JPH0259204B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing an Al-Mg-Si aluminum alloy ingot for extrusion, which has a casting structure with excellent homogenization processability. [Conventional technology] Conventionally, Al-Mg-Si represented by 61S and 63S
When obtaining an extruded material from a series alloy, an ingot for extrusion is made from the molten alloy by a continuous casting method or a semi-continuous casting method, and then the polarized components generated during casting are homogenized as a solid solution, and By causing the phase transformation (transformation from β crystal to α crystal) of the iron-based crystals existing between the dendritic structures (dendrites) in the casting structure of the ingot and the spheroidization of the crystals, the ingot is For example, in the case of 61S and 63S alloy materials, the ingot is heated to a temperature around 550℃ for several hours in order to improve the extrusion processability of the product and the mechanical properties and surface treatment properties of the extruded product obtained. The so-called homogenization treatment of heating and holding is performed, and then this ingot is preheated to the extrusion temperature during extrusion processing, extrusion processing is performed, and the extruded material is further heat treated at 160 to 200°C for several hours as an aging treatment. ing. [Problems to be Solved by the Invention] Figure 1a is a conceptual diagram showing the thermal history of the alloy material in the conventional process when extruding 61S or 63S alloy ingots as described above. As is clear, in the conventional process, it is necessary to perform two heat treatments, homogenization treatment and preheating operation, before extrusion processing, and in the homogenization treatment, the temperature is heated to a high temperature of 540 to 580℃ for several hours. It was necessary to maintain heating for a long period of time, and a large amount of thermal energy was required. In addition, this type of Al-Mg-Si aluminum alloy extruded material is often used for construction materials, vehicles, etc., and in this case, the surface of the extruded material is A colored film is often formed by anodizing, but in this case, among the iron-based crystals that crystallize in the cast structure of the alloy ingot, β-crystals (β-AlFeSi) are When present in large quantities,
The colored anodic oxide film formed on the extruded product often has a non-uniform color tone, so it is necessary to convert it into α-crystal (α-AlFeSi). During the homogenization process, the ingot is heated and held at a high temperature for a long time (for example, heated to 580℃ for 2 hours).
If the cooling rate to room temperature after homogenization treatment is inappropriate, some of the solid solution components will re-precipitate, and this will cause the preheating treatment during extrusion processing to occur. However, the problem could not be resolved satisfactorily even if the problem was solved by the above methods, so there was a risk of deterioration of the quality characteristics of the extruded material. The present invention solves the above-mentioned problems when producing Al-Mg-Si aluminum alloy extruded materials, has excellent homogenization processability, and can always stably produce high-performance extruded materials through extrusion processing. The object of the present invention is to provide a method for producing an ingot for extrusion that can be obtained. [Means for Solving the Problems] That is, the present invention was made as a result of studies to achieve the above object, and contains 0.2 to 1.5% by weight of magnesium, 0.1 to 0.8% by weight of silicon, and 0.05 to 0.05% of iron as essential components.
1.0% by weight and contains up to 0.5% by weight each of copper, manganese and chromium as impurities, or in addition to the above elements further 0.001-0.20% by weight of Ti and
B0.0001 to 0.04% by weight, and the silicon content (X) weight% and the iron content (Y) weight% are the second
A continuous or semi-continuous casting method is applied to the molten aluminum alloy, which is located within the region connecting coordinates A, A, C, and E on the X-Y diagram shown in the figure, and consists of the remainder aluminum and other unavoidable impurities, By performing casting while cooling at a cooling rate of 28°C/sec or more, the proportion of α-AlFeSi crystals (hereinafter referred to as α ratio) among the iron-based crystals contained in the cast structure of the ingot can be reduced to 70%. %, a suspended crystal volume fraction of less than 20%, and a dendrite arm spacing of less than 25 μm. This paper proposes a method. [Function] The details of the present invention and its function will be explained below. In alloy ingots obtained by casting molten Al-Mg-Si aluminum alloys such as 61S and 63S, it usually exists unavoidably in the raw aluminum base metal.
