Manufacturing method for aluminum alloy material with single layer thermal bonding function

Abstract

A method for producing a single-layer aluminum alloy material which exhibits a heat-welding function and contains 2.00-3.00 mass% of Si, 0.01-0.50 mass% of Fe and 0.80-1.50 mass% of Mn, said method involving a casting step for performing twin roll-type continuous casting for forming a sheet material having a thickness of 3-12mm by rotating a roller having a diameter D(mm) at a circumferential speed v(mm / min) so as to satisfy 0.057*v+0.0016*D≤33.54.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an aluminum alloy material having a thermal bonding function in a single layer. [Background technology]

[0002] Twin-roll continuous casting is a method in which molten metal such as aluminum is supplied between a pair of chilled rolls (hereinafter referred to as twin rolls) arranged above and below each other, and is formed into a plate material by solidifying it through contact with the twin rolls.In addition, the molten metal is continuously deformed into a plate material by applying a load from the twin rolls.

[0003] Although twin-roll continuous casting offers relatively lower productivity than conventional sheet metal manufacturing methods, which involve sequential processes such as semi-continuous casting and hot rolling, it can produce thin sheets directly from molten metal, thereby eliminating or simplifying the hot rolling process and effectively reducing energy consumption. Furthermore, twin-roll continuous casting produces a sheet metal with a fast cooling rate during casting, allowing a large amount of solute elements to be supersaturated in the aluminum matrix. Furthermore, the subsequent thermo-mechanical process allows for the precipitation of a larger number of fine precipitates, thereby reducing grain coarsening in the sheet metal during the joining and heating process. Furthermore, the pinning effect, which suppresses dislocation movement during plastic deformation of the material, improves strength. From these perspectives, attempts have been made in the past to produce thin metal sheets, such as aluminum, using twin-roll continuous casting. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-25378 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the production of sheet materials by twin-roll continuous casting, there is a problem in that centerline segregation is likely to occur. As the molten metal solidifies during the cooling process by the twin rolls, some of the solute elements that have formed a supersaturated solid solution in the solidified solid phase are expelled from the solid phase side to the liquid phase side through the solidification interface, causing segregation phenomenon in which the solute elements concentrate between the dendrites near the solidification interface. This causes centerline segregation, where solute elements become concentrated, at the center of the thickness of the plate material (center of plate thickness), which is the position where final solidification is completed, and also causes casting defects such as voids due to solidification shrinkage in the same area.

[0006] If significant centerline segregation occurs near the center of the plate thickness, it will remain in the subsequent rolling process and in the coil after the rolling process. The centerline segregation remaining inside the coil has a high solute concentration and a different structure from the aluminum base material, significantly reducing brazability. When processed into fin material, defects caused by centerline segregation can cause cracks and lead to fin breakage. Furthermore, during the heat treatment process, blister defects can occur due to volume expansion caused by remelting of the centerline segregation. Therefore, it is necessary to apply technologies to reduce centerline segregation. However, due to the large solute content and wide range, it is difficult to completely remove centerline segregation using heat treatments such as diffusion.

[0007] The present invention has been made in light of the above-mentioned problems, and has an object to provide a method for manufacturing an aluminum alloy material in which centerline segregation is reduced. [Means for solving the problem]

[0008] The method for producing an aluminum alloy material of the present invention is a method for producing an aluminum alloy material having a single layer thermal bonding function, which contains 2.00 to 3.00 mass% Si, 0.01 to 0.50 mass% Fe, and 0.80 to 1.50 mass% Mn, and includes a casting step of performing twin-roll continuous casting to form a plate material having a thickness of 3 to 12 mm by rotating a roll having a diameter D (mm) that satisfies the following formula (1) at a peripheral speed v (mm / min):

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[0009] The manufacturing method of the aluminum alloy material configured as described above can obtain an aluminum alloy material with reduced centerline segregation. The inventors of the present invention have established the manufacturing method of the aluminum alloy material of the present invention based on engineering results of actual casting and numerical analysis.

