US3058857A - Doubly-oriented aluminum iron magnetic sheets - Google Patents

Description

Oct. 16, 1962 D. PAvLovlc El'AL 3,

DOUBLY-ORIENTED ALUMINUM IRON MAGNETIC SHEETS Filed Aug. 1, 1956 3 Sheets-Sheet l Fig.l.

Rcillingfition/ Magnetic B Properties O [loo] Od y Mo netic A M zfgr l gic rogerfles Properties A-Cube on Edge or Single Orientation B-Oube on Face or Double Orientation Single and Double Crystal Orientofions E-Punchinq DOUBLY-ORIENTED ALUMINUM IRON MAGNETIC SHEETS Filed Aug. 1, 1956 Oct. 16, 196 D. PAVLOVlC ETAL 5 Sheets-Sheet 2 d d h M M. m R R m M u 0 O h. c C s w e .w b m .1. w .m 7% D s O M 0 e F A I 4 2 I o 0 ON m 0 m 5". P C D u u u n u u 0 m w m w m P w u 0 00- x uB O O- ::n m

Torque Curves 5.5 7; Al-Fe Magnetic Sheet Hal- Fig.3.

Oct. 16, 19 D. PAVLOVIC El'AL 3,058,8 57

DOUBLY-ORIENTED ALUMINUM IRON MAGNETIC SHEETS Filed Aug. 1, 1956 3 Sheets-Sheet. 3

Fig.5.

0 Calculated-Doubly Oriented-Cube on Face .2 n Calculated-singly Oriented-cube on Edge E A Actual-singly Oriented-Cube on Edge x Actual-Unoriented 0'408'0'1'20'1'60'2'00'2'40 Magnetizing Force Oersteds Integrated Magnetization Curves far singly an Doubly Oriented Magnetic Sheet Fig.6.

Fig.4.

' Torque Curves n 2.4%Al-Fe o Doubly Oriented n 6 m l E 0 C o l8 0 45 90 l35 l80 Degrees tram Flg Rolling Direction Torque per Volume WITNESSES v \NVENTQRS Q Dusan Pavlovic Karl Foster W 8 John A. Osborn United States Patent DQUBLZ This invention relates to doubly-oriented aluminum iron magnetic sheets and processes for producing them.

It has long been desirable to have available magnetic sheet material that is doubly oriented, that is, the crystals or grains of the alloy have a cube on face orientation in the plane of the sheet that the optimum magnetic properties extend in two directions substantially at right angles to each other in the plane of the sheet. Further it is desirable that the optimum magnetic properties in these two directions should be approximately equal. Such doubly oriented sheet material would have important practical applications in the electrical industry in the manufacture of electrical motors, generators, transformers and numerous other varieties of electrical devices.

It has been proposed heretofore to produce magnetic sheets from aluminum iron alloys. In particular, in Patent 2,300,336 there is disclosed a process for producing sheets of magnetic aluminum iron alloy wherein the alloy is oriented to some extent. However, not only are the kinds of orientation present in doubt, but the extent of desired orientation and the magnetic properties are relatively low such that the products set forth in this patent have not been as satisfactory as, nor comparable with available silicon iron alloy magnetic sheets, for example. Singly oriented silicon iron magnetic sheets are so far superior to the magnetic aluminum-iron sheet available heretofore that such aluminum-iron magnetic sheets has not been competitive therewith.

The object of the present invention is to provide a process for producing doubly oriented aluminum-iron alloy magnetic sheets having greatly improved optimum magnetic properties in two directions in the plane of the sheet.

A further object of the invention is to provide a process for producing magnetic sheets from aluminum iron alloys by initially hot rolling a billet or ingot of the alloy to a plate of substantial thickness and then cold rolling the plate twice to apply a cold reduction of 60% to 90% each time, with an intermediate anneal and a final anneal.

A still further object of the invention is to provide a doubly oriented magnetic sheet of aluminum iron alloy produced by a double cold rolling process having substantially similar optimum magnetic properties in two directions at right angles to each other.

Other object of the invention will in part be obvious and will in part appear hereinafter.