Or, iron added to improve the surface quality of extruded materials and silicon in the alloy components combine to form α-
AlFeSi crystal (α crystal), β-AlFeSi crystal (β crystal),
Various forms of iron-based crystallized substances such as Al ₃ Fe and Al ₆ Fe crystallize in the ingot structure as intermetallic compounds, but among these, β-crystalline substances inhibit extrusion processability and are difficult to extrude. It is known that it deteriorates the surface treatment properties of materials. However, once β crystals are precipitated in the ingot during casting from a molten alloy, heat treatment at high temperatures and for a long period of time is required to transform the crystals and turn them into α crystals, as described above. . However, according to the inventors' investigation, the majority of the iron-based crystallized substances formed in the ingot obtained by casting the alloy, especially more than 70%, is α-crystallized. Furthermore, the suspended crystal volume percentage in the casting structure of the ingot is less than 20% and the dendrite arm spacing is
Ingots obtained by casting with an alloy composition and casting conditions that result in a thickness of less than 25 μm have good homogenization properties and the structure can be easily homogenized, so it can be easily processed by short heat treatment. It was found that extrudability was good, and extruded materials with excellent quality characteristics could be stably obtained with good reproducibility after extrusion. Furthermore, according to the research conducted by the inventors, it was found that an ingot with a high alpha ratio can be easily obtained when iron and silicon are contained in the alloy in a ratio that establishes a specific interrelationship. . Fig. 2 is a diagram showing the content ranges of iron and silicon such that an ingot with a high alpha rate can be easily obtained according to the present invention, with the horizontal axis representing the amount of silicon and the vertical axis representing the amount of iron. It is something. If an alloy containing iron and silicon is used within the shaded area surrounded by coordinates A, B, C, and D in Figure 2, there is a fairly high probability that it will form in the ingot. It is possible to make iron-based crystals into alpha crystals, but it is more certain that the volume fraction of suspended crystals in the ingot is 20
By casting the ingot under casting conditions such that the α-crystallization is less than %, α-crystallization can be promoted with good reproducibility. In the present invention, as described above, in addition to setting the alpha ratio of iron-based compounds in the cast structure of the ingot to more than 70% and keeping the suspended crystal volume percentage to less than 20%, the dendrite arm stratum in the cast structure is Another requirement is that the pacing be less than 25 μm, which requires the cooling rate of the molten alloy to be 28°C/sec or more, preferably 30°C/sec or more when casting the molten alloy. There is. Furthermore, if a molten alloy having the alloy composition of the present invention is cast under such cooling conditions, the number of floating crystals will be drastically reduced, and the volume fraction occupying the ingot will be an extremely small value of less than 20%. It was found that this also had a favorable effect on the alpha crystallization of iron-based compounds formed in the ingot structure. In this way, by setting the dendrite arm spacing in the cast structure of the ingot to less than 25 μm, crystallization occurs at the boundaries of dendrite cells.
Particles of eutectic compounds such as Mg ₂ Si and iron-based crystallized substances become fine, making their diffusion and phase change easier, making it possible to sufficiently homogenize the ingot structure with short heating times. It is thought that α-crystalization of β-crystals will also become easier. In the present invention, it is recommended to use continuous or semi-continuous casting as the casting method. In the present invention, the α ratio of the ingot is determined as follows. That is, appropriate samples are taken from the ingot and analyzed with an X-ray microanalyzer to determine the iron crystallization,
When silicon is simultaneously analyzed and the ratio of the X-ray counts of both elements is taken, the Fe/Si ratio is 5 or more in the case of α crystal, and 3 or less in the case of β crystal. Therefore α
The rate is determined by using the method described above to determine a certain number (generally about 50) of iron-based crystals that intersect when the sample is moved in a certain direction, and which are identified as α-crystals. Calculate and judge by counting the number of crystallized substances and expressing this as a percentage. In addition, dendrite arm spacing is generally determined using a method known as the cutting method.
