(1. 陜西科技大學 機電工程學院，西安 710021；
2. 西北工業(yè)大學 航空學院，西安 710072)
摘 要: 鎂鋰(Mg-Li)合金是現(xiàn)今最輕的金屬結(jié)構(gòu)材料，在航空航天及交通運輸?shù)阮I(lǐng)域具有重大的應用價值。但鑄造鎂鋰合金絕對強度低限制了其發(fā)展和應用。在Mg-Li二元合金中添加鋁(Al)、鋅(Zn)和稀土元素釔(Y)三種強化元素制備Mg-Li-Al-Zn-Y五元鑄態(tài)鎂鋰合金來提高鎂鋰合金的力學性能。利用X射線衍射儀(XRD)、掃描電子顯微鏡(SEM)和力學性能測試對比研究添加稀土Y前后鑄態(tài)Mg-8Li-3Al-3Zn合金中相組成、微觀組織和力學性能，揭示稀土元素Y對鑄態(tài)Mg-8Li-3Al-3Zn合金的增強機制和斷裂機理。結(jié)果表明：鑄態(tài)Mg-8Li-3Al-3Zn合金主要包含3種相：基體α-Mg、第二相AlLi和MgLi2Zn。添加1.0%(質(zhì)量分數(shù))Y后，鑄態(tài)鎂鋰合金中AlLi相消失，并析出了大量富集在α-Mg晶界處的硬質(zhì)Al2Y相，合金的晶粒發(fā)生細化。與Mg-8Li-3Al-3Zn(抗拉強度134.40 MPa、屈服強度96.46 MPa和伸長率7.5%)相比，Mg-8Li-3Al-3Zn-1Y抗拉強度、屈服強度和伸長率依次為189.99 MPa、128.2 MPa和7.8%，分別提高了41.4%、32.9%和4%。合金的斷裂方式由解理斷裂轉(zhuǎn)變?yōu)闇式饫頂嗔选ｈT態(tài)鎂鋰合金力學性能的提高主要歸因于Al2Y的形成及其對α-Mg相的細化作用。
關(guān)鍵字: 鎂鋰合金；稀土釔；顯微組織；力學性能；增強機制
（1. College of Mechanical and Electrical Engineering, Shaanxi University of Science and Technology, Xi’an 710021, China;
2. School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China）
Abstract:The magnesium-lithium alloy is the lightest metal structural material and has great application value in the fields of aerospace and transportation at present. However, the development and application of as-cast magnesium-lithium alloy are greatly limited because of the low absolute strength. Three strengthening elements of aluminum (Al), zinc (Zn) and rare-earth element yttrium (Y) were added to obtain the as-cast Mg-Li-Al-Zn-Y alloy. The purpose is to use alloying to enhance the mechanical properties of Mg-Li alloy. The phase composition, microstructure and mechanical properties of as-cast Mg-8Li-3Al-3Zn-xY (x=0, 1) alloy were compared and analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM) and mechanical properties testing to reveal the reinforcement and fracture mechanism of rare-earth element Y on as-cast Mg-8Li-3Al-3Zn alloy. The results show that the microstructure of the as-cast Mg-8Li-3Al-3Zn alloy mainly consists of matrix α-Mg, AlLi and MgLi2Zn phases. With adding 1% Y (mass fraction), the AlLi phase disappears and a large amount of high-temperature hard phase Al2Y enrich at the primary α-Mg grain boundary. Moreover, the microstructure is significantly refined. Comparing with Mg-8Li-3Al-3Zn alloy (134.40 MPa, 96.46 MPa and 7.5%), the Mg-8Li-3Al-3Zn-1Y exhibits an optimum combination of tensile properties with the tensile strength, yield strength and elongation of 189.99 MPa, 128.2 MPa and 7.8%, which are improved by about 41.4%, 32.9% and 4%, respectively. The improvement of the mechanical properties is attributed to the secondary phase and grain refinement strengthening. By analyzing the fracture morphology, the fracture mode of as-cast alloy is changed from cleavage fracture to quasi-cleavage fracture.
Key words: Mg-Li alloys; yttrium; microstructure; mechanical properties; enhancement mechanism
