Preferential penetration path of gallium into grain boundary in practical aluminium alloy

Abstract

The preferential penetration of a liquid metal along grain boundaries (GBs) in polycrystalline metals is a well-known phenomenon. Gallium-decorated GB networks in rolled aluminium alloys have been visualized three-dimensionally using the high-resolution synchrotron radiation computer tomography (SRCT). The distribution of gallium concentration along GBs was measured using X-ray absorption. Statistical correction for blurring was performed to raise accuracy of the measurement, and then compared with orientation mapping by the SEM/EBSP method on the surface of a tomographic specimen. The pancake-like grain microstructure formed by a rolling process causes the anisotropy of penetration direction. Although the gallium penetrated into high-angle GBs, all of the high-angle GBs are not necessarily decorated by the gallium. The reason for this may be explained by considering geometrically possible penetration paths that seem to be dependent on local grain arrangement and GB structure through each path. The dependence of the gallium concentration on the rotation axis of misorientation has been found along the high-angle GBs. Especially, GBs with a specific misorientation (〈221〉 as a misorientation axis) showed high gallium concentration.

Acknowledgements

The SR experiment was performed with the approval of JASRI through proposal numbers 2004B0457-NI-np. The authors would like to thank Dr. W. Ludwig for a fruitful discussion and also Mr. H. Makino for an experimental collaboration. We also would like to acknowledge support by the Grant-in-aid for Scientific Research from the Japan Society for the Promotion of Science under Contract No. 15560606 and 17360340.