AZ91-0.75Ce稀土镁合金差热分析及β相形成规律  

Differential Thermal Analysis and Formation Regularity of βPhase in AZ91-0.75Ce Rare Earth Magnesium Alloy

作　　者：张燕龙[1] 杨伟[1] 周珍珍[1] 陈胜娜[1] 陈寿辉[1] 夏卫[1] 

机构地区：[1]南昌航空大学轻合金加工科学与技术国防重点学科实验室

出　　处：《特种铸造及有色合金》2014年第5期541-544,共4页Special Casting & Nonferrous Alloys

基　　金：国家自然科学基金资助项目(51164028);轻合金加工科学与技术国防重点学科实验室开放课题资助项目(GF201201003)

摘　　要：采用真空感应熔炼方式,研究了稀土元素Ce对AZ91镁合金铸态组织的影响。利用差热分析仪,通过对稀土镁合金熔化和凝固过程进行实时分析,研究了不同冷却速率(10、20、40和80℃/min)条件下β相的形成规律。结果表明,稀土元素Ce有利于细化AZ91合金的基体组织,同时形成Al-Ce化合物相,有效抑制晶界处β-Mg17Al12离异共晶相的形成。此外,Ce含量为0.75%的AZ91合金导致其液相线温度由605℃下降到583℃。近平衡凝固条件下,随冷却速率提高,液固界面前沿溶质扩散不及时,热分析曲线中共晶峰的相对面积不断增加,β共晶相含量逐渐升高。由于冷速的增加缩短了固态相变时间,导致共析转变过程中所形成的层片状β相含量降低。Influences of RE element Ce on as-cast microstructure of AZ91 magnesium alloy were investigated by vacuum induction melting method. Then, the melting and solidification processes for rare earth magnesium alloy were analyzed by differential thermal analysis （DTA） with different cooling rates, such as 10 K/min, 20 K/min, 40 K/min and 80 K/min, in order to understand the formation regularity of β phase. The results show that Ce element can refine grain size in the microstructure of AZ91 alloy and can effectively suppress the occurrence of divorced eutectic β-Mg17 Al12 phase in grain boundary as a result of the formation of Al-Ce compound. Addition of 0. 75 % Ce can decrease the liquidus temperature of AZ91 alloy from 605℃ to 583℃. Under the condition of near equilibrium solidification, the increase of cooling rate results in insufficient solute diffusion ahead of liquid-solid interface front, which enhances the relative area of eutectic peak in DTA curves and indicates the increase of volume fraction of divorced eutectic β-Mg17A112 phase. In addition, the lamellar volume fraction for secondary precipitated β phase is decreased, which can be attributed to the decrease of eutectoid transition time because of higher cooling rate.

关 键 词：稀土镁合金 Β相 差热分析 冷却速率 

分 类 号：TG146.22[一般工业技术—材料科学与工程] TG113.12[金属学及工艺—金属材料]