(蘭州理工大學(xué) 甘肅省有色金屬新材料省部共建國(guó)家重點(diǎn)實(shí)驗(yàn)室，蘭州 730050)
摘 要: 采用等溫?zé)崽幚矸ㄑ芯緼l含量對(duì)Mg-7Zn合金半固態(tài)組織的影響。結(jié)果表明：添加Al元素后，合金的固相率隨溫度變化曲線逐漸下移。在相同的等溫處理工藝下(580 ℃保溫30 min)，隨著Al含量的增加，合金的固相顆粒尺寸逐漸減小，圓整度顯著提高，同時(shí)固相率明顯降低。非枝晶組織主要包括球狀及類似球狀的初生固相顆粒α1-Mg，水淬二次凝固形成細(xì)小的等軸晶α2-Mg以及晶界處和包裹在初生顆粒間的共晶組織。隨保溫時(shí)間的延長(zhǎng)，Mg-7Zn-xAl合金非枝晶組織中的初生固相顆粒的尺寸逐漸增加，形狀因子逐漸降低，而在后期處于固液平衡階段，固相率的變化不明顯；同時(shí)，固相顆粒粗化符合Ostwald熟化機(jī)制，且Al元素的加入減小了初生固相顆粒的粗化速率，從而在較寬的保溫時(shí)間范圍內(nèi)可獲得細(xì)小圓整的固相顆粒。
關(guān)鍵字: Al含量；Mg-Zn-Al合金；半固態(tài)；粗化
（State Key Laboratory of Gansu Advanced Non-ferrous Metal Materials,
Lanzhou University of Technology, Lanzhou 730050, China）
Abstract:The effect of Al addition on semi-solid microstructures of Mg-7Zn alloy was investigated by isothermal heat-treatment. The results indicate that the solid fractions of alloys are declined by elevated temperature when adding Al into Mg-7Zn alloy. With Al content increasing, the equivalent particle size gradually decreases, the roundness significantly increases and the solid fraction decreases at the same isothermal treatment process (580 ℃, 30 min). The non-dendritic microstructures are composed mainly of globular and similar globular primary particles α1-Mg, the finer equiaxial α2-Mg which forms from quench in water, and the eutectic distributes on the grain-boundary and within the primary solid particles. With holding time increasing, the size of primary solid particles of non-dendritic microstracture of Mg-7Zn-xAl alloy gradually increases and the shape factor decreases, which has no visible effect on the solid fraction of alloys at the solid-liquid equilibrium stage. Simultaneously, the parimary particle size coarsening with holding time obeys the Ostwald ripening mechanism, and adding Al element into Mg-7Zn alloy results in a decrease of coarsening rate of solid particles in semi-solid slurry, consequently, it can obtain the perfect semi-solid microstructure on the wide range of holding time.
Key words: Al content; Mg-Zn-Al alloy; semi-solid; coarsening
