US2539246A - Method of making aluminum clad steel - Google Patents

Description

Jan. 23, 1951 F. R. HENsEL 2,539,246

METHOD oF MAKING ALUMINUM CLAD STEEL Filed Oct.v'7, 1944 11 /lu//v//wr/M 1,2 1g

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` TWINS/7E 30 (mwN/www0 28 .STEEL v 2297 vf/e i I 4 /ll/M//VVM l ZZ? (ama/vm 42 #LUM/NUM .8.45.5 ZOY SIL V51? STEEL 4 I N V EN TOR. franz j?. fc/'mel WMM Patented Jan. 23, 1951 METHOD OF MAKING ALUMINUM CLAD STEEL Franz R. Hensel, Indianapolis, Ind., assigner to P. R.. Mallory & Co., Inc., Indianapolis, Ind., l corporation of Delaware Application October 7, 1944, Serial No. 557,703

2 Claims.

This invention relates to overlay metals of aluminum bonded to an iron group metal, and particularly to aluminum-steel overlay metal and its manufacture, and to aluminum-lined bearings.

2 The silver layer may be deposited by conventional electroplating methods. A suitable method is the following:

Silver plating on steel An object of the present invention is to improve 5 For an adherent plate of silver on steel sur- .alummum overlay metal and-the methods of ma?" face condition is of prime importance. The ideal 111g 1li and t0 improve alummum lmed bearmgs' surface is a chemically clean mirror finish Other Objects f the invention Wm be apparent To plate on a rolled steel surface from the description and claims.

In the drawings; m 1. Degrease 1n an organic solvent.

Figure 1 is a diagrammatic illustration of a 2 Electl'O-Clean aIlOdCallyprocess for making aluminum-steel overlay metal; A phosphate or silicate cleaner may be used,

Figure` 2 is a Sectional elevation illustrating such as Ano'dexn or uoakte #9011: another method of bonding aluminum to steel; p n

Figure 5 illustrates an aluminum lined bearing 3. Rinse, half shell embodying features of the present in- 4, sulfuric acid dip; vention. 10% acid by volume.

A number of methods of producing aluminum Time 1 minute, clad steel have been tried heretofore. One meth 5 Rinseod comprises dipping steel into a bath of molten 5 Copper gash; aluminum. `This method results in only a very s ti thin superficial layer which adheres to the steel olucon ,d by the formation of an iron-aluminum compound Fopper (f yam e-- "oz/gal" 1'4-2'0 which is extremely brittle. Another method com- Pre s? mm Cyamde 81'1 prises the rolling together 0f a thin aluminum To,assu,lm hydroxide 4'55 foil and steel. Again the bonding action is based n'sodlum phfspha 2 on the formation of the brittle iron-aluminum Copper modes' o compound which win fracture in bending and Temperatur? F 17o-175 which has a very low fatigue strength. It has Cflrrem denslty 45 A S-F also been suggested that a layer of zinc be inter- Tlme "mmutes" 2 posed between the aluminum and steel to avoid '7. Rinse the brittle iron-aluminum layer. This layer does 8. Sodium cyanide dip: not prevent the brittleness altogether and is char- 40 oz./ga1. acterized by low melting point and low strength. 40 sec,

The present invention overcomes all the objec- 9, Silver strike: tions of the prior methods and provides a strong, S 1 t. ductile fatigue resistant bond. This is accom- 40 ouslfn" .d rt 5 plished by providing a silver bonding layer be- Payer .cyam ed-grams per d1 er" tween the aluminum and steel. P tassium cyau e't 1 The preferred method of making the overlay To asslurl Car Ona e "0"-- 15 metal comprises bonding a layer of silver to the Cempeadure F- 90"95 steel surface and another layer of silver to the Tllrren ensl y 0A' S'F' aluminum surface and then bonding the layers me "Seconds" 20 together by heat and pressure. 10. Silver plate:

