US3902930A

US3902930A - Method of manufacturing iron-silicon-aluminum alloy particularly suitable for magnetic head core

Info

Publication number: US3902930A
Application number: US339829A
Authority: US
Inventors: Takeo Sata; Tomoo Yamagishi; Kanzaburou Iijima
Original assignee: Nippon Gakki Co Ltd
Current assignee: Nippon Gakki Co Ltd
Priority date: 1972-03-13
Filing date: 1973-03-09
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02
Also published as: DE2312430B2; GB1376852A; NL7303477A; DE2312430A1

Abstract

A silicon layer is first formed on the surface of an ironaluminum (Fe-Al) alloy and is then diffused into the Fe-Al alloy by subjecting the silicon layer thus formed on the alloy to a substantial amount of heat, so that an iron-silicon-aluminum alloy or the so-called sendust alloy can be produced. The Fe-Al alloy may be ion-bombarded before the silicon layer is deposited thereon, so as to prevent the silicon layer from peeling off during the silicon-layer-depositing process. According to another aspect of this invention, an Fe-Al alloy is siliconized through the chemically siliconizing process and then the silicon contained in the siliconized alloy is diffused to obtain the resultant sendust alloy. By the adoption of this invention, sendust alloys having a greater range of thickness, from thin to thick, can be produced without any complicated process, and moreover, the layer of silicon will never come off during the manufacturing process. The sendust alloy thus produced is quite suitable for use as the core material of magnetic heads requiring highly desirable performance.

Description

United States Patent [191 Sata et al.

[4 1 Sept. 2, 1975 METHOD OF MANUFACTURING IRON-SILICON-ALUMINUM ALLOY PARTICULARLY SUITABLE FOR MAGNETIC HEAD CORE [75] Inventors: Takeo Sata; Tomoo Yamagishi;

Kenzaburou Iijima, all of Hamamatsu, Japan [73] Assignee: Nippon Gakki Seizo Kabushiki Kaisha, Japan [22] Filed: Mar. 9, 1973 [21] Appl. No.: 339,829

148/3l.55, 111, 112, 113, 188, 189, 1.5; 117/106 A, 107, 107.2 R, 130; 204/164, 192

[56] References Cited UNITED STATES PATENTS 2,193,768 3/1940 Masurnoto et a1. 75/124 2,911,533 11/1959 Damask l48/l.5 3,159,511 12/1964 'Taguchi et al..... 148/111 3,224,909 12/1965 Sixtus et al. 148/113 3,230,074 l/1966 Roy et al. 75/124 3,347,718 10/1967 Carpenter et al. 148/11'1 3,384,517 5/1968 Harper et a1 75/124 3,385,725 5/1968 Schmeckenbecher 1 17/130 3,423,253 l/1969 Ames et a1. 148/113 3,681,152 8/1972 Staley et a1. 148/113 3,718,502 2/1973 Gibbons 148/188 3,756,867 9/1973 Brissoneau et a1 148/1 1 1 Primary ExaminerWalter R. Satterfield Attorney, Agent, or FirmCushman, Darby & Cushman [5 7] ABSTRACT A silicon layer is first formed on the surface of an iron-aluminum (Fe-Al) alloy and is then diffused into the Fe-Al alloy by subjecting the silicon layer thus formed on the alloy to a substantial amount of heat, so that an iron-silicon-aluminum alloy or the so-called sendust alloy can be produced. The Fe-Al alloy may be ion-bombarded before the silicon layer is deposited thereon, so as to prevent the silicon layer from peeling off during the silicon-layer-depositing process.

According to another aspect of this invention, an Fe-Al alloy is siliconized through the chemically siliconizing process and then the silicon contained in the siliconized alloy is diffused to obtain the resultant sendust alloy.

By the adoption of this invention, sendust alloys having a greater range of thickness, from thin to thick, can be produced without any complicated process, and moreover, the layer of silicon will never come off during the manufacturing process. The sendust alloy thus produced is quite suitable for use as the core material of magnetic heads requiring highly desirable performance.

3 Claims, 2 Drawing Figures METHOD OF MANUFACTURING IRON-SILICON-ALUMINUM ALLOY v PARTICULARLY SUITABLE FOR MAGNETIC HEAD CORE BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to an iron-silicon aluminum alloy or the so-called sendust alloy, especially suitable for use as magnetic head cores. More particularly, the present invention concerns a method of making a sendust alloy by diffusing silicon in an Fe-Al alloy and also concerns a magnetic head core made of such an Fe-Si-Al alloy.

