0.3% Cr, 0.05-1.5% Mn, 0.05-0.3% V, and 0.005-0.1% Ti, and having the balance Al with inevitable impurities, is used. The alloy with this composition is refined in an Ar atmosphere by the ordinary method and an ingot having fine crystalline grains is obtained by the direct- cooling semi-continuous casting method. Soaking treatment is applied to this ingot to allow elements, such as Li and Mg, to enter into solid solution sufficiently and also to allow crystallized substances to enter into solid solution partially and make them small. Subsequently, the ingot is extruded, by which the solidified structure of the ingot is broken and uniformized. Then, refining treatment, cold working, artificial aging treatment, etc., are applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Al alloys have been widely used as structural extruded materials because of their excellent extrudability compared to alloys such as Fe and Cu. In particular, JIS6N01 alloy (Al-
Mg-Si) is a medium-strength alloy.
One alloy (Al-Zn-Mg based) has been applied to railway vehicle structures as a high-strength welding structural alloy.

[0003] In recent years, however, there has been a demand for further increasing the speed of railway vehicles and, for that purpose, reducing the weight thereof. On the other hand, Al-L has been actively researched and developed as a structural material for aerospace because of its lower density than conventional general-purpose Al alloys.
Although there is an i-based alloy, the study of its practical application for railway vehicle structures is still behind.

[0004] In order to reduce the weight of a railway vehicle structure, it is of course important to reduce the density of the material, but in order to reduce the weight per unit area of the extruded material used, that is, to achieve a reduction in thickness. It is essential to improve the extrusion processability at the same time as improving the material strength.

[0005] Further, the extruded material is manufactured by performing press quenching and then performing a T5 tempering treatment only for tempering in order to omit the solution treatment and quenching treatment after extrusion. For this reason, it is important that the extruded material has excellent hardenability. However, extruded T5
Al-Li alloys for tempering have hardly been applied, and there are few reports on the effects of alloy compositions and their manufacturing conditions on the material properties.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and aims to develop an Al-Li high-strength extrusion alloy suitable for a railway vehicle structure and the like. It is an object of the present invention to provide an Al-Li alloy material having particularly excellent extrudability and hardenability.

[0007]

The present inventors have conducted various experiments and studies in order to achieve the above object, and as a result, it has been found that C, which is a skeletal component exhibiting strength in a conventional Al-Li alloy, is used.
The present inventors have found an alloy having a new component constitution excluding u from the constitution, and have accomplished the present invention.

Specifically, the Al-Li alloy of the present invention having excellent extrudability and hardenability is 1.5 to 3.0% by weight of Li (hereinafter the same), and 0.3 to 1.0 of Mg. 0%
And Zr 0.05-0.3%, Cr 0.05-0.3
%, Mn 0.05-1.5%, V 0.05-0.3%,
It contains one or more of 0.005 to 0.1% of Ti, and the balance is made of unavoidable impurities and Al.

The meanings of the constituent elements of the Al-Li alloy according to the present invention and the reasons for limitation are as follows. Li: an element indispensable for lowering the density and improving the strength of the alloy. In the aging process at the time of the final heat treatment in the production of the alloy, Li combines with Al and precipitates as a δ 'phase (Al3Li), contributing to the improvement in strength. Although the mechanism of the improvement of quenchability by Li has not yet been elucidated sufficiently, from the findings of previous studies, since Li has a large effect of trapping frozen atomic vacancies during quenching, the presence of Li causes other effects. It is considered that diffusion of solute atoms is hindered, progress of precipitation during the quenching treatment is suppressed, and this contributes to improvement of quenchability. If the Li content is less than 1.5%, the effects of lowering the density and increasing the strength are small, and if it exceeds 3.0%, the ductility and toughness are greatly reduced.

[0010] Mg: an element effective in improving the strength of the alloy. That is, the Mg element forms a solid solution in the matrix, and the strength of the alloy is improved by so-called solid solution strengthening. Mg also has the effect of promoting the precipitation of the δ ′ phase by reducing the solid solubility limit of Li, thereby improving the strength of the alloy. When the content of Mg is less than 0.3%, the effect of improving the strength and reducing the density is insufficient. When the content exceeds 1.0%, the deformation resistance during hot work is significantly increased, and the extrudability is large. descend.

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 the strength and ductility of the alloy.
If the content is less than 0.05%, recrystallization occurs and the microstructure becomes large, so that the strength is not so much reduced but the ductility is remarkably reduced. If it exceeds 0.3%, the effect of the addition is saturated, and at the same time, huge crystals containing Zr are generated, resulting in a decrease in strength and toughness.

