US2800709A - Method of making composite stock - Google Patents

Description

July 3%195? R. F. GAUL. 28@@7@9 METHOD OF MAKING COMPOSITE STOCK Filed Aug. 22, 1952 V INVENTOR.

, RAYMO D 3 SAUL A ATTORNEY United btates Patent 2,800,709 r METHOD or MAKlNG COMPOSITE sTocK Raymond F. Gaul, Solihull, Warwickshire, England, as-

signor to Kaiser Aluminum & Chemical Corporation, a corporation of Delaware Application August 22, 1952, Serial No. 305,839

4 Claims. (Cl. 29-4723) 7 This invention relates to multilayer metallic billets, method of making such billets and to methods of producing composite metal stock therefrom. More particularly, it concerns multilayer billets, their assembly, and production of composite sheets or plates therefrom composed of aluminum and aluminum alloys or of two or more different aluminum alloys.

In the past, it has been the custom in the production of composite or clad stock to assemble the composite billets of different metals prior to rolling by attaching plates or liners of one metal to ingots of the other metal by wire or bands of steel or other suitable metal. This wire, which held the assembly together during preheating and placement on the mill, then had to be removed after the ingot was laid on the entry end of the rolling mill and prior to performing the so-called sticking or bonding passes. In many cases, the liners would slip while beingtransported by crane to and from the preheating baskets which are used for holding the ingots while in the soaking pits. The liners also had a tendency to slip when being laid on the rolling mill table, or upon rolling. Slippage of the liners caused the small fusion welds formed between the ingot and liner during soaking to break. Also, slippage of the liners necessitated a repositioning operation resulting in a drop in liner temperature which tended to cause improper bonding of the liner to the ingot during the sticking or bonding passes. Moreover, the liner often slipped out of position on rolling, and spread across the width of the ingot such that it either overhung the ingot edges or fell short thereof. After the liner has spread across'the width of the ingot by rolling the ingot and liner'broadside, as is generally the case, the ingot is rolled lengthwise through the mill. At this stage the ingot edges are also rolled by edge rolls. If the liners overhang the'edge of the ingot, the overhanging metal is bent, or ripped, and may be bent onto the ingot surface. This piece of metal when rolled into the ingot surface will usually cause a considerable amount of finished products to be rejected. Also, where the liner, upon rolling, fails to cover the ingot surface due to slipping, the composite stock is rejected due to bare metal, that is, exposure to core metal. Loss of the composite stock by rejection also occurs, particularly with ingot clad with thinliner stock, due to excessive blistering of the liner caused by wrinkling of the liner on the sticking passes. The breakage of the fusion welds formed during preheatingdue to liner slippage and the consequent temperature drop in the liner due to the necessity of repositioning the liner appears to be the primary cause of this blistering. I

Welding of liner stock toingots has been attempted in the prior art, but it has not been applied in a successful mannersuch that upon rolling the liner neither falls short of the ingot edges or overhangs the edges. On the contrary, in some instances, the prior art teaches the liner should overlap the edges of the ingot before the composite billet is even rolled. This results in a high scrap loss, rendering the method uneconomical. Further,

I 2,800,709 Patented July 30, 1957 in the prior art it was believed necessary to weld com pletely around the periphery of the billet. This is undesirable and costly since the nature of the liner or cladding metal is normally such that on rolling it flows to a considerable extent over the scalped ingot surface with the result that air is trapped between the cladding and core, thereby producing a blister near the exit end or edge of the composite-billet as it passes through the rolls. Also, applicant is unaware of any teaching of the application of welding liners to ingots, where the liners and core metal are composed of light metals, particularly aluminum and magnesium and their alloys, probably due to difiiculties inherent in this application of welding to such light metals.

Accordingly, one object of this invention is to provide a novel method for making composite sheets or plates from a plurality of layers of metals in which at least two of said layers are of different thicknesses, whereby loss due to rolling in of overhung metal, blistering, and unclad core metal is minimized while at the same time insuring an efiicierit and lower cost welding.

Another object of this invention is to provide a novel method for making a composite sheet of aluminum and aluminum alloys or of different aluminum alloys Whereby a considerable reduction in loss from rolled in metal, blistering and unclad core metal is realized, where the cost of welding the ingot and liner together prior to rolling is minimized, and where a superior bond is obtained.

A more specific object of this invention is to make a bimetallic billet comprising a core and at least one cladding layer of metals in which each cladding layer is on the order of from about l 20% of the thickness-of the composite billet and the nature of the cladding layer is such that upon rolling said cladding layer spreads considerably relative to said core, whereby the thicker core layer of metal projects beyond the thinner layer or layers of cladding metal, so that on subsequent rolling the thinner layer or layers spread across the core such that there is proper bonding of the thinner layer or layers to the core layer and such that there is substantially no over-lapping of the core by the cladding and the resulting composite sheet or plate exhibits substantially no bare or uncladcore metal thereby reducing scrapping loss in the manufacture of composite sheet from such billets.

Anotheriobject of this invention is to make a billet as described above whereby the cladding liners are positively positioned on the core by means of welds against the face or faces of the thicker layer, and in particular where the cost of such welding is reduced by utilizing a series of spaced tack Welds along that edge of the composite billet which enters the mill rolls first with one tack weld applied along each of the two edges which are at to the entry edge and positioned relatively close to the entry edge such that the major portion of the cladding is free to spread across the core providing a secure bond without any blistering.

Another object of this invention is to produce a billet as described above from light metals and their alloys.

Other objects and advantages of the invention will become more apparent from the following description and accompanying drawings.

The method of-making the composite sheet of the present invention, the novel bimetallic billet used in such method, and the method of making said billet overcome the disadvantages of the prior art and accomplish the above objects. This invention comprises the use of a billet made up of, a plurality of layers of metals in which at least two of said layers are of different thicknesses. The thinner layer or layers of said billet are positively positioned on the thicker layer so that the edges of the latter extend beyond the liner edges, the greater extension being on the longitudinal side opposite that side which first enters the rolls. The extension of the ingot surface beyond the liner edge is so dimensioned that upon rolling the ingot broadside or transversely in the sticking or bonding passes, the liner will spread across the width of the thicker layer without either falling short of the edge or overhangingit. The dimension of the ingot extension is readily determined by the relative thickness and width of the ingot and the thickness of the liner, and the respective'extensibility or elongation coefiicients. Only a nominal amount of trial and error experimentation is necessary to determine the proper dimensions of the ingot and liner in any given case. The thinner layer or layers are held in this position by welds, preferably tack welds. This welding provides a positive positioning of the thinner layer or layers of metal upon the thicker layer such that there is no longer any danger of slippage with the ultimate result of having overhanging metal which may be bent under the ingot surface or bare core metal, thereby necessitating scrapping of the metal.

By the use of an inert gas shielded welding process, definitely superior welds are produced since a flux need not be employed. The flux would be corrosive to aluminum and would require that the welds be wire brushed and washed immediately after welding. This would be a ditficult process, for the liner ingot interface adjacent to the weld would act as a trap for the flux. The use of the inert gas shielded welding process results in such satisfactory welds that tack welds may be employed only on that side or edge of the inner layer or layerswhich first enter the rolls and, where desired, welds may be applied on the two sides or edges connected by the first mentioned side but being positioned relatively close to this side, in lieu of welding around the entire periphery of the composite billet, thereby effecting considerable savings in the cost of welding. Further, such welds allow the major portion of the liner which is unattached to move or spread out over the core surface during the rolling operation, thereby achieving good bonding of the layers of metal without blistering or wrinkling as would be the case with a weld completely around or on both sides of the billet.

In the accompanying drawing I have shown a present preferred embodiment of the invention and have illustrated a present preferred method of practicing the same along with an example of the prior art showing the disadvantages of same which are encountered in many instances. In this preferred embodiment, the thicker layer or core is an ingot of one aluminum alloy, while the thinner layer is a plate or liner of a different aluminum alloy, and they will be referred to as such in the detailed description.

In the drawing:

Figure 1 is an isometric view of a bimetallic billet showing the position of the liner with respect to the ingot;

Figure 2 is a transverse cross-section of the billet prior to rolling;

Figure 3 is a cross-section of the billet after the initial rolling passes and prior to rolling endwise through the mill accompanied by edge rolling;

Figure 4 is a cross-section similar to Figure 3 of a billet upon which the liner has slipped due to the lack of positive positioning resulting from the prior art methods, whereby the liner overhangs the edge of the ingot prior to rolling endwise through the mill accompanied by edge rolling; and

Figure 5 is similar to Figure 4 but shows the result of slipping Where the liner falls short of the edge of the ingot after the initial rolling passes and prior to rolling endwise through the mill.

Referring now more particularly to the drawing, the composite billet shown comprises an ingot 1 with a single liner 2, the liner being 1-20% of the thickness of the composite billet. The width of the ingot is substantially greater than the liner. The liner is placed upon the ingot in such a position that when the billet is passed through the rollers, the liner will spread across the width of the ingot such that it neither overlaps the ingot as illustrated in Figure 4, nor falls short of it as illustrated by Figure 5, but instead is even with the edge of the ingot as illustrated by Figure 3. The liner is positively positioned on the ingot by means of fillet welds 3 joining the edge of the liner to the outer face of the ingot, said welds being tack welds. As shown in Figure 1, the ingot liner assembly is provided with three welds on the liner edge which enters the mill first and also one weld is applied at either end of the liner relatively close to the side which enters the mill first. These welds may be on the order of from 1 to 4 inches in length or over depending upon the weight of the liner. The length and number of welds used in any given case should be sufiicient not only for securely attaching the liner to the core but to insure attachment of the liner when the ingot is stood on end during the preheating operation. In such case, the welds necessarily have to be sufficient to support the full weight of the liners. In welding the liner to the ingot, it is the preferred practice to employ an inert gas shielded arc method of the type fully described by Patent 2,504,868, or any other welding method or welding light metals wherein no flux is employed.

It should be pointed out that this invention is not limited to the use of a single liner on one side of the ingot, but instead two liners on opposite sides of the ingot is within the scope of this invention. Moreover, in cases where liners are provided on both sides of the ingot, the chemical compositions of the liners may be the same or different.

I will now proceed to describe a specific example of my method for making a composite sheet of two different aluminum alloys. An ingot of 75 S aluminum alloy (0.15% Si-0.35% Fe-2.5% Mg0.l% Mn1.75% Cu0.2% Cr-5.75% Znbalance Al) measuring 10" by 39" by 106" was preheated for 35 hours at 900 F., after which it was cooled for A hour with the lid of the soaking pit removed. The temperature was then cut back to 800 F. and held there for 8 hours. The ingot was then scalped from 10" by 39" by 106" to 9" by 39" by 106", after which it was clad with a liner stock of 72 S aluminum alloy (1.0% Zn0.05% Cu0.05% Mn-Fe-i-Si 0.5% maX.-balance Al) measuring .465" by 30 /2" by 102", said liners being positioned by tack welds employing an inert gas shieldedarc method as previously described.

The liner was positioned upon the ingot surface such that the liner edge which would enter the mill first was spaced about 1" away from the corresponding edge of the ingot. The opposite side or edge of the liner was spaced about 7 /2 from the corresponding ingot edge while the ends of the liner were spaced about 2" in from the ends of the ingot. The welds on the side and ends of the liner were approximately 2" in length. All the welds were made with a aluminum alloy weld filler rod containing 7.5% Si0.4% Fe--0.05% Cubalance Al.

In the welding of the liners to the ingots, it has been found desirable in most instances to'place the welds on the ingot surface such that they are not made in the liquated zone, that is, the zone which comprises the skin of the ingot wherein high alloy content is present. Welds made on this outer skin portion have a tendency to be weak. Generally, however, the scalping operation removes all or substantially all of the liquation Zone on the ingot surface so that this problem is not present.

The composite billet was then preheated to 950 F. for 14 hours, after which the temperature was cut back to 340 F. and held for 7 hours before rolling. This composite billet was then rolled in a wide 4-high reversing hot-mill at a temperature of 700 F. to 775 F., several sticking passes being carefully made using a reduction of one liner thickness on each of the first two sticking passes. The composite billet was initially rolled broadside with the long side of the billet having the three 2" long tack welds entering the rolls first, the liner having been positioned on the billet such that upon the completion of-these passes the liner spread across the width of the billet, such that the liner neither over-rung the edge of the billet or fell short of it. The billet was then turned and passed through the rollers endwise, the billet being given several edge rolling passes during the lengthening passes.

Although the above example illustrates the case where one of the long side edges of the billet enters the mill first, there are instances where the long side does not form the entry edge into the mill. In such a case, the edge of the liner on one end is welded to the end edge of the ingot, and the .composite billet is passed through the mill in a lengthwise direction with no broadside operation being performed.

In production run of 42 clad ingots which was made using ingots of 75 S aluminum alloy as above set forth and which were clad using welding equipment employing the method of Patent 2,504,868 for making the welds, the positions and length of the welds and the positioning of the liner was as above described. These 42 ingots all rolled well on the 120" hot mill without any serious effect which could be attributed to the positioning of the liners on the ingot.

As another example of the application of the method of the instant invention, a production run was made of fourteen 75S ingots clad with 72S alloy liners being .165" thick by 32" wide, the remaining dimensions of the liners, those of the ingot, and the heat treatment and rolling procedure being the same as in the first example discussed hereinbefore with the exception that the side of the liner opposite that side which enters the mill first was spaced about 6" from the corresponding ingot edge. These clad ingots were rolled down to .25" by 48" by 252" with good results.

The principal causes of defective ingots which must be scrapped attributable to the method of positioning the liners on the ingots, are blistering or incomplete bonding of the liner to the ingot, and bare metal caused by failure of the liner to spread completely across the face of the ingot. Comparative tests were made whereby the percentage losses upon inspection due to these causes, between liners positioned by welding and liners positioned by wiring were made. The results of these tests are shown in the following table:

A comparison of welded liners and wired liners From the above table it can be seen that the use of welded liners has approximately halved the percentage of losses attributable to the method of positioning the liner upon the ingot.

