Applying Precipitates as Getter for Impurities in 6000 Series of Aluminum Alloys during Recycling Process.

研究了过量的硅、镁和杂质铁对6061铝合金析出的影响。它们被单独添加到6061基合金中，也作为(Si+Fe)和(Mg+Fe)的组合添加。峰值硬度随Si和(Si+Fe)的加入而增加，随Fe、Mg和(Fe+Mg)的加入而降低。比热-温度曲线、电阻率-温度曲线、透射电子显微镜和能谱分析表明，不同合金的时效硬化析出物是相同的，但在AlFeSi和AlSiFeMnCr系中形成的金属间化合物夹杂物的浓度随合金成分的不同而不同。夹杂物将有效地减小晶粒尺寸，防止抗拉强度下降。在凝固和热轧过程中形成的夹杂物和中等尺寸的析出物的形成，降低了母材中的有效硅含量，导致镁-硅型前驱体和析出物减少，硬度和抗拉强度降低。在所有合金中，夹杂物和中等尺寸析出物中的硅含量约为10~20at%，因此，有效硅的减少取决于这些相的体积分数，而过量的Fe和Mg增加了这些相的体积分数。当Mg/2&t；Si^*=Mg/2&lt；Si-2/3(Fe-0.05)时，Si的有效含量为Si^*=Si-2/3(Fe-0.05)，而当Mg/2&lt；Si-2/3(Fe-0.05)时，Si^*=mg/2。在6061铝合金中，过量的Fe作为杂质元素的加入，不影响时效硬化的析出相，但会加速弥散相的形成，从而阻止再结晶过程中的晶粒长大，从而恢复合金的拉伸强度。

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.