本文關(guān)鍵詞：鎂鋰合金的微觀組織及其腐蝕行為研究　出處：《太原理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 鎂鋰合金 腐蝕行為 腐蝕產(chǎn)物 軋制

【摘要】：鎂合金具有比強(qiáng)度高、塑性好、抗高能粒子穿透力、生物相容性好等特征,是航空航天、軍事武器、臨床醫(yī)學(xué)、汽車、核工業(yè)等方面最理想并具有巨大發(fā)展?jié)摿Φ慕Y(jié)構(gòu)材料之一。隨著工業(yè)化生產(chǎn)對(duì)于材料輕量化的要求越來越高,Li作為一種低密度的金屬,添加至鎂合金中能極大地降低鎂合金的密度,鎂鋰合金受到越來越多的關(guān)注。但是Li的化學(xué)活性較高,對(duì)于鎂鋰合金的腐蝕行為及腐蝕機(jī)理還需要進(jìn)一步的研究。本文利用真空感應(yīng)熔煉法制備了不同成分的Mg-x Li合金(x=3,8,14,wt%)。采用X射線衍射儀、金相顯微鏡、顯微維氏硬度計(jì)等對(duì)鑄態(tài)、均勻化退火和軋制后的鎂鋰合金的微觀組織和力學(xué)性能進(jìn)行了測(cè)試與表征。同時(shí)采用動(dòng)電位極化、恒電流析氫、掃描電鏡和透射電鏡相結(jié)合,詳細(xì)研究了Li含量對(duì)于退火態(tài)、軋制態(tài)鎂鋰合金在0.1M Na Cl溶液中的腐蝕行為的影響。通過研究,可以得出以下結(jié)論:(1)鑄態(tài)Mg-3Li合金和Mg-14Li合金的組織由單一的α相或者β相組成,而Mg-8Li合金則由雙相組織組成,針狀的α相分布在β相之中。合金的硬度值隨著Li含量的增加由54.5HV降低至37.7HV。經(jīng)過退火處理(Mg-3Li合金和Mg-8Li合金在350℃下均勻化退火8h,Mg-14Li合金采用380℃,5min的固溶處理和350℃,8h的均勻化退火),鎂鋰合金的枝晶消失,Mg-3Li合金和Mg-14Li合金的晶粒尺寸分別為108.6μm和187.9μm。(2)退火之后,鎂鋰合金在0.1M Na Cl溶液中的腐蝕行為研究表明,Mg-3Li合金在浸泡初期的耐蝕性較好,Mg-8Li合金的腐蝕速率最大。在0.1M Na Cl溶液中,Mg-3Li合金和Mg-14Li合金的腐蝕特征為點(diǎn)蝕,而Mg-8Li合金由于α和β相之間存在電位差,電位較負(fù)的β相先被腐蝕,合金出現(xiàn)較為明顯的絲狀腐蝕特征。(3)在長(zhǎng)時(shí)間浸泡之后,Mg-3Li合金表面膜層分布著大量的裂紋,而Mg-14Li合金的腐蝕產(chǎn)物膜層相對(duì)致密。這是由于Mg-3Li合金表面的腐蝕產(chǎn)物以Mg(OH)2為主,而Mg-14Li合金則由Li2CO3組成。Cl-會(huì)破壞鎂合金表面的Mg(OH)2膜層,使得表面出現(xiàn)活化中心,加速鎂合金的腐蝕。而Mg-14Li合金表面Li2CO3膜層在Na Cl溶液中能較為穩(wěn)定的存在。(4)對(duì)鎂鋰合金(Mg-3Li,Mg-8Li,Mg-14Li)進(jìn)行熱軋?zhí)幚?250℃,70%下壓量),變形后鎂鋰合金的晶粒沿著軋制方向被拉長(zhǎng)。Mg-3Li合金和Mg-8Li合金的硬度分別從54.5HV和42.3HV增加至75.2HV和52.3HV,由于β相加工硬化的程度較小,Mg-14Li合金的硬度值從37.9HV增加至39.3HV。(5)軋制Mg-3Li合金的腐蝕速率最小,Mg-8Li合金耐蝕性最差。動(dòng)電位極化的結(jié)果表明,軋制之后,鎂鋰合金腐蝕行為的主要影響過程是陽(yáng)極過程。金屬表面膜層的致密度是影響鎂合金的腐蝕行為的重要因素,軋制處理之后的Mg-3Li合金的腐蝕產(chǎn)物膜層與退火態(tài)相比,膜層致密度較高,這是由于軋制使得Li在腐蝕過程中更容易擴(kuò)散,Li2CO3填充在膜層中的縫隙中,提高了其致密度。
[Abstract]:Magnesium alloys with high specific strength, good plasticity, high energy particle penetration resistance, good biocompatibility and other characteristics, is aerospace, military weapons, clinical medicine, automotive. Nuclear industry is one of the most ideal structural materials with great potential for development. With the industrial production of materials for light weight requirements are increasingly high Li as a low density metal. The density of magnesium alloys can be greatly reduced by adding them to magnesium alloys, and more and more attention has been paid to magnesium lithium alloys. However, Li has higher chemical activity. The corrosion behavior and corrosion mechanism of magnesium-lithium alloy need further study. In this paper, Mg-x Li alloy with different composition is prepared by vacuum induction melting. The as-cast state was obtained by X-ray diffractometer, metallographic microscope and microhardness micrometer. The microstructure and mechanical properties of the magnesium-lithium alloy after homogenization annealing and rolling were tested and characterized. At the same time, potentiodynamic polarization, constant current hydrogen evolution, scanning electron microscopy and transmission electron microscope were used. The effect of Li content on corrosion behavior of rolled and annealed magnesium-lithium alloy in 0.1M NaCl solution was studied in detail. The following conclusions can be drawn: (1) the microstructure of as-cast Mg-3Li alloy and Mg-14Li alloy is composed of a single phase or 尾 phase, while the Mg-8Li alloy is composed of two phases. The hardness of the alloy decreases from 54.5 HV to 37.7 HV with the increase of Li content. Mg-3Li alloy and Mg-8Li alloy were homogenized at 350 鈩，

本文編號(hào)：1357549