Fig. 4. The ternary phase diagram for the Al-Si-Fe system is shown.
Al-Si-Fe三元体系合 金相图
models to explain microsegregation. One can now cal- culate the amount of non-equilibrium eutectic according to a model proposed by Brody and Flemings (B-F). Te B-F equations may be used to calculate the composition of liquid during solidification, and the fraction of solid at which the eutectic forms. Te B-F works well for the ele- ments commonly found in aluminum castings and for all but extremely fast freezing rates. (Te model works well in other metal systems for most elements. However, a correc- tion factor is needed for elements that diffuse rapidly—for example, carbon dissolved in iron or steel castings.)
Macrosegregation Macrosegregation is the redistribution of solute ele-
ments on a larger scale. In net-shaped castings this is caused by the motion of fluid inside the casting and usually is related to feeding. Macrosegregation is most easily seen in copper-containing alloys. An example is shown in Fig. 4. Tis X-ray shows a section of a cylinder head cast in 319 alloy. Two risers are visible at the top. Both show shrinkage cavities. Underneath the risers are dark bands in the casting, where copper-rich liquid has been “sucked into” the casting. Risers are placed in the mold to feed liquid to the
solidifying metal, whose volume shrinks by 5-7% during solidification. When the risers are not sufficiently large, they will feed the casting late in the solidification when
快速凝固外几乎所有的铝铸件中常见的元素。（该模 型也适用于其它金属体系中的大多数元素，但是，扩 散迅速的元素需要校正系数，例如，溶解于铸铁或铸 钢的碳元素。）
宏观偏析
宏观偏析是在更大范围内溶质元素的再分配。在净 形铸造中，宏观偏析由铸件内部流体运动引起，通常 与补缩有关。宏观偏析最容易在含铜合金中发生。如 图4所示的例子，这张X光片是319合金缸盖铸件的一 部分。顶部可见两个冒口。都显示产生了缩孔。冒口 下方是铸件暗带，其中富铜液相已被“吸入”铸件。 冒口放置在铸型中，给凝固中的铸件补充金属液， 凝固过程中金属液体收缩为5-7％。当冒口不够大时， 冒口对铸件的凝固补缩滞后，此时剩余金属液富集就 会铜元素（和其他溶质元素）。
这类的宏观偏析也可以在铝硅合金铸件发生，但是 很难通过X射线观察到。（铝和硅之间的密度差比铝和 铜之间小得多。）
Fig. 5. Solidification paths for Al-5% Si alloys are plotted. Al-5%Si合金凝固路径
Fig. 6. Solidification paths for Al-9% alloys are plotted. Al-9%Si合金凝固路径
56 |
FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION September 2014
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82