合金成分对Mg-Zn-Y合金准晶形貌和体积分数的影响

利用铁模铸造法制备Zn/Y=6:1(原子比)的Mg-Zn-Y合金,通过XRD,SEM,EDS,TEM和DSC等研究合金成分对Mg-Zn-Y合金相组成、Mg_3Zn_6Y准晶相(准晶Ⅰ相)形貌和体积分数的影响。结果表明:Mg-Zn-Y合金的相组成、准晶Ⅰ相形貌、体积分数及其生成反应与合金成分密切相关。随着合金中Zn和Y元素含量的减少,准晶Ⅰ相的形成反应由单一的包晶反应到包-共晶反应再到完全共晶反应。当合金中Y含量≥7%(原子分数,下同)时,合金由(Mg, Zn)_5Y、准晶Ⅰ相、Mg_2Zn_3和Mg_7Zn_3相组成,且以叠层状形式分布在合金组织中。合金在凝固过程中通过包晶反应形成多边形块状准晶Ⅰ相;当Y含量<7%时,合金中除(Mg, Zn)_5Y、准晶Ⅰ相和Mg_7Zn_3相外,还析出了Mg相。当合金中Y含量在5%～7%时,准晶Ⅰ相通过包晶和共晶反应生成,以共晶反应为主。当Y含量≤4%时,准晶Ⅰ相完全通过共晶反应形成(Mg+I-phase)层片状共晶组织。所研究的合金中均生成了体积分数大于27%的准晶Ⅰ相,Mg₃₀Zn₆₀Y₁₀合金中准晶Ⅰ相的体积分数最高,约为77%。

Effect of alloy composition on morphology and volume fraction of quasi-crystalline of Mg-Zn-Y alloy

Mg-Zn-Y alloys with a Zn/Y=6∶1(atomic ratio) were prepared by steel mould casting method. The effect of alloy composition on phase constituents as well as the morphology, volume fraction of Mg 3Zn 6Y quasi-crystalline phase (quasi-crystalline I-phase) in Mg-Zn-Y alloys was investigated by XRD, SEM, EDS, TEM and DSC. Results show that the phase constituents, the morphology, volume fraction and formation mechanism of Mg 3Zn 6Y quasi-crystalline I-phase in the Mg-Zn-Y alloys are closely related to alloys’ compositions. The formation reaction of quasi-crystalline I-phase is transferred from fully peritectic reaction to the combination of peritectic and eutectic reactions, and to completely eutectic reaction with the decrease of Zn and Y content in the alloys. When the Y content is and more than 7%(atom fraction), the alloys are composed of (Mg,Zn) 5Y, quasi-crystalline I-phase, Mg 2Zn 3 and Mg 7Zn 3 phases and they are distributed in a layered form in the alloy, and the quasi-crystalline I-phase takes the polygonal form by peritectic reaction during solidification. When the Y content is less than 7%, Mg phase precipitates in the alloys and their microstructure consists of (Mg,Zn) 5Y, quasi-crystalline I-phase, Mg 7Zn 3 and Mg phases. When the Y content is between 5% and 7%, the quasi-crystalline I-phase is precipitated by peritectic and eutectic reaction, and eutectic reaction, which dominates the precipitation of quasi-crystalline I-phase. When the Y content is and less than 4%, the quasi-crystalline I-phase forms totally a (Mg+I-phase) lamellar eutectic microstructure by eutectic reaction. The volume fraction of quasi-crystalline I-phase is all greater than 27%,and in Mg 30 Zn 60 Y 10 alloy is the maximum (about 77%) among the studied alloys.