Mg_2Si及Si粒子在Al-Mg-Si合金晶间腐蚀中协同作用机理的多电极偶合研究

通过测定Al-Mg-Si合金晶界各组成相的极化曲线及不同Mg/Si比Al-Mg-Si合金晶界组成相(AlMg_2Si及Al-Mg_2Si-Si)间的动态电化学偶合行为,研究了不同Mg/Si比Al-Mg-Si合金的晶间腐蚀机理。研究表明,晶界Si电位比其边缘Al基体正,在整个腐蚀过程中作为阴极导致其边缘Al基体的阳极溶解。晶界Mg_2Si电位比其边缘Al基体负,在腐蚀初期将作为阳极而发生阳极溶解;由于Mg_2Si中活性较高元素Mg的优先溶解,不活泼元素Si富集,致使Mg_2Si电位正移,甚至与其边缘Al基体发生极性转换,导致其边缘Al基体的阳极溶解。Mg/Si1.73的Al-Mg-Si合金晶界只存在不连续分布的含Mg、Si的析出相,不能在晶界形成连续腐蚀通道,合金不表现出晶间腐蚀敏感性。Mg/Si1.73的Al-Mg-Si合金晶界同时析出含Mg、Si析出相和Si粒子;腐蚀首先萌生于Mg_2Si相;而后,Si粒子一方面导致其边缘无沉淀带严重的阳极溶解,另一方面通过加速Mg_2Si和晶界无沉淀带的极性转换,协同促进了Mg_2Si边缘无沉淀带的阳极溶解,即腐蚀沿晶界Si粒子及Mg_2Si粒子边缘的无沉淀带发展。Si粒子促进了腐蚀的发展,导致合金表现出严重的晶间腐蚀敏感性。     

压铸AlMg5Si2Mn合金的腐蚀和腐蚀疲劳行为

研究压铸AlMg5Si2Mn合金的电化学腐蚀、晶间腐蚀和腐蚀疲劳机理。结果表明:合金的自腐蚀电位和点蚀电位分别为-1220和-690 mV,钝化区间约为530 mV,说明合金的耐腐蚀性能良好。合金的晶间腐蚀倾向明显,这主要是由于Mg2Si相自腐蚀电位较低,且(Al+Mg2Si)共晶区的体积分数较大(29.6%)。电化学腐蚀反应和Mg2Si自身溶解产生的氢元素导致疲劳试样表面发生阳极溶解,加速了疲劳裂纹的萌生,从而显著降低了合金的疲劳寿命。腐蚀疲劳试样的裂纹主要是沿晶界扩展。氢元素也导致合金塑性下降,造成应力腐蚀开裂。     

Si、Mg含量对Al-Mg-Si合金显微组织及显微硬度的影响

通过添加不同含量Si和Mg,研究Si、Mg对Al-Mg-Si合金显微组织与显微硬度的影响。采用扫描电子显微镜（SEM）、X射线衍射仪（XRD）和显微硬度计分别对合金的微观形貌、相组成及显微硬度进行测试分析。结果表明：合金中主要有初生α-Al、骨骼状Mg2Si相、板片状共晶Si,还会出现少量的Al9Si、Al8Si6Mg3Fe、Al0.3Fe3Si0.7 和Al0.5Fe3Si0.5。随着Si含量的增加,Al-Mg-Si合金中α-Al枝晶变得细小,初生硅含量增加。随着Mg含量的增加,α-Al枝晶变粗、变大,从α-Al基体和初晶Si中的析出相逐渐明显,Mg2Si强化相聚集长大,同时α-Al初生晶尺寸增大。随着Si含量的增加,Al-Mg-Si合金的显微硬度也随之提高。随着Mg含量的增加,合金显微硬度先增大后减小。     

6082铝合金电化学腐蚀行为及晶间腐蚀机理研究

通过动电位极化曲线和微观腐蚀路径分析,研究了不同均匀化处理条件下和工艺状态下的6082铝合金电化学腐蚀行为,并且探讨了其腐蚀机理。结果表明,随着6082铝合金均匀化温度升高或时间延长,其电化学腐蚀后的腐蚀产物Al(OH)_3逐渐增多、增厚,腐蚀电流密度逐渐减小,合金的耐腐蚀性能增强;对于T6态锻造和T1态挤压的合金,由于锻造流线和挤压流线的组织形态差异,使腐蚀产物Al(OH)_3的分布位置不同,从而使锻造合金的腐蚀电流密度比挤压合金的要小,耐腐蚀性能更好;合金塑性变形流线中分布有颗粒状Si晶体和AlMnFeSi第二相颗粒。当腐蚀溶液与第二相Si粒子接触时,首先在Si粒子与基体之间的界面产生腐蚀,形成腐蚀裂纹。当腐蚀逐步扩展至晶界或亚晶界处时,由于晶界上连续分布的β?-Mg_2Si析出相与晶界无沉淀析出带(PFZ)构成连续的微型原电池,从而形成网状晶间腐蚀。     

