雙相型鎂鋰合金拉伸機械性質之延－脆轉換破壞特性及應變速率效應探討

Effect of Strain Rate on Tensile Mechanical Properties and Failure with Ductile-Tobrittle Transition Behaviors of the Dual-Phase Magnesium-Lithium Alloy

楊崇煒(Chung-Wei Yang) ； 呂傳盛(Truan-Sheng Lui) ； 陳立輝(Li-Hui Chen)

《興大工程學刊》 22卷2期 (2011/08) Pp. 55-64

https://doi.org/10.6287/JENCHU.2011.2202.01

摘要

本研究針對(α+β)雙相Mg-10.3Li-2.4Al-0.7Zn(wt.%)鎂鋰合金(LAZ1021)擠型材自低於室溫(-25℃)至250℃溫度區間進行拉伸試驗，並施以不同拉伸初始應變速率(1.67 × 10^(-3) s^(-1)及1.67 × 10^(-4) s^(-1))，藉以探討雙相型LAZ1021合金在不同變形溫度下的拉伸機械性質與延伸率變化之應變速率要因。微觀組織解析發現LAZ1021合金之富鎂α相具有沿擠型方向延伸變形之織構，經影像分析結果得其體積分率約為30%。拉伸測試結果顯示雙相LAZ1021合金之降伏強度(YS)、抗拉強度(UTS)均隨拉伸溫度上升而下降，然而於低溫下之總延伸率(TE)不佳（低於5%），當拉伸溫度提升至100℃以上則TE顯著提升至約60%。根據拉伸結果亦發現雙相型LAZ1021合金具有延－脆轉換效應，其延－脆轉換溫度(DBTT)區間約在室溫至100℃左右，值得注意的是在降低拉伸應變速率情況下，DBTT亦隨之往低溫區偏移，仍具有延－脆轉換特性。拉伸破壞面之觀察發現低溫拉伸破壞呈現由富鎂α相主導之脆性劈裂破斷，且α/β相界面亦容易產生裂紋；高延伸率之試片破壞面則呈現典型靨渦狀延性破壞特徵，並發現因α/β相界裂紋引發之空穴合併所導致之空穴化現象，隨著提高拉伸溫度而趨於顯著。

關鍵字

雙相鎂－鋰合金 ； 拉伸機械性質 ； 應變速率 ； 延－脆轉換

並列摘要

The present study focuses on investigating tensile mechanical properties and failure behaviours of the (α+β) dual-phase Mg-10.3Li-2.4Al-0.7Zn (wt.%, LAZ1021) extruded alloy. The tensile tests of LAZ1021 specimens are performed at -25℃ to 250℃ with varying different initial strain rates of 1.67 × 10^(-3) s^(-1) and 1.67 × 10^(-4) s^(-1). Microstructural observation results show that the Mg-rich α-phase is deformed and elongated along the extrusion direction. After quantitatively calculating by an image analyzer, the volume fraction of α-phase is about 30% (vol. %). Tensile testing results show that the tensile strength and elongations of the dual-phase LAZ1021 alloy are sensitive to the deformation temperatures. The yield strength (YS) and the ultimate tensile strength (UTS) decrease with increasing deformation temperatures. The total elongation (TE) is lower than 5% at lower deformation temperatures, but the TE is significantly increased to higher than 60% with increasing deformation temperatures to higher than 100℃. According to tensile testing results, a significant ductile-to-brittle transition phenomenon is occurred for the dualphase LAZ1021 alloy. The ductile-to-brittle transition temperature (DBTT) intervals can be recognized at about room temperature to 100℃. It is worth noting that the DBTT will shift to a lower temperature with decreasing tensile initial strain rate. From the observation of tensile fracture surface, brittle fracture with cleavage failure within the Mg-rich α-phase and α/β interface decohesion cracks are occurred at lower deformation temperatures. The dimpled rupture behavior for specimens with higher elongation is resulted from the cavitation effect due to the α/β interfacial cavities coalescence and interlinkage. Failures with dimpled ruptures occurred from the cavitation is more significant with increasing deformation temperatures.

並列關鍵字

dual-phase Mg-Li alloy ； tensile mechanical properties ； strain rate effect ； ductile-to-brittle transition