JP2006037148A - Aluminum alloy hard sheet for can barrel and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an aluminum alloy hard sheet having an excellent balance of strength, ironing workability, flange formability and an earing ratio as the material for a can barrel by a low cost process in which process annealing after hot rolling is obviated. <P>SOLUTION: The Al alloy hard sheet is composed of an Al-Mg-Mn based alloy, and in which n value is 0.01 to 0.2, and the rate of success in severe ironing is ≥70%. The hot rolled sheet as an intermediate product thereof has an electric conductivity of 30 to 50%, a crystal grain size (ASTM) of ≥4.0 and a cube orientation density of 5 to 10. Regarding its production method. hot rolling conditions (a hot rolling starting temperature, a material temperature in each sheet thickness in the process, Ln(Z) value, a strain rate, a hot rolling finishing temperature and a cooling rate) are strictly prescribed, after the hot rolling, process annealing is not performed, and it is finished only by cold rolling. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hard plate of an Al-Mg-Mn-based aluminum alloy used for a can body for a two-piece aluminum can (generally a DI can body) or a can body of an aluminum bottle having resealability, and a method for producing the same, In particular, despite its high strength before and after paint baking, an aluminum alloy hard plate for a can body having excellent ironing workability before paint baking, flange formability after paint baking, and low deep-drawing ears, and its manufacturing method, and The present invention relates to a hot rolled sheet for an aluminum alloy hard plate for a can body.

  In general, the manufacturing process for two-piece aluminum cans (DI cans) is to form can bodies by deep-drawing and ironing the can body material, and then trimming to the specified dimensions and shape. Apply degreasing and cleaning, then paint and print, bake (baking), then neck and flange the can body edge, and wind it together with a separately formed can lid (Seaming processing) is usually performed.

  In addition, as aluminum bottle cans having resealability, there are so-called 1-piece bottle cans and 2-piece bottle cans, and the former and the latter have slightly different production methods. In the case of the above-described one-piece bottle can, the same process as the above-described two-piece aluminum can (DI can) is performed, and mouth molding (skirt molding, screw molding, curl molding) is performed instead of the final flange processing. On the other hand, in the case of the latter two-piece bottle can, deep-drawing and ironing / flange processing are performed on the material for the can body to form a can body with flange, then top dome molding (necking / drawing), can After performing bottom flange trimming, degreasing and cleaning, painting and printing, baking (baking), hole forming, skirt forming, screw forming, curl forming, and other can bottom flange processing It is usual to perform tightening.

  As a material for a can body of a two-piece can or a bottle can manufactured as described above, a JIS 3004 alloy hard plate made of an Al-Mg-Mn alloy has been widely used. This 3004 alloy is excellent in ironing workability, and it exhibits a relatively good formability even when subjected to cold rolling at a high rolling rate in order to increase the strength. Therefore, it is suitable as these can body materials. It is said that.

  In addition, as a manufacturing method of such a hard plate made of 3004 alloy, generally, after casting by a DC casting method or the like, the ingot is homogenized, and further, a predetermined plate is obtained by hot rolling and cold rolling. A method is generally used in which the thickness is increased and intermediate annealing is performed for recrystallization in the process before cold rolling after hot rolling or in the middle of cold rolling.

  By the way, it is strongly desired to reduce the thickness of an aluminum can body (a two-piece aluminum can and an aluminum bottle can) mainly from the viewpoint of reducing material costs. And when thinning in this way, it is important to increase the strength of the material in order to avoid problems such as a reduction in buckling strength of the can accompanying the thinning, especially in the case of bottle cans In addition to the can body, it is necessary to ensure the required strength not only in the can body but also in the shoulder and the neck of the can.

  Moreover, in order to ensure the high productivity at the time of manufacture of DI can containing a bottle can, in order to prevent the can running out at the time of ironing, it is necessary for ironing workability to be favorable.

  Furthermore, when flange processing is required like the can body of a two-piece can, in order to prevent the occurrence of flange cracking, excellent flange formability (expandability) is required.

  In addition, as a material for the DI can body, it is desired that the ear rate at the time of DI molding is stable and low. That is, the stable and low ear rate at the time of DI molding is important from the viewpoint of improving the yield at the time of DI molding and preventing can barrel breakage due to cutting off of the can barrel.

  Here, these strengths, ironing workability, flange formability, and ear rate are not necessarily good if any one is excellent, it is necessary that these balances are good and comprehensively excellent. Moreover, as a manufacturing method, it is important that the manufacturing cost is low in addition to the various requirements from the material characteristics as described above.

By the way, in the general manufacturing method of the conventional hard plate for 3004 alloy can body, as described above, intermediate annealing is performed for recrystallization before cold rolling after hot rolling or in the middle of cold rolling. It is normal. If the conventional main manufacturing processes are classified from the viewpoint of such intermediate annealing, they can be divided into the following processes (a) to (c).
(A) Hot rolling-batch annealing process This is a method of annealing using a box annealing furnace (batch annealing furnace; BAF) having a slow heating rate after normal hot rolling.
(B) Hot rolling-continuous annealing process This is a method of annealing using a continuous annealing furnace (CAL) having a high heating rate after normal hot rolling.
(C) Cold rolling intermediate continuous annealing process This is a method of annealing using a continuous annealing furnace having a high heating rate in the middle of cold rolling after normal hot rolling.

Further, in addition to the processes (a) to (c), there is a method (d) as follows.
(D) Self-recrystallization process This is a method in which the material is self-recrystallized (self-annealed) in the state after hot rolling by controlling the temperature at which hot rolling rises above the recrystallization temperature of the material.

  Among the processes (a) to (d) as described above, when the processes (a), (b), and (d) are applied, all of the obtained can body materials have ironing workability. There is a common problem of being inferior. Of these, in the process (d), if the ironing workability is to be improved, the material strength has to be lowered, which causes a problem of insufficient strength. Furthermore, when the process of (c) is applied, although ironing workability is excellent as a can body material, there is a problem that flange formability is inferior. In addition, in the processes (a), (b), and (c) that require annealing for recrystallization after hot rolling, there is a problem that the manufacturing cost is high.