2. Description of the prior art Sendust alloy is of a high hardness and a high magnetic permeability. Accordingly, it is suitable for use as the material of, for example, magnetic recording (or reproducing) heads for video tape recorders or for audio tape recorders. In a video tape recorder, for instance, it is necessary to make a high density recording of signals onto a magnetic recording tape and also to reproduce such signals recorded on the tape. For this purpose, the magnetic heads of the recorder are required to have a high ability of performance. These magnetic heads, in turn, require that their core is made of a magnetic material having a high magnetic permeability with little loss of permeability during use. The majority of this loss occurring in the magnetic material is represented by the eddy current loss. This eddy current loss decreases more as the specific resistance by volume of the material increases higher. For this reason, it has been the practice to construct the core of a magnetic head by laminating, in several layers, sheets of the material as thin as possible to impart a required magnetic characteristic. There have been used permalloy and ferrite made in the aforementioned fashion. It is, however, desirable to use sendust alloy from the viewpoint such as the magnetic permeability. However, this sendust alloy is very high in its hardness and accordingly it is quite difficult to shape it into a plate form by rolling. For this reason, in the preparation of thin sendust alloy plates, it has been the practice to rely on the following methods. One of them is to obtain thin plates from a pre-cast alloy block by cutting it with a grinder or by electrolytic cutting or discharge cutting. Another one of them is to manufacture thin plates by subjecting powder of material to sintering at high temperature or to discharge-sintering or to rolling. Still another one of them is to obtain thin plates by vapor plating method from the vapor of a compound of iron, aluminum, silicon or the like. However, each of these known methods requires a fairly long time till the product is obtained. Moreover, such a known method has further drawbacks that the manufacturing process is complicated or that it is difficult to produce thin plates. One such known method has a difficulty in producing thick plates, and another known method has a difficulty in processing the material into a required shape.

SUMMARY OF THE INVENTION It is, therefore, a primary object of the present invention to provide a method of easily making a high quality iron-silicon-aluminum or sendust alloy of a desired shape.

Such iron-silicon-aluminum or sendust alloy intended to produce by the method of this invention is an alloy consisting preferably of 4 to 8% of aluminum, 8 to 12% of silicon and the remainder of iron.

Another object of the present invention is to provide a method of especially making very thin sendust alloy with easiness.

It has been found by the inventors that the aforesaid objects can be attained basically by first forming a silicon layer on the surface of an Fe-Al alloy or by first siliconizing an Fe-Al alloy through the siliconizing process and then by diffusing the silicon into the alloy.

However, in the case where the silicon is deposited on the surface of the Fe-Al alloy, it sometimes occurs that the layer of silicon comes off during the manufacturing process.

Therefore, it is a further object of the present invention to provide a method which ensures that the layer of silicon does not come off during the manufacturing process of an Fe-Si-Al alloy by the said diffusion method.

Still another object of the present invention is to provide magnetic head cores made of a sendust alloy prepared according to the above-mentioned method of the present invention.

These as well as other objects, features and advantages of the present invention will become apparent by reading the following detailed description of the invention when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a photograph of actual size showing the state in which a layer of silicon is formed on an Fe-Al alloy which has not been given an ion bombardment treatment.

FIG. 2 is a'photograph of real size showing the state in which a layer of silicon is formed on an Fe-Al alloy according to the method of the present invention- DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will hereunder be described in further detail by referring to the accompanying drawings. An iron-silicon-aluminum or sendust alloy intended to produce by the method of this invention is an alloy consisting preferably of 4 to 8% of aluminum, 8 to l2of silicon and the remainder of iron.

According to the method of manufacturing such a sendust or iron-silicon-aluminum (Fe-Si-Al) alloy according to the present invention, there is first formed a layer of silicon on the surface of an iron-aluminum (Fe-Al) alloy (for example, Al; 6%, the remainder Fe), and then the resulting alloy is subjected to a high temperature to diffuse silicon into the Fe-Al alloy, thereby making a sendust alloy consisting of Fe-Si-Al.