It is calculated by measuring the number of dendrites in an arbitrary area of the ingot using an optical microscope and an image analysis device, and dividing the observed length by the number. As for the determination of the suspended crystal volume fraction, an arbitrary cross-sectional sample of the ingot was etched with an etching agent such as caustic soda as described above, and the area from the ingot surface to the radial center axis was divided into four areas at equal intervals, and the sample was examined using a stereoscopic microscope ( Observe the area ratio of floating crystals in each region over two or more fields of view using a magnification of 10x), and measure the average area ratio of floating crystals in each region from the surface side.
When F ₁ , F ₂ , F ₃ and F ₄ are used, the suspended crystal volume fraction can be determined using the following approximate formula. F=7F ₁ +5F ₂ +3F ₃ +F ₄ /16 The composition range of the Al-Si-Mg alloy of the present invention was determined for the following reason. That is, 0.2-1.5% by weight of magnesium and 0.1-0.8% by weight of silicon are such age-hardening Al-Mg
- This indicates the range normally included in Si-based alloys; below the lower limits of both elements, the effect of improving the strength of the alloy through age hardening is poor, and above the upper limits, the extrudability deteriorates, which is not preferable. The amount of iron content in the alloy is related to the silicon content and has an important influence on the alpha ratio of iron-based compounds that occur in the ingot structure, which is the gist of the present invention.
Within the range of silicon content and iron content of 0.05 to 1.0% by weight as described above, and when the silicon and iron contents are respectively (X) weight% and (Y) weight%,
Each coordinate on the X-Y diagram as shown in Figure 2, A...(0.1, 0.05) I...(0.1, 1.0) U...(0.8, 1.0) E...(0.4, 0.05) Within the area surrounded by When the temperature is within this range, α-crystals are likely to be formed, and by casting the molten alloy under the specific casting conditions shown in the present invention within this range, the iron-based crystals in the ingot can be removed. The α rate can be further increased. Iron contained in the alloy has the effect of improving the mechanical strength of the alloy, but when its content is less than the lower limit of the above range, the effect of improving the strength of the alloy is insufficient, Moreover, if the upper limit is exceeded, the amount of iron-containing compounds formed in the alloy becomes excessive, which significantly reduces the workability of the alloy, which is not preferable. When casting the alloy, 0.001 to 0.20% by weight of titanium and boron are added, which are the usual addition amounts of titanium and boron, which are often added as necessary grain refiners in this type of Al-Mg-Si alloy.
Addition of both in the range of 0.0001 to 0.04% by weight not only does not interfere with the effects of the present invention, but also has a positive effect on optimizing the suspended crystal volume ratio, adjusting the α ratio, and dendrite arm spacing. This is preferable because it has the effect of If the amounts of titanium and boron added are each less than the lower limit of the above-mentioned range, a sufficient crystal refining effect cannot be obtained during alloy casting, and if it exceeds the upper limit, no further crystal refining effect can be obtained. In addition, coarse crystals of TiB ₂ tend to form in the alloy, which may cause surface defects such as laser streaks in the extruded material, which are both undesirable. In addition, the effects of the present invention cannot be achieved by containing up to 0.5% by weight of copper, manganese, and chromium, which have traditionally been added for purposes of improving alloy strength or mixed as impurities in this type of Al-Mg-Si alloy. There is no problem as it will not interfere in any way. In the Al-Mg-Si alloy ingot obtained by the present invention, most of the iron-based crystallized substances present in the ingot structure are α-crystallized, and micro-segregation is finely dispersed. Since it has excellent homogenization properties due to However, since the ingot is sufficiently homogenized, the resulting extruded material product has better mechanical properties, surface quality, etc. than conventional products. Furthermore, since the ingot according to the present invention