  Here, as a prior art method that has already been proposed as a method for manufacturing a DI can body made of an Al-Mg-Mn alloy, for example, there are methods as shown in Patent Literature 1 to Patent Literature 9, Among them, the methods of Patent Literature 2 to Patent Literature 7 all require annealing after hot rolling or in the middle of cold rolling, and have problems in terms of cost as described above. In addition, in the case of the methods of Patent Document 1, Patent Document 8, and Patent Document 9, all of them are still insufficient in obtaining a material having a good balance of strength, ironing workability, flange formability, and ear ratio performance. .

Japanese Patent Laid-Open No. 10-310837 JP-A-11-256290 JP 11-256291 A Japanese Patent Laid-Open No. 11-256292 JP 2000-234158 A JP 2001-40461 A JP 2002-212691 A JP 2003-203105 A JP-A-11-140576

  The present invention has been made against the background described above, and is a material which can satisfy various properties desired as a DI can body material such as a two-piece aluminum can and an aluminum bottle can in a balanced manner, that is, having high strength and ironing at the same time. The purpose of this invention is to obtain an aluminum alloy hard plate for a can body at a low cost, which has a good balance and flange formability, a stable and low ear ratio, and a comprehensive balance of these characteristics. In particular, an object of the present invention is to provide a method for obtaining a high-quality can body material as described above in a process that does not require annealing after hot rolling.

  As a result of repeated various experiments and studies by the present inventors to solve the above-mentioned problems, the hot rolling conditions are strictly and appropriately controlled, and the hot rolled sheet performance is appropriately controlled. While omitting annealing for recrystallization after rolling, it was found that a high-quality DI can body material having an excellent balance of various performances as described above can be obtained, and the present invention has been made.

  That is, in this invention, it is premised on manufacturing by a process that does not perform intermediate annealing after hot rolling (intermediate annealing between hot rolling and cold rolling, or intermediate annealing in the middle of cold rolling). However, in such a process in which intermediate annealing is not performed after hot rolling, the performance of the hot rolled sheet immediately after the end of hot rolling greatly affects the performance of the final sheet (can body material). As a result of repeated experiments and examinations by the present inventors, the electrical conductivity, crystal size, texture (crystal orientation) of the hot-rolled sheet after hot rolling is completed, and further, the amount of Mg in the intermetallic compound is appropriately set. As a result, it was found that a material having an excellent balance of strength, ironing workability, flange formability, and ear ratio can be obtained as the final plate.

  In addition, in order to appropriately control the electrical conductivity, crystal size, texture, and amount of Mg in the intermetallic compound as described above, various conditions in the hot rolling process, particularly each stage of thickness reduction. It has been found that it is necessary to appropriately control the material temperature, the strain rate of each pass, and the Z value (Zener-Holomon Parameter) as an index of hot strain accumulation in each pass.

  In addition, by properly regulating not only the component composition but also the n value that is an index of work hardening performance and the success rate of severe ironing as the conditions of the final plate, a material that has an excellent balance of various performances as described above It was found that can be obtained.

  Specifically, the aluminum alloy hard plate for a can body of the invention of claim 1 has Mg 0.5-2.0%, Mn 0.5-2.0%, Fe 0.05-0.8%, Si 0.05 -0.8%, Cu 0.05-0.7% is contained, the balance is made of an aluminum alloy consisting of Al and inevitable impurities, and the work hardening index n value is in the range of 0.01-0.2. Moreover, the success rate of severe ironing is 70% or more.

  Moreover, the aluminum alloy hard plate for can bodies of the invention of claim 2 is the aluminum alloy hard plate for can bodies according to claim 1, further comprising Cr 0.05 to 0.5%, Zn 0. It contains one or more of 05 to 0.8% and Ti 0.001 to 0.20%.

Furthermore, in the method for producing an aluminum alloy hard plate for a can body according to the invention of claim 3, the aluminum alloy having the component composition defined in claim 1 or 2 is cast, and then homogenized in a temperature range of 500 ° C. or higher. And then hot rolling
(1) Hot rolling is started within a range of 300 to 550 ° C,
(2) controlling the material temperature in the range of 300 to 470 ° C. between a thickness of 150 mm and 20 mm in the hot rolling process;
(3) The material temperature from the thickness 20 mm in the hot rolling process to immediately before the final hot rolling pass is controlled within the range of 270 to 420 ° C.,
(4) Ln (Z) value (Note: Z indicates Zener-Holomon Parameter) in each pass having a thickness of 150 mm or less in the hot rolling process is controlled within a range of 20-50,
(5) The hot rolling end temperature is in the range of 270 to 350 ° C.,
(6) In the cooling process from a temperature in the range of 270 to 350 ° C. after the hot rolling up to a temperature range of 100 ° C. or less, the average cooling rate up to 100 ° C. is controlled to 100 ° C./hr or less,
The hot-rolled sheet obtained by the above (1) to (6) is cold-rolled at a rolling rate of 50% or more without performing intermediate annealing, and the work hardening index n value is 0.01 to 0. The aluminum alloy hard plate for a can body is obtained in the range of .2 and the success rate of severe ironing is 70% or more.

  According to a fourth aspect of the present invention, there is provided a method for producing an aluminum alloy hard plate for a can body according to claim 3, wherein each pass having a thickness of 20 mm or less in the hot rolling process is provided. Is controlled such that the distortion speed in each path becomes higher in the subsequent path, and the distortion speed in the final path is controlled to 50 / second or more.

  On the other hand, Claim 5 and Claim 6 are intermediate products in the process of manufacturing the aluminum alloy hard plate for can bodies according to claim 1 or 2, that is, hot rolled plates for aluminum alloy hard plates for can bodies. Is stipulated.

  That is, the hot rolled sheet for an aluminum alloy hard plate for a can body of the invention of claim 5 is the hot rolled plate for an aluminum alloy hard plate for a can body of claim 1 or 2, 3. An aluminum alloy having the component composition according to claim 2, having an electrical conductivity in the range of 30 to 50% IACS, a crystal grain size of 4.0 or more in ASTM number, and a cube orientation density of a random sample. 5 times or more and 100 times or less.

  The hot-rolled sheet for an aluminum alloy hard plate for a can body according to claim 6 is the hot-rolled plate for an aluminum alloy hard plate for a can body according to claim 1 or 2, Item 2 is an aluminum alloy having the composition described in item 2, and the amount of Mg contained in the intermetallic compound existing in the hot-rolled sheet is in the range of 0.01 to 0.2%. To do.

