ANNEALING OF HEAT-TREATED ALLOYS

are normally quenched in cold water. The temperature before quenching should be 85°F or less. Sufficient cold water should be circulated within the quenching tanks to keep the temperature rise under 20°F. This type of quench will ensure good resistance to corrosion, and is particular y important when heat-treating 2017 and 2024 alloys. HOT WATER QUENCHING.—Large forgings and heavy sections can be quenched in hot or boiling water. This type of quench is used to minimize distortion and cracking, which are produced by the unequal temperatures obtained during the quenching operation. The hot water quench will also reduce residual stresses, which improves resistance to stress corrosion cracking. SPRAY QUENCHING.—Water sprays are used to quench parts formed from alclad sheets and large sections of most alloys. Principal reasons for using this method are to minimize distortion and to alleviate quench cracking. This system is not usually used to quench bare 2017 and 2024 due to the effect on their corrosion resistance. Annealing Annealing serves to remove the strain hardening that results from cold working and, in the case of the heat-treated alloys, to remove the effect of the heat treatment. Annealing is usually carried out in air furnaces, but salt baths may be used if the melting point of the bath is low enough. A bath made up of equal parts by weight of sodium nitrate and potassium nitrate is satisfactory. ANNEALING OF WORK HARDENED MATERIAL.—Annealing of material that was initially in the soft or annealed condition but which has been strain-hardened by cold working, such as 1100, 3003, 5052, etc., is accomplished by heating the metal to a temperature of 349 ±5°C (660 ±10°F). It is only necessary to hold the metal at this temperature for a sufficient length of time to make certain that the temperature in all parts of the load has been brought within the specified range. If the metal is heated appreciably above 354°C (670°F), there is a partial solution of the hardening constituents, and the alloy will age harden while standing at room temperature unless it has been cooled very slowly. If the temperature is not raised to 343°C (650°F), the softening may not be complete. The rate of cooling from the annealing temperature is not important. However, a slow cool is desirable in case any part of the load may have been heated above the recommended temperature range. ANNEALING OF HEAT-TREATED ALLOYS.— The heat-treatable alloys are annealed to remove the effects of strain hardening or to remove the effects of solution heat treatment. To remove strain hardening due to cold work, a 1-hour soak at 640° to 660°F, followed by air coding, is generally satisfactory. This practice is also satisfactory to remove the effects of heat treatment if the maximum of softness is not required. To remove the effects of partial or full heat treatment, a 2-hour soak at 750° to 800°F, followed by a maximum cooling rate of 50° per hour to 500°F, is required to obtain maximum softness. To remove the effects of solution heat treatment or hardening due to cold work, the high zinc-bearing alloy 7075 should be soaked 2 hours at 775°F, air cooled to 450°, and soaked 6 hours at 450°. The stabilizing temperature at 450° is necessary to precipitate the soluble constituents from solid solution. The annealing of solution heat-treated material should be avoided whenever possible if subsequent forming and drawing operations are to be formed. If such operations are not severe, it is generally advantageous to repeat the solution heat treatment and form the material in the freshly quenched condition. RECOMMENDED READING LIST NOTE: Although the following references were current when this TRAMAN was published, their continued currency cannot be assured. Therefore, you need to be sure that you arc studying the latest revision. Nondestructive Inspection Methods, N A V A IR 01-1A-16, Naval Air Systems Command Headquarters, Washington, D.C., 1 March 1990, Change 1, 1 April 1991. Aerospace Metals–General Data and Usage Factors, NAVAIR 01-1A-9, Naval Air Systems Command Headquarters, Washington, D.C., 22 November 1967, Change 19, 1 September 1989. Aeronautical and Support Equipment Welding, NAVAIR 01-1A-34, Commander, Naval Air Systems Command, Washington, D.C., 1 October 1987, Change 1, 1 May 1991. 15-45