Low-energy intergranular fracture in Al-Li alloys

作者：Pasang T^*; Symonds N; Moutsos S; Wanhill R J H; Lynch S P

来源：Engineering Failure Analysis, 2012, 22: 166-178.

DOI：10.1016/j.engfailanal.2012.01.006

• Aluminium-lithium alloys
• Thermal stability
• Intergranular fracture
• Grain-boundary segregation
• Slip-mode

An age-hardened Al-Li-Cu-Mg-Zr alloy (AA8090) used for a substantial part of the structure of a helicopter (in order to save weight) exhibited low-energy intergranular fracture during accidents, resulting in extensive damage. With this experience in mind, various hypotheses for brittle intergranular fracture in Al-Li alloys are reviewed, and possible remedial measures outlined. The effects of variables such as alloy composition, ageing times and temperatures, crystallographic texture, and test temperature on brittle-intergranular-fracture resistance are described, and it is concluded that lithium segregation to grain boundaries is primarily responsible for brittle intergranular fracture. Lithium segregation occurs mainly during the primary ageing treatment; but secondary ageing during service, where temperatures can reach 50-80 degrees C, could increase lithium segregation and further increase susceptibility to brittle intergranular fracture. The evidence also suggests that the prevalence of a planar-slip-mode in Al-Li alloys, resulting in dislocation pile-ups at grain boundaries, is not responsible for brittle intergranular fracture, contrary to widespread opinion.

• 出版日期2012-6