As the methods of forming a layer of silicon on the surface of an Fe-Al alloy, there are those methods one of which is to heat silane or dichloro silane or the like in a vacuum vessel to evaporation-deposit silicon on the surface of the alloy. Another method is to deposit silicon on the surface of the alloy by sputtering in a vacuum vessel. Each of these methods may be employed.

In order to effect diffusion of silicon in an Fe-Al alloy, an Fe-Al alloy on which a layer of silicon has been formed is heated in a diffusion furnace to diffuse silicon into this alloy, thereby making a sendust alloy. However, in case a silicon layer is deposited by heating an Fe-Al alloy plate as stated above, there is the fear that the thus formed layer of silicon comes off the surface of the alloy plate due to the difference in the expansion coefficient between the formed silicon layer and the Fe-Al alloy plate carrying this layer when the latter plate is cooled close to room temperature. In such an instance, the fear of this silicon layer to come off can be eliminated by performing the diffusion treatment while maintaining the silicon layer-coated Fe-Al alloy plate at a high temperature, preferably from 900 to 1,300C.

The aforesaid Fe-Al alloy which is used in the aforesaid process may be formed into a plate having a thickness of 5 to 500 micrometers (pm), which can be easily obtained by rolling and also can be easily punched. Using this alloy plate, depositing a layer of silicon thereon and then diffusing silicon therein, it is possible to obtain a sendust alloy of a desired shape such as a plate having a considerable thickness or having a small thickness or a plate of a shape formed by punching. In case a thin plate of Fe-Al alloy is not of an extremely complicated configuration, it is still possible to punch this alloy plate even after silicon has been diffused therein.

As an alternative method of making a sendust alloy, there is considered a method by first depositing Al on the surface of an Fe-Si alloy plate (Si the re mainder Fe), and then by diffusing Al in this Fe-Si alloy. This method, however, is not practical in that it is difficult to roll the Fe-Si alloy. Also, there is considered a method of making a sendust alloy either by the use of an Fe-Si alloy containing therein silicon to such a degree as will permit rolling of this alloy and by depositing both Al and Si in appropriate amounts onto this alloy, or by the use of an Fe-Si-Al alloy containing therein both Si and Al to such a degree as will permit the rolling of this alloy and by depositing thereon Si and Al in appropriate amounts, and by diffusing Si and Al into the resulting alloy having Al and Si deposited thereon as a layer. In each of these methods, it is to be understood that, because Si diffuses quicker than does Al, there is a difficulty in the control of the ratio of silicon and aluminum in such layer and the control of the temperature for the diffusion, thus making these methods impractical.

When compared with these methods mentioned in the preceding paragraph, the method of making a sendust alloy according to the present invention which is designed to form a silicon layer whose diffusion speed is greater than aluminum on the surface of an Fe-Al alloy and to diffuse silicon into this alloy is most advantageous.

Next, there will be described an example of the aforesaid method of the present invention.

An Fe-Al alloy plate containing 6% of aluminum is rolled to a plate of 0.05 mm in thickness. Then, the surface of this alloy plate is cleaned by electrolytic polishing. The resulting alloy base plate is placed in a vacuum vessel in which silicon is heated to cause silicon to evaporate by the use of an electron beam. As a result, a layer of silicon having a thickness of 0.014 mm is deposited on the surface of the thin Fe-A] alloy plate. In the same way, a layer of silicon having a thickness of 0.014 mm is deposited on the other side of said thin alloy plate. Thereafter, the resulting thin plate is placed in a diffusion furnace held at 1,200C to subject it to a diffusion treatment for 60 minutes in a high purity hydrogen currents to prevent oxidation of silicon.

The sendust alloy plate made according to the method described above shows the following magnetic characteristic at 0.4 A/m:

initial relative magnetic permeability 8,000 maximum relative magnetic permeability 25,000

Thus, the aforesaid method of manufacturing a sendust r alloy of the present invention is shown to be superior to the prior art. In the above-described example, the diffusion treatment is carried out at a temperature of l,200C for 60 minutes in a hydrogen gas. However, it is further ascertained that the temperature may range from 900 to l,300C and that the time during which such temperature is maintained is varied depending on the temperature selected and the thickness of the Fe-Al alloy as well as the amount of silicon. Instead of the hydrogen gas used in the above-mentioned example, a helium, argon, or nitrogen gas may be used, or the diffusion treatment may be carried out in a vacuum.

