(1.甘肅工業(yè)大學(xué) 材料科學(xué)與工程學(xué)院， 蘭州 730050;
2.西安交通大學(xué) 金屬材料強度國家重點實驗室，西安 710049;
3.西安電子科技大學(xué) 機電工程學(xué)院， 西安 710043)
摘 要: 用SEM和TEM對金屬型鑄造并經(jīng)18個月自然時效的Z A27合金的微觀組織進行了觀察。結(jié)果表明：ZA27合金凝固的初生相為富Al的樹枝狀α ′相，隨后在α′相周圍形成一層富Zn的包晶β相，最后剩余液體發(fā)生共晶反應(yīng)，共晶β優(yōu)先依附于包晶β相形核、長大，而共晶η則在包晶β相間形成一層薄膜，在有些區(qū)域則形成棒狀共晶組織；在隨后的冷卻及時效過程中，β發(fā)生胞狀分解形成規(guī)則的共析α+η層片組織或不規(guī)則的復(fù)雜形狀組織，共析胞以共晶η相為基形核，并向枝晶中心生長，使α′相也分解為層片α+η組織，當(dāng)其生長被α′中心的連續(xù)分解所阻擋時，致使其芯部形成細(xì)小的α+η顆粒組織；富Cu的ε相存在于所有η相中。
關(guān)鍵字: ZA27合金；金屬型鑄造；自然時效；微觀組織
ZA27 alloy
（1.School of Materials Science and Engineering，
Gansu University of Technology，Lanzhou 730050，China;
2.State Key Laboratory of Mechanical Behavior for
Materials， Xi′an Jiaotong University，
Xi′an 710049，China;
3.School of Mechanical and Electronic Engineering，
Xi′an University of Electronic Science and Technology，
Xi′an 710043, China）
Abstract:The microstructure of permanent mold casting ZA27 alloy was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) after natural aging for 18 months. The solidification begins with the formation of aluminum-rich α′ dendrites，followed by the peritectic reaction wherebya zinc-rich β phase forms around the edges of the primary phase. Finally，the solidification is completed by formation of eutectic β and η phases，the β phase joining the peritectic β phase and the η phase remaining as thin film in the inter dendritic regions. In some regions，the eutectics form in the form of fibrous β within η phase. The morphologies of the eutectics are determined by the size of the eutectic pools. On cooling after casting and on aging， both of the β phases decompose into well-formed eutectoid α+η lamellae or irregularly complex structures through cellular reaction. These cell colonies nucleate on the eutectic η phase and grow into the low-aluminum α′ phase cores of the dendrites to make the α′ phases form lamella structures. But the growth of these lamellae is always retarded by the continuous decomposition of the α′ phase in the dendritic cores and they decompose into mixture of fine zinc-rich η phase in a n aluminum matrix. The Cu-rich ε phase particles form in all η phases.
Key words: ZA27 alloy；permanent mold casting；natural aging； microstructure
