A. Danielou, C. Hénon, J. C. Ehrstrom, Alcan, Voreppe, France; P. Lequeu, Alcan Pechiney Rhenalu, Issoire, France; K. P. Smith, Alcan Rolled Products, Ravenswood, WV
Al-Cu-Li alloys are well known for their benefits in reducing density and increasing modulus, proportionally to their Li content. In addition, third generation Al-Cu-Li alloys have excellent resistance to corrosion in accelerated testing and after seacoast exposure. The compositions and processing of these alloys have been optimized to offer different toughness/static balances depending on the application in aircraft: 2195 with high static properties for compression-dominated panels, 2050 with good toughness/static balance for medium to thick gauge plate for integral structures, 2196 with high damage tolerance and low density for lower wing skins, 2198 with high damage tolerance for fuselage sheet.
The paper shows the mechanical properties obtained on these recently-developed alloys, as well as their corrosion resistance.
The damage tolerance of these alloys has been studied in open hole fatigue, fatigue crack growth, assembled samples, and crack branching. Al-Cu-Li alloys exhibit very good behaviour in fatigue crack growth, especially for short fatigue cracks. This benefit is also obtained for assembled samples such as LLT (Low Load Transfer) for upper wing skin in alloy 2195-T8.
Crack branching is a phenomenon that could occur for thick plates loaded in L-S direction: the crack deviates through the grain boundaries in L direction instead of S direction. The crack branching level obtained for thick plates in last generation alloy 2050-T8 is similar to that of incumbent 7050-T74 alloy.
In slightly under-aged or T8 temper, the Al-Cu-Li alloys exhibit very good resistance to sea-coast exposure. Moreover, performance in accelerated laboratory tests are superior compared to conventional alloys in all product forms. A summary of available data will be presented.
The opportunities offered by these improvements over incumbent alloys’ durability and damage tolerance with regard to inspection interval and design service life will be discussed.
Summary: Al-Cu-Li alloys are well known for their benefits in reducing density and increasing modulus, proportionally to their Li content. In addition, third generation Al-Cu-Li alloys have excellent resistance to corrosion in accelerated testing and after seacoast exposure. The compositions and processing of these alloys have been optimized to offer different toughness/static balances depending on the application in aircraft: 2195 with high static properties for compression-dominated panels, 2050 with good toughness/static balance for medium to thick gauge plate for integral structures, 2196 with high damage tolerance and low density for lower wing skins, 2198 with high damage tolerance for fuselage sheet.
The damage tolerance of these alloys has been studied in open hole fatigue, fatigue crack growth, and assembled samples. Al-Cu-Li alloys exhibit very good behaviour in fatigue crack growth, especially for short fatigue cracks.
In slightly under-aged or T8 temper, the Al-Cu-Li alloys exhibit very good resistance to sea-coast exposure. Moreover, performance in accelerated laboratory tests are superior compared to conventional alloys in all product forms. A summary of available data will be presented.
The opportunities offered by these improvements over incumbent alloys’ durability and damage tolerance with regard to inspection interval and design service life will be discussed.
