Papers by Author: Brian M. Gable

Abstract: The effect of Si additions on vacancy behavior following solution treatment and quenching was studied for an Al-Cu-Mg-Ag alloy system using positron annihilation lifetime spectroscopy (PALS). Both the initial positron lifetime and steady state positron lifetime increase as the Si concentration increases. This behavior is interpreted in terms of Si interacting with vacancies, leading to their retention in the alloy. The ability of PALS to monitor vacancy behavior after solution treatment should allow the improved prediction of phase transformation kinetics and hence the tailoring of ageing treatments.

Abstract: Nuclear magnetic resonance (NMR) was used to systematically monitor the amount of copper in the matrix of various age hardenable Al-Cu alloys as a function of ageing treatment. These NMR results were used to compare the measured amount of copper residing in the matrix during microstructural evolution with that suggested from the equilibrium phase diagrams. Our results indicate that the matrix copper composition for under- and peak-aged microstructures is generally far from equilibrium, with much more copper in solution than expected based on equilibrium phase diagrams. NMR is shown to be a sensitive and efficient metallurgical characterization technique to monitor the partitioning of solute in both non-equilibrium and equilibrium phases.

Abstract: The ability to improve mechanical properties through trace alloying additions that enhance the precipitation-hardening response has been a cornerstone of aluminium research and alloy development. It is now known that many of these alloying additions are beneficial (or deleterious) because of their influence on the competitive precipitation kinetics, in many cases arising from the formation of chemical and structural heterogeneities in the matrix. In order to better our understanding of this phenomenon, the earliest stages of microstructural evolution of indium precipitates and θ' plates in an Al-Cu-In ternary alloy have been investigated. Quantitative microstructural characterization reveals that there is a correlation between the size of the pre-existing indium particle and the resulting heterogeneous precipitation kinetics, with larger indium particles favouring θ' precipitation.