(東北大學(xué) 材料與冶金學(xué)院 材料成型與控制工程研究所，沈陽 110004)
摘 要: 采用熔鑄、大變形軋制(加工率大于92%)和硝酸鹽浴退火方法制備Mg-7.83%Li 合金與Mg-8.42%Li合金細(xì)晶板材，研究合金的超塑性、顯微組織、空洞與斷裂形貌和變形機(jī)制。計(jì)算α相(5.7%Li)和β相(11%Li)的擴(kuò)散系數(shù)和Gibbs自由能，討論573 K時(shí)超塑性晶粒長大的原因。結(jié)果表明：Mg-7.83Li和Mg-8.42Li合金分別獲得850%和920%的最大超塑性；Mg-7.83Li合金在573 K時(shí)發(fā)生了顯著的超塑性晶粒長大；在573 K和1.67×10−3 s−1條件下制備的Mg-8.42Li合金中的空洞較少，且在變形區(qū)中隨機(jī)而孤立地分布。斷裂形貌觀察發(fā)現(xiàn)Mg-8.42Li合金在573 K和5×10−4 s−1條件下發(fā)生穿晶斷裂；Mg-7.83Li合金在573 K和1.67×10−3 s−1條件下發(fā)生沿晶界韌窩斷裂。歸一化實(shí)驗(yàn)數(shù)據(jù)與考慮位錯(cuò)數(shù)量的變形機(jī)制圖對比表明合金超塑性變形機(jī)制為晶格擴(kuò)散控制的位錯(cuò)調(diào)節(jié)的晶界滑移。
關(guān)鍵字: 鎂鋰合金；超塑性；晶粒長大；原子擴(kuò)散；熱力學(xué)；空洞；斷裂；變形機(jī)制
mechanism of super-light two-phase Mg-Li alloys
（Institute of Materials Forming and Control Engineering, School of Materials and Metallurgy,
Northeastern University, Shenyang 110004, China）
Abstract:The fine-grained sheets of Mg-7.83%Li alloy and Mg-8.42%Li alloy were prepared by melting and casting, heavy rolling (reduction more than 92%) and nitrate bath annealing method, and their superplasticity, microstructure, cavitation, fracture morphology and deformation mechanism were investigated. The diffusivities and Gibbs free energy of α phase (5.7%Li) and β phase (11%Li) at 573 K were calculated to discuss the reason of superplastic grain growth. The results show that a few cavitations distribute randomly and isolatedly in the gauge length in Mg-8.42Li alloy at 573 K and 1.67×10−3 s−1. The transgranular fracture appears at 573 K and 5×10−4 s−1 in Mg-8.42Li alloy and dimple fracture along grain boundary appears at 573 K and 1.67×10−3 s−1 in Mg-7.83Li alloy. The maximum superplasticity of 850% and 920% are obtained in Mg-7.83%Li alloy and Mg-8.42%Li alloy. Obvious superplastic grain growth at 573 K appears in Mg-7.83Li alloy. The comparison of normalized experimental data with deformation mechanism map incorporating dislocation quantities inside grains reveals that the dominant deformation mechanisms in two alloys are grain boundary sliding accommodated by slip controlled by lattice diffusion.
Key words: magnesium lithium alloy; superplasticity; grain growth; atomic diffusion; thermodynamics; cavitation; fracture; deformation mechanism
