Ultrasound-induced equiaxial flower-like CuZn5/Al composite microstructure formation in Al/Zn–Al/Cu joint

Evolutions of the microstructure and properties of Al/Zn–Al/Cu joints exposed to ultrasonic waves during solidification were investigated. An anisotropic microstructure was exhibited in the joint without ultrasonic treatment during solidification. However, a homogeneous microstructure displayed with equiaxial flower-like CuZn5/Al composites interspersed with refined α-Al grains and Zn–Al eutectics was obtained in the joint treated with ultrasound during solidification. The CuZn5 flower showed an isotropic growth from a CuZn5 “shell” on a α-Al nucleus, and the formation was ascribed to the combined effects of ultrasound-induced erosion of base metals and ultrasound-aided grain refinement. Compared with the joint without ultrasonic treatment, the interlayer in the ultrasound-treated joint showed a 26.17% increase in hardness and a 37.99% decrease in the coefficient of thermal expansion (CTE).