Nondestructive detection of the T1 phase in Al-Li alloys

Al--Li alloys have attracted the interest of aerospace industries for some time now, since the use of such alloys reduces the weight of an airframe by roughly 10%. The production of these alloys, however, requires precise thermal and/or thermomechanical treatments to ensure required material properties. In the efforts to characterize the thermal history and the mechanical properties of Al--Li alloy 2090 by NDE techniques, a strong deviation from the general rule that the conductivity increases with aging is noted. This deviation occurs on samples aged at 200 deg C for extended periods, as shown. Most exciting about the results is the fact that it appears possible to detect an excess of T1 phase present in the material by a combination of two NDE techniques--a conductivity in combination with a hardness measurement. Neither technique is sufficient by itself to provide evidence for the undesirable T1 phase. 12 ref.--AA(UK/US).