For a better understanding of the nature and objects of the invention, reference should be had to the following detailed drawings and description, in which:

FiGURE 1 is a perspective view of a sheet with single and double oriented crystals therein;

FIG. 2 is a graph with curves showing the variation in permeability of single and double cold rolled aluminum iron for various angles with respect to the rolling direction;

FIG. 3 is a graph with torque curves of specimens of single and double cold rolled 3.5% aluminum iron alloy;

FIG. 4 is a graph with a torque curve of double cold rolled 2.4% aluminum iron alloy;

FIG. 5 is a graph with curves of the integrated magnetic properties for various magnetic sheets;

3,058,857 Patented Oct. 16, 1962 FIG. 6 is a plan view of a stator punching;

FIG. 7 is a plan view of segmental punchings;

FIG. 8 is a plan view of an L-punching; and

FIG. 9 is a plan view of an E-punching.

In accordance with the present invention, it has been discovered that magnetic sheets having double crystal orientation may be produced from aluminum-iron alloys comprising from 1% to 10% by weight of aluminum, and the balance being iron, except for incidental impurities. FIG. 1 illustrates the differences in the magnetic characteristics based on the crystals making up the grains of magnetic sheet where a single and double orientation, respectively, has been obtained. It is Well known for cubic crystals of alloys of this range of proportions of aluminum in iron that magnetic properties in this cube edge direction are optimum. Permeability in other directions of the crystal, such as the [110] direction, that is, on a diagonal across a cube face, is low compared to that in the cube edge or [100] direction. A in FIG. 1 indicates that the cubic crystals making up the grains in a singly oriented material have only one of the edges of the cube located in the rolling direction. A doubly oriented grain as shown in B of FIG. 1 has two cube edges lying in the plane of the sheet so that there are two directions perpendicular to one another within the plane of the sheet which give optimum magnetic properties.

Magnetic sheets having double crystal orientation such that two cube edges lie in the plane of the sheet may be produced from the aluminum iron alloys comprising from 1% to 10% by weight of aluminum and the balance being iron except for incidental impurities, by a process comprising: (1) initially hot rolling of an aluminum iron ingot or billet to a thickness of the order of from 0.25 to 0.6 inch, (2) cold rolling the plate to effect a reduction in thickness of 60% to (3) annealing the resulting cold rolled sheet for a period of time at a temperature to remove stresses and recrystallize the 'metal, (4) again cold rolling the sheet to ellect a second reduction in thickness of from 60% to 90% to produce a sheet having the desired gauge of the order of 0.03 inch and less, and (5) finally annealing the sheet fora specified time and temperature. By this process there results a doubly oriented magnetic sheet wherein a high proportion of the grains have a cube on face orientation in the plane of the sheet. The best results are obtained for compositions comprising 2% to 8% of aluminum. The optimum magnetic properties are secured most regularly if the reduction during each cold rolling is at least 70% in steps (2) and (4).

More specifically, aluminum iron alloys for the practice of the present invention are prepared from ingots, billets or slabs of an alloy from 1% to 10% aluminum, the balance being iron, except for incidental components and impurities. The incidental impurities preferably should not exceed 0.01% carbon, and sulphur and phosphorus are usually present in amounts of less than 0.005%, and only small amounts of oxygen and nitrogen are present in the alloy. There may be present small amounts of components such as silicon in amounts of the order of 0.01 to 0.05%, and manganese in amounts of the order of 0.01%. Other elements may be present in small amounts.

The alloy may be prepared by melting in an electric furnace under vacuum or in air, the desired proportions of relatively pure iron and aluminum. Good results have been obtained from the alloys melted in an open air induction furnace. Attention should be directed to insuring substantially uniform admixture of the aluminum with the iron. In some instances a melt of relatively pure iron may be prepared by an oxygen purification treatment as set forth in US. Patents 2,741,554 and 2,741,555 and to the molten iron there is added the pure aluminum in the 3 required proportions, usually in a second crucible under a protective atmosphere, with appropriate measures taken to assure a thorough admixture of the aluminum into the relatively pure iron.

In making sheets, the aluminum-iron ingots or heavy billets or forged slabs of the alloy in the desired composition, are heated to a temperature of the order of from 800 C. to 1 100 C. and hot rolled or hot forged to produce a plate of a thickness of from 0.25 inch to 0.6 inch thickness. The plate may be of any suitable width.

