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

研究了过量Si、Mg和杂质Fe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。比热与温度曲线、电阻率与温度曲线的测量以及透射电镜和能量色散x射线分析表明，合金中导致时效硬化的析出物是相同的，但AlFeSi和AlSiFeMnCr体系中形成的金属间夹杂物各元素的浓度随合金成分的不同而不同。夹杂物可以有效地减小晶粒尺寸，防止拉伸强度下降。随着被认为是凝固和热轧过程中形成的夹杂物和中等大小的析出相的形成，基体中Si的有效含量减少，导致Mg-Si型前驱体和析出相减少，硬度和抗拉强度下降。在所有合金中，夹杂物和中等大小的析出物中Si的含量约为10% ~ 20%，因此，有效Si的减少取决于这些相的体积分数，过量的Fe和Mg使这些相的体积分数增加。当Mg/2>Si^*时，Si^*=Si-2/3(Fe-0.05)，当Mg/2<Si-2/3（Fe-0.05）时，Si^*=Mg/2。在6061铝合金中添加过量的Fe杂质元素，不影响时效硬化析出相的形成，但会加速弥散颗粒的形成，从而阻止再结晶过程中的晶粒长大，使合金的抗拉强度得到恢复。

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.