US3290125A

US3290125A - Composite sheet metal article

Info

Publication number: US3290125A
Application number: US323216A
Authority: US
Inventors: Michael J Pryor
Original assignee: Olin Corp
Current assignee: Olin Corp
Priority date: 1963-11-13
Filing date: 1963-11-13
Publication date: 1966-12-06
Anticipated expiration: 1983-12-06

Description

United States Patent 6 ice The present invention relates generally to improved metal processing and to articles formed thereby, and more particularly to a process for producing a unified com- ,posite metal article 'having distinct but integral layers of different h'ardness and ductility and having distensions raised lirom one side thereof to form a series of internal tubular passageways.

The present invention is an improvement over that disclosed in co-pending application S.N. 160,282, filed December 18, 1961, in the names of I. Broverrnan and M. J. Pryor, now US. Patent 3,196,528. 'Ilh at application disclosed a process and articles-formed thereby wlhich contemplated the addition of a small amount of zirconium to aluminum alloy 1100 (in accordance with the Aluminum Associations standard designations) to produce an aluminum-zirconium sheet having improved physical characteristics over the base i100 alloy. A method was disclosed for fabricating composite b-i-alloy articles produced tfirorn the base 1100 aluminum and the aluminumzirconium alloy. The present application isdirected to improvements in processing 1100 and other aluminum alloy sheets to produce a similar composite article without the necessity of using any additional alloying elements in the base metal.

As is well known in the art, sheet metal panels having component layers of different hardness and ductility find considerable utility in the heatexchange field and particularly in refrigeration equipment in which the panels are employed as evaporators in .the freezing compartments of such equipment. These e vaporatorsare formed of sheet metal panels having internal passageways disposed between bulged out or distended portions of the thickness of the panel, and they are highly susceptible to so called ice pick damage. 'Ilhis damage is caused by the use of an ice pick or other sharp instrument in the course of defrosting and removing accumulations of frost or ice from within the freezing compartment.

This difficulty is alleviated to a surprising extent by fabricating the panel which forms the evaporator so asto provide a partially or completely (flat smooth exterior surface on a lhard layer of metal, and to have the passageways formed at least predominantly or wholly from distensions raised only from the opposite softer, more ductile layer of the unified sheet forming the panel.

It is a primary concern of this invention to develop large differences in mechanical properties between two component sheets of the same base alloy by varying the size :and distribution of particles of insoluble constituents in the primary fabrication treatment. In this way, high strength differentials, which are essential for producing superior one side flat products, can be made without incurring the additional changes lfor expensive alloys 'EEOII the flat component of the composite. Also, by the'practice of the present invention there is achieved a highly desirable and beneficial product without the attendant cost involved in additional processing which is necessary to the addition of other alloying elements.

In achieving the article as generally described above, certain desirable conditions exist for the formation of an effective one sidefla-t inflationpanelcontaining internal passageways, principal among these being the development of an identity of physical properties during initial formation of the panel blank, coupied with a dissimilarity of these same properties during subsequent iiorrna tion of-the finished'article from the panel blank. More specifically, it-is desirable to maintain dimensional control and alignment of the component sheets of the blank during initial pressure bonding which is facilitated by a similarity of physca-l properties such as hardness andductility! between theatwocomponentsheets. On the other hand, duiingthe subsequent inflation step, to form the coolant passageways, itis desirable-that one of the component sheets remain substantiall yorent'ir -elyundis tonted, -i.e., flat, and that the passageways befonmed'by} expansion of the other 'or softer component sheets- Ac cordingly, one of theprinciplal objects of this invention is the provision of a process by which a pair of component sheets are fabricated and assembled .together to form a composite blank having groups of physical characteristics which yield a substantial differential in yield strength between the component sheets of the composite. It is another object of the present, invention to provide a process for making a composite metal article having component layers of different strength in which the component layers are formed from identical alloys.

