In the present study, various microstructural features, such as particles and pores, have been visualized in cast and wrought aluminum alloys by employing X-ray tomography apparatuses with a wide range of spatial resolution. Special care is dedicated to evaluate an identical sample for each entire series of imaging experiments. The X-ray tomography apparatuses used include the one performed at a synchrotron radiation facility, which has a spatial resolution level close to the theoretical limit of the projection-type imaging, in addition to two industrial apparatuses. It has been shown that even if industrial apparatuses, which inevitably possess limited spatial resolution levels, are used, the real size and fraction of microstructural features can be estimated by performing imaging experiments above a certain spatial resolution level. It would be, so far as the authors are aware, the first time to demonstrate the feasibility of laboratory-scale X-ray tomography imaging in microstructural observation in a systematic manner, especially focusing on spatial resolution and quantitative capability.

View full abstract

Aluminum matrix composites reinforced by vapor grown carbon fibers (VGCF) were fabricated by powder can extrusion. Extrusion ratio was 9 or 16. Temperature and heating duration were changed to investigate the effect of extrusion condition on properties of composites. Measurement of micro-Vickers hardness, tensile strength was conducted and microstructure such as VGCF orientation was characterized. When extrusion temperature was higher or when heating duration was longer, mechanical strength was lower, but fracture strain was higher. In addition, reinforcing efficiency to aluminum was higher for longer heating duration and higher extrusion ratio, due to improved VGCF orientation. Strength was modeled considering load bearing by VGCF, VGCF orientation, work hardening of matrix due to thermal expansion mismatch of VGCF and aluminum and Orowan looping mechanism. From those results and the observation of aluminum grain in composites, reinforcing mechanism of VGCF reinforced composites was discussed.

View full abstract