The hot rolled plate is cooled to substantially room temperature, below at least 600 C. and preferably below 100" C., and then is drastically cold rolled to effect a reduction in thickness of from 60% to 90%. For a plate of about 0.5 to 0.6 inch in thickness the reduction in thickness will be greater, that is, about 90%, while when working with the thinner hot rolled plate the reduction in thickness will be of the order of 70%; As a result of this first cold rolling there will be produced a relatively thick cold rolled sheet which is then annealed at a temperature of from 700 C. to 1050 C. for at least fifteen minutes in order to remove stresses and to recrystallize the metal. Longer annealing times may be employed and good success has been had with annealing times of one hour at 1000 C. It has proven to be undesirable to anneal at a temperature of 1100 C. or higher after this initial cold rolling since the recrystallization does not proceed in a satisfactory manner. In particular, excessive grain size results at excessive temperatures. The magnetic product after this first cold rolling and annealing is not particularly satisfactory for use in electrical apparatus.

The annealed sheet is then cooled to substantially room temperature and subjected to further severe cold rolling to effect a second reduction in thickness of from 60% to 90% to produce a sheet of a thickness to meet the requirements of the particular electrical device to be made therefrom. Ordinarily, the sheet will be of a'thickness of not in excess of 0.03 inch. During the second cold rolling the crystal structure resulting from the first anneal is effectively changed. It is the crystal structure after the second cold rolling, which is not present after the first cold rolling step, that is necessary for the development of a structure orientation during the final anneal.

The thin cold rolled sheet produced by the second cold rolling is then subjected to a second anneal at a temperature of from 900 C. to 1050 C. for a period of time of at least one hour. The annealing may be applied to the sheets for as long as 12 hours at 1000 C. without detriment. However, if the annealing temperature is 1100 C. or higher, a magnetically inferior product results. This second anneal results in a diiferent texture than was present in the sheet after the first annealing treatment. A 'very high proportion of all of the crystals or grains of the sheet after the second anneal now have a cube on face orientation in the plane of the sheet. Tests have indicated that the edges of the cube are oriented substantially both in the direction of the rolling and in a direction perpendicular to the rolling direction in the face of the sheet. Consequently, the crystals are oriented to have their optimum magnetic properties in the direction of the rolling and in the direction of right angles thereto. V

In order to provide for the optimum magnetic properties, it is necessary to conduct the second anneal for a time and temperature such that the average grain diameter does not exceed approximately one millimeter. Good results are obtained where the average grain diameter is from 0J1 to 0.5 millimeter.

The annealing is preferably carried out in a hydrogen atmosphere in order to reduce oxides and remove carbon. In some cases the atmosphere may comprise an. inert gas, such as argon, alone, or admixed with hydrogen. The gases should be of a low dew-point, for example 20 C. and lower.

The resulting magnetic sheets after the final anneal will 4 be of a thickness of from about 0.03 inch to 0.005 inch and thinner. For use in electrical motors and generators, particularly desirable sheet thicknesses are from 0.03 inch to 0.02 inch. For some purposes sheets of a thickness of 0.04 inch are required.

The aluminum iron alloy magnetic sheets produced by the double cold rolling and double annealing treatment of the present invention exhibit substantially higher magnetic properties in the two directions along which preferred orientation takes place as compared to sheets otherwise similarly produced by a single cold rolling and annealing process. Referring to FIG. 2 of the drawings, there is illustrated the permeability at 10 oersteds for 2.4% aluminum iron magnetic sheets. The sheet from which the data of curve A were obtained was produced by hot rolling the aluminum iron ingot to a plate of a thickness of one-half inch which was then cold rolled twice, effecting areduction of each time, the final sheets having a thickness of 0.025 inch, with an anneal at '1000 C. for one hour being applied after the first cold rolling operation and then following the second cold rolling by a two hour anneal at 1000 C. The sheet used in the test indicated by curve B was prepared by hot rolling 2.4% aluminum iron to a thickness of one-eighth inch followed by a single cold roll to produce a sheet of a thickness of 0.025 inch which was then annealed at 1000 C. for two hours. Both cold rolled sheets were of a width of approximately 13 inches and Epstein strips were cut from the sheet at varying angles with respect to the rolling direction. The Epstein strips were annealed in dry hydrogen at 1000 C. for two hours before being tested magnetically.

