On the mechanical response of aluminum alloy 6061-T6 under extreme strains and strain rates, and rapid heating

Abstract

The flow stress of aluminum alloy 6061-T6 produced by conventional thermomechanical methods has been investigated under the application of strains up to 80% at a strain rate of the order of 50001/s, and temperatures ranging from ambient to near melting. The high strain and strain rate deformation was imposed using a Kolsky bar compression apparatus equipped with a fast pulse-current heating system to reach the target temperatures at high heating rates. The flow stress was measured under strains, strain rates, temperatures and heating rates that match thermomechanical conditions developed in the primary shear zone of a specially designed machining with chip pulling test method. Flow stress error is estimated by statistics obtained from experimental replicates. It is expected that these measurements will enable the formulation of realistic machining models for Al6061-T6. Temperature measurements were obtained using non-contact infrared (IR) full field imaging together with embedded micro-thermocouple (TC) point probing. The TC measurements were used to estimate the emissivity of the aluminum specimen via separate, in situ calibration tests, and to track temperature evolution during the compression, also via separate testing, not compromising the flow stress measurements. Type-K TC measurements were made using the separated junction principle by embedding the TC wires into two micromachined holes in the specimen. The temperature measurement technique is discussed in detail, and temperature uncertainties are estimated. The Kolsky bar and machining test with chip pulling will be used going forward to study the effect of heating time on the dynamic thermal softening behavior of Al6061-T6, which has been shown to be time-sensitive under quasi-static loading when temperatures exceed 200°C, due to Mg-Si precipitate growth.