The preferred method of applying the silver to Soluti n the steel and to the aluminum is electroplating Sg .d ,2 although other methods may also be enployed 5. T1 Lamy "i-*grams per' mer" .6 such as silver vapor deposition, pressur/e bonding Pot im assmm cyan de D2 or fusion bonding. It is essential/that the silver To asslurl carbonate "g"- 38 adhere tightly to the steel 'and therefore the sur- Cempeadure C" 30 face of the steel must be carefully prepared to Hen ensl y 15 A' s' F' receive the-silver layer by cleaning, sand blast- Brightener of the carbondisulflde type may be ing, pickling and bright annealing if necessary.

used.

assegna .at this current density, silver will be deposited the rate oi' .0001" in 2.5 minutes. l

In the experimental work a plate .001" thick was deposited.

The aluminum must also be carefully cleaned and prepared to receive the silver deposit by using tor instance the following method:

Silver plating on, aluminum En plating on aluminum the time required for ancdimng and modification is dependent on the grade of aluminum and the nature of the alloy. The following flow sheet applies to pure aluminum.

i. Degrease with organic solvent. 23. Polish lightly with a mild abrasive. S. Etch in sodium cyanide:

solution- Sodium cyanide grams per liter-- 60 Time minutes l. Anodize:

Solution- Oxalic acid grams per liter-- 30 A. C. current:

Voltagel0 v. at startraised to 50 v. Timeminutes.

isn alkali metal carbonate-chromate may be used in anodizing.

5. Modify anodic iilm:

Solution- Sodium cyanide as above Time-5 minutes.

The modifying treatment may be either basic or acidic, using sodium cyanide or a dilute solution of hydro-uoric acid.

6. Rinse. 7. Nickel plate:

Sclution: (Watts type) Nickel sulfate grams per liter-- 330 Nickel chloride do 30 Boric acid do 30 Hydrogen peroxide to prevent gassing.

Temperature F 140 Current density 25-50 A. S. F.

At 25 A. S. F., nickel will be deposited at the rate of .0001 in 5 minutes. An .0002 plate Was deposited.

Any type of nickel bath may be used.

8. Rinse.

9. Sodium cyanide dip.

10. Silver strike-as in steel. 11. Silver plate-as in steel.

a sufficiently high pressure is applied. It can be stated that this phenomenon is a matter of cold welding. This is entirely different from the usual methods of pressure bonding where it becomes necessary to heat the parts close to their melting points. This type of cold welding is particularly useful in this invention where the cladding material is aluminum having a low melting point. Metals such as copper are undesirable because pressure bonding could only be accomplished at temperatures which are considerably above the melting of the aluminum or the aluminum alloy.

Referring to Figure 1 a process of making silver-steel overlay metal is illustrated diagrammatically. A strip of steel sheet Il is unwound from roll i4 and passes through a cleaning and electroplating apparatus I5 which applies a layer of silver to one surface of the steel strip. An aluminum strip E0 is simultaneously unwound from roll ii and passes through a cleaning and electroplating apparatus i2 to apply a layer of silver to one surface. The two silver plated strips l0 and i3 are then brought together with the silver plated faces in contact and led through a hydrogen furnace it which heats them to pressure bonding temperature in a hydrogen atmosphere. The contiguous strips emerge from the furnace through a hydrogen chamber ill and then pass between pressure rolls i3 and i9 which apply suiiicient pressure to bond the silver surfaces together thus completing the bimetal strip 20 which emerges from the process.

According to another method of carrying out the bonding process the silver coated sheets oi aluminum and steel are placed between pressure plates of a hydraulic press while being simultaneously heated in a reducing atmosphere. Figure 2 shows an arrangement suitable for this method comprising pressure plates 2l and 22 of a hydraulic press between which is interposed a stack comprising the following elements: iirst a Transite plate 23 against pressure plate 22 carrying an induction coil 24 disposed in suitable groovings in the plate. Above the Transite plate are stacked a carbon plate 25, the aluminum sheet 26 coated with silver layer 2l. steel plate 28 coated with silver layer 29 in contact with silver layer 21, carbon plate 30 and upper Transita plate 3l, grooved to carry induction coil 32. A hood 33 operating in a sand'seal 30 encloses the stack and permits the assembly to be enveloped in hydrogen. High frequency currents through induction coils 24 and 32 heat up the carbon plates 25 and 30 and the aluminum and steel layers until the pressure bonding temperature is reached. Pressure is applied either simultaneously or subsequently by pressure plates 2l and 22 to complete the bond between the two silver surfaces. If relatively thick aluminum and steel layers are used, the bonded slab may subsequently be rolled down to a suitable thickness for the use contemplated.

