JPH1068038A - Aluminum-lithium series alloy ingot for rolling and its continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an ingot for rolling for producing an Al-Li series alloy sheet material small in ear cracking at the time of hot rolling and having excellent fracture toughness and to provide a continuous casting method therefor. SOLUTION: This Al-Li series alloy ingot for rolling is the one having a compsn. contg., by weight, 0.5 to 3.0% Li, 1.0 to 3.0% Cu and 0.5 to 2.0% Mg, contg. one or >= two kinds among suitably amounts of Zr, V, Mn, Cr and Ti as structure refining agents, contg., at need, 0.2 to 0.6% Ag and/or 0.2 to 0.7% Zn, and the balance Al with inevitable impurities, and in which the area ratio of the dendrite cell structure in the cross section in the perpendicular direction to the rolling direction of the ingot 7 is regulated to <=80%. The ingot 7 is produced by a semiconductor casting method under the following conditions. Namely, the temp. 11 of the molten metal is regulated to 680 to 850 deg.C, as for the quantity 11 of cooling water, it is equivalent in the case of that W1 for a water cooled mold and that W2 for the outer circumference of the ingot, and it is regulated to 500 to 2000ml/cm/min per unit ambient length of the cross section in the horizontal direction of the ingot and per unit time, and the discharging rate of the ingot from a mold 1 is regulated to 35 to 110mm/min.

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 ingot for rolling and a continuous casting method thereof, and more particularly to a method for producing an ingot of Li 0.5
~ 3.0%, Cu 1.0 ~ 5.5%, Mg 0.5 ~ 2.
For rolling, an Al-Li-based alloy containing 0% as an essential component and selectively containing a structure improving element, etc., is capable of obtaining a rolled sheet excellent in rollability that does not cause ear cracks during hot rolling and fracture toughness. The present invention relates to an ingot and a continuous casting method thereof.

[0002]

2. Description of the Related Art Al-Li alloys, especially Li1.0-
3.0%, Cu 1.0-4.0%, Mg 0.5-2.0
% As an essential component, and further, 0.04 to 0.16% of Zr.
As the wrought alloy comprising Al and the balance of impurities and Al, there are conventionally known international standard alloys such as 2090, 2091, 8090, and 8091, which have excellent properties such as low density, high strength, and high elastic modulus. It is widely used as a structural material for equipment and aircraft, and is expected to be put to practical use as a lightweight structural material for transportation equipment such as automobiles and rail vehicles.

[0003] Despite being known to have such excellent properties, there are various difficulties in putting this kind of alloy to practical use. That is, the Al-Li-based alloy described above tends to cause edge cracking during hot rolling, and it is difficult to stably obtain mechanical properties, particularly fracture toughness, of a rolled product sheet.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and relates to an ingot for producing an Al-Li alloy sheet and a method for producing the same, and particularly to an edge cracking property during hot rolling. An object of the present invention is to provide an Al-Li alloy ingot for rolling and a continuous casting method thereof for producing a product sheet material having less fracture and excellent fracture toughness. In the present invention, excellent fracture toughness means
The fracture toughness value of the product sheet material required for aircraft materials and the like is 25 MPa√m or more, and this is set as the target value.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, the edge cracks and the fracture toughness of the product sheet during hot rolling are all closely related to the structure of the alloy ingot. The present inventors have found that the ingots have been greatly affected, and have invented an ingot having an optimum structure requirement and a continuous casting method thereof.

That is, specifically, the Al-Li alloy ingot for rolling according to the first aspect of the present invention has a Li of 0.5 to 3.0%,
Cu 1.0-3.0%, Mg 0.5-2.0%, Zr
0.06-0.3%, V 0.06-0.3%, Mn0.
06-0.3%, Cr 0.06-0.3%, Ti0.0
One or two or more of 2 to 0.3% and, if necessary, 0.2 to 0.6% of Ag and / or Zn 0.2
An alloy ingot containing about 0.7%, the balance being unavoidable impurities and Al, characterized in that the dendrite cell structure area ratio of a cross section in a direction perpendicular to the rolling direction is 80% or less.

