Evaluation of stress corrosion resistance and corrosion fatigue fracture behavior of ultra-high-strength P/M Al–Zn–Mg alloy

Quasi-static tensile tests in air and slow strain rate tests (SSRTs) in a 3.5% NaCl solution were conducted in an ultra-high-strength P/M Al–Zn–Mg alloy fabricated through powder metallurgy. Attention is also paid to fatigue strength and fatigue crack growth behavior in laboratory air and in a 3.5% NaCl solution. The alloy has extremely high strength of about 800 MPa. However, elongation at break remains small, at about 1.3%. The final fracture occurs by a macroscopically flat crack normal to the tensile axis, with little reduction in area and little shear lip on the periphery of a smooth sample. However, it fails microscopically in a ductile manner, with dimples. Dimple size is less than 1 μm, because the grain size of the alloy is extremely small. Strengthening mechanisms operating in the alloy are: small grains, sufficient metastable η′ phase in a matrix, and intermetallic compound acting as a fiber reinforcement. The SSRT strength in a 3.5% NaCl solution decreases slightly at a very low strain rate, that is smaller than those observed in aluminum alloys sensitive to stress corrosion. This means that the crack initiation resistance to stress corrosion is superior. However, under cyclic loading, the corrosion fatigue strength becomes lower than that conducted in air, because pitting corrosion on a sample surface acts as a stress concentrator. Crack initiation site of quasi-static and fatigue failure of the alloy is at inclusions, and hence, it is essential to decrease inclusions in the alloy for the improvement of the mechanical properties. Fatigue crack resistance of the alloy is inferior to conventional Al–Zn–Mg alloys fabricated by ingot metallurgy, because the fatigue fracture toughness, or ductility, of the alloy is inferior to other Al alloys, and intergranular cracking promotes crack growth. However, no influence of 3.5% NaCl solution on corrosion fatigue crack growth is observed, although an investigation is required into whether stress corrosion crack growth occurs or not, and at the same time, and of corrosion fatigue crack growth behavior at lower stress intensity. The fracture surface and crack initiation sites are closely examined using a high-resolution field emission type scanning electron microscope, and the fracture mechanisms of the alloy are discussed.     

The effects of trace Sc and Zr on microstructure and internal friction of Zn–Al eutectoid alloy

The damping properties of Zn–22 wt.% Al alloys without and with Sc (0.55 wt.%) and Zr (0.26 wt.%) were investigated. The internal friction of the determined by the microstructure has been measured in terms of logarithmic decrement (δ) using a low frequency inverted torsion pendulum over the temperature region of 10–230 °C. An internal friction peak was separately observed at about 218 °C in the Zn–Al alloy and at about 195 °C in Zn–Al–Sc–Zr alloy. The shift of the δ peak was found to be directly attributed to the precipitation of Al₃(Sc, Zr) phases from the alloy matrix. We consider that the both internal friction peak in the alloy originates from grain boundary (GB) relaxation, but the grain boundary relaxation can also be affected by Al–Sc–Zr intermetallics at the grain boundaries, which will impede grain boundary sliding. In addition, Al–Sc–Zr intermetallics at the grain boundaries can pin grain boundaries, and inhibit the growth of grains in aging, which increases the damping stability of Zn–22 wt.% Al alloy.     

Fatigue behaviour of monotectoid-based Zn–Al–Cu alloys in 3.5% NaCl and 1% HCl solutions

One binary Zn–40Al and three Zn–40Al-based ternary alloys containing 1%, 3%, and 5% Cu were produced by permanent mold casting. Their fatigue behavior was investigated in 3.5% NaCl and 1% HCl solutions by a rotary bending fatigue test machine at a frequency of 33.3 Hz. The stress amplitude versus number of cycles to failure (S–N) curves of the alloys was plotted for both environments. Corrosion degradation factors of the alloys were determined. The corrosion environments reduced the fatigue strength and fatigue life of the alloys considerably. However, acid solution was found to be more detrimental for these alloys than the salt water. In addition, copper content was found to be less effective on the fatigue strength and fatigue life of the alloys in both salt water and acid solution than it was in air. Corrosion degradation factor of the alloys increased with increasing copper content up to approximately 3%, above which it decreased as the copper content increased. It was also shown that the fatigue data obtained from the monotectoid-based Zn–Al–Cu alloys in the corrosive environments obey the Basquin's law.     