In some cases the carbon plates 25 and 30 may be eliminated in the assembly described and the aluminum and steel plates heated directly by the induction coils. The plates may also be heated by a hydrogen flame or by substituting heating coils for the induction coils 24 and 32. In this case the heating coils are mounted as closely to the aluminum and steel plates as possible.

Another suitable method consists in stacking a number of bimetal assemblies on top of each other into a furnace operating in a non-oxidizing atmosphere. Hydraulic or mechanical means are provided to move the bottom of the furnace against the bimetal stacks thereby exerting sufficient pressure to cause cold welding of the silver faces to each other.

It is sometimes desirable, especially where subsequent reductions are to be made, to place the aluminum slab into a recess 'in the steel. The recess may be formed by a machining operation or by use of apre'rolled steel section such as a U or I section. The steel recess may be electroplated with silver or coated with silver has been carefully cleaned and coated with silver and then placed in the recess after which the assembly is heated and rolled in a reducing atmosphere to complete the bond.

If the side walls of the steel section are tightly crimped over the coated aluminum to force the latter into intimate contact with the coated steel, it will not always be necessary to roll the assembly in a reducing atmosphere as sumcient pressure will be maintained between the surfaces to substantially exclude oxidizing gases prior to bonding. The higher expansion coemcient of aluminum also promotes a tight joint.

Figure 3 shows a steel U section 36 lined with a silver layer 36 and enclosing a slab of aluminum 3l to be bonded to the silver plated steel surface. The edges lof the steel are crimped over at 38 to substantially seal the joint preparatory to rolling.

Figure 4 shows an assembly using a steel I section 39 both grooves of which are plated with silver layers 40 after which aluminum slabs Il are inserted and the edges 42 of the steel :langes are turned over on top of the aluminum slabs.

After bonding, the assemblies are rolled down to the desired thickness, the flanges on the steel members preventing the spreading of the more plastic aluminum during rolling and thus maintaining the same ratio of aluminum to steel as the overall thickness is reduced.

While the thickness of the silver bonding layers may vary considerably, it is preferred for most applications that the total thickness of silver between the aluminum and steel amount to between .0003 to .006". Thus where both the aluminum and steel surfaces are plated with silver prior to bonding, each layer of silver may be within the range .00015 to .003. If the bonded overlay metal is subsequently reduced by rolling, the thickness of the silver layer will of course also be reduced in the nished bimetal.

Silver offers several advantages in the making of aluminum-steel overlay metals as described herein. The silver bonds readily to both aluminum and steel and while the metallurgical characteristics of this excellent bond are not completely understood, it is believed that the bonds consist of a combination of ilne silver, silveraluminum alloys and silver-iron alloys. Since silver welds readily to itself at relatively low temperatures such as 350 to 500 C. the bonding can be produced without the detrimental eiects of overheating the aluminum.

Various steels may be used in forming the overlay metal such as ductile carbon or alloy steels in addition to low carbon steel. Commercial aluminum or aluminum base alloys may be used for the aluminum component.

y Austenitic steels such as nickel, nickel manganese, nickel chromium compositions may also be used having a coefllcient of expansion matching the coeflicient of the aluminum or aluminum alloy, or in some cases the steel may be selected to match the coefcient of the silver layer. s In place of steel, ductile nickel and cobalt base alloys may be used, such as Monel'metal, and the standard nickel-manganese alloys, such as A, B, C and D nickel.