[0010] The derivation of Equation (1) is explained below. As mentioned above, centerline segregation in the center of the thickness direction during twin-roll continuous casting occurs when some of the solute elements supersaturated in the solid phase are expelled from the solid phase to the liquid phase through the solidification interface and concentrated at the solidification interface. In other words, centerline segregation is caused by the size of the solid-liquid region, where the liquid and solid phases coexist, remaining near the center of the thickness direction when the molten aluminum supplied from the nozzle tip between the twin rolls begins to solidify and is cooled by the twin rolls. As a result, the length of the solid-liquid region in the center of the thickness direction determines the presence and extent of centerline segregation. In other words, the longer the length of the solid-liquid region in the center of the thickness direction, the longer the time spent in the solid-liquid region. This increases the amount of solute elements expelled from the solid phase, resulting in significant centerline segregation. Conversely, the shorter the solid-liquid region in the center of the thickness direction, the less solute elements are expelled from the solid phase, resulting in minor centerline segregation. The solid-liquid phase region here refers to the physical distance between a position where the temperature of molten aluminum at the center of the plate thickness becomes the liquidus temperature of the aluminum alloy material (hereinafter referred to as the liquidus temperature position) and a position where the temperature becomes the solidus temperature (hereinafter referred to as the solidus temperature position).

[0011] Therefore, the inventors of the present invention used numerical analysis to calculate the distance at which the temperature at the center of the plate thickness in twin-roll continuous casting is below the liquidus temperature and above the solidus temperature of an aluminum alloy material, and found a correlation with centerline segregation in actual casting tests. The model system and model formula used in the numerical analysis will be described in detail below.

[0012] Figure 1 shows a schematic diagram of a model used to perform a numerical analysis of the center of the strip thickness during twin-roll continuous casting. The numerical analysis range was from the nozzle tip, where the molten aluminum comes into contact with the twin rolls, to the center of the rolls, and the strip thickness t was set to 6-7 mm. Numerical analysis was performed based on a two-dimensional heat transfer equation assuming the center of the strip width. Here, the temperature distribution of the molten aluminum and strip material within the numerical analysis range was calculated, and the distance L between the liquidus temperature position and the solidus temperature position was calculated using numerical analysis.

[0013] The following equation (2) shows the heat conduction equation as the basic equation for numerical analysis. The following equation (3) defines the solid fraction. Here, ρ A ,C A ,κ A ,H,f S ,T L ,T S is a physical property value of the aluminum alloy material, and can be derived from the chemical composition of the aluminum alloy material. A :density, C A : specific heat, κ A : thermal conductivity, H: latent heat, f S :Solid phase ratio, T L :Liquidus temperature, T S : solidus temperature. The molten aluminum and the plate material move parallel to the x direction perpendicular to the y direction, which is the direction of the line connecting the central axes of the upper roll 5a and the lower roll 5b that make up the twin rolls, from the nozzle tip to between the rolls. The x direction means the casting direction, and the distance L means the distance in the x direction. In addition, in the following formula (2), the specific heat C A is from the equivalent specific heat method.

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[0014] The heat generated by processing Q when the molten aluminum is completely solidified in the area where it comes into contact with the roll surface, the so-called contact arc length area. HTaking into account the above, a numerical analysis was carried out for the region between the solidus temperature position and the roll center position. H is obtained by the following equation (4), where σ y is the yield stress of the plate material at 500°C, and h O is the delivery thickness, h S is the thickness at the end of solidification, v is the roll peripheral speed (assumed to be equal to the casting speed here), L S is the distance from the solidus temperature position at the center of the plate thickness to the roll center position, and RH is the heat conversion rate of the work performed by the rolls. The roll center position is the midpoint of the line segment connecting the central axes of the upper roll 5a and the lower roll 5b that make up the twin rolls.

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[0015] The heat transfer between the roll and the molten aluminum and between the roll and the plate material is related by the following equation (5): R is the roll surface temperature, h R-A is the heat transfer coefficient between the roll surface and the molten aluminum or plate material. The following equation (6) shows the basic formula for heat conduction inside the roll. R ,C R ,κ R is the physical property value of the roll, specifically, ρ R :density, C R : specific heat, κ R The diameter D of the upper roll 5a and the lower roll 5b and the physical property value ρ R ,C R ,κ R is the same.

