US3850705A - Low oil-canning aluminum alloy forgings - Google Patents

Low oil-canning aluminum alloy forgings Download PDF

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Publication number
US3850705A
US3850705A US00393954A US39395473A US3850705A US 3850705 A US3850705 A US 3850705A US 00393954 A US00393954 A US 00393954A US 39395473 A US39395473 A US 39395473A US 3850705 A US3850705 A US 3850705A
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oil
canning
forging
section
quench
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US00393954A
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C Furney
R Couchman
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Alcoa Corp
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Aluminum Company of America
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Priority to US00393954A priority Critical patent/US3850705A/en
Priority to FR7428348A priority patent/FR2242481B1/fr
Priority to GB35830/74A priority patent/GB1485045A/en
Priority to CA207,402A priority patent/CA1042770A/en
Priority to IT52832/74A priority patent/IT1029571B/it
Priority to JP10128874A priority patent/JPS5624711B2/ja
Priority to AU72913/74A priority patent/AU475582B2/en
Priority to DE19742442204 priority patent/DE2442204C3/de
Priority to US05/519,689 priority patent/US3996075A/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon

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  • ABSTRACT The method of making a heat treated aluminum alloy forging exhibiting reduced oil-canning in oil-canning-susceptible sections upon machining, including bonding insulation onto an oil-canningsusceptible section of an age-hardenable aluminum alloy forging with 'a bonding agent effective for main- 52 us. c1. 148/13.l, 148/159 taining a bond during heating solution heat t 51 ⁇ Int, Cl. c2211/04 ment, solution heat treating h thus-insulated forging.
  • the present invention relates to the manufacture of aluminum alloy forgings, and, more particularly to the manufacture of aluminum alloy forgings exhibiting reduced oil-canning in oil-canning-susceptible sections.
  • oil-canning may occur in which the web section may suddenly or slowly'deflect away from the cutting tool. Deflection may also be toward the cutting tool, and this can result in a gouging or tearing of the web section.
  • the metal deflection is much like that occurring on the bottom of an oil can when the bottom is being worked for dispensing oil onto an area to be lubricated thus the term oil-canning. Oil-canning can make it impossible to achieve desired thinness or tolerance in a production" part.
  • a method of making a heat treated aluminum alloy forging including the steps of bonding insulation onto an oil-canning susceptible section of an age-hardenable aluminum alloy forging with a bonding means for maintaining a bond during heating for solution heat treatment, solu tion heat treating the thusdnsulated forging, and, with the insulation still on the section, subjecting the solution heat treated forging to a quench for maintaining precipitable components of the alloy in solution in the oil-canning-susceptible section, whereby, upon machining, said section will exhibit reduced oil-canning.
  • FIGS. 1A anad 1B are elevational cross sections
  • FIG. 2 is a perspective view of an aircraft forging with a portion broken away to reveal the relative position and thickness of its web sections.
  • FIG. 3 is a process flow diagram.
  • FIG. 4 is a photograph of one web section, with surrounding rib portions, of a forging as illustrated in FIG. 2 at a certain stage in a process according to the present invention.
  • FIGS. 5 and 6 are graphs of oil-can" warpage in inches versus web thickness in inches.
  • FIG. 7 is a photograph of a forging as in FIG. 2 at a certain stage in a process according to the present invention.
  • FIGS. 8 and 9 are graphs as in FIGS. 5 and 6.
  • FIG. 1A there is shown a forging 10 formed by a cylindrical wall or rib section 11 and a base or web section 12.
  • forging 10 is provided in, for example, 7075 aluminum alloy with rib and web thicknesses of one inch, solution heat treated at 870F, and quenched in water at 60 to F, age-hardened at 250F for 24 hours, and the lower side of web 12 in FIG. 1A is then gradually machined off, a certain web thickness is eventually reached at which web 12 suddenly becomes unstable and pops upwards in FIG. 18, away from the cutting tool, into an oil-canned" position 13.
  • I oil-canned
  • FIG. 2 illustrates a ribbed and webbed forging of a precipitation hardenable aluminum alloy material.
  • the design is such as may be used in airplane manufacture.
  • the ribs 14 and 16 are, in this example, only on one side of the webs 15.
  • following forging and age-hardening such a forging may be machined all around, including both sides of the webs, to tolerance.