Cracking of AFNOR 7020 aluminium alloy component: A metallurgical investigation

Aluminium alloy of Al–4.5Zn–1.5Mg system, belonging to age hardenable, high strength category is being used for the fabrication of various components. The Al alloy component was part of a conduit line for filling the liquid chemical to its storage tank. The component consisted of an extruded tube, TIG welded to a bulb, which was fabricated from Al alloy forgings. A crack was observed on the conduit tube at the region where tube was welded to the bulb. Detailed investigations were carried out on the cracked component, which revealed insufficient working of the ingot during forging, resulting in remnant cast structure along with a heavy network of low melting point compound throughout the material. The cracks, which were initiated under the stresses induced during thermal treatment, machining and assembly, were found propagating through the eutectic network.

This paper highlights the investigations carried out on the failed components.     

铝及铝合金全光亮化学镀镍磷合金工艺优选

化学镀镶前的预处理对镀层性能非常重要,目前常用的预处理方法存在许多缺陷.为此,通过对各种预处理工艺的筛选,确定了适用于铭合金化学镀镍磷合金的条件预处理工艺并预镀中间层,然后在传统化学镀镶磷镀液中加入镀镍中间体和无机盐,组合出了一种新的全光亮化学镀镍磷合金工艺,探讨了镍液主要成分和工艺条件对沉积速度、镀层耐蚀性和外观质量...     

铝合金导电管腐蚀失效原因分析

用于高压隔离开关的铝合金导电管存在着严重而普遍的腐蚀问题,危及高压隔离开关的正常运行.运用能谱分析、金相分析和电子探针等技术对铝合金导电管的破损原因进行了分析.结果表明,导电管存在着高度定向的纵向显微组织和局部脱溶,Cu,Fe等有害元素的相在晶界处大量连续析出,造成晶界附近出现贫化区,由于导电管的工作环境为近海海洋大气带,其中含有大量的侵蚀性阴离子,众多因素是导电管的腐蚀成因.其腐蚀过程为先在表面发生点蚀,然后发展成晶间腐蚀,在晶间腐蚀和内应力的协同作用下最终开裂形成剥蚀.     

Ni-W-Al2O3泡沫合金的复合电沉积制备

针对以往电沉积制备合金高温下易氧化或存在环境污染的问题,采用复合电沉积方法制备了Ni-W-Al2O3泡沫合金,并对该合金泡沫的形貌、镀液组分与合金中Al含量的关系和合金的抗拉强度、抗腐蚀性、高温抗氧化性进行了研究.结果表明:该合金泡沫骨架平整,合金中Al含量随着镀液中Al2O3含量的增加而增加;泡沫合金抗拉性能随着Al含量增加先缓慢下降,在Al含量超过6.50%时,显著下降;本泡沫合金的耐腐蚀和抗高温氧化性能均优于Ni-W泡沫,Al含量在5.05%时,耐中性盐雾腐蚀和耐高温氧化性能最佳.     

Corrosion behaviour of hot dip zinc and zinc-aluminium coatings on steel in seawater

A comparative investigation of hot dip Zn-25Al alloy, Zn-55Al-Si and Zn coatings on steel was performed with attention to their corrosion performance in seawater. The results of 2-year exposure testing of these at Zhoushan test site are reported here. In tidal and immersion environments, Zn-25Al alloy coating is several times more durable than zinc coating of double thickness. At long exposure times, corrosion rate for the Zn-25Al alloy coating remains indistinguishable from that for the Zn-55Al-Si coating of similar thickness in tidal zone, and is two to three times lower than the latter in immersion zone. The decrease in tensile strength suggested that galvanized and Zn-55Al-Si coated steel suffer intense pitting corrosion in immersion zone. The electrochemical tests showed that all these coatings provide cathodic protection to the substrate metal; the galvanic potentials are equal to −1,050, −1,025 and −880 mV (SCE) for zinc, Zn-25Al alloy and Zn-55Al-Si coating, respectively, which are adequate to keep the steel inside the immunity region. It is believed that the superior performance of the Zn-25Al alloy coating is due to its optimal combination of the uniform corrosion resistance and pitting corrosion resistance. The inferior corrosion performance by comparison of the Zn coating mainly results from its larger dissolution rate, while the failure of the Zn-55Al-Si coating is probably related to its higher susceptibility to pitting corrosion in seawater.     