It will be observed from the curves in FIG. 2 that the double cold rolled aluminum iron has a permeability at 10 oersteds approximately 50 greater at both the 0 and orientation as compared to the single cold rolled sheet. This difference in permeability in the zero and 90 directions is a substantial improvement and quite meaningful in the application thereof in electrical devices. The dip in permeability at 45 orientation is meaningful, for if there is little change in permeability as the direction of flux tothe sheet changes, there is little crystal orientation. It necessarily follows that an increase in double orientation will bring about a dip in permeability at the 45 angle relative to that at 0 or 90.

Torque curves were prepared by testing identically sized samples of single cold rolled and double cold rolled aluminum iron alloy. FIG. 3 is a plot of torque curves for single and double cold rolled 3.5% aluminum iron alloy. FIG. 4 is the curve for double cold rolled 2.4% aluminum alloy. In FIG. 3 the four torque peaks are substantially greater for the double cold rolled aluminum iron as compared to the single cold rolled aluminum iron. Furthermore, the differences between the successive peak torque values are less, both numerically and percentagewise, for the double rolled aluminum iron alloy than for the single cold rolled aluminum iron alloy. It is desirable for use in the electrical apparatus that the torque peaks be reasonably equal for best results. It will be noted that the differences between the torque peaks are of the order of 13% for the double cold rolled alloy and over 20% for the single cold rolledv alloy.

The following examples are illustrative of the invention: i

7 Example I There was melted in a vacuum furnace electrolytic iron and aluminum bar of a purity of 99.9%, the aluminum being introduced to provide approximately 3% by weight of aluminum in iron. During the melting the iron was introduced first into the crucible and was purified by passing thereover a stream of wet hydrogen and then dry hydrogen in order to reduce the carbon and oxygen content. The aluminum was added under an argon an 80% The sheet specimens were then annealed two hours at 15,000 gausses.

atmosphere. The melt was cast into a vertical steel mold to produce an ingot of the alloy. The ingot was heated to a temperature of approximately 1000 C. and

'was hot rolled to provide a plate of a thickness of onehalf inch. The hot rolled plate was annealed in a hydrogen atmosphere for one ing the plate to room temperature, it was cold rolled to efiect a reduction of 80%. The resulting thick sheet was cut into a number of specimens. The thick sheet specimens were heat treated at different temperatures, some at 700 C., others at 1000 C. and still others at 1200" C. forone hour. Dry hydrogen of a -50 C. dew-point was used as the annealing atmosphere. The annealed specimens were then given a second cold rolling to efiect reduction to a final thickness of 0.025 inch.

1000 C. in hydrogen. Hollow square members were punched from each of the sheets and annealed one hour at 1000 C. The specimens annealed at 700- C. after the first cold rolling had an induction at 10 oersteds of 14,700 gausses. Hollow square members from the sheets annealedat 1000 C. had an induction at 10 oersteds of The hollow square members which had been subjected .to 1200 C. for the first anneal had an induction of 14,200 gausses at 10 oersteds. The first anneal at 1200? C. had resulted in a very large grain size in the one-eighth inch thick sheet.

Example 11 i .In another series of tests on a 3% iron aluminum alloy, produced as in Example I, the annealing temperature after the first cold rolling operation was 1000 C. for one hour. The specimens were then uniformly cold rolled to 0.025 inch and then annealed for one hour at temperatures of 1000 C. for one group, at 1100 C. for a second group, and at 1250 C. for a third group. The average grain diameter for the members annealed at 1000 C. was approximately 0.1 millimeter and the induction at 10 oersteds was 14,700. The samples annealed at 1100 C. and 1250 C. had an average grain diameter in excess of one millimeter and the induction was 14,200 and 14,100 gausses, respectively, in a field of 10 oersteds.

Example 111 Double cold rolled sheets of a thickness of 0.025 inch produced from 0.5 inch thick hot rolled plates containing 2.4% and 3.5% aluminum iron, respectively, were prepared by following the procedure of Example I. The sheets, after being annealed at 1000 C. for one hour in hydrogen following the second cold rolling, were tested to determine their magnetic properties. The 2.4% aluminum iron alloy sheets had an induction of 15,200 gausses at 10 oersteds. :For comparison, a single cold rolled sheet of the same alloy and of the same thickness had an induction of 14,500 gausses. The double cold rolled 3.5% aluminum alloy when tested as Epstein samples had an induction of 16,200 gausses at 10 oersteds. All of these specimens showed a high magnetic induction in the plane of the sheet both in the rolling direction and in a direction 90 to the rolling direction.