  • the problem of oil-canning can make it impossible to achieve a desired thinness with tolerance at desired strength levels and endangers the economic viability of aluminum alloy forgings for certain applications.
  • a process according to the present invention is illustrated by a flow diagram in FIG. 3.
  • a webbed forging is made, then insulation is bonded onto a web, following which the forging is heated to the solution heat treatment temperature. With the insulation still on the web, the forging is quenched, for example, with water of temperature between 60 and 80F. It is then possible to machine the web without experiencing unacceptable warping during machining to tolerance.
  • FIG. 3 is a flow diagram of only one embodiment of the present invention.
  • the forging may receive a preliminary machining before the step of bonding.
  • the forging may, for example, be agehardened after the step of quenching and before the step of machining.
  • the Insulation Insulation can be provided on the forging in the form of a coating of a suitable cement.
  • Another technique is to use the cement to bond an additional insulating material, such as glass cloth, to the forging. Considerable perseverance was required to find satisfactory cements.
  • a number of cements including sodium silicate, percent phosphoric acid, a mixture of l) 40 percent of minus-325 tabular alumina and 2) 60 percent of 85 percent phosphoric acid, and calcium aluminate cement, together with a number of proprietary cements, would fall off of a forging during its solution heat treatment in a furnace.
  • the cement material may be used to bond, for example, glass cloth in place on forging webs to act as insulation.
  • Exemplary glass cloth suitable in the practice of the present invention is a cloth having a weave of 16 filaments by 14 filaments, a thickness of 0.0138 inches, and a weight of 9.55 ounces per square yard available commercially as Burlington Industries glass cloth N0. 7500, a 42 X 32 weave of 0.0070 inch thickness and 5.95 ounces per square yard weight available commercially as Burlington lndustries glass cloth No. 1528, and a glass cloth off weave 32 X 29, 0.0060 inch thickness, and 4.90 ounces per square yard weight available as Burlington Industries glass cloth No. 1510.
  • equation (8) can be approximated by:
  • time C (T) the C-curve for 0,, i.e., critical time as a function of temperature in Kelvin to reduce attainable strength to 0,
  • C-curves for yield strength can be determined from interrupted quench data using graphical analyses, but graphical methods suffer from the disadvantage that effects of precipitation during the quench to the intermediate temperature and from the holding temperature to room temperature are ignored.
  • a new method of determining C-curves from data obtained by either isothermal or nonisot'hermal precipitation was developed by Staley and Evancho. Usingan iterative procedure, constants in the C-curve equation are determined to provide the best fit of the data to equation l0).
  • the values of the constants K through K may be determined empirically using the following steps:
  • the C-curve calculated is for the property level selected in step 3.
  • a computer program may be written to do the calculations.
  • the ratio (T /a time-temperature data and property for each sample, and candidate values for K, K are input.
  • a quench factor 1' for each sample is calculated, and regression and error analyses are made.
  • new constants are selected until the sum of the squared residuals is minimized. See D. J. Wilde, Optimum Seeking Methods, p. 145, Prentice-Hall Inc., Englewood Cliffs, New Jersey, 1964. Constants K K and 03, are output.
  • Equation (14) need be adjusted.
  • K, to K remain the same.
  • equation (14) is altered only by having 63.6 Iksi in place of72.42 ksi.
  • the quench factor 1' is calculated using data taken from the postulated time-temperature curve to express equation (13) in terms of t for the evaluation of equation (2).
  • the calculated 7 is then substituted in equation (1
  • a'quench factor 7 appropriate to achieve the desired yield strength may be obtained from equation (14).
  • a quench required to give the appropriate quench factor 1' may be selected by experiment and equation (2).
  • C 0.995 0,,,,,, ,.(T) is. expressed as C(t).
  • thei n tegration of equation (2) is performed to see if the desired quench factor 1' results.
  • a computer program may be written to generate tables of T(X,!) versus t, as I increases from zero. For example, time t can be incremented in 0.01, 0.10, or 1.0- sec. steps depending on the anticipated rate of quench, among other things a function of L. For each trial set of quench conditions, a table of values can be generated and plotted on translucent graph paper. The experimental quench curve is plotted the same way to the same scale. The values of X, L, T Tp, S, and D used in the computation of T(X,! versus 1 are the same as those used for the experimental quench. Trial values for H and C are selected.
  • the two quench curves i.e., the computed one and the experimental, are compared visually by laying one curve over the other. H and C are adjusted and a new table generated and plotted until the experimental curve is duplicated as closely as possible. Special attention is given to matching the slope of the experimental curves in the region where the critical time on the C-curve is the lowest for the particular alloy of interest.
  • Equations and ([6) assume that H and C are constant rather than temperature dependent. C is known to vary at least 10 percent over the quench range in the case of aluminum alloy 7075. The value ofH changes during the quench as the water at the surface of the forging begins with stable film boiling, changes to nucleate boiling, then to convection cooling. An evaluation that assumes H and C as constants represents an approximation; but for practical application, errors as high as $10 percent (usually the error is lower) in these values still give usable results. There is no known general analytical solution to the differential equations that allow H and C to be functions of temperature.
  • equation (15) In going from equation (15) to equation (12) it is customary to use T,, 5/9[T(X,t) 460], since equation (15) will ordinarily be evaluated in Fahrenheit while equation (12) is in Kelvin. In this manner, one can determine an appropriate H for giving the desired value of 0'. Then the insulation corresponding to the determined H value is applied to the web section and the forging is solution heat treated and quenched.
  • a web section can be machined to vary the web thickness and thus the value of L in Biots Modulus.
  • BI is calculated and a number of roots, 6,, are solved in equation (16). Normally, only 8 roots are used, but more may be used, if so desired. In general, more roots are required as Bl increases.
  • Equation (2) is integrated numerically for any value of X to calculate the quench factor 1 at the chosen X value. Commonly chosen values of X are X L (surface), X L/2 (midpoint) and X 0 (centerpoint).
  • the average quench factor may be determined by integrating equation (15) with respect to X and dividing by L to calculate the average temperature, T, through the web. The result is sin 6,, 69-1-6, sin 6,, cos 6,,
  • This average quench curve, equation (17), is used together with equation (16) in equation l2) and thence in equation (2) for the average quench factor from X 0 to X L.
  • insulation is applied to an oil-canning-susceptible web section to an extent such that the average quench factor in the web section is greater than the average quench factor in the surrounding rib sections, i.e., the ribs quench faster, in order to reduce overall warpage in the forging.
  • the quench factor is used in equation 14 to estimate the yield strength. This program allows the mechanical properties to be calculated directly from the quench conditions.
  • EXAMPLE l I A forging, as illustrated in FIG. 2, of type 7075 aluminum alloy was subject to oil-canningwhen being machined to size.
  • the forging had an overall length of 24 /2 inches, an overall width of inches, a transverse rib l4 thickness of 1% inches, a longitudinal rib 16 thickness of 1% inches, and a web thickness of 0.622 inch.
  • a yield strength of 60,000 psi in the web sections would be satisfactory.
  • equation (14) adjusted for T73 heat treat conditions (i.e., o 63.6 ksi), it is determined that a quench factor 7 of 10.55 would give a yield strength of 60,321 psi. This would be satisfactory for a web section of the forging.
  • equations (16), (13), and (2) are used to determine which trial value of the Biot Modulus would give a quench factor of 10.55 at X 0.
  • suitable web thickness (2L) and average surface heat transfer coefficient (H) to give such modulus can be determined.
  • Constants used in the various equations are: T,- 870F; T; 46F; thermal conductivity C 92.5 BTU-ft/ft -hr-F; specific heat S 0.25 BTU/lb-F; density D 172.8 lbs./cu.ft.; and diffusivity a 2.141 ft /hr.
  • the fbrging was immer sed i n hot water to float away as much of the machining oil as possible and then dipped into a nitric acid bath to get rid of any remaining oil.
  • the forging is then roughened by immersing it in a caustic soda bath for approximately one minute.,This is followed by a rinse in water and a dip into a nitric acid bath to remove smut resulting in the caustic soda bath.
  • the caustic soda bath was a 5 percent aqueous sodium hydroxide solution at to F.
  • a suitable nitric acid bath is an aqueous solution containing 60 to 70 percent by weight nitric acid; temperature is the ambient temperature.