Although the examples set forth above are directed to aluminum alloys, it is to be understood that the instant invention is eminently suited for producing composite metal stock from magnesium and magnesium alloys as well as from other light metals.

While I have shown and described a present preferred embodiment of the invention, it is to be distinctly understood that the invention is not limited thereto but may Cit otherwise be variously embodied within the scope of the following claims.

What is claimed is:

1. A method of making multi-layer metal assemblies for rolling from a plurality of layers of metals of different composition wherein at least two of said layers are of substantially different thicknesses and the nature of the thinner layer of metal is such that upon rolling the said thinner layer spreads considerably relative to the thicker layer comprising the steps of assembling said layers of metals whereby the thicker layer of metal extends beyond the thinner layer of metal, said layers being superposed, joining the thinner layer of metal to the face of the thicker layer by tack welds along that edge of the composite billet which enters the mill rolls first with one tack Weld applied along the two edges which are degrees to the entry edge and positioned adjacent thereto such that the major portion of the thinner layer is unattached to the thicker layer and is free to spread over the surface of the thicker layer.

2. The method of claim 1 whereby the metals employed are magnesium metals.

3. The method of claim 1 whereby the metals employed are aluminum metals.

4. A method of making composite sheet and plate from a plurality of layers of metals of different composition wherein at least two of said layers of metals are of substantially diiferent thicknesses and the nature of the thinner layer is such that upon rolling the said thinner layer spreads considerably relative to said thicker layer comprising the steps of forming a multi-layer metal assembly by assembling said plurality of layers of metals whereby the thicker layer of metal extends beyond the thinner layer of metal, said layers being superposed, joining the thinner layer of metal to the face of the thicker layer by tack Welds applied along that edge of the composite billet which enters the mill rolls first with one tack weld applied along each of the two edges which are at 90 degrees to the entry edge and positioned adjacent said edge such that the major portion of the thinner layer is unattached to the thicker layer and is free to spread out over the surface of the thicker layer, and rolling said assembly until a sheet of the desired thickness is produced.

References Cited in the file of this patent UNITED STATES PATENTS 300,730 Peddcr June 17, 1884 959,517 Griffith May 31, 1910 1,667,787 Jaeger May 1, 1928 1,792,377 Jordan Feb. 10, 1931 1,956,818 Acre May 1, 1934 1,975,105 Keller Oct. 2, 1934 2,017,757 Keller Oct. 15, 1935 2,064,684 Ostendorf Dec. 15, 1936 2,354,006 Gauthier July 18, 1944 2,366,168 Bakarian Jan. 2, 1945 2,366,185 Diehl Jan. 2, 1945 2,395,877 Keene Mar. 5, 1946 2,423,810 Goulding July 8, 1947 2,468,206 Keene Apr. 26, 1949 2,473,686 Keene June 21, 1949 2,539,247 Hensel Jan. 23, 1951 FOREIGN PATENTS 407,942 Great Britain Mar. 26, 1934 628,197 Great Britain Aug. 24, 1949 690,908 Great Britain Aug. 24, 1949 481,082 Canada Feb. 12, 1952

Claims (1)

1. A METHOD OF MAKING MULTI-LAYER METAL ASSEMBLIES FOR ROLLING FROM A PLURALITY OF LAYERS OF METALS OF DIFFERENT COMPOSITION WHEREIN AT LEAST TWO OF SAID LAYERS ARE OF SUBSTANTIALLY DIFFERENT THICKNESSES AND THE NATURE OF THE THINNER LAYER OF METAL IS SUCH THAT UPON ROLLING THE SAID THINNER LAYER SPREADS CONSIDERABLY RELATIVE TO THE THICKER LAYER COMPRISING THE STEPS OF ASSEMBLING SAID LAYERS OF METALS WHEREBY THE THICKER LAYER OF METAL EXTENDS BEYOND THE THINNER LAYER OF METAL, SAID LAYERS BEING SUPERTHE THICKER LAYER BY TACK WELDS ALONG THAT EDGE OF THE COMPOSITE BILLET WHICH ENTERS THE MILL ROLLS FIRST WITH ONE TACK WELD APPLIED ALONG THE TWO EDGES WHICH ARE 90 DEGREES TO THE ENTRY EDGE AND POSITIONED ADJACENT THERETO SUCH THAT THE MAJOR PORTION OF THE THINNER LAYER IS UNATTACHED TO THE THICKER LAYER AND IS FREE TO SPREAD OVER THE SURFACE OF THE THICKER LAYER.

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