Mathematical Modeling of the Solidification Structure Evolution in the Presence of Ultrasonic Stirring
- PDF / 1,690,690 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 35 Downloads / 258 Views
ION
ULTRASOUND technology is a powerful technological tool that affects a material. Ultrasonic vibrations can significantly affect heat and mass transfer in liquids, modify the structure and properties of solids, and interfere with the interactions of solids and liquids. The primary causes result from ultrasonic cavitation, acoustic streaming, and movement of dislocations associated with propagation of ultrasound waves in media. Ultrasonically induced cavitation consists of the formation of small cavities (bubbles) in the molten metal followed by their growth, pulsation, and collapse. These cavities are created by the tensile stresses that are produced by acoustic waves in the rarefaction phase.[1] The common benefits of applying ultrasound include (1) significant improvement of product quality, (2) reduction of power consumption, and (3) decreasing considerably the duration of a production process. There are a significant number of potential applications of ultrasound (as part of acoustics) to fields in life sciences, physics, chemistry, and engineering, the most promising ultrasonic applications being in the agriculture, food and light industries, goods manufacturing, biotechnology, LAURENTIU NASTAC, Professor, is with the Department of Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, AL 35487-0202. Contact e-mail: [email protected] Manuscript submitted May 19, 2011. Article published online June 15, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
metallurgy, mineral processing, environmental protection, medicine, and energy systems areas. Relevant applications include structural refinements of solidifying metals with applications to continuous casting as well as to remelting processes (vacuum arc remelting (VAR), electroslag remelting (ESR), electron beam remelting (EBR), and plasma arc melting (PAM)) for Ti alloys, specialty steels, and superalloys. Additional potential applications include die-casting, semi-solid metal processing, and forging of high fractions of fine spherical grains. Some critical technologies that have immediate application to the manufacturing industry are as follows[1–7]: (1) ultrasonic degassing of Al alloys; (2) ultrasonic tempering of cast low alloying steels to improve toughness and strength; (3) ultrasonic irradiation to relieve internal stresses; (4) use of ultrasound to enhance homogenization heat treatment; (5) ultrasonic irradiation to enhance surface heat treatment processes (diffusion-based processes); (6) grain refinement during welding; and (7) ultrasonic cold/hot welding. An example of one of the most promising applications is the use of ultrasonic energy for grain refinement during casting of Al- and Mg-based alloys, for achieving an optimized microstructure (free of solidification-type defects such as pores and segregation with a uniform distribution of secondary phases and inclusions), which is conducive to improved material properties. Another relevant application is a quick method of degassing of Al-based alloys using ultrasonic vibrations. Complete VOLU
Data Loading...
