(陜西理工學(xué)院 材料科學(xué)與工程學(xué)院，漢中 723003)
摘 要: 研究往復(fù)擠壓Mg-4Al-2Si (AS42)合金的顯微組織和晶粒細(xì)化機(jī)制。結(jié)果表明：擠壓過程中發(fā)生受位錯(cuò)攀移控制的動(dòng)態(tài)再結(jié)晶，隨擠壓道次的增加，合金的晶粒尺寸迅速減小；對(duì)合金擠壓8道次后，得到晶粒細(xì)小、均勻分布的等軸晶組織，晶粒尺寸由鑄態(tài)的45 µm減小至1.5 µm，此時(shí)，合金組織的細(xì)化趨于穩(wěn)定，達(dá)到細(xì)化極限；晶粒細(xì)化機(jī)制是在往復(fù)擠壓過程中通過累積動(dòng)態(tài)再結(jié)晶，使再結(jié)晶得以徹底完成；增加位錯(cuò)密度和加劇晶界畸變使再結(jié)晶形核數(shù)目增多；大量擠壓破碎、均勻分布的Mg2Si第二相顆粒成為再結(jié)晶形核核心，從而使晶粒得以細(xì)化；往復(fù)擠壓11道次時(shí)，由于擠壓溫度過高，導(dǎo)致晶粒發(fā)生異常長大，最大尺寸約為10 µm。本試驗(yàn)條件下晶粒發(fā)生異常長大的溫度閥值約為400 ℃。
關(guān)鍵字: 鎂合金；Mg-4Al-2Si合金；往復(fù)擠壓；動(dòng)態(tài)再結(jié)晶；晶粒細(xì)化
中圖分類號(hào)：TG146.2；TG142.1 文獻(xiàn)標(biāo)志碼：A
reciprocating extrusion process
（School of Materials Science and Engineering, Shaanxi University of Technology, Hanzhong 723003, China）
Abstract:The microstructures and grain refinement mechanisms of Mg-4Al-2Si (AS42) alloy by reciprocating extrusion (RE) were investigated. The results show that the dynamic recrystallization controlled by dislocation climbing occurs during the RE process. The grain size of the alloy decreases rapidly with increasing RE pass. The grain size of the as-cast alloy deceases from 45 µm to 1.5 µm after RE 8 passes, here the grain refinement is up to the limit. The mechanisms of grain refinement are that, during RE, the recrystallization is completed thoroughly by accumulative dynamic recrystallization, the nucleation numbers of recrystallization increases with increasing dislocation density and grain boundaries distortion severity, and the massive broken Mg2Si particles become nucleating center of dynamic recrystallization, thus, resulting in the grain refinement. The grain begins to coarse up to 10 µm due to high temperature after RE 11 passes. Under the experimental conditions, the blow-threshold temperature of the grain coarse is about 400 ℃.
Key words: Mg alloy; Mg-4Al-2Si alloy; reciprocating extrusion; dynamic recrystallization; grain refinement