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[0016] Table 1 shows the physical properties of the aluminum alloy used in the numerical analysis. [Table 1]

[0017] Numerical analysis was used to calculate the distance L between the liquidus temperature position and solidus temperature position at the center of the thickness of strip produced by twin-roll continuous casting under various casting conditions. Figure 2 shows an example of the results of the numerical analysis, showing the effect of the roll diameter D and roll peripheral speed v on the distance L. Note that the roll diameter D and roll peripheral speed v are sometimes simply referred to as diameter D and peripheral speed v. As shown in Figure 2, there is a clear tendency for the distance L to decrease as the roll diameter D decreases and the roll peripheral speed v decreases. Using these results, linear regression was used to formulate the distance L (mm) as a function of the roll diameter D (mm) and peripheral speed v (mm / min), yielding the following equation (7):

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[0018] Furthermore, aluminum alloy materials were produced in actual casting experiments under several casting conditions to confirm the presence or absence of centerline segregation in the center of the plate thickness. From these segregation investigation results and the numerical analysis results shown in Figure 2, it became clear that a distance L of 20 mm or less is sufficient to sufficiently reduce the occurrence of centerline segregation in the center of the plate thickness. Therefore, the following equation (8) can be obtained as the condition for preventing the occurrence of centerline segregation. The above-mentioned equations (1) and (C1) are modifications of the following equation (8).

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[0019] A more preferable range of conditions can be defined by the following formula (9). This is because the shorter the distance L, the less likely centerline segregation is to occur in the center of the plate thickness, and shows the relationship between the roll diameter D and the peripheral speed v that allows this distance L to be 16 mm or less.

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[0020] Here, the molten metal temperature according to the present invention needs to be controlled and managed to be at or below a temperature 80°C higher than the liquidus temperature of the aluminum alloy material. If the molten metal temperature is high, an unsolidified region is likely to remain in the center of the plate thickness, making defects more likely to occur in the center of the plate thickness. From the perspective of the present invention, a lower limit for the molten metal temperature is not required. However, if the molten metal temperature is low, casting problems may occur due to solidification occurring within the nozzle tip, and as the plate thickness increases, the deformation resistance of the twin rolls becomes significant, increasing the equipment load. Therefore, a lower limit for the molten metal temperature may be determined from this perspective. The molten metal temperature is measured at a position just before the head box or nozzle tip. If the temperature there is not more than a temperature 80°C higher than the liquidus temperature, it can be assumed that the molten metal temperature (casting temperature) upon reaching the rolls is lower than that temperature. The preferred temperature control range just before the head box or nozzle tip is a temperature 20 to 80°C higher than the liquidus temperature of the aluminum alloy material. This temperature range is a casting temperature range in which twin-roll casting can be performed stably.

[0021] Furthermore, the preferred range for the roll diameter D is from 100 mm to 1500 mm. If the roll diameter D is small, the cooling capacity of the sheet material is insufficient, and the sheet material cannot be completely solidified, which is likely to cause problems such as molten metal leakage. Furthermore, if the roll diameter D exceeds 1500 mm, the equipment becomes too large and is not practical. The more preferred range for the roll diameter D is the range of 500 mm to 1300 mm, which is widely used industrially.

[0022] The desirable range for the roll peripheral speed v is between 300 mm / min and 700 mm / min. If the roll peripheral speed v exceeds 700 mm / min, the time for solidification of the molten metal by the roll becomes shorter, the thickness of the solidified shell growing from the roll becomes thinner, and in extreme cases, it may even lead to leakage of the molten metal (molten metal). Furthermore, if the roll peripheral speed v is below 300 mm / min, the thickness of the solidified shell growing from the roll becomes thicker, resulting in significant deformation resistance from the roll and a significant increase in equipment load. Furthermore, an excessively slow roll peripheral speed v may cause solidification to occur from inside the nozzle, as the molten metal does not flow smoothly.

