Yuhou Yang

The Refining Mechanism of Super Gravity on the Solidification Structure of Al-Cu Alloys

There is far less study of the refining effect of super gravity fields on solidification structures of metals than of the effects of electrical currents, magnetic and ultrasonic fields. Moreover, the refining mechanisms of super gravity are far from clear. This study applied a super gravity field to Al-Cu alloys to investigate its effect on refining their structures and the mechanism of interaction. The experimental results showed that the solidification structure of Al-Cu alloys can be greatly refined by a super gravity field. The major refining effect was mainly achieved when super gravity was applied at the initial solidification stage; only slight refinement could be obtained towards the end of solidification. No refinement was obtained by the super gravity treatment on pure liquid or solid stages. The effectiveness of super gravity results from its promoting the multiplication of crystal nuclei, which we call “Heavy Crystal Rain”, thereby greatly strengthening the migration of crystal nuclei within the alloy. Increasing the solute Cu content can increase nucleation density and restrict the growth of crystals, which further increases the refining effect of super gravity. Within this paper, we also discuss the motile behavior of crystals in a field of super gravity.

Effect of Super Gravity on the Solidification Structure and C Segregation of High-Carbon Steel

In this research, super gravity field was introduced in the solidification process of high carbon steel. The experimental results show that the solidification structure of Fe–1 wt% C steel can be largely refined by applying super gravity at the cooling rate of 10 °C/min. Both the primary and secondary dendrite length was markedly reduced. In addition, the eutectic structure in the inter-dendrite was also refined with the obvious reduce of eutectic space. However, the macro-segregation of C along the direction of super gravity was caused with higher weight percent at the upper area than that at the bottom of the sample. The mechanism of solidification structure refinement and the C macro-segregation of Fe–1 wt% C steel in super gravity field were also discussed in this paper.

Removing Impurity Element of Copper from Pb-3%Cu Melt by Super Gravity

Super gravity field was introduced to remove impurity element of copper from Pb-3%Cu melt. The samples obtained by the gravity coefficient G≥200, time t≥30 minutes and temperature T=673 K appear significant layers and the copper phase present gradient size distribution along the super gravity. The copper phase gathers in the upper and middle areas of the sample and it is hardly to find any copper particles in the bottom area of the sample with the gravity coefficient G=400, time t=60 minutes and temperature T=673 K. The mass fraction of copper in the tailing lead is up to 7.090%, while that in the refined lead is just 0.204%. Considering that the mass fraction of copper is 3.034% in the parallel sample, the purification rate of lead bullion is up to 93.274% after super gravity treatment. The lead bullion can be high-effectively purified by super gravity.

Separation of Non-Metallic Inclusions from Aluminum Melt by Super Gravity

An innovative method is investigated to separate inclusion particles from liquid metal by super gravity. To make clear the characteristics of the inclusion separation, Al melt containing MgAl2O4 particles with diameters less than 150 μm has been treated under various super-gravity fields. The thickness of particle-accumulated layer formed at the bottom of the sample and the area fraction, number density and size of inclusions were measured. It is found that the thickness of the particle-accumulated layer decreases and the area fraction of particles at this location increases with the increase of super-gravity field. With the gravity coefficient G=500, time t=2 min, and temperature T=1023 K, it is hardly to find any solid particles in the upper and middle areas of the sample and the separation efficiency is up to 90%.