Mg-Sn共晶合金的凝固组织演化及晶体生长机理

Solidification structure evolution and crystal growth mechanism of Mg-Sn eutectic alloy

采用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)和能谱仪(EDS),研究自由凝固下Mg-Sn共晶合金在不同凝固阶段的组织、相的生长形态及相组成等。探讨Mg-Sn共晶合金的晶体生长机制以及冷却速度对合金显微组织的影响。结果表明:Mg-Sn亚共晶合金中的凝固组织为六角蔷薇花状的初生α-Mg相和共晶Mg/Mg_(2)Sn层片组织的混合结构;Mg-Sn过共晶合金中的凝固组织为棱角分明的初生Mg_(2)Sn金属间化合物相和共晶Mg/Mg_(2)Sn层片组织的混合结构;在亚共晶成分范围内,随着Sn含量的增加,初生α-Mg相含量减少,共晶相含量增多;随着冷却速率的提高,合金组织得到了明显的细化;初生α-Mg相为非小平面相,初生Mg_(2)Sn金属间化合物相为小平面相。

Optical microscope,X-ray diffractometer,scanning electron microscope and energy dispersive spectrometer were used to study the microstructure,phase growth morphology and phase composition of free solidified Mg-Sn eutectic in-situ composites at different solidification stages.The crystal growth mechanism of Mg-Sn eutectic in-situ composite and the effect of cooling rate on the microstructure of the alloy were investigated.The results show that the solidification structure of Mg-Sn hypoeutectic alloy is hexagonal rose-like primaryα-Mg phase and eutectic Mg/Mg_(2)Sn lamellar mixed structure.The solidification structure of Mg-Sn hypereutectic alloy is a mixed structure of angular primary Mg_(2)Sn intermetallic compound phase and eutectic Mg/Mg_(2)Sn lamellar structure.With the increase of Sn content,the quantity of primaryα-Mg phase decreased and the content of eutectic phase increased.With the increase of cooling rate,the microstructure of the alloy is obviously refined.Theα-Mg primary phase is a non-faceted phase,and the primary Mg_(2)Sn intermetallic compound phase is a faceted phase.