INFLUENCE OF ULTRASONIC MELT TREATMENT ON STRUCTURE FORMATION IN ALUMINIUM ALLOYS WITH HIGH AMOUNT OF TRANSITION METALS

摘要

During casting of aluminium, ultrasonics can be used to promote the formation of a fine, uniform, non-dendritic grain structure. From previous investigations it is known that the main condition for obtaining a fine equiaxed grain structure is a combined action of grain refiners and an intense ultrasound inducing cavitation on a solidifying melt. Additions of transition metals (Zr, Ti etc.) can significantly increase the number of nucleation sites without using an Al-Ti-B master alloy. Many commercial wrought aluminium alloys contain these elements because they also prevent recrystallization. The paper describes the results on the influence of zirconium and titanium in hypo- and hyperperitectic concentrations on structure formation during ultrasonic melt treatment (UST) in the liquid state. In separate experiments, model binary Al-Zr and Al-Ti alloys are solidified with and without UST. The final microstructure is analyzed qualitatively and quantitatively.