Ultrasonic evaluation of semi-solid metals during processing

Abstract

Ultrasonic velocity and attenuation measurements for three different semi-solid (SS) aluminum (Al) alloy billets (A356, A357 and 86S) and one dendritic sample (A356) were performed in the temperature range between room temperature and ~575 °C using a non-contact laser-ultrasonic technique. It was found that there are measurable differences in ultrasonic velocity and attenuation between SS and dendritic samples and these differences 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 (high temperature probe) was used to perform real time ultrasonic monitoring. We have observed 10 MHz ultrasonic 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 in a viscous liquid Al alloy (A356) at 610 °C. This information should enable us to determine whether the processed part has the desired thixotropic structure or not, and then to properly adjust heating and other process parameters.

High-temperature (>500°c) wall thickness monitoring using dry-coupled ultrasonic waveguide transducers

“…Jen and co-workers [23], [24], [25], [26] have tried to limit the number of modes traveling in a thin bar by adding an attenuative cladding on the outside of the bar, the bar usually being tapered. This is essentially an attempt to remove the effects of the waveguide boundaries by reducing the amplitude of reflections from the surface.…”

Aluminum buffer rods for ultrasonic monitoring at elevated temperatures

“…From [22], the ultrasonic longitudinal wave velocity in the Al decreases about 1.1 (m/s)/ • C between room temperature and 500 • C at 10 MHz. According to our experience, the shear wave velocity decreases similarly but with a slightly higher slope than the longitudinal wave velocity.…”

“…According to our experience, the shear wave velocity decreases similarly but with a slightly higher slope than the longitudinal wave velocity. The ultrasonic attenuation in the Al increases about 0.01 dB/cm between room temperature and 500 • C at 10 MHz [22]. In our experiments, because the echoes reflected from the Al probing end/sample interface and those from the other side of the sample are used to evaluate the velocity and attenuation in the sample, the temperature effects on the velocity and attenuation in the Al rod itself are not of a concern.…”

Novel Concept to Detect an Optimum Thixoforming Condition of Al-Al3Ni Functionally Graded Material by Wavelet Analysis for Online Operation

“…Many studies to evaluate the semi-solid state during processing have been reported. Ultrasonic, for example, is applied to monitor the condition of semi-solid metals during processing [ 26 ]. A process using acoustic emission to determine the semi-solid condition by induction heating [ 27 ] is also reported.…”