[0007] The Al-Li for rolling according to the second aspect of the present invention.
The continuous casting method of the system alloy ingot is Li 0.5-3.0%,
Cu 1.0-3.0%, Mg 0.5-2.0%, Zr
0.06-0.3%, V 0.06-0.3%, Mn0.
06-0.3%, Cr 0.06-0.3%, Ti0.0
One or two or more of 2 to 0.3% and, if necessary, 0.2 to 0.6% of Ag and / or Zn 0.2
A molten alloy containing about 0.7% and the balance of unavoidable impurities and Al is poured into a water-cooled cylindrical mold, and cooling water is sprayed directly on the periphery of the ingot immediately below the mold through an ingot forming process. In the semi-continuous casting method of drawing the ingot from the mold, the molten alloy is in the range of 680 to 850 ° C,
The water-cooled mold for cooling water W ₁ and the cooling water W ₂ that is sprayed directly to the ingot (ml), the unit circumferential length of the horizontal cross section of the ingot L (cm) and the unit time (min.) Per, W ₁
= W ₂ = 500-2000 ml / cm / min. , The drawing speed of the ingot is 35 to 110 mm / min. It is characterized by being adjusted to.

The reasons for limiting the chemical components in the alloy of the present invention will be described. Li: Li is a lightening element and a metastable phase δ ′.
Precipitates, contributing to strength improvement and high rigidity. If the Li content is less than 1.0%, the effects of weight reduction and strength improvement are insufficient, and if it exceeds 3.0%, casting crack susceptibility increases and a coarse metastable phase δ 'is formed. As a result, the elongation value and the toughness of the alloy are reduced, so the upper limit of the amount of Li is set to 3.0%.

Cu: Cu is an Al-Cu-based plate-like precipitate (Al ₂ Cu), an Al-Cu-Li-based plate-like precipitate Al ₂ Cu, or an Al-Cu-Li-based precipitate phase. (T ₁ phase)
To contribute to the improvement of strength and toughness. However, if the content is less than 1.0%, the effect is not sufficient.
If it exceeds 0%, the effect is saturated and at the same time, the lightening effect is reduced. When the Mg content is less than 1.0%,
The Cu content is desirably 1.5 to 3.0%, and when the Mg content exceeds 1.0%, the effect of improving the strength by Mg can be expected. Therefore, the Cu content is about 1.0 to 2.5%. But it is good.

Mg: Mg strengthens the alloy without lowering the elongation value and the toughness due to the solid solution effect, and at the same time, Al-
Cu-Mg based metastable phase plate-like precipitate S 'phase (Al-C
uMg), thereby further contributing to strength improvement. If the Mg content is less than 0.5%, the effect of improving strength is not sufficient, and if it exceeds 2.0%, the strength is improved but the toughness and elongation value are reduced. Therefore, Mg is 0.5 to
A range of 2.0% is desirable.

Zr, V, Mn, Cr and Ti: These elements have the effect of refining the alloy structure and suppressing recrystallization, and are required to make the alloy structure fine and unrecrystallized. Effective and preferred ranges are Zr, V,
Mn and Cr are 0.06 to 0.3%. If the content exceeds the upper limit, a coarse intermetallic compound of Al and these elements is formed, and the strength, toughness and elongation value are reduced. If the content is less than the lower limit, a sufficient effect cannot be obtained.

The proper amount of Ti is 0.02 to 0.06%, which makes the microstructure of the ingot finer, and according to experiments by the present inventors, according to experiments by the present inventors, as shown in FIG. The inclusion of the refinement element has the effect of increasing the dendrite cell structure area ratio. If the amount exceeds the upper limit, crystallized substances increase and toughness and ductility decrease. If the amount is less than the lower limit, a sufficient refining effect cannot be obtained.

Ag: 0.2 to 0.6% of Ag as required
And / or Zn content of 0.2 to 0.7% is effective. Ag is an Al—Cu-based plate-like precipitate θ ′ (Al ₂ C
u) or Al-Cu-Li-based plate-like precipitate T ₁ phase (Al ₂
Promotes the precipitation of CuLi) to form Al-Li-Cu-X (X
The strength of an alloy such as Mg is remarkably improved. If it exceeds the upper limit of the Ag content range, the specific gravity increases and the specific strength decreases greatly, and if it is below the lower limit, a sufficient effect cannot be obtained. Zn0.
The content of 2 to 0.7% improves the corrosion resistance of the Al-Li alloy. If it exceeds the upper limit, coarse compounds are generated at the crystal grain boundaries, and the toughness of the alloy is impaired. If it is less than the lower limit, the effect is weak.

