US3551996A - Process for the production of aluminum-steel composite - Google Patents

Abstract

A HIGH STRENGTH ALUMINUM-STEEL COMPOSITE IS FORMED BY COMPRESSING AT ELEVATED TEMPERATURES AN ASSEMBLED STACK OF AT LEAST TWO SHEETS OF ALUMINUM HAVING STEEL WIRES SANDWICHED THEREBETWEEN, WITH ONE OF THE OPPOSING SURFACES OF THE SHEETS HAVING A GROOVE FORMED THEREIN, THE FORCE UNDER WHICH THE ASSEMBLY IS COMPRESSED BEING SUFFICIENT TO FILL IN THE GROOVE AND THEREBY EXPOSE FRESH METAL SURFACE WHICH FORMS A SUBSTANTIALLY CONTINUOUS METALLURGICAL BOND BETWEEN THE OPPOSING SHEET SURFACES.

Description

1971 E. v. SUMNER ETAL 3,551,996

PROCESS FOR THE PRODUCTION OF ALUMINUM-STEEL COMPOSITE Original Filed Oct. 2, 1967 United States Patent 3,551,996 PROCESS FOR THE PRODUCTION OF ALUMINUM-STEEL COMPOSITE Edwin V. Sumner, Alhambra, Donald Q. Cole, Los

Angeles, and Le Roy W. Davis, San Pedro, Calif., assignors to Harvey Aluminum, Incorporated Application Oct. 2, 1967, Ser. No. 672,048, which is a continuation-in-part of applications Ser. No. 571,301 and Ser. No. 571,322, both filed Aug. 9, 1966. Divided and this application Aug. 14, 1969, Ser. No. 862,132 Int. "Cl. B23k 31/02 U.S. Cl. 29-4723 9 Claims ABSTRACT OF THE DISCLOSURE A high strength aluminum-steel composite is formed by compressing at elevated temperatures an assembled stack of at least two sheets of aluminum having steel wires sandwiched therebetween, with one of the opposing surfaces of the sheets having a groove formed therein, the force under which the assembly is compressed being sufiicient to fill in the groove and thereby expose fresh metal surface which forms a substantially continuous metallurgical bond between the opposing sheet surfaces.

This is a divisional application of co-pending United States patent application Ser. No. 672,048, filed Oct. 2, 1967, which is a continuation-in-part application of our co-pending United States patent applications, Ser. Nos. 571,322 and 571,301 each filed Aug. 9, 1966.

In the conventional manufacture of aluminum-steel composites, steel wire is placed between aluminum sheets in a groove formed in the surface thereof the resultant stacked sheets then being passed between a pair of rolls to force aluminum metal into the groove and about the surface of the wire (see U.S. Patent No. 3,201,862). When high strength steel wire is consolidated according to this process, only a relatively low rolling reduction of the stacked sheets can be effected without rupture of the wire because aluminum being extruded outwardly may stress the brittle wire in contact therewith beyond its elastic limit.

By carrying out this process with only a small rolling reduction in the sheet thickness, the oxide coating on the surface of the sheet remains substantially intact and little or no fresh aluminum surface is exposed to form a sound metallurgical bond. Consequently, the resultant rolled sheets are held together at their surfaces principally by means of weak mechanical bonds formed between the aluminum oxide coatings and usually less than about 15% of the sheet surface is bonded metallurgically to an adjacent sheet. Since rupture of the mechanical bonds and resultant delamination of individual sheets can occur under conditions of high stress, composites produced in this manner are unsatisfactory for many applications.

Efforts have been made to produce a stronger aluminum-steel composite and minimize weak mechanical bonds in its matrix by flame spraying aluminum in an inert atmosphere onto a plurality of spaced steel wires. The sprayed aluminum matrix is, however, relatively weak due to its high porosity and the resultant composite is unsuitable in many applications where high matrix strength is needed. Although the strength of the sprayed matrix can be increased by rolling the composite to reduce its porosity, loading of the steel wire in tension during the rolling operation often causes rupture of at least a portion of the wires and therefore the gain in matrix strength is offset by the loss in strength due to wire rupture.