第二相对Al-Zn-Sn-Ga-Mg合金腐蚀行为的影响

通过分析Al-7Zn-0.1Sn-0.015Ga-2Mg阳极合金中的第二相及其腐蚀特性,研究第二相对该合金腐蚀行为的影响。结果表明:Al-7Zn-0.1Sn-0.015Ga-2Mg阳极合金中的第二相主要为球状和棒状的MgZn2相。MgZn2相的腐蚀电位较α(Al)基体的负,腐蚀电流密度较高且极化电阻较小。MgZn2相对于α(Al)基体为阳极相,其在3.5%NaCl溶液中与α(Al)基体组成腐蚀微电池,引起MgZn2相自身优先溶解,进而引发合金全面溶解。     

残留结晶相对Al-Mg-Si-Cu合金晶间腐蚀行为的影响

采用光学显微镜、透射电镜、X射线衍射、扫描电镜及能谱等研究中性和酸性NaCl腐蚀溶液中残留结晶相对Al-Mg-Si-Cu合金晶间腐蚀行为的影响。结果表明:实验合金含有Mg2Si和Al4.01(MnFeCrCu)Si0.74两种残留结晶相。在中性和酸性溶液中,Mg2Si相通过Mg优先溶解,由阳极转换成阴极,进而造成基体点蚀。Al4.01(MnFeCrCu)Si0.74相在中性溶液中作为阴极,导致周围Al基体发生点蚀,而在酸性溶液中只发生自身腐蚀。当点蚀发生在晶界上时,能直接诱发晶间腐蚀;而当点蚀发生在晶内时,则需点蚀扩展至晶界才能诱发晶间腐蚀。不同于中性溶液,酸性溶液中的晶间腐蚀也可以由晶界直接形成。     

时效状态对Al-Cu-Li-Mg-Ag-Zr合金在3.0%NaCl溶液中局部腐蚀的影响

研究了T8态峰时效及T6态峰时效Al 4.0Cu 1.0Li 0 .4Mg 0 .4Ag 0 .14Zr合金在 3.0 %NaCl溶液中的局部腐蚀行为及其电化学阻抗特征。结果表明 :T8态峰时效处理时合金的电荷转移反应电阻大于T6态峰时效时的相应值 ;合金腐蚀初期 ,主要发生沿Cu或Fe含量较高的第二相粒子边缘的孔蚀 ,后期由于亚晶界边缘贫Cu无沉淀带的阳极溶解而出现连续亚晶界腐蚀 ;时效前的预变形减少了贫Cu无沉淀带的宽度 ,可降低亚晶界腐蚀程度     

应力作用下2195Al-Li合金的腐蚀行为研究

通过测量动电位极化曲线、电化学阻抗谱（EIS）,并结合SEM研究恒应力作用下2195Al-Li合金在3．5％NaCl溶液中的腐蚀行为。结果表明,应力增加,材料腐蚀加剧;合金主要腐蚀类型为晶间腐蚀和孔蚀,是由于合金的主要时效强化相为晶内析出的T1（Al2CuLi）相,T1相与基体合金相互交替作为阳极相发生溶解,加速了合金孔蚀;同时晶界处析出粗大的平衡相T2（Al6CuLi3）相,T2相相对周围PFZ为阳极相发生溶解,导致合金发生晶间腐蚀。     

模拟偏析相Al2Zn在3%NaCl溶液中的电化学行为

根据Al-Zn-In合金中偏析相Al2Zn的元素组成熔炼出模拟偏析相合金,测试了模拟偏析相合金和Al-Zn-In合金的自腐蚀电位、极化曲线和交流阻抗谱.结果表明:相对于Al-Zn-In合金,模拟偏析相Al2Zn自腐蚀速率小,自腐蚀电位负,呈现阳极性;Al-Zn-In合金中的偏析相Al2Zn与合金基体构成微区电偶腐蚀,受到阳极极化优先溶解,引起阳极电流效率的损失.     

