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[Technology] Modification of Casting Zinc Alloys
Zinc alloys, especially those containing aluminum, are prone to uneven grain structures during solidification, which can lead to poor mechanical properties and casting defects. To address this issue, a process known as modification or deterioration treatment is commonly applied. This technique significantly enhances the mechanical performance of zinc alloys by refining the microstructure, improving castability, and reducing common defects such as hot cracking and sulfur-related inclusions.
Deterioration treatment is particularly effective in refining the as-cast microstructure of zinc-aluminum alloys, resulting in improved ductility and overall strength. One of the most effective ways to achieve this refinement is by adding small amounts of rare earth elements. These elements help reduce dendritic spacing, eliminate network structures, and promote finer grain formation. Among the modifiers, tin (Qin) and boron-based alloys have shown superior results in grain refinement.
Grain refinement methods can be broadly categorized into chemical, physical, mechanical, and thermodynamic approaches based on their mechanisms. Among these, chemical refinement is widely used in industrial applications. It involves adding specific additives to the molten metal, which then react to form numerous small nuclei that act as sites for crystal growth. This method is cost-effective, easy to implement, and highly efficient in achieving fine-grained structures.
The same grain refiners used for aluminum alloys are also applicable to zinc-aluminum systems. By refining the grain structure, the mechanical properties of the alloy—especially elongation after fracture—are significantly improved. Additionally, the casting characteristics, such as liquid filling ability and feeding capacity, are enhanced, leading to fewer defects like cold shuts, cracks, and macrosegregation in the final product. This makes grain refinement an essential step in the production of high-quality zinc-based alloys.