Factors Influencing Fracture Toughness and Other Properties of Aluminum- Lithium Alloys
ALUMINUM CO OF AMERICA ALCOA CENTER PA ALCOA LABS
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An investigation was made to identify the microstructural features which control the fracture behavior of Al-Li alloys. Tensile, fracture toughness, and selected fatigue tests were conducted on candidate Al-Li alloys Al-Mg-Li, Al-Cu-Li, and Al-Li. In all three alloy systems and most aging conditions investigated, the fracture mode was low energy, intergranular failure. Three microstructural features were considered to correlate with the intergranular failure--the shearable nature of the coherent Al3Lidelta precipitates which leads to dislocation pile-ups at the grain boundaries the growth of a solute depleted, precipitate free zone during aging, and the occurrence of the tramp elements sodium, potassium and sulfur presumably segregated in the grain boundaries. Furthermore, the hydrogen content of the alloys was also shown to be significantly higher than other high strength commercial alloys. All these features would contribute to the low toughness and would tend to promtoe intergranular failure.
- Properties of Metals and Alloys