Mn/Fe摩尔比对A356铸造铝合金富铁相形态的影响Effects of Mn/Fe mole ratio on iron-rich phase morphology of A356 cast aluminum alloy

在含1.0%Fe(质量分数)的A356铝合金中添加不同含量的Mn，采用OM、SEM、EDS及DSC等分析方法研究Mn/Fe摩尔比对富铁相形态的影响及其规律，探讨添加Mn后A356-1.0Fe合金中物相的凝固顺序。结果表明：随着Mn/Fe摩尔比的提高，富铁相形态的演变顺序为：针状→汉字状→树枝状→星形→多边形状，当Mn/Fe摩尔比超过1.2时可基本消除针状铁相。富铁相中(Fe，Mn)/Si摩尔比随富铁相形态的凝固先后顺序逐渐增加，分别为针状富铁相中(Fe，Mn)/Si摩尔比为0.5~0.7，树枝状和汉字状富铁相中(Fe，Mn)/Si摩尔比为的1.2~1.7，星型和多边形富铁相中(Fe，Mn)/Si摩尔比为1.9。富铁相的平均晶粒尺寸和体积分数随Mn/Fe摩尔比的增加先增加后减小，而后再增加。其中当Mn/Fe摩尔比为1.0时，富铁相的平均晶粒尺寸和体积分数均为最小，与A356-1.0Fe合金的相近。此外，Mn的添加有利于提高共晶相和α(Al)基体相的形成温度，有利于多边形富铁相的形成。

Different Mn contents were added to A356 aluminum alloy containing 1.0% Fe (mass fraction). The effects of Mn/Fe mole ratio on the iron-rich phase morphology were studied by analysis methods of OM, SEM, EDS and DSC, and the solidification sequence of phases in A356 alloy with Mn adding was investigated. The results show that the evolution order of the iron-rich phase morphology is needle-like, Chinese script, dendritic, starlike, polygonal with the increase of Mn/Fe mole ratio. The needle-iron phase is eliminated basically when Mn/Fe mole ratio is above 1.2. The (Fe, Mn)/Si mole ratio increases with iron-rich phase morphology solidification sequence namely, 0.5 to 0.7 in needle iron-rich phase, 1.2 to 1.7 in Chinese script and dendritic-like iron-rich phase, 1.9 in star-like and polygons-like iron-rich phase. With increasing the mole ratio, the average grain size and volume fraction of iron-rich phase increase firstly, then decrease and finally increase. The average grain size and volume fraction of the iron-rich phase are the minimum at Mn/Fe mole ratio of 1.0, similar to those of the A356-1.0Fe alloy. Furthermore, Mn addition is beneficial to increase the solidification temperature of eutectic phase and forming temperature of α(Al) matrix phase, thus promoting the forming of polygonal iron rich phase.

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