Power ultrasound highlights various beneficial effects in the treatment of molten metals and alloys, such as structuring, degassing and improved filtration.
Ultrasonic promotes non dendritic solidification of liquid and semi-solid metals.
Ultrasonic treatment can significantly promote the refinement of dendrites and primary intermetallic compounds.
In addition, power ultrasound can be used purposefully to reduce metal porosity or to generate fine pore structure.
Finally, the quality of casting is improved by high power ultrasonic.
Ultrasonic solidification
The formation of non dendritic structures during solidification of the metal melt can affect material properties such as strength, ductility, toughness and / or hardness. Ultrasonic induced grain nucleation: acoustic cavitation and its strong shear force increase the nucleation position and number in the melting process. Ultrasonic treatment (UST) of the melt leads to heterogeneous nucleation and dendrite fragmentation, which significantly improves the grain refinement of the final product.
The ultrasonic improves the grain structure of the melt
Ultrasonic cavitation leads to uniform wetting of non-metallic impurities in the melt. These impurities become nucleation sites, which is the starting point of solidification. Because these nucleation points are produced before the solidification front, the growth of dendrites will not be induced. Dendrite Breakup: dendrite melting usually begins at the root due to local temperature rise and segregation. Strong convection (heat transfer by mass movement of fluid) and shock wave are produced in melt, which makes dendrite structure broken. Due to the extreme local temperature and composition changes, convection can promote dendrite fragmentation and solute diffusion. Cavitation shock waves contribute to the fracture of those melted roots.
Ultrasonic degassing of metal alloy
Degassing is another important role of power ultrasonic on liquid and semi-solid metals and alloys. Acoustic cavitation produces alternating low / high pressure cycles. During the low pressure cycle, small vacuum bubbles occur in the liquid or slurry. These vacuum bubbles act as the nucleus for forming hydrogen and steam bubbles. The bubble rises because of the formation of a larger hydrogen bubble. Sound flow and flow help these bubbles float to the surface and discharge from the melt, thereby removing the gas and reducing the gas concentration in the melt.
Ultrasonic degassing reduces the porosity of metal, thus achieving higher material density in the final metal / alloy products. The ultrasonic degassing of aluminum alloy improves the ultimate tensile strength and ductility of the material. In terms of efficiency and efficiency, the industrial power ultrasonic system is the best in other commercial degassing methods. In addition, the filling process of the mold is improved because of the low viscosity of the melt.
The results of the study on the effect of different ultrasonic treatment time on ti44 al6nb1cr2v
Capillary action in filtration process
The ultrasonic capillary effect (UCE) in liquid metal is the driving effect of ultrasonic assisted melt filtration to remove oxide inclusions. Filtration is used to remove nonmetallic impurities from the melt. During filtration, the melt separates unwanted inclusions through various grids, such as glass fiber. The smaller the mesh size, the better the filtering effect.
Under general conditions, the melt can not pass through two-layer filter, and its pore size is 04.0,4mm. However, under the ultrasonic assisted filtration, the melt can pass through the mesh due to the capillary effect of ultrasonic. In this case, the filter capillary even retains 1-10 μ M of nonmetallic impurities. Because of the enhanced purity of the alloy, the formation of hydrogen pores in oxides is avoided and the fatigue strength of the alloy is improved.
Eskin et al. (2014: 120ff.), ultrasonic filtration can be used with 0.6 × A multi-layer glass fiber filter with 0.6mm mesh (up to 9 layers) is used to purify the aluminum alloy AA2024, aa7055 and AA7075. When the ultrasonic filtration process is in contract with the addition of inoculant, the grain refinement can be realized.
Ultrasound enhancement
Ultrasonic wave has a high effect on the homogeneous dispersion of nanoparticles into slurry. Nanoparticles (such as al2o3/sic, CNTs) are used as reinforcement materials. Nanoparticles were added to the molten alloy and dispersed by ultrasonic. The results show that the sound cavitation and fluidization improve the depolymerization and wettability of the particles, thus improving the tensile strength, yield strength and elongation.
Ultrasonic assisted static casting
Power ultrasound and cavitation
Cavitation occurs when high-intensity ultrasonic is coupled to liquid or slurry. The high power and low frequency ultrasonic can control the formation of vacuoles in liquid and mud. Strong ultrasonic waves produce alternate low / high pressure cycles in liquids. The rapid change in these pressures creates cavities, called bubbles. Ultrasonic induced cavitation bubbles can be considered as the formation of active substances such as free radicals produced in the molecules and chemical micro reactors with high temperature and high pressure on micro scale. In material chemistry, ultrasonic cavitation has a unique potential for local catalytic reactions at high temperature (up to 5000 K) and high pressure (500atm), while the system maintains a macroscopic state close to room temperature and environmental pressure. The ultrasonic treatment is mainly based on the bubble effect. In metallurgy, the University of science and technology is a very advantageous technology to improve the casting of metals and alloys.