ABSTRACT
The effect of scandium on the structure and properties of aluminum and alloys is unique in its integrity. This chapter discusses the influence of TM additions on the structure of cast aluminum and its alloys. It suggests that the formation of solidification nuclei occurs by a mechanism similar to that of the decomposition of a supersaturated solution. The solidification process is highly affected by the solidification rate and the character of alloying elements which cause thermal and constitutional undercooling at the solidification front. Thermal undercooling is the real decrease in temperature at the solidification front with respect to the equilibrium liquidus. The constitutional undercooling results from a change in the liquid-phase composition in the vicinity of the solidification front. Different properties, hardening and softening are caused by different fineness parameters and coherence degrees of ScAl3 precipitate. The chapter concludes that scandium provides unique grain refinement, and thereby positively affects the workability upon casting, welding, and deformation of aluminum alloys.
