Abstract
In this study, an insert mold casting was fabricated by inserting 2024 Al extruded rods into a 2024 Al melt. The molds were kept at a 2024 Al melt for different times. The 2024 Al extruded rods were used to refine the 2024 Al alloy grains because the advantage of this method is that it is contamination free compared with other grain refiners. Moreover, we investigated the macro and microstructure of the ingots. Further, we analyzed the refinement mechanism of the 2024 Al rod on the 2024 Al alloy. Our result showed that when the immersion time of the 2024 Al insert was 0 s, a metallurgical bonding was partly formed between the 2024 Al insert and the 2024 Al alloy mold cast. When the immersion time of the 2024 Al insert increased to 5 s, the 2024 solid insert was dissolved in the liquid; the coarse dendritic grains were replaced by fine equiaxed grains. The refinement mechanism for the insertion of a 2024 Al rod on the 2024 Al alloy was to melt the 2024 Al insert and have it decrease the degree of the liquid superheat, which thus increased the cooling rate and provided a large number of small particles that acted as the nucleus of heterogeneous nucleation. However, these particles were melted gradually in the high-temperature liquid after an increase of immersion time. Thus, the refinement effect of 2024 Al insert on the solidified structure was weakened.
Highlights
Achieving a fine, uniform, and equiaxed grain structure is one of the most important tasks of the solidification process because a fine grain size can reduce hot cracking, porosity, and segregation.it can enhance microstructural homogeneity and improve the mechanical properties of as-cast aluminum alloys [1,2,3,4]
Li et al [9,10] researched the application of single and multiple ultrasonic treatments during semi-continuous casting. These methods have been used successfully in achieving grain-refined structures, but it is not easy to apply these into the Al casting process due to the requirement of the specific equipment when compared with adding grain refiners
The 2024 aluminum alloys were cut into pieces, melted in a steel crucible located in an electrical resistance furnace, followed by degassing, stirring, and slagging
Summary
Uniform, and equiaxed grain structure is one of the most important tasks of the solidification process because a fine grain size can reduce hot cracking, porosity, and segregation It can enhance microstructural homogeneity and improve the mechanical properties of as-cast aluminum alloys [1,2,3,4]. Li et al [9,10] researched the application of single and multiple ultrasonic treatments during semi-continuous casting These methods have been used successfully in achieving grain-refined structures, but it is not easy to apply these into the Al casting process due to the requirement of the specific equipment when compared with adding grain refiners
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