镁锂合金的微观组织及其腐蚀行为研究

发布时间：2017-12-31 01:46

  本文关键词：镁锂合金的微观组织及其腐蚀行为研究　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

  更多相关文章： 镁锂合金 腐蚀行为 腐蚀产物 轧制

【摘要】：镁合金具有比强度高、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、军事武器、临床医学、汽车、核工业等方面最理想并具有巨大发展潜力的结构材料之一。随着工业化生产对于材料轻量化的要求越来越高,Li作为一种低密度的金属,添加至镁合金中能极大地降低镁合金的密度,镁锂合金受到越来越多的关注。但是Li的化学活性较高,对于镁锂合金的腐蚀行为及腐蚀机理还需要进一步的研究。本文利用真空感应熔炼法制备了不同成分的Mg-x Li合金(x=3,8,14,wt%)。采用X射线衍射仪、金相显微镜、显微维氏硬度计等对铸态、均匀化退火和轧制后的镁锂合金的微观组织和力学性能进行了测试与表征。同时采用动电位极化、恒电流析氢、扫描电镜和透射电镜相结合,详细研究了Li含量对于退火态、轧制态镁锂合金在0.1M Na Cl溶液中的腐蚀行为的影响。通过研究,可以得出以下结论:(1)铸态Mg-3Li合金和Mg-14Li合金的组织由单一的α相或者β相组成,而Mg-8Li合金则由双相组织组成,针状的α相分布在β相之中。合金的硬度值随着Li含量的增加由54.5HV降低至37.7HV。经过退火处理(Mg-3Li合金和Mg-8Li合金在350℃下均匀化退火8h,Mg-14Li合金采用380℃,5min的固溶处理和350℃,8h的均匀化退火),镁锂合金的枝晶消失,Mg-3Li合金和Mg-14Li合金的晶粒尺寸分别为108.6μm和187.9μm。(2)退火之后,镁锂合金在0.1M Na Cl溶液中的腐蚀行为研究表明,Mg-3Li合金在浸泡初期的耐蚀性较好,Mg-8Li合金的腐蚀速率最大。在0.1M Na Cl溶液中,Mg-3Li合金和Mg-14Li合金的腐蚀特征为点蚀,而Mg-8Li合金由于α和β相之间存在电位差,电位较负的β相先被腐蚀,合金出现较为明显的丝状腐蚀特征。(3)在长时间浸泡之后,Mg-3Li合金表面膜层分布着大量的裂纹,而Mg-14Li合金的腐蚀产物膜层相对致密。这是由于Mg-3Li合金表面的腐蚀产物以Mg(OH)2为主,而Mg-14Li合金则由Li2CO3组成。Cl-会破坏镁合金表面的Mg(OH)2膜层,使得表面出现活化中心,加速镁合金的腐蚀。而Mg-14Li合金表面Li2CO3膜层在Na Cl溶液中能较为稳定的存在。(4)对镁锂合金(Mg-3Li,Mg-8Li,Mg-14Li)进行热轧处理(250℃,70%下压量),变形后镁锂合金的晶粒沿着轧制方向被拉长。Mg-3Li合金和Mg-8Li合金的硬度分别从54.5HV和42.3HV增加至75.2HV和52.3HV,由于β相加工硬化的程度较小,Mg-14Li合金的硬度值从37.9HV增加至39.3HV。(5)轧制Mg-3Li合金的腐蚀速率最小,Mg-8Li合金耐蚀性最差。动电位极化的结果表明,轧制之后,镁锂合金腐蚀行为的主要影响过程是阳极过程。金属表面膜层的致密度是影响镁合金的腐蚀行为的重要因素,轧制处理之后的Mg-3Li合金的腐蚀产物膜层与退火态相比,膜层致密度较高,这是由于轧制使得Li在腐蚀过程中更容易扩散,Li2CO3填充在膜层中的缝隙中,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，

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