Synergetic effect of surface-active metallic additions on structure modification in aluminium alloys

Main current means to control structure in wrought Al alloys is by adding grain-refining master alloys with insoluble particles (borides or carbides). This produces substantial grain refinement but not necessarily affect the distribution of eutectic particles or internal dendritic structure. In some groups of alloys, e.g. free-machining or recycled alloys, the size distribution and morphology of these secondary particles (soft or hard/brittle particles) as well as the internal dendritic structure of grains are of paramount importance and currently not well controlled unless special external physical fields ( electromagnetic, mechanical or ultrasonic) are used. In addition, free-machining aluminium alloys rely currently on additions of Pb that need to be phased out due to the environmental and health requirements. Hence the search for the chemical means to produce good-quality free-machining and/or recycled alloys with beneficial size, morphology and spatial distribution of soft and hard phase particles is timely and necessary.