In another process for the manufacture of aluminumsteel composites, a mesh of woven stainless steel Wires "ice and soft aluminum wires sandwiched between aluminum sheets is hot rolled and then solution heat treated to merge the aluminum wires into the aluminum sheet (see U.S. Patent No. 3,314,825). The sheets forming this composite are held together, for the most part, by mechanical bonds, the only metallurgical bonds between sheets occurring at the common juncture of the embedded aluminum wire with adjacent sheets. Without the benefit of a continuous and uninterrupted metallurgical bond between the sheets over their entire surface, delamination of these composites can occur in service conditions of high stress.

It is therefore a principal object of the invention to provide an improved aluminum steel composite suitable for use in high stress applications.

Another object is to provide an improved aluminumsteel composite with steel wires embedded in a homogeneous aluminum matrix.

Yet another object is to provide in the consolidation of the steel wire an improved process of forming a sound metallurgical bond between opposing surfaces of the aluminum sheets.

Still another object is to provide in the production of an aluminum-steel composite an improved hot rolling process which effects consolidation of the wire and aluminum sheets without danger of wire rupture.

These and other objects and advantages will become apparent upon reference to the following description, drawings and claims appended hereto.

It has been surprisingly found that a high strength aluminum-steel composite having a homogeneous aluminum matrix can be formed by consolidating steel wire between aluminum sheets, with one of the opposed sheet surfaces having at least one elongated groove therein extending transverse to the direction of the wire. By compressing such an assembly of sheets at an elevated temperature, it was unexpectedly found that the sheets are held together over their surfaces by a substantially continuous metallurgical bond.

The aluminum sheets employed herein preferably have a plurality of substantially parallel grooves or recesses formed in their surface, it being advantageous to space the grooves uniformly over the entire sheet surface. A sufficient number of such grooves are preferably formed in the sheet to increase the surface area thereof from about 5 to 300, more preferably from about to 200 percent.

After cleaning the surface of sheets to be compacted, the grooves can be formed therein by any of the conventional machining operations. Where relatively thin sheet aluminum is to be compacted, such as aluminum foil, wire brushing of the sheet surface can be used to increase the area thereof to from about 2 to 3 fold. Formation of the grooves in the sheet surface during continuous operations can also be achieved, for example, by passing the sheet through a pair of embossing rolls.

By compressing an assembly of such grooved sheets beyond the elastic limit of the aluminum, the surface of the sheet distorts and metal flows into the grooves. Upon disrupting the aluminum oxide film on the sheet surface, fresh unoxidized aluminum is exposed which can, upon contact with the surface of the adjacent sheet, metallurgically bond thereto. To insure the formation of a continuous metallurgical bond over the entire sheet surface, the grooves or other similar deformations in the sheet are preferably spaced uniformly over the surface so that at least some metal movement at or near the sheet surface will occur during compaction. Although there is no limit to the number of grooves which can be used, it is preferred to employ sheets having a suflicient number of grooves to effect complete disruption of the oxide film during compaction.

During compaction, the freshly exposed aluminumox:

idizes almost immediately and the resultant oxide film acts as a barrier to inhibit the formation of a metallurgical bond. To prevent oxidation of the freshly exposed alumi. num surface before it-can be bonded to another surface, it is preferred to carry out the compaction operation either under a vacuum of less than 100 mm. Hg, or else, in an inert atmosphere such as nitrogen or argon.

In rolling a stacked assembly of such sheets, the volume of the assembly is reduced an amount corresponding to the controlled void volume between the sheets created by the grooves or recesses in the sheet surface. During this rolling operation, it is preferred to first' reduce the thickness of the assembly until all voids are eliminated and then roll the resultant compact an additional amount to reduce its thickness up to about percent. Compaction to roll out the controlled void volume can be effected between a first pair of hot rolls with the additional reduc; tion in thickness of the resultant composite ,being optionally achieved by cold rolling'Where such a double rolling operation is employed, it is preferred that the sub sequent cold rolling reduce the composite thickness no more than about 2 percent.