  • the glass cloth was cut into panels matching the dimensions of the webs. These panels were secured to both sides of each web using Fireite ce ment at each of the four corners of every panel.
  • the resulting assembly is illustrated in FIG. 4, the dark patches at the corners of the glass cloth being Fireite cement which has impregnated the glass cloth.
  • the heavier weight No. 7500 cloth used in this example has the advantage that attack on it by' the sodium silicate in the cement is insignificant.
  • the forging, insulated with glass cloth was solution heat treated by leaving it in a furnace at 870F overnight.
  • the furnace heating first brought the forging to 870F and then soaked the forging at this temperature.
  • the quench was in a water bath at 46F.
  • the forging was agehardened to the T73 condition by bringing it to 225F in four hours and holding it at the 225F temperature for six hours. Then the forging was brought to 350F in four hours, followed by holding at 350F for eight hours.
  • the precipitation hardened forging was then machined, first to reduce the web thickness to 0.250 inch, the transverse rib 14 thickness to 0.250 inch,and the longitudinal rib thickness to 0.500 inch. Then, the web was machined incrementally first to 0.200 inch,
  • EXAMPLE II (A COMPARATIVE EXAMPLE) For thepurpose of providing a measure of the reduced oil-canning achieved according to the invention in Example 1, a duplicate 7075 alloy forging was treated under exactly the same conditions as for Example 1, except that (1) no insulation was used and (2) the web thickness was 0.622 inch during quenching. The oilcanning for the side webs is illustrated by Curves D and E in FIG. and for the central web by Curve F in FIG. 6. The reduced oil-canning exhibited by treatment according to Example I is clear from a comparison of Curves A, B, and C with Curves D, E, and F. The me- I chanical properties for this comparative example are presented in Table II. Note that the yield strength is close to the maximum of 63,600 psi.
  • EXAMPLE III STANDARD MINIMUM PROPERTIES
  • EXAMPLE IV An aluminum alloy die forging as described in Example l was immersed in a caustic soda bath for about 5 minutes to remove the forging lubricant and to roughen the surface of the webs to promote bonding of insulation onto the webs. After rinsing, smut was removed by immersion in a nitric acid bath. The web thickness was 0.622 inch. In a potential use of the forging, a web yield strength of 58,500 psi would be acceptable. The same calculations as in Example I are gone through to give a quench factor of 16.12. This quench factor corresponds to a yield strength of 58,660 psi. Using parameters otherwise as in Example 1, a Biot Modulus of 0.10506 is determined by calculation to give this quench factor of 16.12. The eight solutions of 5 are:
  • Example 1 After the water forming the base of the Fibrous Adhesive was dried, the forging was solution heat treated, quenched, and age hardened to the T73 condition as explained in Example 1. Machining was likewise carried out as in Example 1.
  • a forging i.e., an airplane wing rib, made up of rib and web (numerous sizes and shapes up to about 18- inches maximum dimension) sections and having overall dimensions of 8-feet in length, 28 inches at its widest point, and 3 to 4 inches rib breadth
  • a forging i.e., an airplane wing rib, made up of rib and web (numerous sizes and shapes up to about 18- inches maximum dimension) sections and having overall dimensions of 8-feet in length, 28 inches at its widest point, and 3 to 4 inches rib breadth
  • the forging was laid on a flat surface and one end of the forging purposely held flat. The other end was raised by overall warpage only about 1/1 6th of an inch, as compared to up to 2 inches of overall warpage which has resulted when no insulation was placed on the web sections.
  • a method for making a heat treated aluminum alloy forging exhibiting reduced oil-canning in oil-canning-susceptible sections comprising the steps of bonding insulation onto both sides of an oil-canningsusceptible section of an aluminum alloy forging with a bonding means for maintaining a bond during heating for solution heat treatment, solution heat treating the thus-insulated forging, and, with the insulation still on said section, subjecting the solution heat treated forging to a quench for maintaining precipitable components of the alloy in solution in the oil-canningsusceptible section, whereby, upon machining, said section will exhibit reduced oil-canning.
  • time T,- final temperature T, starting temperature a diffusivity of the alloy C'IDS D density of the alloy S specific heat of the alloy ⁇ CU (T) the C-curve for 0,, i.e., critical time as a function of temperature to reduce obtainable strength to a,
  • insulation and'bonding means is, on a dry weight basis, percent sodium silicate and 20 percent asbestos fiber shorts.