  The aluminum alloy hard plate for a can body according to the invention of claim 1 or claim 2 has an excellent balance of various properties required for a DI can body of a two-piece can or a bottle can, particularly strength, ironing workability, flange Good balance between moldability and ear rate. Moreover, according to the manufacturing method of the aluminum alloy hard plate for can bodies of the invention of Claim 3 and Claim 4, intermediate annealing after hot rolling (intermediate annealing between hot rolling and cold rolling, or cold Since the process that eliminates the intermediate annealing in the middle of rolling) is applied, the can body can be manufactured at high cost and at a low cost. It is possible to stably obtain a high-performance can body material excellent in the balance of various characteristics required for, particularly strength, ironing workability, flange formability, and ear ratio. Moreover, if the hot-rolled sheet for aluminum alloy hard plates for can bodies of the inventions of claims 5 and 6 is used, the final excellent performance as described above is obtained while omitting the intermediate annealing after hot rolling. An aluminum alloy hard plate for a can body having a balance can be obtained.

  First, the reasons for limiting the component composition of the aluminum alloy used in the aluminum alloy hard plate for a can body of the present invention will be described.

Mg:
The addition of Mg is effective in improving the strength by solid solution of Mg itself, and can be expected to improve the strength by increasing the work hardening amount accompanying the solid solution of Mg, and further, Mg ₂ Si by coexistence with Si. Therefore, Mg is an indispensable element for obtaining the strength required as a can body material. Further, Mg has an effect of multiplying dislocations at the time of processing, and is therefore effective for making recrystallized grains finer. However, if the amount of Mg is less than 0.5%, the above effect is small. On the other hand, if it exceeds 2.0%, high strength can be easily obtained, but the deformation resistance during DI processing increases and ironing workability and flange forming Worsen sex. Therefore, the Mg content is set in the range of 0.5 to 2.0%. The Mg amount is particularly preferably within the range of 0.7 to 1.5% even within this range.

Mn:
Mn is an effective element that contributes to improvement in strength and formability. In particular, Mn is particularly important for a can body material, which is the intended use of the present invention, because ironing is applied during DI molding. Emulsion-type lubricants are usually used in ironing of aluminum plates, but if there are few Mn-based crystallized products, even if they have the same level of strength, the emulsion-type lubricants alone are not sufficient for lubrication. In addition, appearance defects such as scuffing and seizure called goling may occur. Goling is known to be affected by the size, amount, and type of crystallized matter, and Mn is an indispensable element for forming the crystallized product. If the amount of Mn is less than 0.5%, the effect of solid lubrication by the Mn-based compound cannot be obtained. On the other hand, if the amount of Mn exceeds 2.0%, an Al ₆ Mn primary crystal giant intermetallic compound is generated. Formability will be impaired. Therefore, the amount of Mn is set in the range of 0.5 to 2.0%. Moreover, the solid solution Mn in a product board has the effect which suppresses the recovery | restoration at the time of a process, and the effect which reduces the softening at the time of paint baking here. The Mn content is particularly preferably within the range of 0.7 to 1.5% even within the range of 0.5 to 2.0%.

Fe:
Fe is an element required to promote Mn crystallization and precipitation, and to control the amount of Mn solid solution in the aluminum matrix and the dispersion state of the Mn-based intermetallic compound. Also contributes. In order to obtain an appropriate compound dispersion state, it is necessary to add Fe according to the amount of Mn added. If the amount of Fe is less than 0.05%, it is difficult to obtain an appropriate compound dispersion state and fine crystal grains. A compound is likely to be generated, which may impair ironing workability and flange formability. Therefore, the range of Fe content is set to 0.05 to 0.8%. The Fe content is particularly preferably in the range of 0.2 to 0.6% even within the range of 0.05 to 0.8%.

Si:
The addition of Si contributes to improvement of the strength of the can body material through age hardening by precipitation of Mg ₂ Si-based compounds. Si is an element necessary for generating an Al—Mn—Fe—Si intermetallic compound and controlling the dispersion state of the Mn intermetallic compound. If the amount of Si is less than 0.05%, the above effect cannot be obtained. On the other hand, if it exceeds 0.8%, the material becomes too hard due to age hardening, thereby impairing the moldability. Therefore, the range of Si content is set to 0.05 to 0.8%. The Si content is particularly preferably in the range of 0.1 to 0.5% even within the range of 0.05 to 0.8%.

Cu:
Cu precipitates mainly as an Al-Cu-Mg-based precipitate and contributes to strength improvement. If the amount of Cu is less than 0.05%, the effect cannot be obtained. On the other hand, when Cu is added in excess of 0.7%, although age hardening can be easily obtained, it becomes too hard and ironing workability, flange Impairs moldability and deteriorates corrosion resistance. Therefore, the range of Cu content is set to 0.05 to 0.7%. The Cu content is particularly preferably in the range of 0.1 to 0.4% even within the range of 0.05 to 0.7%.

  In addition to the above elements, Al and inevitable impurities may be basically used, but one or more of Cr, Zn, and Ti may be added as necessary. These Cr, Zn, and Ti will be described in more detail.

Cr:
Cr is an element effective for improving the strength. However, if it is less than 0.05%, the effect is small, and if it exceeds 0.5%, the formation of a giant crystallized product causes a decrease in formability, which is not preferable. Therefore, the range of Cr content when adding Cr is set to 0.05 to 0.5%. A more preferable range of the Cr content is 0.1 to 0.4%.

Zn:
Addition of Zn contributes to strength improvement by aging precipitation of Al—Mg—Zn-based particles, but if less than 0.05%, the effect cannot be obtained, and if over 0.8%, there is a problem with contribution to strength. There is no, but deteriorates the corrosion resistance. Therefore, the range of the Zr amount when adding Zn is set to 0.05 to 0.8%. A more preferable range of the Zn content is 0.1 to 0.5%.

Ti:
In a normal aluminum alloy, a small amount of Ti is added for refining ingot crystal grains. In this invention, a small amount of Ti may be added as necessary. However, if the amount of Ti is less than 0.001%, the effect cannot be obtained. On the other hand, if it exceeds 0.20%, a large Al—Ti intermetallic compound crystallizes and inhibits formability. The amount of Ti was in the range of 0.001 to 0.20%. Further, it is known that the addition of a small amount of B together with Ti improves the effect of refining the ingot crystal grains. Therefore, in the present invention, addition of a small amount of B together with Ti is allowed. Thus, when adding B together with Ti, if the amount of B is less than 0.0001%, there is no effect, and if it exceeds 0.05%, Ti-B based coarse particles are mixed to impair the formability. Therefore, the amount of B when adding B together with Ti is preferably within the range of 0.0001 to 0.05%.

