The relationship between microstructural and plastic instability in AI-4.0 Wt Pct Cu alloy

Abstract

The investigation of the effect of plastic deformation on the stability of theθ′ precipitates in an aluminum-4.0 wt pct copper alloy was performed. The alloy was produced by directional solidification, with Ti added as a grain refiner. Hot compression tests were performed at 200 °C in the strain rate range of 10_-3 to 10_-5 s₁ and equivalent strain up to 0.7 on specimens that had been initially heat treated, also at 200 °C, in order to obtain a uniform distribution of theθ0′ precipitates within the matrix. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of the plastically deformed specimens revealed a very heterogeneous distribution of strain. Also, the regions with localized strain contained randomly distributedθ precipitates of nearly equiaxed shape without any preferred orientation relationships to the matrix. Thus, the plastic deformation initiated the transformationθ′ →θ. The flow stress was reduced in the regions in which this transformation had occurred, which further accentuated the localization tendency of the strain. The combined process,θ′ →θ transformation/strain localization, thus developed in an avalanching way.