According to another embodiment of the present invention, there is provided an improved method of making a sendust alloy such that, during the manufacture of a thin Fe-Si-Al alloy plate by first forming a layer of silicon on the surface of a thin Fe-Al alloy plate and then by diffusing silicon in this alloy by heating the alloy carrying said layer, there occurs no separation of the layer of silicon formed.

More specifically, in the method of manufacturing a thin Fe-Si-Al alloy plate by first forming a layer of only silicon on the surface of a thin plate of Fe-Al alloy obtained by rolling an Fe-Al alloy block having a relatively low hardness than a'sendust alloy and then by diffusing silicon into the alloy by heating the silicon layercarrying alloy plate in an atmosphere such as hydrogen, there has been a difficulty encountered during the step of forming the layer of silicon on the surface of the thin Fe-Al alloy base plate by deposition of silicon by an electron beam or like method because of the fact that, in case the thickness of the silicon layer being formed is of a thickness especially in the order of 5-10, pm, the silicon layer comes off in fibrous manner as shown in FIG. 1. This is considered to be due to the following reasons. One of the reasons is that, owing to the development of contamination, such as oxidation, of the surface of the Fe-Al alloy in its stage before the formation of the silicon layer, the direct deposition of the silicon layer onto the surface of the Fe-Al alloy base plate is obstructed by this contamination. Another reason is that there is a difference in the thermal expansion coefficient between the Fe-Al alloy and silicon layer so that there develops shearing force due to the change in the temperatures of these members, causing the silicon layer to come off the base plate.

This method according to another embodiment of the present invention solves these drawbacks and insures that, during the formation of a silicon layer on the surface of an Fe-Al alloy base, this layer of silicon never comes off the base plate. To this end, the surface of the Fe-Al alloy base plate is subjected to an ion bombarding treatment prior to the formation of a silicon layer on this surface.

This improved method will hereunder be described in further detail. Firstly, a thin Fe-Al alloy plate having a desired thickness of pm or less is prepared by rolling an Fe-Al block. This thin alloy plate is placed within a bell jar filled with argon gas held at a pressure of 10 to 10 mmHg. Thereafter, the surface of the thin plate is subjected to ion bombardment with argon ions for about minutes by the ion bombarding device provided in said bell jar. Then, by an electron beam or like means, a layer of silicon is evaporation-deposited on the surface of the plate to a thickness of about 10 ,um. Thereafter, the resulting plate carrying this silicon layer is heated to diffuse silicon into the alloy. Thus, a thin Fe-Si-Al alloy plate is produced.

FIG. 2 shows such a thin Fe-Al-Si'alloy plate produced according to said'embodiment of the present invention. It is to be noted that this product is made in a manner similar to that for the manufacture of the product shown in FIG. 1 excepting the fact that the former is subjected to ion bombardment. According to this embodiment, the adherency of the silicon layer, as it is being formed, to the surface of the Fe-Alalloy base plate is such that no fibrous peel-off of the silicon layer occurs at all. A peel-off test in which the silicon layer of a specimen plate is first given a number of intersecting cutting lines so that the layer is divided intoa number of small rectangular sections and in which pieces of adhesive tape are attached to the whole surface of the rectangular sections and thereafter are removed therefrom, shows the result that only 50% or less of the small rectangular sections of the silicon layer remained without peeling off the Fe-Al alloy base plate in case this Fe-Al alloy has not been given ion bombardment, whereas this percentage increases to 100% when the method of said embodiment using ion bombardment is adopted. Thus, there has successfully become no local coming-off of the silicon layer as it is being formed on the surface of the Fe-Al alloy base plate. This is considered to be due to the fact that any contamination presem on the surface of the Fe-Al alloy base is removed by the ion bombardment and also that, owing to the surface of this alloy being activated by the argon ions, the silicon layer is caused to more firmly adhere to the base plate, facilitating the deposited silicon to diffuse in the alloy at the surface region thereof.

As stated above, according to this method of the present invention, it becomes possible to form, in a stable manner, a silicon layer of a desired thickness on the surface of a thin Fe-Al alloy base plate, and this is quite advantageous for the manufacture of a thin sendust alloy plate.

