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.

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The microstructures were observed in C-Mn steel and statistical analysis of the inclusions produced when trace amounts of rare earth were added to the steel. The results show that the content of intragranular acicular ferrite decreased in the order of being treated with La þ Ce/La/Ce in C-Mn steel after the treatment of different kinds of rare earths. The optimum mass ratio of La and Ce for La þ Ce combined treatment is 3:1.The best incubation time after Le þ Ce (3:1) treatment is 5 min. The size of inclusion nuclei favouring intragranular acicular ferrite nucleation concentrates in the range of 1-4 mm. The disregistries between rare earth inclusions and a-Fe are small, which plays an important role in rare earth inclusions inducing intragranular acicular ferrite nucleation.

In order to depress the embrittlement induced by grain boundary segregation of arsenic in steel, the effect of Ce addition on the formation of arsenious inclusions and arsenic concentration at grain boundaries were systematically investigated in iron melts. The results showed that different types of arsenious rare earth inclusions were formed with different Ce content. As Ce content increased from 0.037 to 0.095 wt%, the dominant inclusion in the melt was changed from the Ce-S-O inclusion fully coated by Ce-S-As inclusion to the Ce-S-As inclusion completely covered by Ce-As inclusion. Simultaneously, the single Ce-S-As and Ce-As inclusions were also detected when Ce content was more than 0.055 wt%. The amount and average size of inclusions increased with increasing Ce content. Transmission electron microscope analysis indicated that the Ce-As inclusion was the CeAs phase, which was formed during solidification process. Furthermore, concentration of arsenic on grain boundaries after adding Ce was decreased to the level of the matrix.

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In this research, super gravity field was introduced to investigate the macrosegregation behavior of solute Cu in Al-Cu alloys in super gravity field systematically. And the macrosegregation mechanism was also explored by well-designed experiments. When Al-Cu alloys were solidified in super gravity field, the macrosegregation of solute Cu was generated and the solute Cu increases along the direction of super gravity field. The macrosegregation becomes severer with the increasing gravity coefficient and the solute content. When the Al-4.5wt%Cu alloy was solidified in super gravity field of G = 800, the copper content at the bottom position increases up to 8.48 wt% and that at the up position decreases to only 2.58 wt%, resulting in the positive segregation at the bottom and the negative segregation at the top of the sample. The segregation mechanisms are that solute-rich regions, which have a larger density than the main liquid, sediment toward the bottom of the sample under the effect of super gravity, and at the final solidification stage, super gravity can drive the residual solute-rich liquid to flow toward the bottom of the sample along the dendrite space (channel), which formed the super gravity channel segregation.