Mg、Si含量对Al-Mg-Si合金力学性能及耐腐蚀性能的影响

采用布氏硬度试验、拉伸试验、金相显微镜和透射电子显微镜(TEM)等方法,研究了Mg、Si含量变化对Al-Mg-Si合金力学性能和耐晶间腐蚀性能以及析出行为的影响。结果表明:随着Mg、Si含量的增加,Al-Mg-Si合金的时效硬化速率显著提高,时效峰值硬度和强度均提高。在峰值时效状态下,高Mg、Si含量的合金的硬度与抗拉强度最高,但其耐晶间腐蚀性能明显降低。高Mg、Si含量的合金在时效过程中晶内析出了大量细小弥散的β″相,晶界析出相呈细小连续分布;低Mg、Si含量的合金晶内析出的β″析出相尺寸较大,晶界无沉淀析出相。     

Localized corrosion mechanism associated with precipitates containing Mg in Al alloys

To clarify the localized corrosion mechanism associated with precipitates containing Mg in Al alloys, the simulated bulk precipitates of S and β were synthesized through melting and casting. Their electrochemical behaviors and coupling behaviors with α（Al） in NaCl solution were measured. Meanwhile, simulated Al alloys containing S and β particles were prepared and their corrosion morphologies were observed. It＇s found that there exist two kinds of corrosion mechanisms associated with precipitates containing Mg. The precipitate of β is anodic to the alloy base, resulting in its anodic dissolution and corrosion during the whole corrosion process. While, there exists a corrosion conversion mechanism associated with the S precipitate, which contains active element Mg and noble element Cu simultaneously. At an initial stage, S is anodic to the alloy matrix at its periphery and the corrosion occurs on its surface. However, during its corrosion process, Mg is preferentially dissolved and noble Cu is enriched in the remnants. This makes S become cathodic to a（Al） and leads to anodic dissolution and corrosion on the alloy base at its periphery at a later stage.     

Simulation on function mechanism of T1(Al2CuLi) precipitate in localized corrosion of Al-Cu-Li alloys

To clarify the corrosion mechanism associated with the precipitate of Tl(Al₂CuLi) in Al-Li alloys, the simulated bulk precipitate of T1 was fabricated through melting and casting. Its electrochemical behavior and coupling behavior with (Al) in 3.5% NaCl solution were investigated. Meanwhile, the simulated Al alloy containing T1 particle was prepared and its corrosion morphology was observed. The results show that there exists a dynamic conversion corrosion mechanism associated with the precipitate of T1. At the beginning, the precipitate of T1 is anodic to the alloy base and corrosion occurs on its surface. However, during its corrosion process, its potential moves to a positive direction with immersion time increasing, due to the preferential dissolution of Li and the enrichment of Cu. As a result, the corroded T1 becomes cathodic to the alloy base at a later stage, leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery. It is suggested that the localized corrosion associated with the precipitate of T1 in Al-Li alloys is caused by the alternate anodic dissolution of the T1 precipitate and the alloy base at its adjacent periphery.     

Simulation study on function mechanism of some precipitates in localized corrosion of Al alloys

The function mechanism of different types of aging precipitates in localized corrosion of Al alloys was studied. The function mechanism of the precipitates of θ (Al₂Cu) and η (MgZn₂) is validated. The precipitate of θ containing noble element Cu is cathodic to the alloy base, resulting in the anodic dissolution and corrosion of the alloy base at its adjacent periphery. The precipitate of η containing active element Mg is anodic to the alloy base, anodic dissolution and corrosion occur on its surface. Meanwhile, a localized corrosion mechanism conversion associated with the precipitate of T1 (Al₂CuLi) is advanced, which contains noble element Cu and active element Li simultaneously. The precipitate of T1 is anodic to the alloy base and corrosion occurs on its surface at the beginning. However, during its corrosion process, the preferential dissolution of Li and the enrichment of noble element Cu make its potential move to a positive direction. As a result, the corroded T1 precipitate becomes cathodic to the alloy base at a later stage, leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery.     

Study on localized corrosion mechanism of 2195 Al‐Li alloy in 4.0% NaCl solution (pH 6.5) using a three‐electrode coupling system

Localized corrosion morphologies of 2195 Al‐Li alloy with various heat treatment in 4.0% NaCl solution (pH 6.5) were investigated, and its corrosion mechanism was studied using a three‐electrode coupling system of α (Al) substituting for the precipitate‐free zone (PFZ), simulated bulk θ′ (Al₂Cu) and T1 (Al₂CuLi). θ′ acts as cathodic zone in the alloy. At the initial stage, T1 phase is active with respect to θ′ and α (Al), and endures the main anodic current, indicating that anodic dissolution occurs on T1. However, its potential moves to positive direction with immersion time, due to dealloying of Li from T1. As a result, the main anodic dissolution occurs on α (Al) at a later stage. At this stage, as only T1 and α (Al) are coupled, T1 is cathodic to α (Al). In real 2195 alloy, T1 phase is very tiny, and anodic dissolution of T1 and PFZ occurs alternately. These results show that its intergranular corrosion or intersubgranular corrosion is caused by alternate anodic dissolution of T1 phase and PFZ along grain and subgrain boundaries.     

铝合金在海洋环境中的腐蚀研究(Ⅱ)--海水全浸区16年暴露试验总结

总结了铝合金在青岛海域海水全浸区暴露16年的腐蚀结果，防锈铝LF2Y2，LF6M（BL），F21M，180YS在海水全浸区有好的耐蚀性，工业纯铝L4M，锻铝LD2CS的耐蚀性较差，无包铝层的硬铝LY12CZ和超硬铝LC4CS在海水中的耐蚀性很差，硬铝，超硬铝的包铝层起牺牲阳极作用，使基体受到保护，海生物污损对铝合金在海水中的腐蚀有明显影响，镁、锰能提高铝的耐海水腐蚀性，硅明显降低铝的耐蚀性，铜严重损害铝的耐蚀性，腐蚀电位较负的铝合金耐海水腐蚀性较好，腐蚀电位较正的铝合金耐海水腐蚀性较差。     

铝合金在海洋环境中的腐蚀研究（Ⅰ）：——海水潮汐区16年暴露试验总结

总结了铝合金在青岛海域海水潮汐区暴露16年的腐蚀试验结果，防锈铝LF2Y2、LF6M（BL）、F21M、180YS在海水潮汐区有好的耐蚀性，工业纯铝L4M、锻铝LD2CS的耐蚀性较差，硬铝LY11CZ（BL）、LY12CZ（BL）和超硬铝LC4CS（BL）的包铝层起着牺牲阳极作用，使基体受到保护，海生物污损对铝合金的腐蚀有明显影响，镁，锰能提高铝在海水潮汐区的耐蚀性，硅明显降低铝的耐蚀性，铜严重损害铝的耐蚀性。     

Al-Si合金中Si相的团粒化研究

利用金相和电子探针等手段研究了AC8C、ZL104和ZL109牌号的亚共晶及共晶Al-Si合金中共晶和初晶Si相的团粒化。结果表明，用Sr变质处理附以热处理手段相结合的方法可促使共晶Si相呈团粒状。并均匀分布干铝基体上，加入TiB2粒子可进一步促进共晶Si趋于圆滑，甚至使之团球化。使用杆状Al-P中间合金后，可使共晶Al-Si合金析出大量初晶Si，获得过共晶组织，并在一定条件下可促使初晶Si晶粒团粒化，提高活塞的金相等级。另外，在Si、Cu和Mg成分一定的条件下可形成一个球状复合相，为获得真正的球状Si相开辟了新思路。     

Microstructures and corrosion behaviors of Al–6.5Si–0.45Mg–xSc casting alloy

The microstructures and corrosion behaviors of the Al–6.5Si–0.45Mg casting alloys with the addition of Sc were investigated by using scanning electron microscopy, X-ray diffraction, electrochemical measurement techniques and immersion corrosion tests and compared with those of Sr-modified alloy. The results show that Sc has evident refining and modifying effects on the primary α(Al) and the eutectic Si phase of the alloy, and the effects can be enhanced with the increase of Sc content. When the Sc content is increased to 0.58 wt.%, its modifying effect on the eutectic Si is almost same as that of Sr. Sc can improve the corrosion resistance of the test alloy in NaCl solution when compared with Sr, but the excessively high Sc content cannot further increase the corrosion resistance of the alloy. The corrosion of the alloys mainly occurs in the eutectic region of the alloy, and mostly the eutectic α(Al) is dissolved. This confirms that Si phase is more noble than α(Al) phase, and the galvanic couplings can be formed between the eutectic Si and α(Al) phases.     

时效制度对含钪超高强铝合金晶间腐蚀和剥落腐蚀的影响

通过晶间腐蚀、剥落腐蚀和电化学腐蚀试验,结合扫描电镜和透射电镜等分析手段,研究了含钪Al-Mg-Zn-Cu-Zr合金在不同时效状态下的的晶间腐蚀和剥落腐蚀行为。结果表明,合金抗晶间腐蚀和剥落腐蚀能力随着时效时间的延长而提高,在4.0mol/L NaCl+0.1mol/L HNO3+0.4mol/L KNO3(EXCO)溶液中测试的极化曲线也表现出相同的趋势。透射电镜观察表明,晶界析出相和晶界无沉淀析出带(PFZ)是影响合金腐蚀性能的主要因素。随着时效时间的延长,非平衡相η′和S′相逐渐向平衡相η和S相转变,晶界析出相粗化并呈链状分布,PFZ变宽。晶界粗大平衡相的不均匀分布和PFZ阻断了腐蚀的阳极通道,使合金的腐蚀敏感性降低。