Ultrasound-assisted cast-on method: Obtaining high-quality metallurgical bonds between a bare steel insert and A354 aluminum alloy within a composite casting

A bare steel insert is difficult to be bonded to an aluminum alloy using a cast-on method for manufacturing bimetal composite castings. This article describes an ultrasound-assisted cast-on (UACO) approach in obtaining high quality metallurgical bonds between bare steel inserts and A354 aluminum alloy. Hot dip tests were carried out to determine the reaction times required to obtain high quality metallurgical bonds with and without high -intensity ultrasonic vibrations. Ultrasonic vibrations were then applied through the bare steel insert to assist the cast-on method for making bimetal castings. Microstructural characterization revealed that oxide and porosity defects that covered the interface of the steel/melt in a bimetal casting made by conventional cast-on methods were totally removed in castings subjected to high-intensity ultrasonic vibrations. Push-out tests confirmed that the mean shear strength in such composite castings increased with increasing intensity of ultrasonic vibrations, from about 3.1 MPa at 0 mu m amplitude to about 91.6 MPa at about 80 mu m amplitude of ultrasonic vibrations. The mean shear strength associated with the UACO process was about 85 % and 39 % higher than that of the Al-Fin process and Cummins process, respectively. Theoretical analyses were performed to understand experimental results. It is believed that ultrasound induced phenomena that occur at or near the steel/melt interface play an important role in forming high quality metallurgical bonds between bare steel inserts and aluminum castings. Research results suggest that the UACO process can be a cost-effective replacement for various cast-on processes for manufacturing bimetal composite castings of high internal integrity.