962 Experimental Procedures 9621 Materials and Specimens

In the present investigation the aluminum alloys 2024, 6013, 8090, and 2091 were used. Alloy 2024 is the most widely used aircraft structure aluminum alloy; alloy 6013 is weldable; the investigated aluminum-lithium alloys, in addition to their desirable high values of specific strength and specific modulus of elasticity, provide good creep resistance and are considered as candidate materials for the European new-generation civil supersonic aircraft. Chemical compositions of the alloys are given in Table 9.32; the selected materials refer to the aluminum alloy systems Al-Cu, Al-Si-Mg-Cu, and Al-Li. All alloys were received in sheet form of 1.6 mm nominal thickness in the following temper conditions: T3 for alloy 2024, T6 for alloy 6013, T81 for alloy 8090, and T3 for alloy 2091. Tensile specimens were machined according to the specification ASTM E8m-94a [63]; specimens were cut in both longitudinal (L) and long transverse (LT) direction. Prior to tensile testing the specimens were precorroded as described below. Corroded tensile specimens have been also used for the metallographic and stereoscopic corrosion characterization. A portion of the 2024-T351 alloy tensile specimens were first subjected to hard anodization coating and sealing according to MIL-A-8625E specification [64] and then corroded. The thickness of the anodization layer was 50 ^m. Sealing was performed by immersing the anodized specimens in a hot aqueous 5% sodium dichromate solution. Fatigue specimens to derive S-N curves were machined according to the specification ASTM E466-82 [65]; and specimens to measure fatigue crack growth were machined according to ASTM E647-93 [66].

TABLE 9.32 Chemical Composition (in wt %) of Aluminum Alloys 2024, 6013, 8090, and 2091

Aluminum

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