[0023] The preferred range of the plate thickness t is 3 mm to 12 mm. If the plate thickness is less than 3 mm, it is difficult to cast the plate stably, and problems such as molten metal leakage and plate breakage are likely to occur. If the plate thickness t exceeds 12 mm, the deformation resistance of the twin rolls becomes significant, significantly increasing the load on the equipment. [Effects of the Invention]

[0024] As described above, the present invention can provide a method for producing an aluminum alloy material with reduced centerline segregation. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram of the numerical analysis of the present invention. [Figure 2] FIG. 2 is a diagram showing the relationship between the roll diameter, the peripheral speed, and the distance between the liquidus temperature position and the solidus temperature position in the present invention. [Figure 3] FIG. 3 is a schematic diagram of the twin-roll continuous casting method of the present invention. [Figure 4a] FIG. 4a is a photograph of the cross-sectional structure of a plate material in an example of the present invention. [Figure 4b] FIG. 4b is a photograph of the cross-sectional structure of a plate material in a comparative example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The essential elements of the aluminum alloy according to the present invention will be described below. The aluminum alloy material exemplified here is an aluminum alloy material that can be thermally bonded to another member in a single layer without using a joining member such as a brazing filler metal or a filler metal, as a liquid phase exudes from the material itself and supplies the liquid phase necessary for joining. Si is an element that generates an Al-Si liquid phase and contributes to bonding. However, if the Si content is less than 2.0 mass%, a sufficient amount of liquid phase cannot be generated, resulting in little liquid phase seepage and incomplete bonding. On the other hand, if the Si content exceeds 3.0 mass%, the amount of liquid phase generated in the aluminum alloy material increases, resulting in a significant decrease in material strength during heating and making it difficult to maintain the shape of the structure. Therefore, the Si content is specified to be 2.0 to 3.0 mass%. Note that the amount of seeping liquid phase increases with increasing volume and heating temperature. Therefore, it is desirable to adjust the amount of Si content and bonding heating temperature required depending on the structure of the structure to be manufactured.

[0027] Fe not only improves strength by dissolving in the matrix to a certain extent, but also disperses as crystallized or precipitated particles, preventing strength degradation, especially at high temperatures. Fe addition of less than 0.01% by mass not only reduces the aforementioned effect, but also requires the use of high-purity metal, increasing costs. Furthermore, Fe addition of more than 0.50% by mass generates coarse intermetallic compounds during casting, resulting in manufacturability problems. Furthermore, corrosion resistance deteriorates when the joined body is exposed to a corrosive environment (especially one where liquids flow). Furthermore, heating during joining refines recrystallized grains, increasing grain boundary density and resulting in significant dimensional change before and after joining. Therefore, the Fe addition amount is set to 0.01 to 0.50% by mass.

[0028] Mn is an important additive element that, together with Si and Fe, forms Al-Mn-Si, Al-Mn-Fe-Si, and Al-Mn-Fe intermetallic compounds, acting as dispersion strengthening, or dissolving in the aluminum matrix to improve strength through solid solution strengthening. If the Mn content exceeds 1.5 mass%, coarse intermetallic compounds are likely to form, reducing corrosion resistance. On the other hand, if the Mn content is less than 0.8 mass%, the above effects become insufficient. Therefore, the Mn content is set to 0.8 to 1.5 mass% or less.

[0029] As described above, the aluminum alloy material produced by the production method according to the present invention contains predetermined amounts of Si, Fe, and Mn as essential elements to improve resistance to deformation during heating for joining, and may further contain predetermined amounts of one or more elements selected from Zn, Cu, Zr, and Ti as selective additional elements to further improve strength.

[0030] The addition of Zn is effective in improving corrosion resistance through its sacrificial corrosion protection effect. Zn is dissolved almost uniformly in the matrix, but when a liquid phase is formed, it dissolves into the liquid phase and concentrates the Zn in the liquid phase. When the liquid phase seeps out to the surface, the Zn concentration in the seeped area increases, improving corrosion resistance through the sacrificial anode effect. Furthermore, when the aluminum alloy material of the present invention is applied to a heat exchanger, using the aluminum alloy material of the present invention for the fins can also provide sacrificial corrosion protection to protect tubes and the like from corrosion. If the Zn addition amount exceeds 2.0 mass%, the corrosion rate increases and the self-corrosion resistance decreases. Therefore, the Zn addition amount is set to 2.0 mass% or less.

