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A high-speed welding process has been successfully developed for aluminum-lithium alloy joints, the product of which demonstrates a substantial weight-saving potential for aircraft, spacecraft and missile applications. Because dynamic environmental effects, interpreted as corrosion-fatigue crack growth, can lead to a reduction in the strength of airframe, engine, and accessory structures, the corrosion-fatigue cracking susceptibility of aluminum-lithium alloy and its weldment must be understood by aerospace designers if further consideration is to be given to this material.
Corrosion-fatigue crack growth in an optimally welded aluminum-lithium alloy joint was investigated at ambient temperature by alternate immersion in a 3.5% NaCl solution and air. The corrosion-fatigue crack growth rate (da/dN) was evaluated by studying precracked compact-tension specimens and then correlating the results with the applied cyclic stress intensity range (ΔK). The crack and fracture morphology exhibited by tested specimens were investigated with scanning electron microscopy and Auger electron spectroscopy. Metallurgical factors, such as linear grain-boundary precipitation and spherical general precipitation at the crack tip area, were analyzed for the development of a corrosion-fatigue cracking mechanism.
aluminum alloys, corrosion, aluminum-lithium alloy, corrosion fatigue, air-frame, cracking susceptibility, cyclic stress intensity, fracture morphology, marine atmosphere exposure, transoceanic flight, alternate immersion, crack growth rate equation
Senior engineer/scientist, Douglas Aircraft Co., McDonnel Douglas Corp., Long Beach, CA
Structural mechanics engineer, L. Raymond & Associates, LRA Laboratories, Inc., Newport Beach, CA