Ultrasonic evaluation of semi-solid metals during processing

Ultrasonic velocity and attenuation measurements for three different semi-s olid (SS) aluminum (Al) alloy billets (A356, A357 and 86S) and one dendriti c sample (A356) were performed in the temperature range between room temper ature and similar to 575 degreesC using a non-contact laser-ultrasonic tech nique. It was found that there are measurable differences in ultrasonic vel ocity and attenuation between SS and dendritic samples and these difference s are larger as the temperature becomes closer to the complete melt state. In a laboratory setup simulating the barrel section of a thixomoulding or a rheomoulding machine, a clad buffer rod thigh temperature probe) was used to perform real time ultrasonic monitoring. We have observed 10 MHz ultraso nic signals of 30 dB signal-to-noise ratio reflected from a rotating screw with a distance of 5.5 mm between the probe end and the root of the screw i n a viscous liquid Al alloy (A356) at 610 degreesC. This information should enable us to determine whether the processed part has the desired thixotro pic structure or not, and then to properly adjust heating and other process parameters.