It is another object, of the present invention to provide a process for fabricating a one side flat refrigerator panel.

It is another object of the present invention to provide a process of fabricating a composite sheetmetal panel in which differential properties will develop solely from processing of the individual sheet metal components.

It is still. another object of the present invention to provide a process for fabricating a composite sheet metal article having layers of different yield strength in which the layers are composed of identical alloys which attain a final differential of physical propertieswithout the addition of other alloying elements.

It is a still further object of the present invention to provide a sheet metal article having a' hard and soft component layer in which distensions are raised from one side thereof to form internaltubular passageways.

Other objects and advantages of the present invention will become apparent from the following detailed description thereof.

vThe foregoing objects of this invention in their broadest aspect, 'are achieved to .a surprising extent by fabricating a composite sheet metal panel having component layers thereof of different hardness by providing a pair of aluminum alloy sheets having substantially identical composition, one'of the sheets having a coarse particle size dispersion of insoluble constituents present therein and .the other sheet having a fine particle size dispersion of insoluble constituents present therein, forming an integrallyunified composite panel of the'sheets with portions thereof remaining unjoined, partially annealing the comt posite panel withina critical temperature range in which the sheet havingthe coarseparticle size dispersion underof the present invention, .an aluminum base alloy is desired whichhas a major proportion of aluminumwith minor proportions of silicon, iron, copper, manganese, magnesium and zincas impurities, either selectively or 001- a temperature within the range of 900 and 1150 F 3 lectively. The exact proportions of these impurities are not significant to the practice of this invention so long as they are within limits which yield alloys susceptible to the development of dissimilar particulate precipitates of insoluble intermetallic compounds upon different primary heat treatment. Thus, the principles of this invention are applicable to all aluminum alloys which form stable insoluble constituents in the form of intermetallic compounds which have a decreasing solubility rate with decreasing temperature on primary fabrication treatment, i.e., casting, homogenization and initial breakdown hot rolling. It is, of course, vital to the practice of the invention that the intermetallic compounds precipitate either as a coarse particle size dispersion with large interparticle distance or as a fine particle size dispersion with small interparticle distance depending on the nature of primary fabrication treatment. As more fully developed hereinafter, the former type dispersion favors maximum softening rates by recovery upon critical partial annealing after cold working, while the latter type dispersion is effective in retarding the recovery process upon subsequent fabrication treatment.

In general, due to economic and other considerations, moderate strength, common heat treatable aluminum alloys are selected as the material for both component layers of the composite. These alloys are those having aluminum ranging from 95.00% to 99.75% and obtain their strength through strain hardening, of which alloys 1100 and 3003 are typical examples respectively of an aluminum iron silicon group and an aluminum manganese group, both highly suited to the practice of this invention.

In preparing the selected alloys for processing in accordance With the principles of this invention, two individual masses of the same alloy are cast in accordance with conventional casting practice for these alloys. During solidification in the casting procedure iron or iron plus manganese may come out of solid solution, depending upon the alloy composition selected, as the appropn' ate eutectic, While other metallic constituents often remain in solid solution.

Following casting and scalping according to conventional practice, one of the ingots is subjected to a homogenization treatment consisting of a soak of the ingot at for a period of 4 to 72 hours, preferably at an optimum temperature and period within these ranges determined by the alloy selected, for example, 950-1000 F. for about hours for alloy 1100 and l000-1050 F. for about 24 hours for alloy 3003. During this homogenization treatment, the iron eutectic, if formed, is transformed to iron aluminide (FeAl in the AlFeSi group which then reacts with the silicon to form an insoluble AlFeSi intermetallic compound which is produced in the homogenized ingot as a coarse particulate dispersion having large particle size and large interparticle distance, and which is essentially stable during subsequent hot rolling. In the aluminum manganese group, a similar coarse particulate dispersion of MnAl is formed which is also stable during subsequent hot rolling. This form of dispersion favors maximum softening rates upon partial annealing after cold working.

The other of the two ingots is not subjected to the aforementioned homogenization treatment and therefore does not contain the coarse particulate dispersion when the ingot is ready for initial breakdown hot rolling. During the subsequent hot rolling, however, aAlFeSi forms in the AlFeSi group and MnAl forms in the AlMn group under the conjoint action of deformation and temperature. Here multisite fine dispersions with small interparticle distance are formed which will remain stable in subsequent thermal mechanical treatment under 1000 F.

The two ingots can now be processed in an identical fashion down on Roll-Bond starting stock. In accordance with this practice,'the ingots are hot rolledto approximately .250" gage strip, entering the rolls at ,a

temperature between 800 and 1000 F., preferably at about 850 F., and then cold rolled to .125" thickness and interannealed at about 650 to 700 F. for 4 hours, or they may be initially hot rolled down to the .125" gage. During the breakdown hot rolling, the intermetallic compound for the selected alloy is still formed in the sheet from the unhomogenized ingot. However, due to the lower temperature range of the breakdown hot rolling step (800 to 1000 F.) compared to that of the homogenization range to which the other ingot was subjected, and due to the fact that the precipitation occurs under the combined influence of lower temperature and deformation, the intermetallic compound is produced as a fine particle size dispersion which prevents softening by recovery in the low annealing temperature range to which the composite is subjected following pressure Welding. In other words, this fine form of the dispersion favors minimum softening rates upon annealing after cold work- As used in this specification, the terms fine and coarse in reference to the particle size of the intermetallic compound dispersion have reference to those particles which are clearly resolvable or are not resolvable by metallographic microscope techniques at magnifications of approximately 50X.

In the production of a composite blank formed from the two alloys, a sheet is taken from each of the two starting stocks and is prepared for assembly by first cleaning each of the confronting faces of the components by conventional steps such as wire brushing, organic solvent, degreasing, etching in acid solutions, or similar conventional steps.

After such cleaning, a pattern of stop weld material is applied to one or both of the confronting faces of the component by conventional means, the pattern of stop weld material being a foreshortened version in the direction of rolling of the final pattern configuration desired. The components are then assembled together and the as sembly is tack welded at its corners to preserve alignment of the sheets during subsequent processing.

Prior to pressure rolling, the assembly is heated to a temperature within the range of 700 to 950 F., preferablly to about 930 F., and then pressure rolled to about a 65% reduction to firmly weld the two component sheets together in the areas not covered by the stop weld material. The hot rolling is followed, after cooling, by a cold rolling reduction of about 30% to achieve the final blank gage and to produce high strength by cold working.

After cold rolling, a large differential in yield strength of the component sheets can be developed by proper partia-l annealing of the blank. The anneal is carried out in a temperature range in which the component sheet fabricated from the homogenized ingot containing the coarse particulate dispersion of insoluble constituents undergoes considerable loss of strength by recovery, but in which the component sheet fabricated from the unhomogenized ingot containing the fine particulate dispersion of insoluble constituents formed during initial hot break-down rolling undergoes only slight loss of strength by recovery. To obtain the desired high differential in yield strength, this anneal is desirably carried out within the temperature range of 500 to 620 F. for a period of 5 minutes to 10 hours and preferably at a temperature of 585 F. for about 15 minutes for alloy 1100. For alloy 3003, the temperature range for partial annealing is 570 to 655 F. for a similar period of time, with an optimum of 620 for about 15 minutes.

To illustrate the development of this differential in yield strength it has been found that with this type of. partial annealing, fully homogenized 1100 Will soften to yield strength values of around 5,000 psi. minimum, whereas the unhomogenized 1100 can retain strength of up to about 13,000 p.s.i. maximum, thus achieving :a differential in yield strength of about 8,000 p.s.i. between the components of the composite. With respect to 3003, a sheet from the fully homogenized ingot will soften to yield strength values of around 7,000 p.s.i. minimum, whereas unhomogenized 3003 can retain strength of up to about 24,000 p.s.i. maximum, thus achieving a differential in yield strength of about 17,000 p.s.i.

To complete the final article, the composite blank is inflated by the cavity die inflation technique to provide a one side flat combination where the unhomogenized component becomes the flat member and will resist deformation at internal working pressures even with large tube widths, or in the alternative by conventional inflation techniques between the faces of flat platens to achieve a partial one side flat composite.

The following are examples of the practice of the invention and are to be considered as illustrative and not all inclusive.

Example 1 Two individual masses of aluminum alloy 1100 containing 0.57% iron and 0.16% silicon, together with other impurities normal for this alloy, were cast by the DC. casting process. After casting the ingots were scalped and one of the-m was subjected to a homogenization treatment by heating within the temperature range of 950 to 1000 F. for 16 hours. The other ingot was not homogenized but was directly subjected to subsequent fabrication treatment identical to that performed on the homogenized ingot. This treatment consisted of hot rolling the ingots at about 850 F. from 16" to a thickness of 0.22", after which the sheets were cold rolled from 0.22" to 0.125 and annealed at a temperature between 650 and 700 F. for 4 hours.

Subsequently, a sample was taken from each starting stock, and a pattern of stop weld material was interposed between the confronting faces of the sheets, after which they were assembled together, heated -to a temperature of between 930 and 950 for 20 minutes and hot rolled to a reduction of 65% at this temperature, after which they were cold rolled by a reduction of about 30%. The unified sheet was then partially annealed at a temperature of about 585 for minutes. It was found that the component from the homogenized ingot softened to a yield strength of about 5,500 p.s.i. while the component formed from the unhomogenized ingot retained a yield strength after annealing of about 11,000 p.s.i. thereby achieving a strength differential of 5,500 p.s.i.

Example II Two individual masses of aluminum alloy 3003 containing 1.07% manganese, 0.63% iron and 0.23% silicon, together with other impurities normal for this alloy, were cast by the DC. casting process. After casting the ingots were scalped and one of them was subjected to a homogenization treatment by heating Within the temperature range of 1125 to 1150 F. for 16 hours. The other ingot was not homogenized but was directly subjected to subsequent fabrication treatment identical to that performed on the homogenized ingot. This treatment consisted of hot rolling the ingots at about 850 F. from 16" to a thickness of 0.22", after which the sheets were cold rolled from 0.22" to 0.125 and annealed at a temperature between 650 and 700 F. for 4 hours.

Subsquently, a sample was taken from each starting stock, and a pattern of stop weld material was interposed between the confronting faces of the sheets, after which they were assembled together, heated to a temperature of between 930 and 950 for 20 minutes and hot rolled to a reduction of 65% at this temperature, after which they were cold roll-ed by a reduction of about 30%. The unified sheet was then partially annealed at a temperature of about 585 for 15 minutes. It was found that the component from the homogenized in-got softened to a yield strength of about 20,800 p.s.i. while the component formed from the unhomogenized ingot retained a yield achieving a strength differential of 2,700 p.s.i.

It will be apparent from the foregoing description that. there has been provided a method for making a composite metal article and the article formed thereby which: is believed to provide a solution to the foregoing problems: and achieve the aforementioned objects. It is to be under-- stood that the invention is not limited to the examples" described herein which are deemed to be merely illustrative of the best modes of carrying out the invention, but rather is intended to encompass all such modifications as are within the spirit and scope of the invention as set forth in the appended claims.

What I claim and desire to secure by Letters Patent is:

1. A composite sheet metal article comprising:

(A) a first and second component sheet having a pattern of stop weld material there'between, said sheets being integrally unified except in the area of the stop weld material;

(B) said first component sheet consisting essentially of an aluminum base alloy having a coarse particle size dispersion of an insoluble inter-metallic compound present therein;

(C) said second component sheet consisting essentially of substantially the same aluminum base alloy as the first component sheet and having a fine particle size dispersion of said insoluble intermetallic compound present therein;

(D) said component sheets having different yield strength values, with the first com-ponent sheet having the lower value, with distensions raised from the first component sheet corresponding to the pattern of stop weld material.