Like Cr, Mn, and V: Zr, they are elements that contribute to improving strength and ductility by suppressing recrystallization in the microstructure after the final heat treatment. C
When the content of each of r, Mn, and V is less than 0.05%, recrystallization occurs and the microstructure becomes large, so that the ductility of the alloy is reduced. 0.3% Cr, 1.5% Mn
%, V exceeds 0.3%, the effect is saturated, and further addition is wasted.

[0013] Ti is an element that contributes to refinement of the microstructure of the alloy ingot. However, its content is 0.005%
If it is less than 0.1%, the refining effect is insufficient, and if it exceeds 0.1%, crystallized substances increase and ductility and toughness decrease.

F which is usually contained as an impurity in the ingot
e, Si, when the amount exceeds 0.25%, Al-
Fe-Si based crystallization increases, and the ductility and toughness of the final product decrease. Therefore, the contents of Fe and Si are 0.25 each.
It is necessary to regulate to less than%.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, a method of manufacturing an alloy material will be described.
An alloy of the above-described components is melted in an Ar atmosphere by a conventional method, and a fine ingot of crystal grains is obtained by a direct cooling semi-continuous casting method. When the crystal grain size in the ingot is 3 mm or more, the size and distribution of the crystallized substances present at the grain boundaries become coarse and non-uniform,
The ductility and toughness of the final product decrease.

The ingot is soaked at 400 to 550 ° C. By this treatment, elements such as Li and Mg can be sufficiently dissolved in a solid solution, and the crystallized material can be partially dissolved to reduce the size. Then the ingot is 35
Extrude at a temperature of 0-500 ° C. The extrusion ratio is desirably 10 or more in order to break the solidified structure of the ingot to make it uniform.

Finally, a refining process is performed to give predetermined product characteristics. Since the alloy of the present invention has excellent hardenability, it hardens even in the air cooling process during extrusion. Thereafter, if necessary, cold working is performed, and an artificial aging treatment is performed.
Note that, by performing the solution treatment and the quenching treatment in separate steps prior to the aging treatment, it is possible to obtain a mold material having a higher strength.

[0018]

EXAMPLES Alloys having the components shown in Tables 1 (inventive alloys) and 2 (comparative alloys) were melted by a conventional method and cast into a 150 mm-diameter extruded billet by a semi-continuous casting method. The ingot was soaked at 450 ° C. and then at 520 ° C. in two stages. Thereafter, the ingot was heated to 420 ° C., hot extruded at a ram speed of 4 inches / minute, and had a thickness of 4.0 m.
m of extruded specimens were produced. The cooling at the time of extrusion was accompanied by quenching as cooling with a fan.

[0019]

[Table 1]

[0020]

[Table 2]

The extruded material is subjected to solution heating in an Ar gasoline furnace at 520 ° C. for 30 minutes, and then subjected to two kinds of cooling conditions, ie, (1) water cooling (about 1000 ° C./sec), and (2) air cooling (about (2 ° C./sec). Finally, artificial aging treatment was performed under peak aging conditions. Extrusion processability was determined using the measured extrusion pressure as an index. Further, strength and ductility were evaluated by a tensile test.

Table 3 (alloy of the present invention) and Table 4 (comparative alloy) show the extrusion pressure (GPa) and tensile strength (σ) of each alloy.
B; MPa), elongation (%) and density (g / cm3). As is clear from the results in Table 2, the alloy No. of the example of the present invention. In 1 to 10, the extrusion pressure is 100 GPa
The extrudability was superior to that of the JIS7N01 alloy of the comparative example, and a high strength with a tensile strength of 380 MPa or more was obtained in the water-cooled quenched material, and the density was 2.56 g.
/ Cm3 or less, it was recognized that the material had an extremely high specific strength.

On the other hand, in the alloy No.
No. 11 has a low density of Li and a low hardenability due to a low Li content. No. No. 13 has insufficient strength because of a small amount of Mg. No. In No. 14, the extrudability was significantly reduced due to the large amount of Mg. In No. 15, giant crystals are formed, and the strength is insufficient.

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

According to the Al-Li alloy of the present invention,
Because of its excellent extrudability and hardenability, high strength can be obtained after aging even if the quenching after solution heat is slow cooling such as air cooling, and an extruded material with high specific strength can be easily produced. Therefore,
For example, it is an extruded material having characteristics required for a lightweight structural material of a railway vehicle or the like, and greatly contributes to this field.

Claims (1)

[Claims] 1. The method according to claim 1, wherein the content of Li1.5 to
3.0%, Mg 0.3-1.0%, Zr 0.05-
0.3%, Cr 0.05-0.3%, Mn 0.05-
1.5%, V0.05-0.3%, Ti0.005-
An Al-Li alloy having excellent extrudability and hardenability, characterized in that it contains one or more of 0.1%, and the balance consists of unavoidable impurities and Al.