The double cold rolled, doubly oriented aluminum iron magnetic sheets of the present invention are particularly well suited for the making of laminations for motors and generators. The permeability in two directions at right angles will enable a substantial increase in the magnetic flux density in the laminations.

Referring to FIG. of the drawings, there is illustrated curves plotting the induction in kilogausses for varying magnetizing forces for unoriented, singly oriented and doubly oriented material. The two upper curves comprise theoretical calculations. All of the curves are integrated values. It will be noted that the topmost curves, calculated for double oriented material, shows a much greater induction for all magnetizing fields up to 250 oersteds than does the curve immediately below it hour at 1000 C. After coolwhich is calculated for single oriented or cube on edge magnetic material. Actual tests have been made of a number of samples of singly oriented magnetic sheets and it will be observed that the curve for such singly oriented material approaches the calculated curve at approximately oersteds. It is evident that the actual values obtained by using unoriented or hot rolled magnetic sheet, shown in the lowest curve, is, for all practical purposes, substantially the same as the singly oriented material. At all levels of applied magnetizing field, it is seen that the magnetic induction is much higher for the doubly oriented material than the singly oriented material.

The curve of FIG. 5 illustrates the improvement which may be obtained by using the doubly oriented material of the present invention for laminations of dynamoelectric machines such as motors and generators in which the magnetic flux must travel in all directions with respect to the rolling direction. Motor and generator laminations comprising a complete ring punched from a single sheet of the double oriented material will exhibit the improvement in magnetic properties over singly oriented material in the same manner as the uppermost curve of FIG. 5 excels the lower curves.

tooth and then flows in a transverse direction along the arcuate edge 16. The double orientation is indicated at 18. For rotors the teeth will project radially outwardly from. a central portion. The average magnetic properties of a doubly oriented stator or rotor punchings will correspond to the top curve of FIG. 5.

For large electrical motors and generators the laminations are punched as segments or sectors as illustrated in FIG. 7. The magnetic sheet 20, having double orientation as shown in direction 22 along the length of the sheet and direction 23 transverse thereto, is punched to provide a series of magnetic segments 24 in which the teeth 26 are essentially parallel to the one preferred orientation 22 along the length of the sheet 20. Slots 28 are present between the teeth to receive coils therein. An arcuate edge 30 on each segment 24 is essentially parallel to the other preferred orientation 23. Magnetic flux developed in each of the teeth 26 travels in the one direction 22 of easiest magnetization, and then passes along the arcuate edge 30 also in the other direction 23 of easiest magnetization. The magnetic segments 24 of FIG. 7 will exhibit properties superior to those indicated in the top curve of FIG. 5. An assembled motor or generator comprising the lamination segments of FIG. 7 will possess outstanding characteristics.

In static induction devices, such as transformers and magnetic amplifiers, the double oriented magnetic sheets may be cut or punched into various shaped laminations to take advantage of such characteristics. In such laminations there are at least two linearly extending portions at right angles to each other, parallel to or in line with the two directions of preferred orientation of the magnetic material. In FIG. 8 is shown an L-punching 40 comprising one leg 42 and another leg 44 at right angles thereto. The L-punching 40 is so cut from a sheet of the doubly oriented aluminum-iron material of the present invention that one preferred orientation 46 is parallel to leg 42 while the other preferred direction 48 of orientation is parallel to leg 44. Transformers and other electrical devices built from the L-punchings 40 will exhibit outstanding magnetic properties.

Referring to FIG. 9, there is illustrated an E-punching 50, comprising a side 52 from which projects lengths 54, 56 and 58 at right angles thereto. The punching 50 is so made with respect to a sheet of doubly oriented aluminum-iron that one preferred direction 60 of orientation is parallel to side 52, and the other preferred direction 62 of orientation is parallel to the lengths 54, 56 and 58. Such laminations will give optimum magnetic cores.

It will be understood that the above description and drawings are exemplary and not limiting.

