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 5C (660 10F). 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 354C (670F), 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 343C (650F), 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 660F, 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 800F, followed by a maximum cooling rate of 50 per hour to 500F, 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 775F, 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.

Aerospace MetalsGeneral 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.