定向凝固速率对Al-Al_2Cu过共晶合金中组织形态及取向变化的影响

Effect of Directional Solidification Rate on Microstructure and Orientation of Hypereutectic Al-Al_2Cu Alloy

对Al-40%Cu(质量分数)过共晶合金在2、10和100μm/s速率下进行定向凝固实验,观察了不同速率下的组织形态,并分析造成组织形态差异是由于各相之间的竞争生长所致;采用X射线衍射技术对过共晶合金中Al_2Cu相进行宏观极图测试并计算其取向分布函数(ODF),同时采用EBSD技术对定向凝固样品进行微观取向测试。结果表明:当定向凝固速率为2μm/s时合金组织为全共晶组织(Al/Al_2Cu),其中的Al_2Cu相取向集中在(001)方向;随着凝固速率增加到10μm/s时,Al_2Cu相优先共晶相生长形成初生Al_2Cu相枝晶组织,具有小平面相生长特征,其取向主要集中在(001)方向;当凝固速率达到100μm/s时,Al_2Cu相枝晶为非小平面特征的复杂枝晶形貌,其取向集中在(100),(110)和(001)等方向;且Al_2Cu相枝晶沿着平行于定向凝固热流方向生长。XRD宏观取向结果表明,取向更为集中的定向凝固组织在相对较低的抽拉速率下可以得到很好地控制。

The microstructure and orientation of directionally solidified Al-40%Cu hypereutectic alloy were investigated,and the different microstructures were formed because of the growth competition between eutectic phase and the primary Al2Cu phase.By X-ray diffraction techniques,the pole figures of Al2Cu phase were tested within the macro-orientations and the orientation distribution function（ODF） was calculated.Meanwhile the micro-orientations of directional solidification samples were determined by EBSD.At the directional solidification rate 2 μm/s,the microstructure is all eutectic（Al/Al2Cu） phase,in which Al2Cu phase has the orientation of（001） direction;however,at 10μm/s the primary Al2Cu phase dendrite with faceted characteristic grows ahead of eutectic phase,which has mainly（001） orientation.When the solidification rate reaches 100 μm/s,Al2Cu phase with non-faceted characteristic grow into complex morphology,and its orientation focuses on the（100）,（110） and（001） directions.Al2Cu phase grows along with the direction of heat flux.The results of XRD analysis show that dendritic morphology and orientation can be well controlled under directional solidification with relatively lower rate.