has excellent homogenization properties as described above, when performing the extrusion process, the heat treatment step shown in FIG. Immediately before starting the extrusion operation, the ingot is heated and held at 580 to 640°C for no more than 10 minutes to undergo a high-temperature, short-time heat treatment, and immediately after the holding is completed, it is usually carried out for this type of alloy. An extruded material of excellent quality can also be obtained by performing extrusion processing by cooling to a temperature range of 300 to 500°C, which is the extrusion rate. By adopting such a shortened process, it is possible not only to improve productivity and reduce energy consumption compared to the conventional extrusion manufacturing process, but also to keep the ingot after homogenization treatment at room temperature. Since some of the alloy solute components do not re-precipitate due to cooling to a certain temperature, it can also contribute to improving the quality of the extruded material. FIG. 1b is a conceptual diagram showing such an extrusion process. If this is compared with the conventional extrusion process shown in FIG. 1a, it will be obvious how the shortened extrusion process using the ingot of the present invention contributes to improved productivity and energy savings. When such a shortened process is adopted, the ingot homogenization temperature immediately before the start of the extrusion operation is
If the temperature is lower than 580℃, the diffusion rate of solute components in the ingot matrix decreases, so the retention time required to achieve the homogenization effect increases rapidly, and the effects of improving productivity and reducing energy consumption become less noticeable. Furthermore, if the heat treatment temperature exceeds 640°C, it is not preferable because it causes local melting of the low melting point phase in the ingot structure and deteriorates the quality of the extruded product. In addition, the heating retention time is 10
A holding time of about 1 to 2 minutes is sufficient, especially when the upper limit temperature is around 640°C. Obtaining a sufficient homogenizing effect with such a short holding time can be achieved for the first time by using the ingot obtained by the present invention, and it is possible to achieve a sufficient homogenization effect for the first time by using the ingot obtained by the present invention. This cannot be achieved using ingots. The purpose of rapidly cooling an ingot that has been heated to a high temperature to the extrusion temperature is to prevent the eluted components from re-precipitating as much as possible.To do this, the ingot surface should be cooled at a cooling rate of 20℃/second or more. It is better. In addition to the direct extrusion method, indirect extrusion method and other known extrusion methods are adopted for extrusion using the ingot according to the present invention. It is no different from that in alloys. Further, the extruded material thus obtained is then cooled in accordance with a conventional method, subjected to age hardening treatment under desired conditions depending on the use, and subjected to anodization treatment etc. before being used. [Example] Next, an example of the present invention will be described. Example 1 Alloy composition: Mg0.52% by weight, Si0.40% by weight,
Fe0.22wt%, Cu0.01wt%, Mn0.03wt%,
For comparison, the alloy composition contains 0.001% by weight of Cr, 0.004% by weight of Ti, and 0.001% by weight of B, with the balance consisting of aluminum and other unavoidable impurities (alloy of the present invention). .48% by weight,
Fe0.18% by weight, Cu0.01% by weight, Mn0.007% by weight,
An alloy containing 0.001% by weight of Cr, 0.004% by weight of Ti, and 0.002% by weight of B, with the balance consisting of aluminum and other unavoidable impurities (comparative alloy: the correlation between the iron and silicon contents is shown in Figure 2) The same semi-continuous casting equipment was used for casting (outside the range of the present invention as shown by the mark), and casting conditions (casting conditions of the present invention): Molten metal temperature: 720°C Casting speed: 75 mm/min Cooling rate: 30°C/sec Casting conditions (comparative casting conditions): A cylindrical ingot with a diameter of 203 mmφ and a length of 1200 mm was cast under two casting conditions: molten metal temperature: 700°C, casting speed: 100 mm/min, cooling rate: 25°C/sec.