Impurities: Fe 0.3% or less, Si 0.2
% Is an acceptable impurity without impairing the effects of the present invention, but in order to more strictly prevent a decrease in toughness due to the formation of compounds, segregation at grain boundaries, etc., Fe 0.10% or less, Si 0. 10% or less is preferable. Na, C
Since alkali and alkaline earth elements such as a and K cause cracking at the time of hot working of the alloy, each 10 pp
m or less.

FIG. 2 shows a network dendrite cell structure formed when the temperature of the molten metal at the time of casting is relatively low or when an appropriate amount of a crystal grain refiner such as Ti is added. FIG. 4 schematically shows a dimension of a cell size (hereinafter, referred to as DCS). FIG. 3 shows a dendrite structure having protrusions inside a network structure formed when the temperature of the molten metal is relatively high, and the dimension of dendrite arm spacing (hereinafter referred to as DAS) is shown on the right side of the figure. .

In a typical ingot, both structures generally coexist. However, the present inventors have found that an ingot capable of obtaining a target value of fracture toughness of a product sheet material has a dendrite cell structure having a cross section perpendicular to the rolling direction. It was found that the area ratio was in the range of 80% or less. If the area ratio exceeds 80%, the target value cannot be obtained regardless of the DCS value.

BEST MODE FOR CARRYING OUT THE INVENTION

The production of the ingot according to the present invention is carried out by a semi-continuous casting method, and the temperature of the molten alloy is selected in the range of 680 to 850 ° C. at the time of pouring into the mold. When the temperature is lower than 680 ° C., it is recognized that the area ratio of the dendrite cell exceeds 80%. If the temperature exceeds 850 ° C., L
The reaction of the i component with oxygen, hydrogen, and nitrogen in the atmosphere is activated, and the quality of the ingot is deteriorated due to the loss of the Li component and an increase in nonmetallic inclusions.

The molten metal is poured into a water-cooled cylindrical mold, and the ingot is lowered while the cooling water is sprayed directly on the periphery of the ingot immediately below the mold through the ingot forming process. At this time, the cooling water amount W ₁ for the water-cooled mold and the cooling water W ₂ (ml) directly sprayed on the ingot are the unit circumferential length L (c) of the horizontal section of the ingot.
m) and per unit time (min.), W ₁ = W ₂ = 5
00 to 2000 ml / cm / min. Within the range
The dendrite cell structure area ratio can be controlled to the upper limit or less.If the cooling water amount is less than the lower limit, the molten metal leaks easily from the lower edge of the mold, and if it exceeds the upper limit, the cooling water overflows onto the molten metal surface in the mold. There is a danger of molten metal explosion.

The speed of drawing out the ingot from the mold, that is, the speed of descent, is 35 to 110 mm / min. It is adjusted to. This range tends to limit the area ratio of the dendrite cell structure to 80% or less, and if it is less than the lower limit, the depth of the molten metal in the mold is insufficient, and the surface defects such as perspiration on the surface of the ingot and the hot water boundary become large, and the cutting amount is reduced. It is not good to be forced to increase. Further, it causes difficulties such as difficulty in operating the pouring distributor. Also,
If the upper limit is exceeded, cracks in the ingot tend to occur.

[0020]

FIG. 1 is a schematic vertical sectional view of a casting apparatus used in an embodiment of the present invention, which is a continuous casting apparatus used for producing a general aluminum alloy ingot for rolling. The molten alloy 2 is protected from a melting and holding furnace (not shown) in an inert gas atmosphere such as Ar, and the primary cooling water 5 is passed through a gutter 3 and a distributor 4.
The molten metal is injected into a relatively rectangular tubular mold (1) having a transverse cross section, and a solidified shell is formed on the outer periphery of the molten metal body. Cooling water (6) is directly sprayed on the solidified shell to cool, and the formed columnar ingot 7 is held by a vertically movable pedestal (8), descends downward, and is pulled out of the mold (1).

The temperature of the molten metal is measured by a thermometer (11) at a position immediately before injection into the mold (1), and the primary cooling water (5) supplied to the cooling jacket of the mold (1) is measured by a water meter (10). And the drawing speed of the ingot is measured by a speedometer (9), respectively. Secondary cooling water (6), which is cooling water directly sprayed on the ingot, is sprayed from a slit or a spray hole at an inner lower end of the cooling jacket and flows down through the surface of the ingot.

Table 1 shows the three components of the Al-Li alloy tested in this example. In addition, two types (A1, A2) in which the amount of Ti was changed were added to the A alloy. The ingot obtained by semi-continuous casting under the above-mentioned conditions under various conditions is chamfered, homogenized, heat-treated, hot-rolled, and further tempered (solution treatment, cold-rolling, aging treatment) by a conventional method. ) To produce a product plate.

