T.O. 1-1A-9
3-39. Time at temperature. This factor will vary depending upon the type of anneal (partial or full), metal, thickness, method of
furnace charging and similar factors. Avoid excessive time at temperature to prevent growth, diffusion and discoloration, especially
when annealing clad alloys.
3-40. When fully annealing, no attempt should be made to shorten the annealing cycle because the soluble constituents go into
solution as the temperature is increased. If the material is then cooled rapidly the soluble constituents remain in solution and the
material does not attain fully annealed mechanical properties.
3-41. Annealing and subsequent forming of material previously heat treated should beavoided if conditions and time permit. The
recommended method is to repeat the solution heat treatment and immediately perform the forming or drawing operation.
3-42. Recommended times and temperatures for annealing various alloys are as follows:
a.
Annealing of Work-Hardened Alloys. All of these alloys except 3003 are annealed by heating to 650° F and no higher than
775° F, holding at temperature until uniform temperature has been established throughout the furnace load, and cooling in air or in
the furnace. Annealing temperature shall not exceed 775° F to prevent excess oxidation and grain growth. The 3003 alloy is
annealed by heating to 775° F at a relatively rapid rate and holding at the minimum soaking period necessary to attain temperature
uniformity and then cool as cited above.
b.
Annealing of heat-treated alloys (wrought). These alloys (except 7075) are annealed by heating to 775° F for not lees than 1
hour and most instances 2-3 hours. Material is then cooled at a rate of no greater than 50° F per hour until the temperature is 500° F
or below. Rate of coating below 500° F is not restricted; cool as desired. Alloy 7075 is fully annealed by heating to 775°F-850° F
(higher temperature utilized for material having smaller amount of cold work), soaking for 2 hours at temperature, cooling in air,
reheating to 450° F, holding at this temperature for 6 hours and then cooling to room temperature. Alternate 7075 annealing
methods:
(1)
If forming is to be accomplished immediately after annealing, heat to 775° F, 2-3 hours; air cool.
(2)
If alloy is to be stored for an extended period before forming, heat to 670° -700° F, 2 hours; cool in air; reheat to 450°
F; hold at this temperature for 4 hours and then cool in air.
(3)
Intermediate anneal during cold working of "O" condition material; heat to 670° -700° F, ½ hour maximum, or heat to
910°-930° F until uniform temperature is attained; cool in air. A part shall not be annealed using the 910°-930° F
temperature more than 3 times.
c.
Annealing of cast alloys. Castings are annealed by heating to 650° -750° F holding for approximately 2 hours, and cooling
to room temperature. The purpose of such annealing are for the relief of stresses and attainment of dimensional stability.
d.
Partial annealing of heat-treated material. When heat-treated materials are annealed as specified for annealing of the work-
hardened alloys, the effect of heat-treatment Is reduced considerably, but not completely. The partially annealed material is only to
be utilized when moderate but not secure operations are to be performed. If difficulty is experienced with forming partially annealed
material, recommend that "O" fully annealed material be utilized.
3-43. Heat treating temperatures and times. Aluminum alloy should be heat treated at the temperature given in Table 3-7. The load
should be held within the heat-treatment range (after the coldest part has reached the minimum of the range) for a sufficient time to
insure that specified properties will be developed. In some cases sample testing will be required to ascertain that specified properties
are developed. Suggested soaking periods are given in Tables 3-8 and 3-9 for the common alloys. In instances where new alloys
are involved it will be necessary to consult the specification for the alloys, Specification MIL-H6088 or the manufacturer for the
appropriate heat treat data. In case of conflict the correct Military/ Federal specification will be the governing factor.
3-44. QUENCHING. To effectively obtain the desired qualities in aluminum alloys it is necessary that the interval between removing
the charge from the furnace and immersion in the quenching water be maintained at the absolute minimum (See Table 3-10).
3-45. Wrought alloy products must be quenched by total immersion in water or by a drastic spray quench. Forgings of 2014, 2017,
2117 and 7075 are quenched in water at temperatures in excess of 100° F. 7079 forgings are generally quenched in water at
temperatures less than 100° F to obtain optimum mechanical properties, however a hot water quench (180° F) should be used
whenever possible providing the lower strength associated with the quench is satisfactory. The hot water quench lowers the residual
stresses considerably. This is desirable from the point of view of reducing stress corrosion susceptibility.
3-46. Charging of furnace and baths. Individual pieces of materials or parts should be racked or supported to prevent distorting if
possible and permit free access to the heating and quenching medium. The above is necessary to maintain the form of the material
involved and to facilitate heating to the specified temperature and quenching rapidly. To prevent distortion it is necessary in some
cases to provide jig and fixture support for complex contoured (formed) parts. However, the jig used shall be so constructed that it
will not restrict the contact required with the heating medium of the part being treated.
NOTE
Parts formed that are unavoidably distorted should be reformed immediately after quenching.
Change 16 3-19
