MIL-STD-1568 Materials And Processes For Corrosion Prevention And Control In Aerospace Weapons SystemsThis standard establishes the requirements for materials, processes and techniques, and identifies the tasks required to implement an effective corrosion prevention and control program during the conceptual, validation, development and production phases of aerospace weapons systems. The intent is to minimize life cycle cost due to corrosion and to obtain improved reliability.

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MIL-STD-1568C

TABLE I.  Rating for resistance to SCC aluminum alloys in the short transverse grain direction

(STDG) - Continued.

All aluminum sheets used in external environments and interior corrosive environments shall be clad on both sides except where the design requires surface metal removal by machining, chemical milling, adhesive bonding or where alloys of the 1000, 3000, 5000, or 6000 series type are used.

5.2.3.1.4  Shot peening for stress corrosion resistance and fatigue life improvement.  All critical surfaces of all structural forgings, machined plate and extrusions, where accessible after final machining and heat treatment, shall be completely shot peened in accordance with

SAE AMS2430, ensuring 100 percent coverage as a minimum or placed in compression by other suitable means, except for alloys having a demonstrated stress corrosion resistance of 173 MPa (25 ksi) or higher in the short transverse direction and web areas under 2.03 mm (0.080 inch) thick where no short transverse grain is exposed by machining.  Those areas of forgings

requiring lapped, honed, or polished surface finishes for functional engineering requirements shall be shot peened prior to such subsequent surface finish operations.  All aluminum products with an ASTM G47 stress corrosion threshold less than 173 MPa (25 ksi) shall, after shot peening, have essentially no residual surface tensile stresses in the final heat treated and

machined condition.  Attachment points for primary structure shall be shot peened for fatigue life improvement.  Finish clean-up of shot peened surfaces as required for fit up shall not exceed

0.076 mm (0.003 inch) of surface removal for aluminum alloys.

5.2.3.1.5  Stress corrosion factor.  High strength aluminum alloy parts shall be designed, manufactured, assembled, and installed so that sustained residual tensile stresses are minimized to prevent premature failures due to stress corrosion cracking.

5.2.3.2  Low alloy, high strength steels.  All low alloy, high strength steel parts, 1241 MPa (180 ksi) ultimate tensile strength (UTS) and above, including fasteners, require corrosion preventative metallic coatings by a process proven to be nonembrittling to the alloy/heat treatment combination.  Applicable metallic coatings and finishes are described in subsequent sections of this document.

5.2.3.2.1  Limitation on use of protective metallic coatings.  Soft surface coatings such as cadmium, nickel-cadmium, and aluminum shall not be used for sliding or wear applications.

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