7 According to still another embodiment of the present invention, the iron-silicon-aluminum alloy is produced by first siliconizing an Fe-Al alloy base plate through the chemically siliconizing process and then by diffusing the siliconized alloy at a high temperature. Explaining an example of this method, a block of Al-Fe alloy consisting, for example, of 5.6% of aluminum the remainder of iron and having been shaped previously by a predetermined method is rolled to have a desired thickness, for example, 0.2 mm (a thickness range of 0.1 to 2 mm is preferred). This plate of alloy is then punched into the shape of, for example, the core of a magnetic head. This shaped thin Al-Fe alloy plate is introduced into, for example, a reaction furnace held at l,200C. Into this furnace is supplied, for example, an argon gas current containing 10 volume percent of silicon tetrachloride (SiCl at the rate of 100 cc per minute. Under this condition, siliconizing of the Fe-Al alloy base plate is conducted for 10 minutes. As a result, silicon tetrachloride reacts against the Al-Fe alloy plate and silicon infiltrates in the region close to the surface of the Al-Fe alloy plate, forming there a layer of infiltrated silicon or siliconized layer. The resulting alloy plate having saidlayer of infiltrated silicon close to the surface of this alloy is placed in a diffusion furnace held at, for example, l,200C and is heated for 30 minutes in hydrogen gas currents of high purity to perform diffusion of silicon in the Al-Fe alloy. Instead of the hydrogen gas, a helium, argon, or nitrogen gas may be used, or the diffusion is carried out in a vacuum. During this diffusion treatment, the component silicon contained in the siliconized layer which has been formed close to the surface of the Al-Fe alloy plate is caused to diffuse uniformly in the alloy. Thus, a sendust alloy is produced. In the example set forth above, the reaction and diffusion furnaces are held at a temperature of 1,200C, but the temperature at which the reaction and diffusion furnaces are held may range from 900 to 1,300C. Also, the volume percent of the silicon tetrachloride contained in the argon gas may be from I to 20 volume'percent.

According to this method, rolling or desired punching is performed on the Al-Fe alloy plate in the stage before being added with silicon. Thus, it is possible to arbitrarily set the thickness and configuration as required. This method is especially effective in the manufacture of a sendust alloy of a small thickness. If such thin pieces of sendust alloy prepared according to this method are used as the magnetic material of the core of magnetic heads for instance, it is possible to construct a core by laminating several very thin pieces of sendust alloy one upon another. Thus, it is possible to obtain a highly capable magnetic head presenting a very low loss of eddy current and yet exhibiting an excellent magnetic characteristic. More specifically, a sendust alloy plate prepared in the manner described above is heated at 1,000C for minutes in a high purity hydrogen, then cooling it to 700C at which temperature the plate is held for 30 minutes. Thereafter, the plate is cooled from 700C to room temperature at the rate of lowering by 300C per hour. The resulting alloy plate having received the aforesaid heat treatment, which is now used as a magnetic material, shows a magnetic characteristic: at 0.8 A/m, the initial relative magnetic permeability of 8,000 and the maximum relative magnetic permeability of 35,000. Thus, a sendust alloy having a very good magnetic characteristic is obtained.

According to this method, only 10 minutes are required for the siliconizing process and only 30 minutes for the diffusion as stated above. If the Al-Fe alloy is prepared in advance, or even when the entire steps are included, the time required for the manufacture is markedly reduced so that it is possible to remarkably enhance the productivity.

By adopting the aforesaid siliconizing process which is conducted in a silicon compound atmosphere, it is possible to form a siliconized layer containing silicon of at least 15% or higher in content. Thus, it is possible to manufacture a sendust alloy having a silicon content of a high percentage. Also, it is possible to freely control the percentage of silicon to be contained in the alloy by setting the condition of the reaction furnace, the condition of the atmosphere and time as required. Thus, it is possible to obtain a sendust alloy having such a quality as is optimum for the purpose of use.

In the example described above, a mixed atmosphere consisting of argon current containing silicon tetrachloride is used. It should be understood, however, that the type of atmosphere is not limited thereto, but a mixed atmosphere consisting of silicon tetrachloride and hydrogen or nitrogen as a carrier, or a mixed atmosphere consisting of silane or dichloro silane and hydrogen or argon or nitrogen as a carrier may be used also.

As stated above, according to the method of the present invention, it is possible to manufacture a very thin sendust alloy of high quality suitable for use as the material of, for example, magnetic head cores or a sendust alloy of high quality having a desired configuration, within a short period of time and with ease.

