Experimental assessment of structure and property predictions during hot working

Abstract

Uniaxial compression experiments were conducted in the hot-working range for a commercial purity aluminum alloy using constant strain-rate tests and strain-rate drop tests producing strain hardening, strain softening, and steady-state deformation behaviors. The structure of the deformed material was characterized by microhardness and grain shape. A single internal state variable constitutive model for flow stress was developed using the microhardness data to quantify the state variable. The change in the grain aspect ratio was related to the imposed bulk strain in the samples. The constitutive model was incorporated into a finite element program. A critical experimental assessment of predictions of the spatial variation in structure and properties throughout a workpiece was then made using a tapered compression specimen. Comparisons with experimental results indicated that the load was underpredicted by 10 pct and the microhardness by 6 pct, while the severity of the strain gradients was overpredicted. This was concluded to be due to an underprediction of the work-hardening rate at low strains. Additional calculations made with alternative constitutive models showed that the internal state variable model predicted the applied force much more accurately than alternative models.