Effect of nano Al (Scx−1Zrx) precipitates on the mechanical and corrosion behavior of Al‐2.5 Mg alloys

Microanalytical, mechanical, and corrosion studies were undertaken to investigate the effect of nano‐precipitates of Al(Sc_x−1Zr_x) on the mechanical and corrosion characteristics of Al 2.5 alloy containing 0, 0.15, 0.3, 0.6, and 0.9 wt% of Sc with 0.15 wt% Zr. Addition of 0.3% Sc significantly increased the yield strength due to small precipitates sizes (5–19 nm) and the high coherency of the nano‐particles. Largest contributor to the strength was grain boundary strengthening caused by pinning of grain boundary precipitates. The alloys showed a good resistance to corrosion in 3.5 wt% neutral chloride solution. The alloy offered a high passivation tendency because of homogeneous coherent nano Al(Sc_x−1Zr_x) precipitates. The nano precipitates interfaces and homogeneously distributed Al₃Sc precipitates offer a high degree of corrosion resistance to Al 2.5 Mg Sc alloys compared to conventional aluminum alloys, such as Al 6061 and Al6013.     

On the Stress corrosion cracking behaviour of aluminium alloy sheet in an aqueous solution of 3% NaCl + 0.3% H2O2

The stress corrosion cracking (SCC) behaviour of aluminium alloy sheet was investigated in the long transverse direction using the slow strain rate testing technique. The synthetic environment used was an aqueous solution of 3% NaCl + 0.3% H₂O₂. No indications of SCC sensitivity are observed for the alloys 2024-T351, 8090-T81, and 2091 CPHK-T8X. The alloys 2091 T8X and 6061-T4 are found to be susceptible to intergranular stress corrosion cracking. At strain rates below 4 · 10^?7 s^?1, the slow strain rate testing technique indicates a slight SCC sensitivity with alloy 6013-T6. Fractography reveals transgranular stress corrosion cracking. Transgranular stress corrosion cracking is also observed with 6061-T4 specimens which are dynamically strained at strain rates below 5 · 10^?7 s^?1. Aqueous 3% NaCl solution with hydrogen peroxide addition promotes pitting and intergranular corrosion. The loss of ductility caused by these corrosion processes interferes with the evaluation of the results of the slow strain rate testing technique.     

Effect of pH on the polarization behavior of Zr65Al7.5Ni10Cu17.5 amorphous alloy in a phosphate-buffered solution

The present study evaluates the effects of surface finishing and dissolved oxygen in phosphate buffered saline solution on the corrosion behavior of Zr₆₅Al_7.5Ni₁₀Cu_17.5 amorphous alloy for the application of the alloy to biomaterials. Non-polished and polished alloys were polarized in deaerated electrolyte, and the polished alloy was also polarized with various concentrations of dissolved oxygen. The surface of the alloy was characterized using X-ray photoelectron spectroscopy. The corrosion resistance of the alloy decreased with metallic nickel and hydroxide ion in surface oxide after polishing. The pitting corrosion resistance also decreased with the hydroxide ion after polishing. On the other hand, the pitting-corrosion resistance increased with aerating 4% O₂ because of the decrease of hydroxide ion and adsorbed phosphate ion in the surface oxide. However, oxygen above 4% O₂ prevented dissolution of nickel, causing the decrease of the pitting-corrosion resistance. When the pH was 2.2, the dissolved oxygen did not influence the pitting-corrosion resistance because of the increased solubility of the surface oxide.     

Effect of Gd on microstructure and stress corrosion cracking of the AZ91-extruded magnesium alloy

AZ91 and AZ91–xGd (x = 0.5, 1.0, 1.5 wt%) magnesium alloys are extruded into plates. The addition of Gd promotes the formation of Al₂Gd, effectively reducing the volume fraction of the β-Mg₁₇Al₁₂ phase and making the banded structures of the extruded magnesium alloys thinner. The corrosion weight loss tests and electrochemistry analyses demonstrate that Gd significantly improves the pitting resistance of the AZ91 in 3.5-wt% NaCl solution saturated with Mg(OH)₂. Slow strain rate tensile tests show that in a corrosive environment, compared with AZ91, the elongation to failure of the AZ91–1.0Gd alloy is increased by 47%, and the alloy exhibits excellent stress corrosion resistance in this study. The fracture mode of AZ91 is changed from typical intergranular fracture to a mixture of transgranular and intergranular fracture in the corrosion solution by adding Gd. The mechanism of Gd to improve the stress corrosion resistance of the AZ91 magnesium alloy is that Gd increases the corrosion resistance, especially the pitting of AZ91.     

