Technological Development for Neutralizing Contamination by Impurities in Recycled Aluminum Alloys by Control of Solidification Reaction

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Effects of impurities, which contaminate the melts during recycling, and useful elements for removal of the impurities on mechanical properties of the recycled aluminum alloys were investigated. Furthermore, shapes and sizes of the crystallized compounds, and grain size were altered by an application of electromagnetic casting and micro alloying, and their influences on mechanical properties were also evaluated.(1) When Mn and Zr, which are effective for removal of iron from the melt, are added to the 6061 AI-Mg-Si alloy, a compound containing Si increases with an increase in Mn content and, therefore, age hardenability is lowered and proof stress and tensile strength decrease. The manganese content in the alloy with 0.3% Zr should be less than 0.4mass% to guarantee the tensile properties specified by JIS.(2) When Si, which contaminate 3003 A1-Mn alloy from a cladding material, and Ca, which is an effective element for the removal of Si from the melt, are added to the alloy, the amount … More of a A1-Fe-Si compound increases as Si content increases, resulting in increases in proof stress and tensile strength, but a decrease in elongation. An addition of Ca above 0.3% gives rise to the disappearance of the A1-Fe-Si compound and the crystallization of a large amount of coarse A1ィイD26ィエD2(Fe,Mn) compound, and consequently, to remarkable degradation of elongation.(3) Application of electromagnetic casting to the fabrication of a thin 5052 A1-Mg slab makes the crystallized compounds to be very fine and uniformly distributed. Therefore, even when the amount of crystallized compounds increases with an increase in Fe content, the compounds are useful for the dispersion strengthening and refining of the recrystallized grains. As a result, it is possible to increase proof stress and tensile strength while maintaining enough elongation with Fe content of up to 0.81%.(4) As a result of adding small amount of Mn, Sr and Ca to 6N01 Al-Mg-Si alloy containing 0.7% Fe, it is found that Sr addition of 0.005% refines A1-Fe-Si compound and improves proof strength and tensile strength of T4-treated specimens and elongation of T6-treated specimens, resulting in satisfying JIS requirement on tensile properties Less