  Furthermore, the aluminum alloy hard plate for a can body of the present invention not only regulates the composition of the alloy as described above, but also defines the work hardening index of the plate, that is, the so-called n value, and the success rate of severe ironing. These will be described next.

The work hardening index (n value) is various indices of work hardening at the time of various processing of materials and various forming processes.
σ = F · ε ⁿ (1)
Defined by Where σ is true stress, ε is true strain, and F is a constant.

  Such a work hardening index n value affects the strength, formability, and workability of the final product (can body). When the work hardening index n value is less than 0.01, work hardening is difficult to proceed, so that the strength tends to be insufficient, and wrinkles are likely to occur during the molding of the bottom and neck portions of the can. On the other hand, if the n value exceeds 0.2, the work hardening of the material proceeds excessively, the flange cracking sensitivity becomes high, the flange formability is lowered, and the ironing workability may be lowered. Therefore, in the present invention, the work hardening index n value of the aluminum alloy hard plate for can bodies is set within a range of 0.01 to 0.2. Here, the n value is obtained in the range of 2 to 3% by taking a JIS No. 5 test piece in parallel with the rolling direction.

  Furthermore, in order to evaluate the iron can workability of DI can body efficiently and with high accuracy, the present inventors have conducted experiments and examinations. When the ironing die is removed and the ironing rate (55%) of the first and third ironing dies is set to be severe, and the ironing process (severe ironing) is performed, the can breaks out of 100 cans. It has been found that the ratio of not working is extremely effective as an index of ironing workability. And when the success rate of such a severe ironing reached 70% or more, it was found that ironing workability could be considered good, and this value was defined as the ironing workability index of the aluminum alloy hard plate for can bodies of the invention. .

  Furthermore, in this invention, as the final plate (aluminum alloy hard plate for can body), in order to stably obtain a material excellent in balance of strength, ironing workability, flange formability, and ear rate, the aluminum alloy hard plate (final) For hot rolled sheets that are intermediate products in the manufacturing process of plates, that is, hot rolled sheets for aluminum plates for can bodies, electrical conductivity, grain size, texture (crystal orientation), and intermetallic compounds Mg content is defined. The reason is as follows.

  In this invention, as a manufacturing process of the aluminum alloy hard plate for the can body, in order to reduce costs, a process that does not perform intermediate annealing immediately after the end of hot rolling or in the middle of subsequent cold rolling is applied. In such a process, the performance of the hot rolled sheet after completion of hot rolling greatly affects the performance of the final sheet. As a result of various experiments and examinations by the present inventors, the control of the conductivity, crystal grain size, texture (crystal orientation) of the hot rolled sheet in the stage after the hot rolling is completed, and further to the intermetallic compound It was found that control of the amount of Mg contained was extremely important for the balance of the strength, ironing workability, flange formability, and ear ratio of the final plate, and these were defined as conditions for the hot rolled plate.

  Specifically, first, the electrical conductivity of the hot-rolled sheet is a value that serves as an index of the solid solution amount of the element dissolved in the material, and has a large effect on work hardening. Since it is an important factor affecting the strength of the material, the ironing workability, and the flange formability through the curability, in this invention, it was decided to regulate within the range of 30-50% IACS. Here, if the electrical conductivity of the hot-rolled sheet is less than 30% IACS, the amount of the solid solution element is too large, and the work hardening index n value of the final sheet may exceed 0.2, in which case high strength is obtained. Therefore, ironing workability and flange formability are reduced. Further, if the electrical conductivity after hot rolling exceeds 50% IACS, the amount of solid solution elements is too small, and the work hardening index n value of the final plate may be reduced to less than 0.01, and accordingly. There is a risk of lack of strength. The electrical conductivity of the hot rolled sheet is preferably in the range of 35 to 45% IACS. The work hardening index n is not only influenced by the electrical conductivity, but also by the crystal orientation, the size and distribution density of the precipitates as described below.

  Next, the fineness of the crystal grains is an important factor contributing to the improvement of strength and uniform deformation. Therefore, the crystal grain size is extremely important for the balance between the strength of the material, ironing workability, and flange formability. If the grain size at the hot-rolled sheet stage is less than 4.0 in the ASTM number, the structure of the final sheet will not be fine in the process that omits the intermediate annealing, so that the sheet has good strength, ironing workability, and flange formability. It becomes difficult to obtain. Therefore, the crystal grain size at the hot rolled sheet stage is determined to be ASTM number 4.0 or more. Preferably, the ASTM number is 7.0 or higher.

  Furthermore, the texture (crystal orientation density) at the stage of the hot-rolled sheet, particularly the cube orientation density, not only greatly affects the ear rate of the final sheet, but also affects the anisotropy of slip deformation, Through the anisotropy of the slip deformation, it affects the ironing workability and flange formability of the final plate. The appropriate range of the cube orientation density in the hot rolling stage is 5 times or more and 100 times or less that of the random sample in view of the balance of the ear ratio, the ironing workability, and the flange formability of the final plate. If the cube orientation density in the hot-rolled sheet is less than 5 times or more than 100 times that of the random sample, ironing workability and flange formability are lowered, and it is difficult to obtain a low ear ratio.

  Furthermore, the dispersion status (distribution density, size) of intermetallic compounds present in hot-rolled sheets, particularly Mg-containing intermetallic compounds (Mg-based intermetallic compounds), determines the strength and ear ratio of the final sheet. It has a great influence on ironing processability. Also, here, the amount of Mg in the intermetallic compound present in the hot-rolled sheet (the ratio of Mg contained in the Mg-based intermetallic compound to the entire sheet) is an indicator of the dispersion status of the Mg-based intermetallic compound. Become. Therefore, in the present invention, the amount of Mg contained in the intermetallic compound present in the hot-rolled sheet is a ratio with respect to the total amount of all intermetallic compounds (total amount of intermetallic compound) in the entire hot-rolled sheet. It is specified within the range of 0.01 to 0.2% by mass.