机械镀锌-锰、锌-铝-锰合金工艺及镀层的耐蚀性能

为了获得性能良好的含锰合金镀层,以机械镀锌和机械镀锌-铝工艺为基础,通过调整活化剂和促进剂的种类及用量,开发了机械镀锌-锰合金工艺.利用该工艺可在钢基表面获得不同配比的锌-锰及锌-铝-锰合金镀层,对镀层进行了5%NaCl溶液喷雾加速腐蚀试验及全浸加速腐蚀试验,并与机械镀锌层进行了对比.结果表明,各种配比的锌-锰合金镀层的耐蚀性能优于机械镀锌层,且其耐蚀性随着锰含量的增加而增加;锌-铝-锰合金镀层的耐蚀性能比镀锌层提高数十倍.     

热浸镀新型高耐蚀锌合金镀层的成分设计及试验研究

为了开发出低成本高耐蚀性合金镀层,通过对新型合金镀层成分进行正交试验设计,在冷轧钢板、热轧钢板及角钢表面通过热浸镀制备不同成分的锌合金镀层,对镀层的锌液流动性、锌灰质量、可镀性、耐蚀性进行了试验研究。结果表明:添加Mg、Ni、Al和V的合金镀层耐蚀性普遍优于传统镀锌和镀Zn-Ni-V合金镀层,Mg对于耐蚀性的影响最显著,Al和Mg元素对合金镀层可镀性的影响最大,在试验含量范围内Ni和V含量对合金镀层可镀性的影响不显著,新型高耐蚀性锌合金镀层成分中各元素的优化水平组合为Mg含量0.3%~0.5%,Al含量≤0.02%,Ni含量0.06%、V含量0.04%。     

锌镍合金镀层耐蚀性的研究

通过理论以及实验讨论了锌镍合金镀层耐蚀性的机理和影响镀层的耐蚀性的几种因素，以期为锌镍合金电镀工艺生产提供参考。     

锌镍合金镀层耐腐蚀性的研究

锌镍合金层具有优异的耐蚀性,从全硫酸盐体系中用电沉积的方法制备了纯锌镀层和锌镍合金镀层.应用能量色散X射线分析仪检测了合金层的相对含量.通过中性盐雾试验、极化曲线、交流阻抗和腐蚀浸泡等试验方法研究了镀层的耐腐蚀性能.试验表明,含镍16%的锌镍合金镀层的腐蚀电位较纯锌镀层的腐蚀电位正移230 mV,该合金的耐盐雾性能达到1 000 h,是相同厚度纯锌镀层的4.5倍,具有优良的耐腐蚀性.     

铝合金铆钉化学着色工艺及着色膜的耐蚀性能

为了获得色泽纯正、耐蚀性优良的铝合金着色膜,以(NH<,4>)<,2>MoO<,4>,NH<,4>Cl为主体,以着色膜耐蚀性为目标,通过对不同水平的可控因素的正交试验极差分析,研制了一种铝合金小零件化学着色配方,获得了最佳工艺参数:15 g/L(NH<,4>)<,2>MoO<,4>,30 g/L NH<,4>Cl;着色...     

梯度复合铝合金的缝隙腐蚀研究

研究了2024/3003铝合金板材在梯度复合面之间的缝隙腐蚀行为,观察了不同腐蚀时间下2024/3003铝合金梯度复合面的宏观和微观腐蚀形貌,总结了合金的腐蚀失重和腐蚀速率变化规律.结果显示:2024/3003梯度复合铝合金板材在缝隙腐蚀的开始阶段,平均腐蚀失重较快,平均腐蚀速率逐渐升高,在250 h以后,平均腐蚀失重减慢,平均腐蚀速率迅速降低,并逐渐趋向稳定.     

二元配合物中电镀锌镍合金的结构与抗腐蚀性

为深入了解碱性锌酸盐体系的工艺参数对锌镍合金镀层结构和耐蚀性的影响,在以四乙烯五胺(TEPA)为镍离子主络合剂、三乙醇胺(TEA)为辅助络合剂的碱性镀液中电沉积制备了锌镍合金镀层,利用电子能谱、X射线衍射、极化曲线和电化学阻抗谱等方法表征镀层的组成结构和在氯化钠溶液中的耐腐蚀性.结果表明:镀层含镍原子数分数11.54%~20.12%,为γ-Ni2Zn11+纯Zn两相结构(低含镍原子数分数时)或单一γ相结构(较高含镍原子数分数时),γ相晶粒在(600)方向上具有不同程度的择优取向性;随着镀液中镍原子数分数的提高,镀层的腐蚀电位正移,阻抗增加,耐蚀性提高;当电流密度为2 A/dm2时,镀层的腐蚀电位和电荷传递电阻最高,耐蚀性最好.     

固溶热处理对5083F铝合金耐腐蚀性能的影响

用5083F铝合金制造的船舶在海洋环境中以高速或高流速等状态运行时会受到少量腐蚀,适当的热处理可改善其耐腐蚀性能。通过硬度、转折电位、不同时效时间下的阴极极化电流密度及慢应变速率试验找到了防止腐蚀的最佳热处理条件,即在420℃下加热样品30 min,然后在水中冷却;最佳时效条件是样品在180℃下时效240 min。在海水中的慢应变速率试验(SSRT)显示,最佳条件下热处理略降低了试样的强度,但增加了伸长率和断裂时间,热处理提高了其抗腐蚀性能。     

氧化镧对刷镀镍磷镀层的改善作用

采用腐蚀失重法和极化曲线法，研究了稀土氧化物（La2O3)对刷镀镍磷合金镀层在10％HCl中耐蚀性的影响。结果表明，镀液中加入适量La2O3可明显改善镀层的耐蚀性，分析讨论了稀土的作用机理。     

Ni-P/Ni-Mo-P镀层耐腐蚀性研究

通过在镀液中加入Na2MoO4的化学沉积法对酸性Ni-Mo-P/Ni-P双层化学镀工艺进行了研究。通过试验，确定了用连续施镀法制备此多元合金镀层的工艺。测定了镀层的性能，特别是对其耐腐蚀性能进行了重点研究。结果表明，镀层的成分及结构对其性能有关键的影响，双层镀镀层性能优于Ni-P单层镀镀层性能。     

化学镀Ni—P—B合金的工艺和耐蚀性的研究

研究化学镀Ni-P-B合金的工艺,对镀液的稳定性以及镀层的结构和耐蚀性进行了分析和研究。实验表明:采用含有稳定剂CdSO_4的镀液施镀,可得到结合力强和非晶态结构的Ni-P-B合金镀层,并具有优良的耐蚀性。     

表面处理对TC21钛合金与铝合金和钢电偶腐蚀行为的影响

通过测定TC21钛合金与铝合金和钢电偶电流的方法,研究了TC21钛合金与铝合金和钢在使用接触时发生电偶腐蚀的敏感性.结果表明:TC21钛合金与铝合金和钢形成的电偶对极易发生电偶腐蚀,不能直接接触使用;对钛合金和铝合金分别进行阳极氧化处理可以在一定程度降低电偶腐蚀敏感性.TC21钛合金与钢形成的电偶对,电偶腐蚀行为与钢的成分有很大关系,对钛合金进行阳极氧化处理,对钢进行镀镉或镀镉-钛处理可以提高表面抗腐蚀性能,降低电偶腐蚀敏感性.当TC21钛合金与铝合金和钢接触使用时,必须采取有效的防护措施.