[0031] Cu is an additive element that dissolves in the matrix to improve strength. If the Cu content exceeds 0.50 mass%, corrosion resistance decreases. On the other hand, if the Cu content is less than 0.05 mass%, the above effect becomes insufficient. Therefore, the Cu content is set to 0.05 to 0.50 mass%.

[0032] Zr precipitates as an Al-Zr intermetallic compound and exerts the effect of improving the strength after joining by dispersion strengthening. Furthermore, the Al-Zr intermetallic compound acts to coarsen the crystal grains during heating. If the amount added exceeds 0.30 mass%, coarse intermetallic compounds are likely to form, which reduces the plastic workability. Therefore, the amount of Zr added is set to 0.30 mass% or less. The preferred amount of Zr added is 0.05 to 0.30 mass%.

[0033] Ti not only improves strength by dissolving in the matrix, but also has the effect of preventing corrosion from progressing in the thickness direction by distributing in layers. If the amount of Ti added exceeds 0.30 mass%, coarse crystals will form, impairing formability and corrosion resistance. Therefore, the amount of Ti added is set to 0.30 mass% or less. The preferred amount of Ti added is 0.01 to 0.30 mass%.

[0034] In the aluminum alloy material according to the present invention, in order to improve the liquid phase characteristics and thereby further improve the joinability, one or more selectively added elements selected from Mg, Ni, Cr, V, Sr, Bi, Na, and Ca may be further added in a predetermined amount as a selectively added element in addition to at least one of the essential elements and the selectively added elements.

[0035] As such elements, one or more of the following may be added as needed: Mg: 0.3% or less, Ni: 0.3% or less, Cr: 0.3% or less, V: 0.3% or less, Sr: 0.1% or less, Bi: 0.3% or less, Na: 0.1% or less, and Ca: 0.05% or less. These trace elements can improve bondability by finely dispersing Si particles and improving the fluidity of the liquid phase. If the amount of these trace elements is less than the preferred range, the effects of finely dispersing Si particles and improving the fluidity of the liquid phase may be insufficient. Furthermore, if the amount of these trace elements exceeds the preferred range, adverse effects such as a decrease in corrosion resistance may occur.

[0036] An embodiment of the present invention will be described below with reference to Fig. 3. The twin-roll continuous casting machine of this embodiment includes a pair of water-cooled twin rolls 5a, 5b arranged above and below each other with a predetermined roll gap 6 between them, and a trough 8 for holding the molten aluminum alloy 1. A nozzle tip 4 for receiving the molten aluminum alloy 1 supplied from the trough 8 is provided at one end of the trough 8, and twin rolls (top roll 5a and bottom roll 5b) arranged above and below the tip of the nozzle tip 4 are in sliding contact with each other and rotating at a peripheral speed v (mm / min). The roll diameters of the top roll 5a and the bottom roll 5b are D (mm).

[0037] Next, a method for manufacturing an aluminum alloy sheet according to an embodiment of the present invention will be described. Molten aluminum alloy 1 containing 2.00 to 3.00 mass% Si, 0.01 to 0.50 mass% Fe, 0.80 to 1.50 mass% Mn, and one or more elements selected from 0.5 to 2.0 mass% Zn, 0.05 to 0.50 mass% Cu, 0.05 to 0.30 mass% Zr, and 0.01 to 0.30 mass% Ti, with the balance being Al and unavoidable impurities, is placed in a trough 8. The molten aluminum alloy 1 placed in the trough 8 is fed through a nozzle tip 4 between twin rolls 5a and 5b rotating at a peripheral speed v (mm / min). The temperature of the molten aluminum alloy needs to be controlled to be 20 to 80°C higher than the liquidus temperature of the aluminum alloy. The molten aluminum alloy material 1 begins to solidify upon contact with the water-cooled twin rolls 5a, 5b, and ultimately becomes an aluminum alloy material with a thickness t (mm). The thickness is cast to a range of 3 to 12 mm. However, in the roll continuous casting of the present invention, the relationship between the roll diameter D (mm) and the roll peripheral speed v (mm / min) during casting is set to satisfy the condition of formula (1). [Example]

[0038] Examples of the present invention and comparative examples will be described below. Note that the following examples are intended to illustrate the effects of the present invention, and the processes and conditions described in the examples do not limit the technical scope of the present invention.

