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

5.2.3.1.2  Aluminum alloy selection limitations.  Mill product forms of aluminum alloys

2020, 7079, and 7178 in all temper conditions shall not be used for structural applications.  The use of 7XXX-T6 aluminum alloys shall be limited to thicknesses not to exceed 6.35 mm (0.250 inch).

5.2.3.1.3  Maximum metal removal.  Maximum metal removal from surfaces of non-stress relieved structural parts after final heat treatment shall not exceed 3.81 mm (0.150 inch) per side unless the final temper of condition has been demonstrated to have a stress-corrosion resistance of 173 MPa (25 ksi) or higher in the short transverse grain direction as determined by a 20 day alternate immersion test specified in ASTM G47.  This requirement is applicable to 2000 and

7000 series alloys, but 30 days shall be used on 2000 series alloys.  Stretch stress-relieved or compression stress-relieved aluminum products shall be used whenever possible.  Maximum metal removal requirements are not intended to apply to mechanically stress-relieved products because of the low level of internal stresses resulting from mechanical stress-relieving.

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

(STDG).

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