Semisolid A356 alloy feedstock poured through a serpentine channel

Fine spheroidal and equiaxed nondendritic microstructures required for semisolid casting can be formed through a serpentine pouting channel. Effects of the pouring temperature and the vertical section length of the serpentine pouring channel were studied. The results indicate that both favorable semisolid microstructures of A356 aluminum alloy can be generated by a serpentine pouring channel, and the solid shell inside the channel can be avoided when the pouting temperature is in the range from 660 to 680℃. It is also shown that the vertical section length of the serpentine pouting channel has a significant influence on the microstructure of the feedstock, namely both the microstructure of the feedstock and the microstructure uniformity in the radial direction get worse when the vertical section length is shortened; moreover, the pouring temperature for obtaining the feedstock with suitable microstructure decreases. The relevant mechanisms were discussed.

Refinement of primary Si grains in Al–20%Si alloy slurry through serpentine channel pouring process

In this study, a serpentine channel pouring process was used to prepare the semi-solid A1-20%Si alloy slurry and refine primary Si grains in the alloy. The effects of the pouring temperature, number of curves in the serpentine channel, and material of the serpentine channel on the size of primary Si grains in the semi-solid A1-20%Si alloy slurry were investigated. The results showed that the pouting temperature, number of the curves, and material of the channel strongly affected the size and distribution of the primary Si grains. The pouring tempera- ture exerted the strongest effect, followed by the number of the curves and then the material of the channel. Under experimental conditions of a four-curve copper channel and a pouring temperature of 701℃, primary Si grains in the semi-solid A1-20%Si alloy slurry were refined to the greatest extent, and the lath-like grains were changed into granular grains. Moreover, the equivalent grain diameter and the average shape coefficient of primary Si grains in the satisfactory semi-solid A1-20%Si alloy slurry were 24.4 μm and 0.89, respectively. Finally, the re- finement mechanism and distribution rule of primary Si grains in the slurry prepared through the serpentine channel pouring process were analyzed and discussed.

Refinement of primary Si grains of A390 alloy slurry through serpentine channel pouring process

In this paper, the serpentine channel pouring process for preparing a semi-solid A390 alloy slurry and refining the primary Si grains of the A390 alloy, was used. The effects of the pouring temperature, the cooling water flow and the number of the curves on the size of the primary Si grains in the semi-solid A390 alloy slurry were investigated. The results show that the pouring temperature, the cooling water flow and the number of the curves have a major effect on the size and the distribution of primary Si grains. Under the experimental condition of the four-curve copper channel whose cooling water flow was 500 L·h-1 and the pouring temperature was 690 oC, the primary Si grains of the semi-solid A390 alloy slurry were refined to the greatest extent and the lath-like grains were changed into granular ones. Additionally, the equivalent grain diameter and the average shape factor of the primary Si grains of the satisfactory semi-solid A390 alloy slurry are 18.6 μm and 0.8, respectively. Further, the refinement mechanism of the primary Si grains through the serpentine channel pouring process was analyzed and discussed. In summary, the primary Si nuclei could be easily precipitated due to the chilling effect of the channel inner wall, thus the primary Si grains were greatly refined. Meanwhile, the subsequent alloy melt fluid also promoted the separation of primary Si grains from the inner wall, further refining the primary Si grains.

Enhancing heat transfer at the micro-scale using elastic turbulence

Small concentrations of a high-molecular-weight polymer have been used to create so-called ＂elastic tur- bulence＂ in a micro-scale serpentine channel geometry. It is known that the interaction of large elastic stresses created by the shearing motion within the fluid flow with streamline curvature of the serpentine geometry leads initially to a purely-elastic instability and then the generation of elastic turbulence. We show that this elastic turbulence enhances the heat transfer at the micro-scale in this geometry by up to 300% under creeping flow conditions in comparison to that achieved by the equivalent Newtonian fluid flow.

Improvement of machining consistency during through-mask electrochemical large-area machining

Electrochemical machining(ECM) is an important machining technique for the aeronautical manufacturing industry. Through-mask ECM is a form of ECM for machining metal parts with a hole array. In order to extend the machining area, a serpentine flow channel with multiple curves was used for through-mask ECM. With the extension of the flow channel, ensuring a machining consistency along the flow channel has been a challenge. The electrolyte conductivity is the main factor affecting the machining consistency. To analyze the change rules of the electrolyte conductivity, variations in the bubble rate and the temperature of the electrolyte in the electrolyte flow were explored under different power sources. Results indicate that pulse-power machining can reduce variations in the bubble rate and the temperature in the serpentine flow channel, and then the electrolyte conductivity can be stabilized within a very small range. Experiments using through-mask ECM were conducted in two types of power sources. Experimental results support the importance of pulse-power machining. A 14×28 hole array with a 2.5 mm diameter was fabricated by a pulsed power source. The aperture deviation of the hole array is less than 0.05 mm, and the roundness deviation is less than 15 lm when fabricated with pulse machining.

Microstructure and rheological properties of a semisolid A356 alloy with erbium addition

The effects of erbium addition on the rheological properties and microstructure of a semisolid A356 alloy were studied.The semisolid slurries were prepared through the serpentine channel technique before they were thixoformed using parallel-plate compre ssion with cylindrical discs.The grain and globule size decreases as the Er content increases,resulting in an improved and uniform distribution of spherical primaryα-Al phase within the semisolid slurry.The addition of the Er modifies the grain morphology and size of theα-Al grains,resulting in a better and more uniform distribution of spherical primaryα-AI phase within the semisolid slurry.As a result,rheocast quality index increases with the addition of Er,which is suitable for the thixoforming process.The A356 alloy without Er has the highest viscosity herein.The viscosity decreases,and the flow characteristics of the semisolid feedstock are expected to improve when Er is added as a result of the refinement of primary a-Al and modification of eutectic silicon.Furthermore,the refined semisolid A356 alloys with Er show a slightly larger fraction of highangle grain boundaries compared to that for the unrefined alloy.