[0039] An aluminum alloy material containing 2.46% by mass of Si, 0.196% by mass of Fe, 1.21% by mass of Mn, and further containing 1.483% by mass of Zn and 0.024% by mass of Cu was produced to a plate thickness of 6 to 7 mm by twin-roll continuous casting as shown in the above-mentioned embodiment. Table 2 shows an overview of the examples and comparative examples. In addition to the casting conditions, Table 2 also shows the L value obtained by numerical analysis, and also shows the results of cross-sectional structural observation of the actual cast plate material to determine whether centerline segregation was present.

[0040] [Table 2]

[0041] In Example (No. 1), casting was performed at a casting temperature of 660°C, a roll diameter of 485 mm, and a roll peripheral speed of 500 mm / min, and no centerline segregation was observed. In this case, the distance L obtained by numerical analysis was 15.63 mm. Example (No. 2), which only changed the casting temperature from Example (No. 1), also showed similar results.

[0042] In Comparative Example (No. 5), casting was performed at a casting temperature of 660°C, a roll diameter of 485 mm, and a roll peripheral speed of 640 mm / min, resulting in significant centerline segregation. Similar results were observed in Comparative Example (No. 6), which was obtained by changing only the casting temperature from Comparative Example (No. 5).

[0043] Figures 4a and 4b are photographs of the cross-sectional structure of an example (No. 1) and a comparative example (No. 5). The horizontal direction of the paper in Figures 4a and 4b corresponds to the casting direction, and the vertical direction of the paper corresponds to the plate thickness direction. No centerline segregation was observed in the example (No. 1) in Figure 4a, but significant centerline segregation was observed in the comparative example (No. 5) in Figure 4b.

[0044] Table 2 shows calculation examples of the distance L when aluminum alloy materials having the same chemical composition as those in the examples and comparative examples are cast under various casting conditions. The casting conditions in calculation examples (Nos. 7 to 10) are such that the distance L is 20 mm or less, and therefore it is believed that centerline segregation can be reduced. On the other hand, the casting conditions in calculation examples (Nos. 11 to 19) are such that the distance L is greater than 20 mm, and therefore it is believed that centerline segregation becomes significant. [Explanation of symbols]

[0045] 1...Molten aluminum alloy 2...Liquidus temperature position of aluminum alloy 3...Solidus temperature position of aluminum alloy 4...Nozzle tip 5...Twin rolls (5a: upper roll, 5b: lower roll) 6...Roll gap 7...Aluminum alloy plate material 8...Gutter L: Distance between the liquidus temperature position and solidus temperature position at the center of the plate thickness (mm) D...Roll diameter (mm) v...Roll peripheral speed (mm / min) t…Plate thickness (mm)

Claims

1. A method for producing an aluminum alloy material having a thermal bonding function in a single layer, the aluminum alloy material containing 2.00 to 3.00 mass% of Si, 0.01 to 0.50 mass% of Fe, and 0.80 to 1.50 mass% of Mn, The method includes a casting step of performing twin-roll continuous casting to form a plate material having a thickness of 3 to 12 mm by rotating a roll having a diameter D (mm) that satisfies the following formula (C1) at a peripheral speed v (mm / min), A method for manufacturing aluminum alloy materials. 0.057*v+0.0016*D≦33.54...(C1)

2. The temperature of the molten metal during casting is set to be 20 to 80°C higher than the liquidus temperature. The method for producing the aluminum alloy material according to claim 1.

3. The diameter D and the peripheral speed v satisfy the following formula (C2): The method for producing an aluminum alloy material according to claim 1 or 2. 0.057*v+0.0016*D≦29.54...(C2)

4. The aluminum alloy material essentially contains 2.00 to 3.00 mass% Si, 0.01 to 0.50 mass% Fe, and 0.80 to 1.50 mass% Mn, and selectively contains at least one of 0.50 to 2.00 mass% Zn, 0.05 to 0.50 mass% Cu, 0.05 to 0.30 mass% Zr, and 0.01 to 0.30 mass% Ti, with the balance being Al and unavoidable impurities. The method for producing an aluminum alloy material according to any one of claims 1 to 3.

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