For silicon in aluminum, m is equal to 11.9F (6.6C) per
weight percent Si. Te last important factor is the solubility of the element in liquid aluminum at typical furnace temperatures. For silicon, this maximum concentration is equal to the eutectic compo- sition, or12.6 weight percent Si. Tese three factors have been tabulated for a number of
important or interesting alloying elements and are shown in Table 1. Several important and interesting things may be gleaned
from Table 1. • Nickel, iron, silicon and copper segregate strongly during solidification.
• Zinc and manganese segregate only moderately. • Manganese hardly segregates at all. The concentration of manganese in solid aluminum is 94% of the liquid. This is an important factor in the improved performance of diecasting alloys, where manganese replaces iron to prevent die soldering.
• The elements below manganese have a value of k greater than one. This means there is a “negative” segregation— the equilibrium concentration in the solid is greater than that in the liquid. As a result, the melting point of alumi- num increases. When another element is added to a binary alloy, there is
a ternary (three element) system. It is somewhat more com- plicated to read ternary phase diagrams, but it is often useful to consult them. Figure 3 shows the liquidus surface for aluminum-rich
alloys in the ternary Al-Zn-Mg system. Tis diagram is similar to a topographic map used for hiking or hunting out- doors. Te contours show the temperature (C) at which solid aluminum begins to form during solidification. A full ternary diagram is an equilateral triangle, but since
度，由液相线的斜率和Al-Si体系的反应所确定。 典型熔炼温度下的液态铝中元素的溶解度是最后 的重要参数。对于硅来说，最大溶解度等于共晶成 分，即12.6%质量分数。
表1所示，列出了一些重要且令人感兴趣的合金 元素的三个参数（溶质分配系数，液相线斜率，最 大溶解度）。
从表1可看出几个重要的、令人关注的信息：
• 凝固中镍、铁、硅和铜强烈偏析。 • 锌和锰偏析有限。 • 锰几乎不偏析。锰在固态铝中含量是液相中的 94%。这是提高压铸合金性能的一个重要因 素，锰替代了铁以防止模具的焊合。
• 锰以下的元素k比1大（溶质分配系数大于1）， 这就意味着有“反”偏析作用——固态平衡浓 度高于液态，因此，铝的熔点提高。 当二元合金中再加入另一种元素时，就是三元体 系。读懂三元相图稍加复杂，但经常有用处。 图3展示了Al-Zn-Mg三元系里的富铝合金的液 相线，其与徒步旅行或者户外打猎的地形图很相 似。其等温线展示了凝固过程中固态铝开始形成的 温度。
一个完整的三元相图是一个等边三角形，但是对 于富铝合金，三角形的顶端（相当于富镁的部分） 被移除了。三元相图的关键点是读出成分坐标。这 个图展示了2个用于正确工序中用于教学的三元共
Table 1. Alloy Constants for Several Elements Calculated from Phase Diagrams 表1：由相图计算得到的几种元素的合金常数
Element 元素
Nickel Iron
Silicon Copper Zinc
Magnesium Manganese Niobium
Chromium Hafnium Tantalum
Molybdenum Zirconium Vanadium Titanium
Distribution Coefficient Melting Point Depression 熔点降低的分配系数
0.007 0.02 0.13 0.17 0.4
0.51 0.94 1.5 2
2.4 2.5 2.5 2.5 4 9
-3.3 -3
-6.6 -3.4 -1.6 -6.2 -1.6 13.3 3.5 8
70 5
4.5 10
30.7 % max 6 1.8
12.6 33.2 50 34
1.9
0.15 0.4 0.5 0.1 0.1
0.11 0.1
0.15 June 2014
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