Numéro
J. Phys. Colloques
Volume 48, Numéro C3, Septembre 1987
4th International Aluminium Lithium Conference
Page(s) C3-745 - C3-751
DOI https://doi.org/10.1051/jphyscol:1987387
4th International Aluminium Lithium Conference

J. Phys. Colloques 48 (1987) C3-745-C3-751

DOI: 10.1051/jphyscol:1987387

THE EFFECT OF AGEING ON THE FATIGUE BEHAVIOUR OF Al-2.3 wt% Li SINGLE CRYSTALS

J. SCHNEIDER, H.-J. GUDLADT et V. GEROLD

Max-Planck-Institut für Metallforschung, Institut für Werkstoffwissenschaften, Seestrasse 92, D-7000 Stuttgart 1, F.R.G.


Abstract
In order to get a better insight into the basic deformation of fatigue in precipitation-hardened Al-Li, experiments have been undertaken on single crystals of a high purity Al-2.3 wt.% Li alloy. The crystals were solution heat treated and aged for different times and temperatures. In laboratory air symmetrical push-pull tests were performed with a constant plastic shear strain amplitude 10-4 < γpl < 9.10-3. For nearly all ageing conditions cyclic hardening and softening effects were very small compared to other precipitation-hardened crystals such as Cu-Co. For specimens aged at 160°C (UA) and 200°C (PA), respectively, the cyclic deformation is characterized by planar slip which is less pronounced for PA specimens. UA specimens showed heavy strain burst effects where the plastic strain reaches up to 10 times the desired amplitude. These strain bursts are induced by the nucleation of planar slip bands and are typical for UA specimens which tend to very extreme planar slip behaviour. Specimens aged at 220°C showed no planar slip, but some short PSBs with their typical extrusions were observed by SEM. The diminution of planar slip with increasing ageing temperature indicates that the degree of strain localization is dependent on the average size of the δ' precipitates in the investigated Al-Li alloy.