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Forging (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)
  • Heat Treatment Of Nonferrous Metals Or Alloys (AREA)
US00393954A 1973-09-04 1973-09-04 Low oil-canning aluminum alloy forgings Expired - Lifetime US3850705A (en)

Priority Applications (9)

Application Number Priority Date Filing Date Title
US00393954A US3850705A (en) 1973-09-04 1973-09-04 Low oil-canning aluminum alloy forgings
FR7428348A FR2242481B1 (it) 1973-09-04 1974-08-14
GB35830/74A GB1485045A (en) 1973-09-04 1974-08-14 Heat treating aluminum alloy forgings
CA207,402A CA1042770A (en) 1973-09-04 1974-08-20 Low oil-canning aluminum alloy forgings
IT52832/74A IT1029571B (it) 1973-09-04 1974-09-02 Pezzi forgiati in lega di alluminio con basso indice di deformazione da tempera in olio
JP10128874A JPS5624711B2 (it) 1973-09-04 1974-09-03
AU72913/74A AU475582B2 (en) 1973-09-04 1974-09-03 Low oil-canning aluminum alloy forgings
DE19742442204 DE2442204C3 (de) 1973-09-04 1974-09-04 Verfahren zur Wärmebehandlung von Metallen und Legierungen
US05/519,689 US3996075A (en) 1973-09-04 1974-10-31 Method for making a heat treated aluminum alloy article

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3996075A (en) * 1973-09-04 1976-12-07 Aluminum Company Of America Method for making a heat treated aluminum alloy article
US4177086A (en) * 1977-03-31 1979-12-04 Societe Pour Le Forgeage Et L'estampage Des Alliages Legers Forgeal Process for the thermal treatment and the quenching of forged articles
US4214925A (en) * 1977-10-25 1980-07-29 Kobe Steel, Limited Method for fabricating brazed aluminum fin heat exchangers
US5681407A (en) * 1993-05-18 1997-10-28 Aluminum Company Of America Method of heat treating metal with liquid coolant containing dissolved gas

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2278903C2 (ru) * 2004-09-24 2006-06-27 Вячеслав Владимирович Алексеев Способ термической обработки листов и сварных соединений сплавов системы алюминий - магний - кремний

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3007427A (en) * 1955-10-17 1961-11-07 Douglas Aircraft Co Inc Press for hot forming metal
US3392568A (en) * 1966-03-23 1968-07-16 North American Rockwell Aluminum alloy workpieces
US3568491A (en) * 1969-05-23 1971-03-09 North American Rockwell Low-temperature stress-relieving process

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3007427A (en) * 1955-10-17 1961-11-07 Douglas Aircraft Co Inc Press for hot forming metal
US3392568A (en) * 1966-03-23 1968-07-16 North American Rockwell Aluminum alloy workpieces
US3568491A (en) * 1969-05-23 1971-03-09 North American Rockwell Low-temperature stress-relieving process

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3996075A (en) * 1973-09-04 1976-12-07 Aluminum Company Of America Method for making a heat treated aluminum alloy article
US4177086A (en) * 1977-03-31 1979-12-04 Societe Pour Le Forgeage Et L'estampage Des Alliages Legers Forgeal Process for the thermal treatment and the quenching of forged articles
US4214925A (en) * 1977-10-25 1980-07-29 Kobe Steel, Limited Method for fabricating brazed aluminum fin heat exchangers
US5681407A (en) * 1993-05-18 1997-10-28 Aluminum Company Of America Method of heat treating metal with liquid coolant containing dissolved gas
US5820705A (en) * 1993-05-18 1998-10-13 Aluminum Company Of America Spray quenching of metal with liquid coolant containing dissolved gas

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JPS5624711B2 (it) 1981-06-08
CA1042770A (en) 1978-11-21
AU7291374A (en) 1976-04-08
JPS5053216A (it) 1975-05-12
GB1485045A (en) 1977-09-08
IT1029571B (it) 1979-03-20
FR2242481A1 (it) 1975-03-28
AU475582B2 (en) 1976-08-26
DE2442204A1 (de) 1975-03-27
FR2242481B1 (it) 1977-07-08
DE2442204B2 (de) 1977-04-28

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