We claim as our invention:

1. In the process of producing sheets of aluminumiron' alloy comprising essentially from 1% to by Weight of aluminum and the 'balance being iron except for incidental impurities, the grains of the sheet being preferentially oriented so that the sheet exhibits optimum magnetic properties in two directions in the plane of the sheet, the steps comprising hot working a 'body of the aluminum-iron alloy at a temperature of the order of from 800 C. to 1100" C. to produce a plate of a thickness of the order of from 0.25 to 0.6 inch, cold rolling the plate to elfect a reduction in thickness of from 60% to 90%, annealing the resulting relatively thick sheet at a temperature of from 700 C. to 1050 C. [for at least minutes to remove stresses and to recrystallize the metal, cold rolling the thick sheet to elfect a second and final reduction in thickness of the order of from 60% to 90% so as to produce a thin sheet of a thickness of the order of 0.03 inch and less, and annealing the thin sheet in a reducing atmosphere at a temperature of from 900 C. 'to 1050 C. for at least one hour to recrystallize the alloy to cube on face grains, which grains have an average diameter not exceeding one millimeter.

2. 'In the process of producing a sheet of an alloy comprising essentially from 2% to 8% by weight of aluminum and the balance being iron except :for incidental impurities, the grains of the sheet being preferentially oriented so that the sheet exhibits optimum magnetic properties in two directions substantially at right angles to each other in the plane of the sheet, the steps comprising hot rolling an ingot of the aluminum iron alloy at a temperature of the order of from 900 C. to 31100" C. to produce a plate of a thickness of approximately 0.5 inc cold rolling the plate to effect a reduction in thickness of from to annealing the resulting relatively thick sheet in hydrogen at a temperature of from 900 C. to 1050 C. for a period of time of about one hour, cold rolling the thick sheet a second and final time to efifect a further reduction of from 60% to 90% to produce a thin sheet of a thickness of not in excess of about 0.040 inch, and annealing the thin sheet in hydrogen at a temperature of from 900 C. to 1050 C. for a period of at least one hour to recrystallize the alloy to produce cube on face grains not coarser than an average of 1 mm. diameter.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Bozorth: Ferromagnetism, 1951, D. Van Nostrand Co., Inc., pages 210 to 220, especially 2117 and 2:18.

Claims (1)

1. IN THE PROCES OF PRODUCING SHEETS OF ALUMINUMIRON ALLOY COMPRISING ESSENTIALLY FROM 1% TO 10% BY WEIGHT OF ALUMINUM AND THE BALANCE BEING IRON EXCEPT FOR INCIDENTAL IMPURITIES, THE GRAINS OF THE SHEET BEING PREFERENTIALLY ORIENTED SO THAT THE SHEET EXHIBITS OPTIMUM MAGNETIC PROPERTIES IN TWO DIRECTIONS IN THE PLANE OF THE SHEET, THE STEPS COMPRISING HOT WORKING A BODY OF THE ALUMINUM-IRON ALLOY AT A TEMPERATURE OF THE ORDER OF FROM 800*C. TO 1100*C. TO PRODUCE A PLATE OF A THICKNESS OF THE ORDER OF FROM 0.25 TO 0.6 INCH, COLD ROLLING THE PLATE TO EFFECT A REDUCTION IN THICKNESS OF FROM 60% TO 90%, ANNEALING THE RESULTING RELATIVELY THICK SHEET AT A TEMPERATURE OF FROM 700*C. TO 1050*C FOR AT LEAST 15 MINUTES TO REMOVE STRESSES AND TO RECRYSTALLIZE THE METAL, COLD ROLLING THE THICK SHEET TO EFFECT A SECOND AND FINAL REDUCTION IN THICKNESS OF THE ORDER OF FROM 60% TO 90% SO AS TO PRODUCE A THIN SHEET OF A THICKNESS OF THE ORDER OF 0.03 INCH AND LESS, AND ANNEALING THE THIN SHEET IN A REDUCTING ATMOSPHERE AT A TEMPERATURE OF FROM 900% C. TO 1050* C. FOR AT LEAST ONE HOUR TO RECRYSTALLIZE THE ALLOY TO CUBE ON FACE GRAINS, WHICH GRAINS HAVING AN AVERAGE DIAMETER NOT EXCEEDING ONE MILLIMETER.

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