The use of Al-Al2O3 cold spray coatings to improve the surface properties of magnesium alloys

Pure Al and 6061 aluminium alloy based Al₂O₃ particle-reinforced composite coatings were produced on AZ91E substrates using cold spray. The strength of the coating/substrate interface in tension was found to be stronger than the coating itself. The coatings have corrosion resistance similar to that of bulk pure aluminium in both salt spray and electrochemical tests. The wear resistance of the coatings is significantly better than that of the AZ91 Mg substrate, but the significant result is that the wear rate of the coatings is several decades lower than that of various bulk Al alloys tested for comparison. The effect of post-spray heat treatment, the volume fraction of Al₂O₃ within the coating and of the type of Al powder used in the coatings on the corrosion and wear resistance was also discussed.     

Effect of Al2O3 reinforcement and precipitates on corrosion behaviour of 2618 and 6061 aluminium MMCs

ABSTRACT

The corrosion resistance features of two different Metal Matrix Composites based on 6061 and 2618 aluminium alloys reinforced by 20% Al₂O₃ particles by stir casting process, were studied in 3.5% NaCl and compared. The composites and their respective base alloys were characterised in terms of microstructure by optical and scanning electron microscopy and in terms of corrosion resistance by polarisation curves and electrochemical impedance. Results show how the presence of Al₂O₃ has different effects depending on matrix composition. In 6061 MMC, Al₂O₃ promotes the formation of Mg₂Si which has a cathodic behaviour altering the pitting susceptibility of the composite. In 2618 MMC, the high content of Cu induces a strong uniform attack. The subsequent increase in the Open Circuit Potential caused a pitting attack.     

Li含量对亚快速凝固2A97铝锂合金的性能及组织演变规律的影响

通过亚快速凝固技术铸造2A97Al-Li合金,借助密度和拉伸测试对合金性能进行分析。同时,利用差热分析(DSC),光学电镜(OM),扫描电镜(SEM)及能谱分析(EDS)对合金显微组织演变进行研究。结果表明：通过亚快速凝固技术和合理的热处理工艺可以有效减少2A97 Al-Li合金中存在的粗大第二相,这对于超低密度Al-Li合金的实现具有十分重要的意义。随着合金中Li含量的增加,Cu原子更倾向于捕获Li原子而形成Al2CuLi相;同时,Al2Cu相相对减少,并出现花瓣状共晶相Al2CuMg;另外,亚快速凝固Al-Li合金的铸态显微组织由树枝晶向胞状晶转变,并促进晶粒细化。然而,随着Li含量由1.5 wt. %升到3.5wt. %过程中,热处理的效果逐渐降低,导致粗大共晶相残留于合金的三角叉晶界处,合金力学性能降低。     

Cu元素对Al-Zn-Mg-Er-Sc-Zr合金组织演变和腐蚀性能的影响

利用Cu元素的含量变化研究了Al₈Cu₄Er相的形成与演变规律及其对Al-Zn-Mg-Er-Sc-Zr合金腐蚀性能的影响。结果表明：随着Cu含量的增加,合金晶粒得到显著细化,但同时固溶态合金不同类型的残余相增多;Al₈Cu₄Er相与Al-Fe相存在伴生关系,二者通过Cu与Fe交互作用实现相的转化,且可表述为如下关系式：;不同成分合金的晶间腐蚀均表现出与残余相密切相关的点蚀特征,含Cu、Er的Al-Fe相虽然具有更小的腐蚀坑尺寸,但网状分布特征使腐蚀深度有所增加;而具有更好耐蚀性能的Al₈Cu₄Er则因相的粗化和它与Al-Fe相的伴生关系导致合金耐蚀性能严重下降。     