In the initial compaction operation where the controlled void volume is rolled out of an assembly, the sheets are preferably maintained at temperatures of from about 400 to 1100, more preferably from about 700 to 900 F. for periods ranging from about 10 minutes to 10 hours, preferably for from about 30 to 120 minutes. Although compaction temperatures lower than 400 F. can be used with certain aluminum alloys, superior metallurgical bonding of the sheet is obtained in most cases using temperatures of at least 400 F. As far as the aluminum-alminum bonding is concerned, elevated temperatures even approaching the melting point of the aluminum are satisfactory. At temperatures above 1100 F., however, it has been found that filaments of most steel alloys are deleteriously affected and soften or become annealed.

The duration of the compaction and heating is important in effecting a strong metallurgical bond, it being preferred to maintain the composite at the elevated temperature until diffusion of aluminum from one sheet to another across the interface therebetween has occurred. Before commencing production on a commercial scale with any particular aluminum and steel alloys, a series of routine tests can be easily conducted to determine the optimum elevated temperature and period of heating for any combination of aluminum and steel alloys.

It has also been found that brittle intermetallic compounds of aluminum and steel form during compaction on the surface of the filaments at temperatures in excess of about 1100 F. It is therefore desirable in conducting routine testing for the determination of the optimum temperatures to inspect the filament surface for the presence of such brittle intermetallic compounds. The steel wire to be consolidated is placed on the sheet surface at an angle transverse to the longitudinal groove or grooves therein. In applications where high tensile strength is required, a plurality of steel filaments can be used between each pair of sheets to produce a composite having the desired tensile strength. Generally, the steel in the composite constitutes from about 1 to 60, preferably from about 10 to 40, more preferably from about 22 to 28 percent by volume. The composites having a low steel content are particularly suitable for use as cladding on atomic reactorfuel .cells. A high steel content composite can be advantageously used in structural applications in which a high strength to weight ratio in one direction is needed. To provide afresh clean surface free of excess oxid film can impair bonding, it is preferred to throughly clean the surface of the aluminum sheet before compaction. A suitable cleaning procedure can be carried out, for ex ample, by first treating in an alkaline bath having a pH of from about 9 to 11, water rinsing, acid rinsing, followed by a warm water rinse. The resultant cleaned sheet canthen .be allowed to stand .andairdry at ambient .tem-

perature. Where the sheet is to be preheated before compaction, the wet sheet from the cleaning baths can be passed directly to a preheater.

Consolidation of the steel wire between sheets of aluminum can be advantageously effected, for example, in a conventional 200 ton hydraulic press having electrically heated dies.-Continuous production is preferably carried out by feeding the sheet aluminum and sheet wire through the nipof a pair of oppositely, rotating, heated, spaced rollers. i

A preferred embodiment showing the composite of the present invention and process by which theyare made is illustrated further in the accompanying drawings, in which:

FIG. 1 is a schematic view in partial section of an arrangement for producing a composite of aluminum and steel according to the present invention;

FIG. 2 is a side elevational view in cross section of an assembly of aluminum sheets with steel wire sandwiched therebetween, illustrating particularly the grooves formed in the surface of the sheet;

FIG. 3 is aside elevational'view taken along line 33 of FIG. 1, illustrating a composite produced according to the present invention; and

FIG. 4 is a side elevational view of a composite of the present invention having several rows of steel wire in an aluminum matrix.

With reference to the drawings, a hot rolling mill shown generally at 1 (FIG. 1) comprises a housing 3 completely encasing the mill, a pair of feed rolls 5 on which is wound aluminum sheet 6, feed roll 7 on which several reels of steel wire or strip can be stored, a pair of opposed, OPT p ositely rotatable, hot rolls 11 and a composite take-up roll 15. Before operation is begun, the housing 3 surrounding the hot mill iseither evacuated, or else, charged with an atmosphere of an inert gas as described hereinbefore. As shown, a plurality of steel wires or strips 8 are continuously removed from feed roll 7 and then sandwiched between aluminum sheets 6 to form an assembly suitable for compaction (FIG. 1).

