Investigation of Grain Refinement and Mechanical Properties of Al-7Si Alloy with Al-5Nb-1B Master Alloy Addition Treated by Ultrasound Treatment

In this research, a novel Al-5Nb-1B master alloy refiner was prepared based on traditional casting methods with the aid of ultrasonic melt-assisted treatment. The outcomes showed that as the ultrasonic power was increased, the primary α-Al and precipitates in Al-5Nb-1B alloy were greatly refined. Among them, the coarse cellular α-Al structure was transformed into fine equiaxed grains, and their size was significantly decreased from 125 to 60 μm when the melt was treated by 1500 W ultrasound power. In addition, the size and shape of Al3Nb and NbB2 phases were optimized after 1000 W ultrasound treatment, and the agglomeration of particles was also effectively eliminated. Meanwhile, the nano-sized NbB2 particles precipitated from Al-5Nb-1B alloy after ultrasonic melt treatment. The influences of acoustic cavitation and acoustic streaming on the characterization of the microstructure in Al-5Nb-1B alloy were analyzed. Subsequently, the α-Al phase was greatly refined into fine equiaxed grains when Al-5Nb-1B master alloy treated by 1000 W ultrasonic power was added to Al-7Si alloy. Moreover, the secondary dendrites arm spacing was significantly decreased to 9.78 μm. Additionally, the tensile testing revealed that the ultimate tensile strength of Al-7Si alloy with the addition of Al-5Nb-1B master alloy was enhanced by 7.1