We claim:

1. In a method for forming iron-silicon-aluminum alloy exhibiting high magnetic permeability, said alloy composed of 4 to 8% aluminum, 8 to 12% silicon, balance iron, the steps of:

a. forming a layer of silicon onto the surface of an iron-aluminum alloy by:

vacuum depositing silicon onto the surface of the Fe-Al alloy by heating a silane or dichlorosilane under vacuum conditions; or

sputtering silicon onto the surface of the Fe-Al alloy under vacuum conditions; and thereafter b. heating the thus-coated alloy of step (a) in a diffusion furnace at a temperature of about 900 to about 1,300C and diffusing the silicon layer uniformly into the underlying Fe-Al alloy, the high temperature employed avoiding separating and improving the adherency of the deposited silicon layer during process, to produce said alloy com- 8 posed of 4 to 8% aluminum, 8 to 12% silicon and balance iron.

2. In a method of forming an iron-silicon-aluminum alloy exhibiting high magnetic permeability, said alloy composed of 4 to 8% aluminum, 8 to 12% silicon, balance iron, the steps of:

a. preparing a Fe-Al alloy plate to the desired configuration;

b. exposing the thus prepared plate to ion bombardment in an argon atmosphere;

c. applying to the surface of the plate a layer of silicon; and immediately thereafter (1. diffusing the silicon layer uniformly into the Fe-Al alloy by heating the coated plate in an atmosphere inert to the silicon layer at a temperature of about 900 to about 1,300C thereby providing an adherent silicon layer onto the surface of and into the plate.

3. The process of claim 2 including the additional step of:

e. cooling the thus-heated plate from the temperature of the diffusion step to 700C and maintaining that temperature for 30 minutes and then cooling to room temperature by lowering the temperature thereof at a rate of about 300C per hour, to produce said alloy composed of 4 to 8% aluminum, 8

to 12% silicon and balance iron.

Claims

1. IN A METHOD FOR FORMING IRON-SILICON-ALUMINUM ALLOY EXHIBITING HIGH MAGNETIC PERMEABILITY, SAID ALLOY COMPOSED OF 4 TO 8% ALUMINUM, 8 TO 12% SILICON, BALANCE IRON, THE STEPS OF, A. FORMING A LAYER OF SILICON ONTO THE SURFACE OF AN IRONALUMINUM ALLOY BY: VACUUM DEPOSITING SILICON ONTO THE SURFACE OF THE FE-AL ALLOY BY HEATING A SILANE OR DICHLOROSILNE UNDER VACUUM CONDITIONS, OR SPUTTERING SILICON ONTO THE SURFACE OF THE FE-AL ALLOY UNDER VACUUM CONDITIONS, AND THEREAFTER B. HEATING THE THUS-COATED ALLOY OF STEP (A) IN A DIFFUSION FURNACE AT A TEMPERATURE OF ABOUT 900* TO ABOUT 1,300*C AND DIFFUSING THE SILICON LAYER UNIFORMLY INTO UNDERLYING FE-AL ALLOY, THE HIGH TEMPERATURE EMPLOYED AVOIDING SEPARATING AND IMPROVING THE ADHERENCY OF THE DEPOSITED SILICON LAYER DURING PROCESS, TO PRODUCE SAID ALLOY COMPOSED OF 4 TO 8% ALUMINUM, 8 TO 12% SILICON AND BALANCE IRON.

2. In a method of forming an iron-silicon-aluminum alloy exhibiting high magnetic permeability, said alloy composed of 4 to 8% aluminum, 8 to 12% silicon, balance iron, the steps of: a. preparing a Fe-Al alloy plate to the desired configuration; b. exposing the thus prepared plate to ion bombardment in an argon atmosphere; c. applying to the surface of the plate a layer of silicon; and immediately thereafter d. diffusing the silicon layer uniformly into the Fe-Al alloy by heating the coated plate in an atmosphere inert to the silicon layer at a temperature of about 900* to about 1,300*C thereby providing an adherent silicon layer onto the surface of and into the plate.

3. The process of claim 2 including the additional step of: e. cooling the thus-heated plate from the temperature of the diffusion step to 700*C and maintaining that temperature for 30 minutes and then cooling to room temperature by lowering the temperature thereof at a rate of about 300*C per hour, to produce said alloy composed of 4 to 8% aluminum, 8 to 12% silicon and balance iron.