2. A composite sheet metal article comprising:

(A) a first and second component sheet having a pattern of stop weld material therebetween, said sheets being integrally unified except in the area of the stop weld material;

(B) said first component sheet consisting essentially of an aluminum base alloy with Fe-l-Si 1.0% maximum and A l 99.00% to 99.75%, said sheet having a coarse particle size dispersion of ot-AlFeSi as an insoluble intermetallic compound present therein;

(C) said second component sheet consisting essentially of substantially the same aluminum base alloy as the first component sheet and having a fine particle size dispersion of said insoluble intermediate compound present therein;

(D) said first component sheet being relatively soft with yield strength values in the order of 5,000 p.s.i. minimum and aid second component sheet being relatively hard with yield strength values in the order of 18,000 p.s.i. maximum, with distensions raised from the first component sheet corresponding to the pattern of stop weld material.

3. A composite sheet metal article comprising:

(A) a first and second component sheet having a pattern of stop weld material therebetween, said sheets being integrally unified except in the area of the stop 'weld material;

(B) said first component sheet consisting essentially of an aluminum base aloy with Mn 1.5% maximum and Al 95.00% to 99.00%, said sheet having a coarse particle size dispersion of MnAl as an insoluble intermetallic compound present therein:

(D) said first component sheet being relatively soft with yield strength values in the order of 7,000 p.s.i. minimum and said second component sheet being relatively hard with yield strength values in the order of 24,000 p.s.i. maximum, with distensions raised pattern of stop Weld material.

References Cited by the Examiner UNITED STATES PATENTS Brown 29197.5

N ock 29-197.5 Steiner et a l. 29-197.5 Buckland 148-132 Peterson 29-1573 Van Camp 29157.3 Wilkins 29157.3 Grenell 29197.3 X Seibel et a1 748--134 X 'Wenger 29157.3 X Broverman et a1. 29157.3

HYLAND BIZOT, Primary Examiner.

Claims

2. A COMPOSITE SHEET METAL ARTICLE COMPRISING: (A) A FIRST AND SECOND COMPONENT SHEET HAVING A PATTERN OF STOP WELD MAERIAL THEREBETWEEN, SAID SHEETS BEING INTEGRALLY UNIFIED EXCEPT IN THE AREA OF THE STOP WELD MATERIAL; (B) SAID FIRST COMPONENT SHEET CONSISTING ESSENTIALLY OF AN ALUMINUM BASE ALLOY WITH FE+SI 1.0% MAXIMUM AND AL 99.00% TO 99.75%, SAID SHEET HAVING A COARSE PARTICLE SIZE DISPERSION OF A-ALFESI AS AN ISOLUBLE INTERMETALLIC COMPOUND PRESENT THEREIN; (C) SAID SECOND COMPONENT SHEET CONSISTING ESSENTIALLY OF SUBSTANTIALLY THE SAME ALUMINUM BASE ALLOY AS THE FIRST COMPONENT SHEET AND HAVING A FINE PARTICLE SIZE DISPERSION OF SAID INSOLUBLE INTERMEDIATE COMPOUND PRESENT THEREIN; (D) SAID FIRST COMPONENT SHEET BEING RELATIVELY SOFT WITH YIELD STRENGTH VALUES IN THE ORDER OF 5,000 P.S.I. MINIMUM AND SAID SECOND OMPONENT SHEET BEING RELATIVELY HARD WITH YIELD STRENGTH VALUES IN THE ORDER OF 18,000 P.S.I. MAXIMUM, WITH DISTENSIONS RAISED FROM THE FIRST COMPONENT SHEET CORRESPONDING TO THE PATTERN OF STOP WELD MATERIALL.