Two billets with a length of 500 mm were collected. X-ray microanalyzer sample from one billet,
Samples for dendrite arm spacing and suspended crystal volume fraction were taken, and each sample was measured using the measurement method described above. The results are shown in Table 1. The other billet was heated to 560°C at a heating rate of 100°C/hour in a homogenizing furnace, maintained at this temperature for two homogenization times of 30 minutes and 2 hours, and then taken out of the furnace. After that, it was cooled to room temperature by fan cooling (cooling rate 200°C/hour), then reheated to 480°C by an electromagnetic induction billet heater, held for 5 minutes, and immediately extruded. I did this. For extrusion, a 1,500-ton hydraulic direct extruder was used to extrude a sash shape with a wall thickness of 3 mm at an extrusion speed of 30 m/min, and after leaving it at room temperature for 3 days,
Aging treatment was performed at 200°C for 2 hours. Table 2 shows the results of measuring the mechanical properties and reflectance of the extruded material obtained, as well as the observation results of the surface appearance after anodizing treatment. Note that a conventional sulfuric acid alumite method was applied to the anodizing treatment of the extruded material. From the results in Tables 1 and 2, the alloys of the present invention were used and the casting conditions of the present invention were used.
The Al-Mg-Si alloy ingot (execution number-1) is
The α rate is as high as 100%, the dendrite arm spacing is 20 μm, and the floating crystal volume rate is 3%.
All of these values satisfy the conditions of the present invention,
In extruded materials obtained from such ingots,
Even when homogenized for an extremely short time of 30 minutes, there is almost no difference in mechanical properties, surface reflectance, and anodizing properties compared to those treated for a long time of 2 hours. On the other hand, an alloy having the composition according to the present invention is obtained under casting conditions that do not conform to the casting conditions of the present invention (Example No.-2) and an alloy according to the present invention with quality characteristics. Extruded material obtained from an ingot obtained from an alloy with a composition deviating from the composition (extrusion number -
3 and -4) are inferior in mechanical properties and anodizing properties, and are made of ingots obtained under conditions that deviate from the present invention, especially in terms of alloy composition and casting conditions (Example No.-4). In this case, the strength, surface reflectance, and anodizing properties of the extruded material obtained by the present invention are significantly superior even when homogenizing for a long time as well as for a short time. death

[Table] Note: Floating crystal volume percentage is expressed as %

[Table] Note: ◎ - Excellent ○ - Average △ - Poor
× - It can be seen that it is poor and inferior. Furthermore, these facts clearly demonstrate that the ingot obtained by the present invention has excellent homogenization processability. Example 2 Alloy composition: Mg 0.52% by weight, Si 0.38% by weight
and Al-Mg containing 0.20% by weight of Fe, 0.05% by weight of Cu, 0.05% by weight of Mn and 0.001% by weight of Cr, with the balance consisting of aluminum and other inevitable impurities.
- Using the same semi-continuous casting equipment as in Example 1, the molten Si-based alloy was cast to a diameter of 200 mm and a length of 200 mm under the following casting conditions.
It was cast into a 1200mm cylindrical ingot. Casting conditions: Molten metal temperature 710℃ Casting speed 80mm/min Cooling rate 28℃/sec A part of the obtained ingot was cut out and the alpha ratio of iron-based compounds in the ingot structure, dendrite arm spacing, and floating crystals were measured. When the volume fraction was measured, α
The ratio was 100%, the dendrite arm spacing was 20 μm, and the suspended crystal volume ratio was 5%, all of which satisfied the conditions of the present invention. Next, from this ingot, two pieces of the same size as in Example 1 were
The book billets were cut, and one of them was subjected to normal homogenization treatment conditions as shown in FIG. 1a in a homogenization furnace similar to that used in Example 1.
That is, the temperature was raised to 560°C at a heating rate of 100°C/hour, held at that temperature for 2 hours, cooled to room temperature by fan cooling, and left for 7 days. The mixture was reheated to 450° C. using the same billet heater as the one used in the heating process, held at the same temperature for 3 minutes, and then extruded. The other one was shortened as shown in Figure 1b, that is, the billet was immediately heated from room temperature to 600°C using a billet heater without being heated and held in the homogenizing furnace, and then the billet was heated at the same temperature. So 5
After holding for 5 minutes, the fan cools down for 5 minutes.