Evaluation of corrosion resistance of magnesium alloys in radiator coolants

Abstract

Coolant corrosion is a major drawback for the use of magnesium alloys in engine and cooling system, but the coolant is not normally intended to prevent corrosion of magnesium alloys. This research assessed the corrosion performance of two magnesium alloys, AZ91D and AM50A, in two newly formulated radiator coolants using immersion test, potentiodynamic polarisation test, and corroded surface analysis. Two coolants were named as Irgacool Plus L and Irgacool Plus S. C7, C8-organic acids and polycarboxylic acid were the main inhibitor species in Irgacool Plus L while Irgacool Plus S was formulated with C7, C8-organic acids and sebacic acid inhibitors. Corrosion rates of magnesium alloys decreased twice in Irgacool Plus L compared with Irgacool Plus S. AZ91D alloy had better corrosion resistance than AM50A alloy in both radiator coolants. Both alloys suffered corrosion due to microgalvanic coupling between cathodic β-Mg₁₇Al₁₂ intermetallic and anodic α-Mg matrix, and the presence of Al₈Mn₅ and Al₁₁Mn₄ intermetallics in AM50A led to further microgalvanic corrosion. A continuous network of β-Mg₁₇Al₁₂ phase and higher Al content α-Mg matrix accounted for better corrosion resistance of AZ91D alloy.     

Corrosion resistance of a new AL 6013-20 SiC(P) in salt spray chamber

Aluminum 6013 alloy (0.82Si, 0.95Mg, and 0.35Mn) is finding increasing usage in new aircraft designs, automotives, and structural applications due to its good stretch forming character in T4 temper (solution heat treated and naturally aged to a substantially stable conditions) compared to alloy 2024 (4.4Cu, 0.6Mn, 1.5Mg, and balance Al) and Al6061 (Si0.51 to 0.71, Fe0.35, Cu0.15, Mn0.85, Mg0.15, 0.25Cr, 0.15Zn, and balanced Al). The newly developed A1 6013 reinforced with 20 vol.% SiC(P) has a higher strength than its unreinforced counterpart. Whereas the corrosion behavior of A1 6013 has been reported in literature, there is no previous data on A1 6013 reinforced with SiC(P). A knowledge of the corrosion behavior of this alloy is crucial to its applications in aerospace, structural, and automotive industry. The first results of corrosion study of this alloy in 3.5 wt.% Na Cl in a salt spray chamber are presented. Three tempers F (as fabricated), O (annealed), and T4 (age hardened and stabilized at room temperature) of the alloy A1 6013-30 SiC(P) were exposed to environmental chamber in accordance with ASTM recommended practice. The corrosion rate of the alloy showed a decrease with increased exposure period and after 800 h of exposure no appreciable change in the rate of corrosion was observed. The lowest rate of corrosion (4.83 mdd) was shown by temper T4 followed by tempers F and O after 1200 h of exposure in the increasing order of corrosion rate. Fluctuations in the corrosion rate with time are related to the kinetics of growth and dissolution of Al(OH)₃ film, which was detected by fourier transformation infrared (FTIR) spectroscopy (FTIS). The film was composed of an inner compact layer and outer bulk layer dependent on the refreshment rate from the bulk solution. Micrograph examination by scanning electron microscopy (SEM) showed the presence of pits covered by aluminum hydroxide gel, which isolates the pit from the bulk solution. The acidic conditions of pits also cause intergranular attack. Pitting was observed to be less pronounced in temper T4 compared to F and O tempers, the former also showing the highest resistance to corrosion. The data generated predict promising application potential of this alloy in environment where resistance to corrosion is also a major consideration.     

热处理制度对6013和6061合金拉伸性能的影响

研究了自然时效（T4）、人工时效（T6）及室温停放对6013和6061合金常温拉伸性能的影响。结果表明：6013合金具有快速时效特性;经热处理后,6013合金的拉伸强度高于6061合金的且两者延伸率均大于10%。研究还表明：6013和6061合金常温拉伸性能的纵、横向差别很小,说明该合金拉伸性能各向异性不明显。文中还就不同热处理制度影响两种合金拉伸性能的原因进行了分析。     

Ni对Zr-Cu-Al系非晶合金在NaCl溶液中腐蚀性能的影响

利用动电位极化和电化学阻抗谱研究了Ni元素对Zr-Cu-Al系非晶合金在3.5wt.%NaCl中性溶液中的电化学腐蚀行为的影响规律。结果表明：含Ni元素的Zr₅₅Cu₃₀Ni₅Al₁₀比Zr₅₅Cu₃₅Al₁₀非晶合金在NaCl溶液中具有更优异的耐腐蚀性能。Zr-Cu-Al系非晶合金在NaCl溶液中发生点腐蚀,圆形腐蚀坑内布满泡沫状孔洞。通过腐蚀前后的元素分布对比,发现Zr-Cu-Al非晶合金在Cl^_-作用下合金元素选择性溶解。含Ni元素的非晶合金形成致密的钝化膜,抑制了金属元素的选择性溶解,从而提高了耐腐蚀性能。研究结果可为耐Cl^_-环境腐蚀非晶合金成分设计及其应用提供参考。     

Modelling the corrosion behaviour of Al2CuMg coarse particles in copper-rich aluminium alloys

The corrosion behaviour of 2024 aluminium alloy in sulphate solutions was studied; attention was focused on the influence of coarse intermetallic Al₂CuMg particles on the corrosion resistance of the alloy. Model alloys representative of the aluminium matrix and of Al₂CuMg coarse intermetallics were synthesized by magnetron sputtering. Open-circuit potential measurements, current-potential curve plotting and galvanic coupling tests were performed in sulphate solutions with or without chlorides. Further explanations were deduced from the study of the passive films grown on model alloys in sulphate solutions. The results showed that model alloys are a powerful tool to study the corrosion behaviour of aluminium alloys.     

Effect of heat treatment on the corrosion resistance of modified aluminum-magnesium alloys in seawater

Study of modified Al-2.5Mg alloys containing chromium, silica, iron, and manganese in various tempers (O, H-18, T-4, T-6, T-18, and H-34) has shown that their corrosion resistance is significantly altered by thermomechanical treatment and the beneficial effect of chromium on microstructural changes. Modified binary Al-2.5Mg alloys in the T-6 and T-4 tempers exhibit a higher resistance to corrosion in Arabian Gulf water than H-34 tempers due to the beneficial effect of chromium on microstructural changes.     

STUDY ON HOT CORROSION RESISTANCE OF A NEW DIRECTIONAL SOLIDIFICATION Ni–BASED SUPERALLOY

研究了新型定向凝固镍基高温合金DZ68的抗热腐蚀性能, 并与K438合金进行了比较. 结果表明: 热处理态DZ68合金组织中几乎没有(γ+γ') 共晶, 碳化物尺寸小,其整体组织比较均匀; 在热腐蚀过程中发生比较均匀的腐蚀, 其外腐蚀层的腐蚀产物主要是(Ni, Co)Cr₂O₄, 内腐蚀层的腐蚀产物主要是Al₂O₃. 热处理态K438合金组织中存在较多的 (γ+γ'共晶和数量较多、尺寸较大的长条状碳化物, 组织均 匀性较差; 在热腐蚀过程中发生不均匀腐蚀, 其外腐蚀层的腐蚀产物主要是NiO, 内腐蚀层的腐蚀产物主要是CrS.两种合金中Ti元素的偏析有促进其它元素偏析的倾向, 使合金组织的均匀性恶化,热腐蚀均匀性变差. 在本实验条件下, DZ68合金的抗热腐蚀性能略好于K438合金.     

Comparison of corrosion- fatigue properties of precorroded 6013 bare and 2024 bare aluminum alloy sheet materials

The corrosion- fatigue resistance of precorroded 6013 bare and 2024 bare aluminum alloy sheet materials was evaluated to compare the effect of corrosion on initiation and propagation of fatigue cracks. The specimens were precorroded in 3.5% NaCl water solution per ASTM G 44 for periods of 4 and 30 days, and then were subjected to cyclic testing to failure in a 3.5% NaCl corrosive environment. The notched 6013 specimens showed better corrosion- fatigue resistance for the longer exposure time only. In all other cases, the 2024 material had better resistance. Fractographic and microstructural examinations sug-gested that the lower corrosion- fatigue life of the 6013 alloy is due to intergranular corrosion. Although the surface corrosion (pitting) on the 2024 alloy appeared severe, there was little evidence of intergranu-lar corrosion in this alloy.     

Effect of grain size on hot cracking resistance of the HAZ metal of welded joints in creep-resisting alloys

Summary

Al₂O₃/6061 aluminium alloy composite was welded to aluminium alloys (6061‐T6, 5052‐H14, 2017‐T4) using an inertia type friction welding machine to investigate the microstructures and hardness distributions of friction welded joints. Regardless of the aluminium alloys used, finer alumina particles and finer grain structures were observed in the area near the weld interface. And the occurrence of mechanical mixing and moving of alumina particles into a region other than the composite were observed clearly on the weld interface. The distance moved by the alumina particles became greater in the order of the alloys, 6061, 5052 and 2017. A softened area was observed in the heat affected zone of all the aluminium alloys. It was found 30 days after welding that the hardness of the welded joint between the composite alloy and 6061 alloy had not changed significantly, whilst that of the welded joint between the composite alloy and 2017 was observed to have recovered to the previous standard 14 days after welding.     

Corrosion of alloys and their diffusion aluminide coatings by KCl:K2SO4 deposits at 650 °C in air

P91 ferritic‐martensitic steel, 17Cr–13Ni and alloy 800 austenitic stainless steels and Inconel 617 alloy have been aluminised to form Fe₂Al₅, (Fe,Ni)Al and Ni₂Al₃ aluminide coatings. These alloys and their corresponding coatings were subjected to corrosion in air by 50:50 mol/mol K₂SO₄/KCl deposits at 650 °C for 300 h. With the exception of the Inconel 617 alloy, significant metal losses (>180 µm) were recorded. These losses were planar for P91 alloy but involved internal corrosion for the two austenitic steels. The (Fe,Ni)Al and NiAl coatings on the austenitic steels and the Inconel 617 alloy were significantly corroded via intergranular and internal chloridation–sulphidation–oxidation. In contrast, the Fe₂Al₅ coating on the P91 alloy coating was virtually unattacked. For the alloys, the relative extents of corrosion damage can be explained in terms of the stability and volatility of metal chlorides formed. For the coatings, STEM/EDS analyses enable clear linkages to be made between the presence and number of Cr‐rich particles on coating grain boundaries and the corrosion damage observed for the coatings.     

Effect of Sr on the Microstructure and Properties of Mg-6Al Alloy

In this study, microstructures and properties of the Mg-Al alloy with strontium addition are studied. After the addition of strontium structure analysis was performed to investigate phase evaluation. The potentiostatic measurements were also carried out in 3.5% NaCl solution with the results showing that the effect of adding strontium element to magnesium- aluminum alloys on corrosion behavior of this metal was strongly dependent on microstructure of the final alloy (e.g. grain size, type, intermetallic compounds, etc.). The major second phase included Al₄Sr and Al₂Sr, but the amount and morphology of these compounds was different in the alloys. The results indicated a reduction in the amount of Mg₁₇ Al₁₂ phase and corrosion rate as well as a rise in the resistance to cavitations.     

Zur Korrosion von Kupferwerkstoffen in Tetrachlorkohlenstoff

Corrosion of copper base materials in carbon tetrachloride Copper (OFHC), two copper zinc alloys (CuZn36 and CuZn15), one nickel-copper alloy (NiCu30Fe), the copper tin casting alloy G-CuSn10, and the copper aluminium casting alloy G-CuAl10Fe were immersed in the following boiling media: carbon tetrachloride dried over P₄O₁₀, carbon tetrachlorid saturated with water and two phase mixtures of carbon tetrachloride and water. The individual samples were positioned within the organic phase, within the aqueous phase, within the vapour phase and within the condensated phase, respectively. OFHC copper, NiCu30Fe, CuZn15 and G-CuAl10Fe are corrosion resistant (corrosion rate ≤ 0,01 mm/y) in dry as well as in water saturated CCl₄. The same statement is valid for alloys CuZn36 and G-CuSn10 which show a corrosion rate of approximately 0,02 mm/y within the condensate of CCl₄ saturated with water. All alloys exhibit more or less corrosion within the two phase mixtures. Within the aqueous phase the materials do not prove to be resistant: they are completely dissolved in less than 30 days. Paralle to the corrosion of CuZn36 and G-CuAl10Fe zinc and aluminium, respectively, went into solution. The vapour phase above the carbon tetrachloride-water mixture consisted of over 90% by volume carbon monoxide. This prove that the corrosion of all materials which had been immersed in the aqueous phase was effected by phosgene.