ABSTRACTAl–Cu melts were used to study interdiffusion under a transverse magnetic field (TMF) using X-ray imaging. A novel gravity-assisted automatic docking device was used to create a long capillary of the diffusion couple. Compared with the results acquired using energy-dispersive spectroscopy, X-ray imaging is more convenient and accurate to determine concentration profiles along long capillaries using the numerous gray value intensities in the imaging. Because a TMF can inhibit melt convection, the interdiffusion coefficient (DAlCu) was reduced after applying a TMF of 2 T. Our results demonstrate that the application of X-ray imaging is an efficient way to study ex-situ diffusion in liquid melts.