Steady-state creep and strain transients for stress change tests in an Al–0.4 wt% Li solid solution alloy

Abstract

Stress‐dip and stress increment tests are performed on an Al–0.4 wt% Li alloy creeping in steady state at 300 °C under a range of applied stresses (σ). The stress exponent of steady‐state creep is determined to be approximately four, typical of pure metals or Class II alloys where recovery creep is rate controlling. The instantancous strains on a sudden stress increment (Δ+) or dccrement (Δ−) are measured and Δ+ is greater than Δ− for all levels of σ and Δσ. Such a behaviour is more typical of Class II alloys than Class I alloys whcre Δ+ ≈ Δ−. Work hardening rates determined from the instantaneous strains varie from about 0.6 to 0.70 times the value for Youngs Modulus, in general decreasing with increasing creep stress. Internal (σi) and effective (σe) stress are determined from the stress dip tests and the ratio σi/σ varied between about 0.8 and 0.9, generally decreasing with increasing σ.σi/σ = 0.8 to 0.9 is intermediate between that prrvioiisly found for pure metals (σi/σ = 0.9 to 1.0) and that for Class I alloys such as AlσMg (σi/σ ≈ 0.7).