[0023]

[Table 1] << Table Note >> A1: A + 0.02% Ti A2: A + 0.07% Ti

Table 2 shows the results of evaluating the characteristics of the ingot, the production conditions thereof, and the product sheet material. The top column of Table 2 shows the melt temperature: the melt temperature at the time of pouring into the mold, and the cooling water: Cooling water amount (ml / cm / min.), Drawing speed: descending speed of ingot from the mold (mm / min.), DAS: DAS (μm),
DCS: DCS (μm), area: area ratio of dendrite cell structure (%), rolling: evaluation of edge cracking degree during hot rolling, and toughness: evaluation of achievement of target value of fracture toughness of product sheet material.

[0025]

[Table 2]

In the evaluation of the right column in the uppermost column of Table 2, the circles indicate the results under the conditions corresponding to the implementation of the present invention. The toughness achieved the target value and could be evaluated as good. In addition, the mark “x” indicates that the target value was not reached and the product was evaluated as defective.

[0027]

As described above, the rolling A according to the present invention is used.
Since the l-Li alloy ingot does not have edge cracks during hot rolling and has excellent fracture toughness of the final product sheet material,
It is suitable as a raw material for manufacturing lightweight structural materials for transportation equipment such as aircraft, automobiles and rail vehicles.

Further, in the method for continuously casting an Al-Li alloy ingot for rolling according to the present invention, the molten metal temperature, the amount of cooling water, and the ingot drawing speed are controlled to specific values without changing conventional general-purpose equipment. By doing so, a high quality ingot for rolling can be reliably obtained, so that a high product yield can be achieved in industrial mass production, and the cost reduction and quality stabilization greatly contribute to the expansion of applications of this kind of alloy sheet.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view of a continuous casting apparatus used in an embodiment of the present invention.

FIG. 2 is a diagram showing a reticulated dendrite cell structure in an ingot, and the right side of the figure schematically shows the dimension of dendrite cell size (DCS).

FIG. 3 is a diagram showing a dendrite structure having projections inside a network structure in an ingot, and the right side of the figure shows a dimension of dendrite arm spacing (DAS).

FIG. 4 is a view showing the effect of the addition of a finer such as Ti on the area ratio of the dendrite cell structure in an Al-Li alloy ingot.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 cooling mold 2 molten alloy 3 gutter 5 cooling water pipe 6 secondary cooling water 7 ingot 9 ingot ingot (drawing) speed measuring means 10 cooling water amount measuring means 11 molten metal temperature measuring means

Claims (2)

[Claims] 1. Li 0.5% by weight (hereinafter the same)
3.0%, Cu 1.0-3.0%, Mg 0.5-2.0
%, Zr 0.06-0.3%, V0.06-0.3
%, Mn 0.06-0.3%, Cr 0.06-0.3
%, 0.02 to 0.3% of Ti, one or more of Ti and, if necessary, 0.2 to 0.6% of Ag, and / or
Alternatively, it is an alloy ingot containing 0.2 to 0.7% of Zn, the balance being inevitable impurities and Al, and the area ratio of the dendrite cell structure in a cross section perpendicular to the rolling direction is 80% or less. Al-Li alloy ingot for rolling. 2. Li 0.5-3.0%, Cu 1.0-
3.0%, Mg 0.5-2.0%, Zr 0.06-
0.3%, V 0.06-0.3%, Mn 0.06-0.0.
3%, Cr 0.06-0.3%, Ti 0.02-0.3
% Or more, and if necessary, Ag
0.2-0.6% and / or Zn 0.2-0.7%
The molten alloy comprising Al and inevitable impurities and Al is poured into a water-cooled cylindrical mold, and cooling water is sprayed directly to the outer periphery of the ingot immediately below the mold through an ingot forming process. In a semi-continuous casting method of drawing a lump from a mold,
The temperature of the alloy melt is in the range of 680 to 850 ° C., and the amount of cooling water W ₁ for the water-cooled mold and the amount of cooling water W ₂ (ml) directly sprayed on the ingot are the unit perimeter (cm) of the horizontal section of the ingot. ) And per unit time (min.), W ₁ = W ₂
= 500-2000 ml / cm / min. , The drawing speed of the ingot is 35 to 110 mm / min. A continuous casting method for an Al-Li alloy ingot for rolling, characterized by being adjusted to: