【作者】 马景灵；

【导师】 文九巴； 李旭东；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2009， 博士

【摘要】 Al-Zn-In系阳极合金由于电化学性能较好,腐蚀产物易脱落,在防腐工程领域逐渐推广应用,是目前国内最有发展前景的牺牲阳极材料,但其电化学性能有待提高,表面溶解均匀性差,至今未有有效的解决方法。稀土元素是细化铝合金的首选元素,锰能有效净化铝合金中杂质铁元素,含硅的铝合金具有极好的铸造性能。因此通过微合金化加入适量的稀土元素细化晶粒改善组织、加入适量Mn降低杂质元素的不利影响及加入适量Si元素减少合金铸造缺陷是解决Al-Zn-In系阳极材料性能缺陷的有效途径。本文通过成分设计,用适量Ce、Mn及Si对Al-Zn-In-Mg-Ti合金进行微合金化,研究表明：对该合金进行微合金化达到了预期目的,经上海材料研究所检测,Al-5Zn-0.02In-1Mg-0.05Ti-(0.5Ce、0.1Si)牺牲阳极材料具有优良的综合电化学性能,其电流效率分别达94%及93%,且合金溶解均匀,其性能指标都高于目前工程上使用的牺牲阳极材料,这两种合金有很好的工业化应用前景。多元微合金化Al-Zn-In-Mg-Ti系合金的组织特点是偏析相增多,而该系合金的电化学性能比Al-Zn-In合金显著提高。因此偏析相对合金的电化学性能有重要作用。这使得对多元微合金化阳极材料的腐蚀机理也不能简单的沿用以前简单合金的腐蚀机理来解释。据此,本文采用X射线衍射(XRD)、扫描电镜(SEM)及透射电镜(TEM)等检测方法确定合金中的主要偏析相,然后采用不同测试技术,如极化曲线、电化学阻抗谱等,结合电化学噪声从不同方面研究合金中的偏析相在腐蚀过程中的变化,在此基础上揭示铝合金阳极溶解机理。结果表明：该系合金都含有MgZn2偏析相,MgZn2偏析相相对于α-Al基体呈阳极,具有活化铝合金且不会引起α-Al自腐蚀的优点,这就保证了该系合金具有较高的电流效率。合金中添加0.5Ce后,一方面晶粒明显细化,晶界溶质元素偏聚带明显窄化,除了MgZn2外还形成阳极性Al2CeZn2偏析相,这些阳极性偏析相是合金溶解的活化点,最终改善了合金不均匀溶解,同时也提高了合金的电流效率。合金中加入0.5Mn后,晶界溶质元素偏聚带窄化,其主要偏析相为MgZn2及A16Mn相,A16Mn细化晶粒及活化合金的效果比稀土元素Ce低,所以,Mn元素对合金综合性能的改善效果不如稀土Ce元素显著。合金中加入0.1%Si后,表现出稳定的良好的综合电化学性能,但Si元素对该合金性能的改善,不是由于偏析相的作用,主要是因为Si元素能明显提高Al合金的铸造性能,减少合金中的铸造缺陷,使合金组织成份均匀。探讨了该系合金在3.5%NaCl溶液中浸泡不同时间的腐蚀形貌、电化学阻抗谱及电化学噪声。结果表明：合金的初始溶解是由点蚀引起的,且点蚀都发生在偏析相处。用目前公认的溶解-再沉积机理无法解释偏析相的活化作用,必须结合偏析相优先溶解引发点蚀进一步解释。合金腐蚀初期的电化学噪声及其小波分析也验证了较高频率的亚稳态及稳态点蚀电位噪声在小波分析各阶能量中相对能量最高。此时电化学阻抗谱高-中频端呈现的感抗弧也表明合金处于点蚀阶段。随着腐蚀时间的延续,除了点蚀继续扩展外,合金晶粒内出现了均匀麻点状蚀坑,经SEM及EDX分析,此时在合金表面能检测到在铸态合金中检测不到的微量In元素,且麻点状蚀坑位置的In含量明显高于其余位置,说明合金此时发生了In元素的溶解-再沉积。在此阶段的电化学噪声及其小波分析同样印证了低频的溶解-再沉积电位噪声在小波分析各阶能量中相对能量最高。电化学阻抗谱低频端呈现出表征点蚀的感抗弧及表征溶解-再沉积的另一容抗弧。表明合金此时处于点蚀及溶解-再沉积共同控制的腐蚀期。随着腐蚀时间的进一步延长。溶解-再沉积的均匀麻点状蚀坑发生在合金整个表面,是合金最后均匀溶解的主要腐蚀形式。均匀腐蚀阶段的电化学噪声及其小波分析同样印证了低频有规律的溶解-再沉积电位噪声在小波分析各阶能量中相对能量最高。电化学阻抗谱低频端呈现出逐渐增大的表征溶解-再沉积的另一容抗弧,验证了合金此时主要以溶解-再沉积的形式腐蚀。因此,Al-5Zn-0.03In-1Mg-0.05Ti系阳极合金在NaCl溶液中的腐蚀包括以下三个阶段：1.腐蚀开始主要是由偏析相引发的点蚀期；2.随后,合金以点蚀及晶粒内部由Zn+、In1+引发的溶解-再沉积两种腐蚀形式同时溶解；3.合金腐蚀后期主要是Zn+、In+引发的溶解-再沉积的均匀腐蚀形式。本文的创新之处在于研制出了Al-5Zn-0.02In-1Mg-0.05Ti-(0.5Ce、0.1Si)两种高性能牺牲阳极材料,其性能均高于目前工程上使用的材料。该类材料中阳极性偏析相引发材料点蚀,活化合金。这类材料的活化有点蚀及溶解-再沉积两种方式。溶解过程包括点蚀、点蚀与溶解-再沉积、均匀腐蚀三个阶段。更多还原

【Abstract】 Al-Zn-In series alloys are the most promising sacrificial anode materials with better electrochemical properties; corrosion product falls off easy and the alloys show great potential in anti-corrosion industry. But theirs electrochemical properties and nu-uniform surface dissolution need to be improved and no effective solution so far. RE element is preferred to refine aluminum alloy, manganese element can purify effectively the iron impuritity of aluminum alloy, and aluminum alloy containing silicon element with excellent casting performance. Therefore, it is an effective way to solve the above problems by microalloying with adding appropriate content rare earth element to refinement microstructure, adding suitable content Mn element to reduce the adverse effect of impurity element, and adding suitable content Si element to reduce the casting defects.In this paper, based on the composition design, the microalloying Al-Zn-In-Mg-Ti alloys with appropriate content of Ce, Mn and Si elements achieve the expected goal. The alloys have excellent integratation electrochemical properties by tested of Shanghai research institute of materials. The current efficiency of the alloys adding 0.5Ce and 0.1 Si element are 94% and 93%, respectively, with uniformity dissolution. The performances of the alloys are higher than the current sacrificial anode materials used in engineering. So the both alloys have good industrial applications perspective.The microstructure characteristic of multi-microalloying of Al-Zn-In-Mg-Ti alloy is distinctness increased precipitates. It is a fact that the electrochemical properties of Al-Zn-In-Mg-Ti alloy are higher than that of Al-Zn-In alloy. Thus the precipitates have an important effect on the electrochemical properties of the alloy. So the corrosion mechanism of the multi-microalloying anode material can’t simply adopt the old corrosion mechanism of simple alloy.Accordingly, the major precipitates phases of the alloy were determined using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Then the corrosion behavior of the alloy was studied by different techniques, such as polarization curves, electrochemistry impedance spectrum (EIS) and so on, combined with the electrochemical noise (EN), based on this to reveal the dissolution mechanism of the alloy. The results show that all the alloys contain MgZn2 precipitates phase, MgZn2 precipitates phase is anode for the a-Al with the advantages of activation the alloy and will not cause the alloy self-corrosion. This ensures that the alloys have a higher current efficiency, but with un-uniformity dissolution lead in the large dendrites and un-uniformity MgZn2 precipitates of the cast alloy.The current efficiency and the un-uniformity dissolution of the alloy adding 0.5Ce were improved resulted in formation of the anode Al2CeZn2 precipitates which refine the grain of the alloy apparently, also act as the activation centers of the alloy. The grain of the alloy adding 0.5Mn was distinctness refine resulted in formation of the anode Al6Mn precipitates. The effect of grain refinement and activation with Mn element is lower than that of the rare earth Ce element. Therefore, the improvement effect of Mn element on the integration performance of the alloy is inconspicuous than that of Ce element. The alloy adding 0.1% Si shown a good stability integrated electrochemical properties. But the improving properties of the alloy are not because of the role of precipitates, mainly because of Si element can increase the casting performance, reduce casting defects, and make the micro structure uniform of the alloy.The dissolution mechanism of the alloy was investigated by the corrosion morphology, electrochemical impedance spectroscopy and electrochemical noise testing in 3.5% NaCl solution at different immersion time. The results show that the initial dissolution of the alloy is caused by pitting corrosion, and pitting get along with precipitates. The activation mechanism of the precipitates phase in the alloy can not be explained by the dissolved-redeposition, so must combine with the mechanism that the priority dissolution of precipitates phase. The EN and the wavelet analysis of the alloy in the early corrosion also verify that the noise energy of the metastable and steady-state pitting take the highest share in the wavelet analysis of the energy bands. At this time, the inductance loop of the EIS in low frequency also correspond with the characterization of the relevant literature to explain the passivation of metal at pitting stage.The mud pits structure appeared in the grain of the alloy in addition to the pitting corrosion continue to expand with the increase of immersion time. It can be detected the trace quantities In elements in the surface of the alloy which could not be detected in the cast alloy by SEM and EDX analysis. The In quantities of mud pits location were significantly higher than that of the rest position in the alloy. It was indicated that the In elements of the alloy has occurred dissolved-redeposition. The EN and the wavelet analysis of the alloy in the corrosion stage also verify that the noise energy of the "dissolved-redeposition" take the highest share in the wavelet analysis of the energy bands. The inductance loop of the EIS at high-frequency which characteriza the pitting and the second capacitive loop which characteriza the dissolved-redeposition also indicated that the corrosion controlled by the pitting and dissolved-redeposition at this corrosion stage. With further increase of the corrosion time, the pittings and the mud structure around the pittings were connected, and finally the entire alloy surface uniformly dissolved. Dissolved-redeposition took place in the entire surface of the alloy which is the major corrosion form at the later dissolution stage. The EN and the wavelet analysis of the alloy in the uniform corrosion stage also confirmed that the noise energy of the dissolved-redeposition with low frequency and regularity take the highest share in the wavelet analysis of the energy bands. The capacitive loop with gradual increase in the low frequency which characteriza the dissolved-redeposition also indicated that the corrosion controlled by the dissolved-redeposition.Therefore, the corrosion of Al-5Zn-0.03In-1Mg-0.05Ti series anode alloy in NaCl solution includes the following three stages:1. the pitting stage resulted in the precipitates phases in the grain boundary at the initially corrosion stages; 2. Subsequently, the alloy dissolve both with the pitting and the dissolved-redeposition by Zn+、In+ internal grain; 3. The dissolution is in mainly uniform corrosion by Zn+、In+ with dissolved-redeposition at the later corrosion stage.The innovation of the article lies in developed two kinds high-performance anode material of Al-5Zn-0.02In-1Mg-0.05Ti-(0.5Ce, 0.1Si) alloys. By identified, the performance of the alloys is higher than the currently materials used engineering. The anode precipitate phases of the alloys cause the alloy pitting and activate the alloy. The corrosion of the materials cause by pitting and dissolved-redeposition together. The corrosion process includes three stages of pitting, pitting and dissolved-redeposition, uniform corrosion.更多还原