More specifically, the Mg-based intermetallic compound contained in the hot-rolled sheet typically includes an Al—Mg—Cu-based (for example, S phase, that is, MgCuAl ₂ ), Mg ₂ Si, and the like. is there. If the amount of Mg contained in such an Mg-based intermetallic compound is less than 0.01% with respect to the entire hot-rolled sheet, the distribution of these Mg-based intermetallic compounds becomes too sparse, resulting in low strength. The ear rate is also unstable. Conversely, if the amount of Mg contained in the intermetallic compound exceeds 0.2% with respect to the entire hot-rolled sheet, the distribution of these intermetallic compounds becomes too dense and the ironing workability deteriorates. In particular, among the Mg-based intermetallic compounds described above, the S phase has a small size and has a large effect on strength and ironing workability. In addition, as intermetallic compounds other than Mg-based, there are Al (MnFe) Si-based, AlMnSi-based, AlFeSi-based, AlMn-based, AlFe-based, etc., and generally 90% or more of all intermetallic compounds are mainly composed of these. These intermetallic compounds other than Mg-based compounds also bring about a certain dispersion strengthening effect as a whole, but the individual particle size is relatively large and the contribution to precipitation hardening is small. Therefore, if the alloy components and the production conditions are within the ranges specified in the present invention, there is no need to consider intermetallic compounds other than Mg-based compounds.

  As described above, in the present invention, the electrical conductivity, crystal grain size, cube orientation density, and Mg content contained in the intermetallic compound at the stage of the hot rolled sheet are respectively defined, and the final sheet (on the hot rolled sheet) These are not stipulated at the stage of cold rolling), but the reason is as follows.

  In other words, in the final plate, the crystal grains are deformed by cold working (cold rolling) to form a fibrous work structure, so it is difficult to measure the crystal grain size, and the cold orientation reduces the cube orientation density. The crystal orientation component becomes complicated due to an increase in the processed texture component, and it becomes difficult to uniformly define the orientation density condition. Furthermore, since the present invention targets a process in which intermediate annealing is not performed after hot rolling, the performance balance of the final sheet after cold rolling is almost determined by the performance index at the stage after hot rolling. Therefore, in the present invention, the conditions of the plate at the stage of the hot rolled plate are strictly defined.

  Next, the manufacturing method of the aluminum alloy hard plate for can bodies of this invention is demonstrated. In addition, in this invention, not only the aluminum alloy hard plate for can bodies which is the final plate, but also a hot rolled plate corresponding to the intermediate product is defined. The manufacturing method is included in the following description of the manufacturing method of the aluminum alloy hard plate for can bodies.

  First, an aluminum alloy ingot having the above alloy composition is cast by a DC casting method (semi-continuous casting method) according to a conventional method. The ingot is then homogenized to homogenize the ingot segregation and optimize the size and distribution of Mn, Fe, and Si-based second phase particles. The size and distribution of the second phase particles influence the crystal grain size and texture of the hot rolled sheet. When the homogenization treatment temperature is less than 500 ° C., not only the homogenization effect is insufficient, but there is a possibility that a fine crystal grain size and an optimum texture cannot be obtained. On the other hand, the upper limit of the homogenization treatment temperature is not particularly restricted, but normally, if it exceeds 640 ° C, eutectic melting may occur, and therefore it is preferably 640 ° C or less. More preferably, the homogenization temperature is in the range of 560 to 630 ° C. The homogenization time is not particularly limited, but if it is less than 1 hour, the homogenization effect may be insufficient, and if it exceeds 48 hours, the economy is impaired. , Preferably within the range of 2 to 16 hours. The ingot that has been homogenized as described above may be immediately subjected to hot rolling as described below while maintaining its temperature, or it may be cooled once and surface milled to maintain surface quality. After carrying out, the hot rolling may be performed again by reheating to the hot rolling start temperature.

After the homogenization treatment, hot rolling is performed as described above. Here, in the case of the present invention, since a process in which annealing is not performed after hot rolling is applied, it is necessary to sufficiently recrystallize after hot rolling, and after hot rolling, it is necessary to cool. Since only hot rolling is performed, the performance of the plate (hot rolled plate) at the stage where hot rolling is finished has a great influence on the performance of the final plate. Therefore, in order to obtain an excellent performance balance as the final plate, the conditions of the plate at the stage of finishing the hot rolling are included in the conductivity, crystal grain size, cube orientation density, and intermetallic compound as described above. Defines the amount of Mg. In order to obtain a hot-rolled sheet that satisfies these conditions, it is necessary to strictly regulate the hot-rolling conditions. Therefore, in the production method of the present invention, the hot-rolling start temperature and the hot-rolling end temperature (heat Material temperature at each sheet thickness stage (especially late to final stage) in the hot rolling process as well as the Ln (Z) value and strain rate of each pass in the late to final stage of the hot rolling process. Etc. are strictly regulated. Specifically, in the manufacturing method of the invention according to claim 3, the following conditions (1) to (6) are defined.
(1) The hot rolling start temperature is controlled within a range of 300 to 550 ° C.
(2) The material temperature in the thickness range from 150 mm to 20 mm in the hot rolling process is controlled within a range of 300 to 470 ° C.
(3) The material temperature from the thickness 20 mm in the hot rolling process to immediately before the final hot rolling pass is controlled within a range of 270 to 420 ° C.
(4) The Ln (Z) value in each pass having a thickness of 150 mm or less in the hot rolling process is controlled within a range of 20-50.
(5) The hot rolling end temperature is controlled within a range of 270 to 350 ° C.
(6) In the cooling process from a temperature in the range of 270 to 350 ° C. after the hot rolling to a temperature range of 100 ° C. or less, the average cooling rate up to 100 ° C. is controlled to 100 ° C./hr or less.

In addition to the above conditions (1) to (6), it is desirable that the following condition (7) is satisfied. The condition (7) is defined by the invention of claim 4.
(7) Each pass having a thickness of 20 mm or less in the hot rolling process is controlled so that the strain rate in each pass becomes higher as the subsequent pass, and the strain rate in the final pass is controlled to 50 / second or more.

  Hereinafter, among these hot rolling conditions, the conditions (1) to (6) defined in claim 3 will be specifically described.

(1) The hot rolling start temperature is controlled within a range of 300 to 550 ° C.
The hot rolling start temperature strongly affects the recovery and recrystallization behavior of the material during hot rolling. When the hot rolling start temperature is less than 300 ° C., recrystallization hardly occurs during rolling, the ductility of the material is lowered, and the edge cracking phenomenon of the plate is likely to occur during hot rolling. On the other hand, if hot rolling is started at a temperature exceeding 550 ° C., coarse crystal grains are easily formed, and the surface quality of the plate is deteriorated. Therefore, the hot rolling start temperature is controlled in the range of 300 to 550 ° C. It was decided. In addition, the preferable range of hot rolling start temperature is 350-500 degreeC.

(2) The material temperature in the thickness range from 150 mm to 20 mm in the hot rolling process is controlled to a temperature within the range of 300 to 470 ° C.
In addition to the hot rolling start temperature and end temperature, the material temperature control during hot rolling is extremely important. In particular, the strict control of the material temperature at the stage after the sheet thickness of 150 mm during the hot rolling process is as follows: It is indispensable and important to control the deposition behavior and recrystallization behavior of the material to control the conductivity, texture, and ear ratio of the material within an appropriate range. If the material temperature in the stage of the plate thickness from 150 mm to 20 mm is less than 300 ° C., serious plate edge cracking may occur during hot rolling. The rate, texture, and ear rate may not be obtained.

(3) The material temperature from the thickness 20 mm in the hot rolling process to immediately before the final hot rolling pass is controlled within a range of 270 to 420 ° C.
This condition is combined with the temperature condition of 150 mm to 20 mm in the thickness of (2) described above, and controls the material precipitation behavior and recrystallization behavior in the hot rolling process, so that the material conductivity, texture, In addition to controlling the ear ratio to an appropriate range, the material temperature is controlled by shifting to a lower temperature side than the temperature condition of (2), thereby accumulating more strain and the material after the hot rolling is completed. It is necessary to make the crystal grain size of the finer. If the material temperature at this stage is less than 270 ° C., serious plate edge cracking may occur during hot rolling. On the other hand, if it exceeds 420 ° C., the progress of recrystallization is accelerated and the required conductivity and texture are increased. In addition to the possibility that the ear rate cannot be obtained, the accumulation of strain is also reduced, making it difficult to obtain fine crystal grains. Even within this range, it is particularly preferable to control the temperature within the range of 280 to 390 ° C.

(4) The Ln (Z) value in each pass having a thickness of 150 mm or less in the hot rolling process is controlled within a range of 20-50.
Here, for example, Z is hot as shown in pages 88 to 89 of the document “Basics and Industrial Technology of Aluminum Materials” (issued by the Japan Light Metal Association on May 1, 1985). The Zener-Holomon Parameter (unit: / second) that is an index of strain accumulation, where the strain rate is E, the activation energy is Q, the gas constant is R, and the temperature is T, the following equation (2)
Z = E · exp (Q / RT) (2)
This is the value obtained by. In the invention of claim 3, the natural logarithm Ln (Z) of the Z value is used for the purpose of controlling hot strain accumulation and recovery / recrystallization of the material in accordance with the temperature conditions of (2) and (3). Is controlled within a range of 20 to 50. Here, if the value of Ln (Z) is less than 20, accumulation of hot strain is insufficient, while if it exceeds 50, recrystallization of the material is promoted. In any case, the required texture, ear ratio, crystal The particle size may not be obtained. The value of Ln (Z) for each pass having a thickness of 150 mm or less is preferably controlled within the range of 25-45. Here, the value of Ln (Z) in each pass can be controlled by appropriately adjusting the strain rate of each pass and the temperature of each pass as is apparent from the equation (2), and in particular, the thickness is 150 mm. Controlling the value of Ln (Z) in each of the following passes within the specific range as described above is extremely effective for obtaining a required texture, ear ratio, and crystal grain size. In the present invention, in calculating the Z value, a value of 37,300 cal / mol is used as the value of the activation energy Q, and a value of 1.987 cal / mol · k is used as the gas constant R.

(5) The hot rolling end temperature is controlled within a range of 270 to 350 ° C.
When the hot rolling finish temperature is less than 270 ° C., it is difficult to obtain a sufficient recrystallized structure. In this case, if the steel sheet is cold-rolled to the final thickness without being annealed as it is, the ears of the DI can become high and the ironing processability is increased. It also causes deterioration. On the other hand, when the hot rolling finish temperature exceeds 350 ° C., the material tends to have a complete recrystallized structure, but there is a possibility that the crystal grains become coarse and the surface quality deteriorates. Therefore, the end temperature of the hot rolling is set in the range of 270 to 350 ° C. Even within this range, a range of 280 to 340 ° C. is particularly preferable. Further, the thickness of the hot-rolled finished sheet is not particularly limited, but is preferably in the range of 3.0 to 1.5 mm in consideration of the balance between the strength and ear ratio of the final sheet and the ironing workability and flange formability.

(6) In the cooling process from a temperature in the range of 270 to 350 ° C. after the hot rolling to a temperature range of 100 ° C. or less, the average cooling rate up to 100 ° C. is controlled to 100 ° C./hr or less.
After the hot rolling is completed, the cooling process from the temperature range of 270 to 350 ° C., particularly the cooling process to 100 ° C. is a process of recrystallization and is a process of growing cube-oriented crystal grains. If the average cooling rate in this process exceeds 100 ° C./hr, recrystallization does not proceed sufficiently, resulting in insufficient formation of cube-oriented crystal grains, which is disadvantageous for controlling the low ear ratio of the final plate. In addition to this, the moldability may also be reduced. This cooling process is also a process in which fine Mg-based intermetallic compounds are produced, and by controlling the cooling rate in this process, the size and distribution of the Mg-based intermetallic compounds can be adjusted appropriately, As a result, it is possible not only to obtain an appropriate material strength after cold rolling, but also to obtain a stable low ear rate. Therefore, the average cooling rate in the cooling process is regulated to 100 ° C./hr or less. Examples of the Mg-based intermetallic compound produced in this process include Al—Mg—Cu-based (for example, S phase MgCuAl ₂ ) and Mg ₂ Si as already described. And as already stated, if the amount of Mg contained in the intermetallic compound in the hot-rolled sheet is less than 0.01%, the distribution of these intermetallic compounds becomes too sparse and tends to be low strength, If the amount of Mg contained in the intermetallic compound exceeds 0.2%, the distribution of these intermetallic compounds becomes too dense and the ironing workability deteriorates. The amount of Mg contained in the intermetallic compound needs to be in the range of 0.01 to 0.2%, and for this reason, control of the cooling process is important.

  Furthermore, in the manufacturing method of the invention of claim 4, in addition to (1) to (6) defined in the manufacturing method of the invention of claim 3 as hot rolling conditions, the conditions of (7) are specified. The condition (7) will be described next.

(7) The strain rate of each pass having a thickness of 20 mm or less in the hot rolling process is controlled to be higher in the subsequent pass, that is, the strain rate of the subsequent pass is controlled to exceed the strain rate of the previous pass. (Hereinafter, such a control method is referred to as a gradual increase method), and the distortion speed of the final path is controlled to 50 / second or more.
By regulating the strain rate during hot rolling in this way, it is organically linked to the temperature conditions of (2) and (3) and the Ln (Z) condition of (4), and the more desirable desirable conductivity. In addition to obtaining a texture, ear ratio and fine crystal grain size, the amount of Mg-based intermetallic compound can be controlled. In general, in the finishing stage in hot rolling, the material temperature is usually relatively low, and by increasing the strain rate in such a stage that the material temperature decreases, the recovery of the structure is suppressed, This is extremely effective for accumulating distortion. A large amount of fine Mg-based intermetallic compound is generated by dislocation pipe diffusion or the like until the processing structure in which strain is accumulated in the hot rolling process is changed to a complete recrystallization structure. Here, unless the strain rate is gradually increased, the accumulation is insufficient, so that the production of fine Mg-based intermetallic compound is insufficient, and the required strength and appropriate ear ratio cannot be obtained on the final plate. Arise. The same problem occurs when the distortion speed of the final pass is less than 50 / second.

  After satisfying each of the above conditions, after hot rolling is finished and the material is cooled to room temperature or near room temperature, not only a complete recrystallization structure is obtained by self-annealing, but also a fine crystal Since the distribution of the structure and the appropriate Mg-based intermetallic compound can be obtained, high-quality product plates with excellent performance balance at low cost can be obtained simply by cold rolling without intermediate annealing. be able to.

  Cold rolling is performed at a rolling rate of 50% or more. Here, when the final cold rolling reduction is set to less than 50% without performing the intermediate annealing, the hot rolled plate thickness is set to 1 mm in consideration of the desirable thickness range of 0.35 to 0.25 mm of the final product plate. It is necessary to make it less than. However, it is extremely difficult in actual operation to make the hot rolled plate thickness less than 1 mm, and if the final cold rolling rate is less than 50%, the strengthening due to the cold work hardening of the material is reduced and sufficient. There is a possibility that a sufficient material strength cannot be obtained, and it is also disadvantageous for the control of the ear rate. Therefore, the cold rolling rate is regulated to 50% or more. The upper limit of the cold rolling rate is not particularly limited, but is preferably 90% or less in consideration of the balance of ironing workability, flange formability, ear rate, and strength.

  The hard plate obtained through the above steps satisfies the conditions for the work hardening index n value (0.01 to 0.2) and the severe success rate condition (70% or more) as described above. , Strength, ironing workability, flange formability, and excellent balance of ear ratio.

  Examples of the present invention will be described below together with comparative examples. The following examples are for explaining the effects of the present invention, and it goes without saying that the processes and conditions described in the examples do not limit the technical scope of the present invention.

  Each alloy of alloy symbols A1 to A6 shown in Table 1 was melted in accordance with a conventional method, and cast into a slab having a thickness of 650 mm by a DC casting method. About the obtained slab, it heated to the temperature of 610 degreeC, the homogenization process hold | maintained for 6 hours was performed, and it stood to cool. Then, chamfering was performed 10 mm per side and heated to the hot rolling start temperature shown in Table 2 and maintained for 2 hours, and then hot rolling was started. In addition, the temperature increase rate in the slab homogenization treatment was in the range of 2 to 200 ° C./hr, and the temperature decrease rate in the cooling process after the homogenization treatment was in the range of 5 to 1000 ° C./hr. In the hot rolling process, the material temperature is measured with the plate thickness of 100 mm, 65 mm, and 30 mm as the representative plate thickness in the plate thickness range of 150 to 20 mm, and when the plate thickness is 20 mm or less, 12 mm and 4.5 mm are respectively measured. The material temperature was measured as the representative plate thickness. Further, the Ln (Z) value of each representative plate thickness and the strain rate of each pass having a plate thickness of 20 mm or less were examined. Note that the hot-rolling finished plate thickness was 2 mm. Detailed conditions in the hot rolling process are shown in Tables 2 and 3.

  After the hot rolling, cold rolling was performed to a plate thickness of 0.285 mm without intermediate annealing to obtain a hard plate. The cold rolling rate is 85.75%.

  In the above process, the electrical conductivity, crystal grain size, crystal orientation density (cube orientation density) at the stage of the hot rolled sheet, and the amount of Mg contained in the intermetallic compound present in the sheet (all metals in the entire sheet) The ratio of Mg in the intermetallic compound to the total amount of the intermetallic compound (mass%) was measured, and the results are shown in Table 4. These measurement methods are as follows.

Conductivity (% IACS)
Using an eddy current conductivity measuring device, measurement was performed using copper and brass as a reference sample.

Grain size:
The cross section parallel to the rolling direction was mapped by the EBSP method, the obtained crystal grains were evaluated by the cutting method, and the grain size number was assigned in comparison with the ASTM standard.

Measurement of crystal orientation density (cube orientation density):
A hot-rolled sheet having a thickness of 2 mm was etched at a depth of 250 μm, 500 μm, 725 μm, and 1000 μm from the surface toward the center of the sheet thickness with a 10% NaOH aqueous solution, and measured at each of these positions. The average value of the cube orientation density was taken as the cube orientation density of the hot rolled sheet. As a measuring device, an incomplete pole figure of {200}, {220}, {111} is measured by the X-ray diffraction Schertz reflection method using the Rigaku Corporation X-ray diffractometer. A three-dimensional crystal orientation analysis (ODF) was performed and examined. In these analyses, data obtained by measuring a sample having a random crystal orientation made from aluminum powder is used in the incomplete pole figure analysis of {200}, {220}, and {111}. The cube orientation density, that is, the density of {100} <001> orientation, was obtained as a multiple of the sample having a random orientation. In this invention, the crystal orientation density is all based on three-dimensional crystal orientation analysis (ODF).

Measurement of Mg content in intermetallic compounds:
The amount of Mg contained in the hot-rolled sheet was examined by the phenol method and determined as a ratio to the total mass of all intermetallic compounds present in the hot-rolled sheet.

