热型连铸锌铝合金的缺陷形成与机理

Defect formation and mechanism of ZA alloy made in continuous casting by heated mold

对 5种典型锌铝合金在热型连铸工艺条件下的连续定向凝固进行了研究 ,探讨该工艺下锌铝合金线材表面缺陷的产生机理 ,并对部分缺陷的组织结构进行了显微分析。结果表明 :只有金属液压头、型口温度、拉铸速度和冷却条件诸工艺参数在一定范围内的协调配合 ,才能拉铸出表面光滑的锌铝合金线材。不合理的工艺参数将导致热裂、表面粗糙、糊状型口和拉漏等缺陷。固液两相区的形状和位置对上述缺陷的形成有重要影响 ,当固液两相区位于型口或型内时 ,凝固界面将向型内凸入 ,如果剩余液体不能抵消凝固收缩 ,就会出现表面粗糙 ;若凝固界面深入型内较多 ,则使型内凝固的铸锭摩擦力过大 ,形成热裂 ;固液两相区移至型外 ,凝固界面将变成平面 ,容易发生拉漏。

The continuous directional solidification technique of five kinds of special ZA alloys with eutectic, peritectic and eutectoid transformation under the condition of continuous casting by heated mold was studies. The mechanism of surface defects appearing in ZA alloy line was discussed and the structure of some defects were analyzed by SEM. The results show that only when the fitting of various technique factors, pressure head, outlet temperature, pulling speed and cooling condition is reasonable under a certain range, can the ZA alloy smooth line be continuously pulled out. Unreasonable technique will result in hot tear, rough surface, mush outlet, leaking and other defects. The shape and location of solid liquid zone have the importance influence on the forming of above defects. When the solid liquid zone is located in the mould outlet or inner mould, the surface of solidification will protrude into the inner mould. If the left liquid can not counteract the solidification contract, the rough surface will appear. If the solidification surface further into the mould, the ingot in mould will have a big friction force when pulling and form hot tear. When the solid liquid zone is moved out of mould, the solidification surface will turn into a plane, which made it easy to form leaking. The vibration or unstable operation will make the ingot winding during pulling.