Jin Junze

Microstructures and mechanical characteristics of electromagnetic casting and direct-chill casting 2024 aluminum alloys

Electromagnetic casting (EMC) technology depends on the electromagnetic force to prevent the metal from touching the mold, leaving the ingot surface very smooth. As a result, the surface imperfections, such as oscillation and subsurface segregation etc. caused by a mold of direct-chill casting (DCC), are avoided. Moreover, the electromagnetic stirring makes the structure become more homogeneous over the entire cross-section. In this paper, 2024 aluminum alloys made by EMC and DCC were analyzed by optical microscope and scanning electron microscope, solution heat treatment and artificial aging was given to investigate the mechanical properties such as hardness, wear resistance and fatigue. Results showed EMC ingots had fine and uniform grain structure, which made the EMC ingots have high hardness and good fatigue. The hardness of EMC specimens increased one time than DCC ones and the fatigue was three times as high as DCC ones in as-cast state. The EMC specimens also expressed an excellent characterization in wear resistance; the weight loss was only a half of DCC specimens.

Effect of fluid flow on dendritic structure of Al-Si alloy

The effect of fluid flow induced by electromagnetic stirring on dendritic structure of Al-4% Si alloy has been investigated experimentally. It was found that the fluid flow modified the dendritic structure, and along with the increasing velocity of the flow, the dendrite spacing changed from large passing small to large.

Thermodynamic criterion of separated eutectic phenomena

About 26 kinds of simple and complex binary eutectics were frozen directionally under the condition of electromagnetic stirring. It was found that anomalous eutectics including most metals/non-metals and some metal/intermetallic eutectics, can be separated on macroscopic scale by flow caused by electromagnetic stirring. Moreover, the eutectics in which one of their component phases possess an entropy of solution over 23 J mol-1K-1 showed notable separation. In addition, process factors also affect the formation of a separated eutectic.

A mathematical model of the deflection deformation in casting solidification

The deformation mechanism during the solidification is analyzed and a mathematical model is proposed based on the experimental results of the beam castings. The model indicates that the key factors leading to the deflection deformation are the thermal bending moment M and the flexural rigidity EJ. The smaller the former and the larger the latter is, the smaller the deflection deformation would be. The experiments are carried out at the various technical conditions, and their results appear good agreement with calculated ones.