  Further, the final plate (aluminum alloy hard plate for can body) obtained as described above was subjected to a tensile test on test pieces before and after being subjected to heat treatment (baking) held at 200 ° C. for 20 minutes assuming coating baking. The mechanical strength (0.2% proof stress) before and after baking was examined, and the work hardening index n value before baking was examined.

  Further, for the above-mentioned final plate, the cup ear ratio and the success rate of severe ironing were examined, the flange formability was examined, and the pressure resistance test of the DI can after being formed into a DI can was conducted to examine the bottom pressure resistance. These results are shown in Table 5. These specific test methods and evaluation methods are as follows.

Tensile test (proof strength before and after baking, n value before baking):
A JIS No. 5 test piece was taken in parallel with the rolling direction and subjected to a tensile test. In addition, the work hardening index n value was calculated | required based on the said (1) Formula in the range of 2-3% of elongation.

Cup ear rate:
A drawing test was conducted on a total of 35 points, 7 points at equal intervals in the longitudinal direction of the coil and 5 points at equal intervals in the width direction, and the cup ear ratio in the 45 ° direction was examined.

Severe ironing success rate:
In DI can molding, the loader die is 1.8mm, the second ironing die of the can body manufacturer is pulled out, and the ironing ratio is set to 55% and the ironing rate of the first and third ironing dies is severe (severe The ratio at which the can breakage does not occur in continuous 100 cans was determined as an index of ironing processability. Here, if the success rate of such severe ironing becomes 70% or more, ironing workability can be considered good.

Flange formability (mouth expandability):
As the flange formability (mouth expandability), the flange formability after four-stage necking was examined. That is, a punch having a 15 ° gradient formed in the DI can opening (radius R0: 29 mm) after four-stage necking is pushed in until the opening edge of the trimmed, cleaned, and baked DI can breaks. The radius of the opening after expanding to the limit at which it can break was defined as R1, and the difference (R1-R0) was determined.

DI can pressure resistance test (bottom pressure resistance):
The internal pressure of the DI can was increased until the bottom was deformed, and the maximum pressure was obtained.

  In Tables 2 to 5, production numbers 1 to 4 are all examples produced according to the method defined in the present invention using alloys within the component composition range of the present invention. In this case, the strength of the final plate, It was confirmed that the balance of the ear ratio, the ironing property, and the flange formability was excellent, and the bottom pressure resistance of the DI can was also good.

  On the other hand, the comparative examples of production numbers 5 and 6 are examples in which the alloy component composition is within the range defined by the present invention, but at least part of the hot rolling conditions is out of the range of the present invention. In the case of the comparative example of production number 5, the flange formability is good, but the strength, the n value of the final plate are low, the 45 ° ear ratio is high, and the ironing property is also reduced. The bottom pressure resistance was also low. In the case of the comparative example of production number 6, the strength was high and the bottom pressure resistance was good, but the ironing property was extremely lowered, and the ear rate and flange formability were also poor. Furthermore, the comparative example of production number 7 is an example in which the component composition of the alloy is outside the range specified in the present invention. In this case, the manufacturing process conditions are within the range specified in the present invention, but the strength after baking, Ear ratio, ironability, and flange formability were all inferior.

Claims (6)

  Mg 0.5-2.0% (mass%, the same shall apply hereinafter), Mn 0.5-2.0%, Fe 0.05-0.8%, Si 0.05-0.8%, Cu 0.05-0.7 The balance is made of an aluminum alloy consisting of Al and inevitable impurities, the work hardening index n value is in the range of 0.01 to 0.2, and the success rate of severe ironing is 70% or more. An aluminum alloy hard plate for a can body characterized by that. The aluminum alloy hard plate for a can body according to claim 1,
As a component of the aluminum alloy, further containing one or more of Cr 0.05 to 0.5%, Zn 0.05 to 0.8%, Ti 0.001 to 0.20%, for a can body Aluminum alloy hard plate. After casting the aluminum alloy having the component composition defined in claim 1 or 2, homogenization treatment is performed in a temperature range of 500 ° C. or higher, and then hot rolling is performed.
(1) Hot rolling is started within a range of 300 to 550 ° C,
(2) controlling the material temperature in the range of 300 to 470 ° C. in the thickness range from 150 mm to 20 mm in the hot rolling process,
(3) The material temperature from the thickness 20 mm in the hot rolling process to immediately before the final hot rolling pass is controlled within the range of 270 to 420 ° C.,
(4) Ln (Z) value (Note: Z indicates Zener-Holomon Parameter) in each pass having a thickness of 150 mm or less in the hot rolling process is controlled within a range of 20-50,
(5) The hot rolling end temperature is in the range of 270 to 350 ° C.,
(6) In the cooling process from the temperature in the range of 270 to 350 ° C. after the hot rolling to the temperature range of 100 ° C. or less, the average cooling rate up to 100 ° C. is controlled to 100 ° C./hr or less,
The hot-rolled sheet obtained by the above (1) to (6) is cold-rolled at a rolling rate of 50% or more without performing intermediate annealing, and the work hardening index n value is 0.01 to 0. A method for producing an aluminum alloy hard plate for a can body, characterized in that an aluminum alloy plate for a can body having a success rate of severe ironing within a range of .2 is 70% or more. In the manufacturing method of the aluminum alloy hard plate for can bodies according to claim 3,
Each pass having a thickness of 20 mm or less in the hot rolling process is controlled so that the strain rate in each pass becomes higher as the subsequent pass, and the strain rate in the final pass is controlled to 50 / second or more. And manufacturing method of aluminum alloy hard plate for can body.   The hot rolled plate for an aluminum alloy hard plate for a can body according to claim 1 or 2, wherein the hot rolled plate is made of an aluminum alloy having the component composition according to claim 1 or 2, and has an electrical conductivity of 30 to 50. % IACS, crystal grain size is 4.0 or more in ASTM number, and cube orientation density is 5 times or more and 100 times or less of random sample, aluminum alloy for can body Hot rolled plate for hard plate.   The hot rolled plate for an aluminum alloy hard plate for a can body according to claim 1 or 2, wherein the hot rolled plate is made of the aluminum alloy having the component composition according to claim 1 or 2, and is present in the hot rolled plate. A hot-rolled sheet for an aluminum alloy hard plate for a can body, wherein the amount of Mg contained in the intermetallic compound is in the range of 0.01 to 0.2%.