According to the present invention, the steel wire is brought into contact with surface 17 of sheet 6 having at least one groove or recess formed in its surface. The wire in the assembly extends transverse to the groove or grooves-in the sheet surface, it being preferred that the wire be placed at an angle normal to the direction of the groove. The assembly is then introduced between hot rolls 11 where it is heated and compressed to move aluminum into the grooves and firmly consolidate the steel wires into the aluminum sheet. The resultant composite 23 (FIGS. 1 and 3) comprises a homogeneous aluminum matrix 27 with steel wires mechanically bonded to and encased therein. If' desired, emerging composite 23 can then be taken up on roll 15, or else,'cut into segments and stacked.

In the arrangement shown in FIG. 1, the aluminum sheet'6 on rolls '5 has been properly grooved, cleaned and dried before being rolled. Although the grooves 19 in sheets 6 are round, grooves of any cross-sectional area can be employed. It can also be seen that sheet 6 are round, grooves of any cross-sectional area can be employed. It can also be seen that sheet 6 is introduced between rolls 11 with the grooves 19-lying substantially parallel to the roller axis, it also being preferred to roll the assembly in the direction of the filaments.

In FIG. 4 several rows of steel wire are shown consolidated into a homogeneous aluminum matrix to form a 'composite'29. Such inulti-layered composites can be produced either in one operation by consolidating several rows of wires between a number of aluminum sheets, or else, by passing several layers of the composites 23 through ahot rolling mill.

From the foregoing description, one skilled in the art can easily ascertain'the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What we claim is:

1. In a process for the production of a metallic composite from an assembled stack of at least two sheets of aluminum having steel wire sandwiched therebetween, wherein one of the opposing sheet surfaces has a groove formed therein extending transverse to the direction of the wire, the step comprising: compressing the assembled stack at an elevated temperature with a sufficient force to fill in the groove and expose fresh metal surface which can form a substantially continuous metallurgical bond between the sheet surfaces.

2. Proces as defined by claim 1, wherein the assembled stack is compressed at a temperature of from about 400 to 1100 F. for a period of from about minutes to 10 hours.

3. Process as defined by claim 1, wherein the assembled stack is compressed at a temperature of from about 700 to 900 F. for a period of from about /2 to 1 /2 hours.

4. Process as defined by claim 1, wherein at least one of the opposing sheet surfaces has a plurality of elongated grooves extending transverse to the direction of the wire.

5. Process as defined by claim 1, wherein the assembled stack is compressed by hot rolling.

6. Process as defined by claim 5, wherein the hot rolling is carried out with the wires extending normal to the axis of the rolls.

7. Process as defined by claim 5, wherein the hot rolling is carried out with the groove in the sheet surfaces extending parallel to the axis of the rolls.

8. Process as defined by claim 1, wherein compression of the assembled stack is carried out in an inert atmosphere.

9. Process as defined by claim 1, wherein compression of the assembled stack is carried out under a vacuum.

References Cited UNITED STATES PATENTS 867,659 10/1907 Hooper 29l96.2 3,201,862 8/1965 Gotoh 29470.5X 3,314,825 4/1967 Forsyth et al 148l2X 3,406,446 10/ 1968 Muldovan 29497.5 3,419,952 l/ 1969 Carlson 29- 472.3 3,449,820 6/1969 Jones et al. 29-497.5X 3,489,534 l/1970 Levinstein 27-471.1X

JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3 551 996 Dated January 5, 1971 Inventor) Edwin V. Sumner, Donald Q. Cole and LeRoy W. Dax

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, Line 70, change "film can impair to ---film which can impair--- Column 4, Line 7, change "200 ton" to ---2000 ton- Signed and sealed this 15th day of June 1971.

(SEAL) Attest:

,EDWARD M.FIETCHER,JR. WILLIAM E. SGHUYLER, Attesting Officer Commissioner of Patem

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