Figure 5 shows another embodiment of the invention wherein a case and silver coated aluminum alloy bearing lining half shell 43 is pressed into a silver coated half shell backing M. The lining is bonded to the backing by simultaneously applying heat and pressure between suitably formed dies in a reducing atmosphere. The two silver coatings weld together into a single bonding layer 45.

The term aluminum in the claims is intended to include aluminum base alloys.

While speciilc embodiments of the invention have been described, it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. The continuous method of making aluminum-steel overlay metal from layers of aluminum and steel which comprises cleaning the bonding surfaces oi the aluminum and steel layers, coating the cleaned surfaces of both said layers with layers of silver having thicknesses not over .003, placing said layers of aluminum and steel together with the silver coatings in contact, preheating the layers in a non-oxidizing atmosphere to a temperature below the melting point of silver and between about 350 and about 500 C., and hot rolling said preheated layers to reduce the thickness of the layers and to permanently bond the layers together.

2. Ihe continuous method of making an aluminum-lined steel-backed bearing which comprises cleaning the bonding surfacesl of an aluminum lining and of a steel backing layer, passing the said layers through individual silver plating baths to deposit thereon coatings of silver having thicknesses not over .003", placing said layers together with the silver coatings in contact, preheating the layers in a nonoxidizing atmosphere to a temperature below the melting point of silver and between about 350 and y500 C., and hot rolling said preheated layers to reduce the thickness of the layers and to permanently bond the layers together.

FRANZ R. HENSEL.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 625,117 Martin May 16, 1899 673,126 Martin Apr. 30, 1901 685,758 Griffith Nov. 5, 1901 757,852 Wachwitz Apr. 19, 1904 894,163 Monnot July 21, 1908 894,164 Monnot July 21, 1908 909,924 Monnot Jan. 19, 1909 929,778 Monnot Aug. 3, 1909 1,156,169 Monnot Oct. 12, 1915 1,554,097 Jordan Sept. 15, 1925 1,731,790 Payne Oct. 15, 1929 1,792,377 Jordan Feb. 10, 1931 1,850,997 Assmann Mar. 29, 1932 2,094,483 Weder Sept. 28, 1937 2,171,040 Merritt Aug. 29, 1939 2,266,276 Schluchter Dec. 16, 1941 2,266,319 Hobbs Dec. 16, 1941 2,269,523 Deutsch Jan. 13, 1942 2,277,023 Steiner Nov. 17, 1942 2,289,572 Underwood July 14, 1942 2,294,404 Hensel Sept. 1, 1942 (Other references on following page) Number Number Great Britain May 7, 1942 OTHER REFERENCEB- P. 130. Aviation. Jan. 1927. pub. by the Gardner Pub. Co., Inc. Copy in- Aviation, voi. 22, Library P.O. T1, 501,' A8.

Pp. 188, 189, 271, 272, Silver in Industry (1940) by Lawrence Addicks, Reinhold Pub. Corp., 330 West 42nd St., New York, N.Y. (Copy in Div. 14.)

Claims (1)

1. THE CONTINUOUS METHOD OF MAKING ALUMINUM-STEEL OVERLAY METAL FROM LAYERS OF ALUMINUM AND STEEL WHICH COMPRISES CLEANING THE BONDING SURFACES OF THE ALUMIUM AND STEEL LAYERS, COATING THE CLEANED SURFACES OF BOTH SAID LAYERS WITH LAYERS OF SILVER HAVING THICKNESSES NOT OVER .003", PLACING SAID LAYERS OF ALUMINUM AND STEEL TOGETHER WITH THE SILVER COATINGS IN CONTACT, PREHEATING THE LAYERS IN A NON-OXIDIZING ATMOSPHERE TO A TEMPERATURE BELOW THE MELTING POINT OF SILVER AND BETWEEN ABOUT 350* AND ABOUT 500* C., AND HOT ROLLING SAID PREHEATED LAYERS TO REDUCE THE THICKNESS OF THE LAYERS AND TO PERMANENTLY BOND THE LAYERS TOGETHER.

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