The Effect of Temperature on the Yield Stress of Al–Li Alloy

Yield stress of aged Al-11.1 mol%Li alloy was measured at temperatures between 77 and 523 K, and the deformation induced dislocation structure was examined by transmission electron microscopy. Strength and dislocation arrangements depend largely both on the aging condition and on the testing temperature. The peak positions in strength vs aging time curves shift to the side of shorter aging time with increasing testing temperature. The mode of interaction between dislocations and δ′-precipitates also varies with the testing temperature. For the specimens aged nearly to the peak strength, the positive temperature dependence of yield stress is observed in the temperature range in which dislocations move in pairs cutting the δ′-precipitates. In the over-aged specimens, dislocations by-pass the precipitates leaving dislocation loops around the precipitates at the beginning of plastic deformation. The shift of peak positions in the aging curves and the variation of the interaction modes between dislocations and precipitates with testing temperature are explained in terms of the positive temperature dependence of cutting stress and the negative temperature dependence of by-passing stress.

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