A process is described for producing an aluminum grain refiner, such as Al-Ti-B grain refiner. Molten aluminum is continuously flowed as a bottom layer along a substantially horizontal or slightly inclined trough. Titanium or boron compounds reducible by aluminum or a mixture of such compounds is added to the surface of the aluminum layer such that a discrete separate layer of these is formed on top of the aluminum layer. Reaction between the aluminum and the titanium and/or boron compounds occurs along the interface between the layers and this reaction may, if desired, be aided by providing relative movement between the layer of molten aluminum and the layer of titanium and/or boron compounds. A surface layer of spent reaction product is removed and a stream of aluminum alloyed with titanium and boron is collected.