| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 2000: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1999: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
Effects of excess Si and Mg, and impurity Fe on precipitation in 6061 aluminum alloys have been investigated. They were solely added to a 6061 base alloy and also added as combinations of (Si+Fe) and (Mg+Fe). Peak hardness increased with addition of Si and (Si+Fe), but decreased with addition of Fe, Mg and (Fe+Mg). Measurements of specific heat vs. temperature curves and electric resistivity vs. temperature curves and transmission electron microscopy and energy dispersive X-ray analyses showed that precipitates contributed to age hardening were same among the alloys, but that intermetallic inclusions in AlFeSi and AlSiFeMnCr systems were formed having variations in concentrations of each elements depending on the compositions of the alloys. The inclusion would be effective to reduce grain sizes and to prevent decreasing in tensile strength. With forming the inclusions and medium-size precipitates, which are considered to be formed during solidification and hot rolling, effective amount of Si is decreased in the matrix, resulting in decrease of Mg-Si type of precursors and precipitates and decrease in hardness and tensile strength. The amounts of Si included in the inclusions and medium-size precipitates are about 10 to 20 at% in all the alloys, therefore, the decrease of effective Si depends on the volume fractions of such phases which are increased by excess Fe and Mg. An effective amount of Si, Si^* would be calculated as Si^*=Si-2/3(Fe-0.05) when Mg/2>Si^*, while Si^*=Mg/2 when Mg/2<Si-2/3(Fe-0.05).
Addition of excess Fe as an impurity element in 6061 aluminum alloy does not affects the precipitates phases which attribute to age hardening, but accelerates formation of dispersoid particles which can prevent grain growth during recrystallization and lead to recover the tensile strength of alloys.
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