Extrusion was performed after cooling to 480°C. In both cases, the same extruder as in Example 1 was used, and the same sash material as in Example 1 was extruded at an extrusion speed of 40 m/min, and then cooled to room temperature by fan cooling, and then kept at room temperature for 5 days. It was left to stand and then aged at 200°C for 2 hours. Table 3 shows the results of measuring the mechanical properties and inspecting the surface appearance of these molds after anodizing.

[Table] Note: ◎ Excellent ○ Fair From the results in Table 3, the extruded material obtained by subjecting the billet obtained from the ingot according to the present invention to the usual homogenization treatment has considerable mechanical properties, Furthermore, although the anodic oxidation properties are good, it is clear that when this is further subjected to a short heat treatment, an extruded material with further improved mechanical properties and anodic oxidation properties can be obtained. Furthermore, from this fact, an ingot with a high α ratio, a dendrite arm spacing of less than 25 μm, and a suspended crystal volume fraction of less than 20% obtained by the production method of the present invention cannot be produced by the conventional production method. It is also well understood that the homogenization processability is far superior to that of the obtained ingot. [Effects of the Invention] As described above, the Al-Mg-Si alloy ingot for extrusion obtained by the production method of the present invention has excellent homogenization processing properties, so it cannot be processed under normal homogenization processing conditions. Of course, it is possible to sufficiently homogenize the ingot structure even if the heating holding time during homogenization treatment is significantly shortened; This not only makes it possible to significantly contribute to energy savings and productivity improvement, but also improves the mechanical properties of extruded products obtained by extruding the obtained ingot. properties and surface conditions,
It can be said to be an industrially effective invention, as it has excellent anodic oxidation properties.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the thermal history in the extrusion process, in which a shows the conventional method and b shows the shortened heat treatment using the ingot of the present invention. Figure 2 shows the Al-Mg-Si alloy of the present invention.
It is a drawing showing the appropriate content range of Fe and Si.

Claims (1)

[Claims] 1. Magnesium 0.2-1.5% by weight, silicon 0.1-0.8%
% by weight and 0.05-1.0% by weight of iron, further containing up to 0.5% by weight each of copper, manganese and chromium as impurities, and silicon content (X) % by weight
and the iron content (Y) weight% are within the area connecting the coordinates A, I, U, and E shown below on the X-Y diagram,
By casting a molten aluminum alloy containing the balance aluminum and other unavoidable impurities using a continuous or semi-continuous casting method while cooling at a cooling rate of 28°C/sec or more, the iron contained in the cast structure is removed. α exceeds 70% of the system crystallized matter.
-AlFeSi crystal, and the floating crystal volume fraction is less than 20%,
Al for extrusion characterized by obtaining an ingot with a dendrite arm spacing of less than 25 μm
-Production method of Mg-Si aluminum alloy ingot. Each coordinate is: A...(0.1, 0.05) B...(0.1, 1.0) C...(0.8, 1.0) E...(0.4, 0.05) 2 Magnesium 0.2-1.5% by weight, Silicon 0.1-0.8
wt%, iron 0.05-1.0 wt%, titanium 0.001-0.20
% by weight and 0.001 to 0.04% by weight of boron, and further contains up to 0.5% by weight of each of copper, manganese and chromium as impurities, and the silicon content (X) by weight and the iron content (Y) by weight are X. - Located within the area connecting coordinates A, A, U, and E shown below on the Y diagram, molten aluminum alloy consisting of the remainder aluminum and other unavoidable impurities is cast at 28℃ using continuous or semi-continuous casting method. By casting while cooling at a cooling rate of 1/sec or more, more than 70% of the iron-based crystallized substances contained in the cast structure are converted to α-AlFeSi crystals, and the suspended crystal volume fraction is reduced to 20%. %
less than the dendrite arm spacing
A method for producing an Al-Mg-Si aluminum alloy ingot for extrusion, characterized by obtaining an ingot with a thickness of less than 25 μm. Each coordinate is A...(0.1, 0.05) B...(0.1, 1.0) U...(0.8, 1.0) E...(0.4, 0.05)