(1. 北京有色金屬研究總院 有研億金新材料有限公司，北京 102200；
2. 北京有色金屬研究總院 有色金屬材料制備加工國家重點實驗室，北京 100088)
摘 要: 利用OM、SEM、XRD及TEM等分析方法，對幾種高Zn含量Al-Zn-Mg-Cu系合金的凝固態(tài)組織進行研究，通過比較不同合金中一次凝固析出相的種類、形貌結(jié)構(gòu)及合金元素在各相中的顯微分布，揭示了不同凝固析出相的形成過程與機理。結(jié)果表明：法系7449、7056合金晶界處粗大析出相為T(Mg(Zn,Cu,Al)2)四元相共晶組織，且大部分共晶組織網(wǎng)層狀結(jié)構(gòu)發(fā)達，共晶組織特征明顯；美系7136與7095合金晶界處粗大的網(wǎng)狀結(jié)構(gòu)第二相數(shù)目大大減少，主要以棒條狀結(jié)構(gòu)存在，且部分粗大第二相是以兩相(T(AlZnMgCu)與θ(Al2Cu))伴生的結(jié)構(gòu)形態(tài)存在；不同合金凝固態(tài)顯微組織的差異是由合金成分的不同而導(dǎo)致的凝固進程的差異造成的；其中，Cu元素含量對凝固態(tài)組織中一次凝固析出相的種類及結(jié)構(gòu)形貌有較大影響。
關(guān)鍵字: Al-Zn-Mg-Cu系鋁合金；顯微組織；非平衡共晶相；凝固析出相
（1. GRIKIN Advanced Materials Co., Ltd., General Research Institute for Non-ferrous Metals, Beijing 102200, China;
2. State Key Laboratory of Nonferrous Metals and Process,
General Research Institute for Non-ferrous Metals, Beijing 100088, China）
Abstract:The solidification microstructure of high zinc-containing Al-Zn-Mg-Cu alloys was studied by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The as-cast microstructure characteristics of alloys 7449, 7056, 7136 and 7095, including the once solidification precipitate type, morphology and the microdistribution of alloying elements, were investigated. And then the formation process and mechanism of different solidification precipitates were analyzed. The results show that the solidification precipitates in grain boundaries of alloy 7449 and alloy 7056 are non-equilibrium eutectic T(Mg(Zn,Cu,Al)2) phases, showing well-developed and obvious lamellar eutectic structure. Whereas, the number of coarse secondary phases that appears lamellar structure in as-cast alloy 7136 and alloy 7095 significantly decreases, and the non-equilibrium eutectic phases in grain boundaries mainly present rod-like morphology. Moreover, a association of T(Mg(Zn,Cu,Al)2) phase with θ(Al2Cu) phase is often observed in the rod-like eutectic phases. The as-cast microstructure is determined by solidification process, which is affected by alloy composition to a great extent. The mass fraction of element Cu plays a crucial role in controlling the type and morphology of the non-equilibrium eutectic phases in grain boundaries.
Key words: Al-Zn-Mg-Cu alloy; microstructure; non-equilibrium eutectic phase; solidification precipitate
