MECHANISMS OFPRECIPITATES FORMATION IN AN Al- Cu- Li-ZrALLOYUSINGDSC TECHNIQUE AND ELECTRICALRESISTANCE MEASUREMENTS

THE ICOSAHEDRAL Al-Li-Cu PHASE

STRUCTURE OF STABLE INTERMETALLIC COMPOUNDS OF THE Al-Li-Cu-(Mg) AND Al-Li-Zn-(Cu) SYSTEMS

The results of a thorough structural study of crystalline intermetallic compounds within the Al-Li-(Cu,Mg,Zn) system are given. Characteristic morphologies of these ternary or quaternary phases are exhibited by concentrated alloys or large single crystals. Typical X-ray powder diffraction data, selected area electron diffraction patterns and high resolution electron microscopy images are shown,...

CASTABILITY OF Al-Li-Mg AND Al-Li-Cu-Mg ALLOYS

The objective of the present work is to study the casting characteristics of various A1-Li alloys, which include fluidity and strengths of the alloys and their interaction with cast molds. Materials investigated are Al-Li-Mg and Al-Li-Cu-Mg alloys with Li content of 2.5 wt%. The results show that sand molds with resin binders are good for A1-Li casting. Ceramic coatings can further reduce the m...

MICROSTRUCURE AND STRENGTHENING OF Al-Li-Cu-Mg ALLOYS

A detailed quantitative model for the strengthening of monolithic alloys and composites due to precipitation strengthening, solution strengthening, grain and subgrain strengthening, strengthening by dislocations and load transfer to ceramic inclusions is presented. The model includes a newly derived description of the effect of a precipitate free zone (PFZ) around the reinforcing phase incorpor...

Embrittlement of Al-Li-Cu-Mg alloys at slightly elevated temperatures: microstructural mechanisms of hardening

When underaged, damage tolerant Al-Li based alloys are exposed to slightly elevated temperatures (60 to 100oC), their strength increases and toughness decreases. To study the first stages of this process, 8090 sheet in three underaged heat treatment conditions, including T3, T81 and a multistage temper, was exposed for 1000 h at 70°C. Using a model for strengthening in combination with a quanti...

CORROSION FATIGUE CRACK PROPAGATION AND INHIBITION IN Al-Zn-Mg-Cu VS Al-Cu-Mg/Li ALLOYS

Age-hardenable aluminum alloys used in aerospace structures are susceptible to environment assisted fatigue crack propagation (EFCP), limiting component durability and safety. The objective is to quantitatively understand EFCP and its inhibition for important aerospace alloys: 7075-T651 (Al-Zn-Cu-Mg), C433-T3 (Al-Cu-Mg), and C47A-T86 (AlCu-Li). EFCP is understood through the hydrogen embrittlem...