In-Situ Observation of Alumina Particles in Molten Aluminum Using a Focused Ultrasonic Sensor

Abstract

Ultrasonic in-situ observation of alumina particles in molten aluminum at temperature up to 800• C is presented. A focused ultrasonic sensor is employed for the high temperature measurement with a high spatial resolution. The sensor mainly consists of a conventional piezoelectric transducer, a taper-shaped clad buffer rod as a waveguide and a cooling system. Martensitic stainless steel is used as a material for the buffer rod and an acoustic lens is fabricated at the probe end of the rod. In order to examine the focusing ability of the acoustic lens, the acoustic field near the focusing zone is numerically evaluated by a finite difference method. Using the developed focused ultrasonic sensor, backscattered echoes from alumina particles of 160 µm suspended in the molten aluminum at 800• C have been observed clearly in pulse echo mode at 10 MHz. The effect of the size and the aggregation condition of the particle on the backscattered echoes has also been examined.

<I>In Situ</I> Observations of Solidification and Melting of Aluminum Alloy Using Ultrasonic Waveguide Sensor

“…The sensor mainly consists of a 5 or 2.25 MHz conventional piezoelectric ultrasonic transducer (UT), an air-cooling pipe and a Ti rod as a waveguide. The basic construction of this sensor is almost the same as the ones used in the previous works, [16][17][18][19][20] except for the waveguide material. The length and diameter of the Ti waveguide are 300 and 30 mm, respectively.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The concept of an ultrasonic waveguide is a common technique for molten metal measurements. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] This technique is rather classical, but it is still attractive because of its simplicity, robustness and cost effectiveness. In this technique, measurements are made using a waveguide while the probe end is immersed in molten metals.…”

“…In order to overcome such difficulty, recently clad waveguides with superior ultrasonic wave guidance and high SNR have been developed. 14,15) Using such clad waveguides, several ultrasonic pulse-echo measurements have been successfully performed for molten Zn, 16) Al 17,18) and Mg 19,20) at temperature up to 800 C.…”

“…Although a stainless steel was used as waveguide materials in the earlier works, [16][17][18][19][20] it is certain that the steel waveguide is slowly and definitely attacked by chemical reactions with molten Al. We have chosen titanium (Ti) as the waveguide material because the sustainability of Ti in molten Al is higher than that of steel.…”

Ultrasonic Sensing: Fundamentals and its Applications to Nondestructive Evaluation

“…These spurious echoes deteriorate the signal to noise ratio (SNR) because of their possible interference with desired signals to be measured. To overcome such difficulty, tapered and clad buffer rods are developed for various applications in materials evaluations and monitoring [26,27,28,29,30,31]. Figure 11 shows the exterior of one of the developed buffer rod sensors, consisting of a tapered clad buffer rod, a cooling pipe and a conventional ultrasonic transducer (UT).…”