复合添加Zr、Cr和Pr对Al-Zn-Mg-Cu合金组织和性能的影响

采用铸锭冶金法制备Al-Zn-Mg-Cu-Zr、Al-Zn-Mg-Cu-Cr-Pr和Al-Zn-Mg-Cu-Zr-Cr-Pr3种合金,通过金相显微、扫描电镜和透射电镜观察以及拉伸性能、极化曲线、应力腐蚀和剥落性能的测试,研究复合添加Zr、Cr和Pr对Al-Zn-Mg-Cu合金组织和性能的影响。结果表明:复合添加Zr、Cr和Pr可有效抑制Al-Zn-Mg-Cu合金回复过程中亚晶的合并和长大,显著抑制再结晶,提高合金抗应力腐蚀和抗剥落腐蚀的性能;与单独添加Zr的合金相比,复合添加Zr、Cr和Pr的合金断裂韧性KⅠC从23.3MPa·m1/2提高到29.3MPa·m1/2,合金应力腐蚀开裂界限应力强度因子KⅠSCC由10.9MPa·m1/2提高到24.5MPa·m1/2,合金的抗拉强度、屈服强度及伸长率都略有提高。     

On the corrosion of binary magnesium-rare earth alloys

The corrosion properties of high-pressure die cast (HPDC) magnesium-rare earth (RE) based alloys have been studied. Binary additions of La, Ce and Nd to commercially pure Mg were made up to a nominal 6 wt.%. It was found that the intermetallic phases formed in the eutectic were Mg₁₂La, Mg₁₂Ce and Mg₃Nd, respectively. Results indicated that increasing RE alloying additions systematically increased corrosion rates. This was also described in the context of the electrochemical response of Mg-RE intermetallics - which were independently assessed by the electrochemical microcapillary technique.This study is a discrete effort towards revealing the electrochemical effect of carefully controlled binary alloying additions to magnesium in order to elucidate the microstructure-corrosion relationship more generally for HPDC Mg alloys. Such fundamental information is seen to not only be useful in understanding the corrosion of alloys which presently contain RE additions, but may be exploited in the design of magnesium alloys with more predictable corrosion behaviour. There is a special need to understand this relationship - particularly for magnesium that commonly displays poor corrosion resistance.     

Breakdown of chromium oxide scales in sulfur-containing environments at elevated temperatures

Structural Fe-Cr-Ni alloys may be rapidly degraded in oxygen-sulfur mixed-gas environments at elevated temperatures unless protective oxide scales can be formed and maintained. The breakaway corrosion process was examined in model alloys of Fe-25wt.% Cr-20wt.% Ni with and without Nb and Zr additions. Oxide scales were preformed in S-free environments and subsequently exposed to oxygen-sulfur mixed-gas atmospheres. Preformed scales were found to delay the onset of breakaway corrosion. The beneficial effects of refractory metal additions were achieved via formation of a barrier layer at the Cr₂O₃ alloy interface.     

The Effect of Water Vapor on Passive-Layer Stability and Corrosion Behavior of Fe–Al–Cr Base Alloys

Although it has been reported that additions of water vapor to high-temperature corrosion environments accelerate corrosion, the role of water vapor on increasing the corrosion rate of Fe–Al–Cr alloys and coatings is not very well understood. In order to better understand these effects, multiple Fe–Al–Cr base alloys were tested at 500°C for 100 hr in three different multi-component corrosive gases with and without water vapor. The three gases were a sulfidizing gas, a mixed oxidizing/sulfidizing gas, and an oxidizing gas. Thermogravimetric testing showed that the corrosion kinetics increased when water vapor up to 6% was added to the atmospheres. The surfaces of the exposed samples were considered carefully to determine if the addition of water vapor changed the morphology of the corrosion products and, more importantly, affected the passive layer. It has previously been shown that the formation of nodules can be caused by the inability of the passive layer to re-heal itself after the presence of a defect allowing fast growing non-protective corrosion products to externally grow from the surface. In this study, the amount of external nodules that formed on the surface of the alloys was shown to increase with the addition of water vapor. An increase in the amount of external nodules present due to additions of water vapor gives an indication that water vapor accelerates the passive-layer breakdown. It was observed that the scale morphology correlated well with the corrosion kinetics for the exposed alloys, which showed that water vapor increased the corrosion rates of the alloys.     

Reports of Meetings

Abstract

The corrosion resistance of a number of stainless steels and nickel alloys in solutions of pure phosphoric acid boiling under reflux and in similar solutions under conditions of heat transfer has been investigated. The effect of phosphoric acid concentrationand alloy composition on the corrosion rates obtained has been evaluated. The effect of additions of impurities such as fluoride, chloride, silicate and ferric ions on the corrosion behaviour of a number of the alloys in concentrated phosphoric acid under conditions of heat transfer has also been determined; such impurities are often present in wet-process plant phosphoric acid at the evaporator stage. The work has demonstrated that the alloys of highest nickel content generally exhibit the best corrosion resistance in such environments. It has also been shown that whilst chloride ion additions considerably increase the aggressive nature of the environment, fluoride additions in general have very little effect.     

Effect of Yb additions on microstructures and properties of 7A60 aluminum alloy

Al-Zn-Mg-Cu-Zr alloys containing Yb were prepared by cast metallurgy. Effect of 0.30% Yb additions on the microstructure and properties of 7A60 aluminum alloys with T6 and T77 aging treatments was investigated by TEM, optical microscopy, hardness and electric conductivity measurement, tensile test and stress corrosion cracking test. The results show that the Yb additions to high strength Al-Zn-Mg-Cu-Zr aluminum alloys can produce fine coherent dispersoids. Those dispersoids can strongly pin dislocation and subgrain boundaries, which can significantly retard the recrystallization by inhibiting the nucleation of recrystallization and the growth of subgrains and keeping low-angle subgrain boundaries. Yb additions can obviously enhance the resistance to stress corrosion cracking and the fracture toughness property, and mildly increase the strength and ductility with T6 and T77 treatments.     

Yb微合金化对Al-Zn-Mg-Cu-Zr合金再结晶行为和性能的影响

采用铸锭冶金法制备了含Yb的Al-Zn-Mg-Cu-Zr合金.通过对硬度、电阻率、强度、应力腐蚀性能的测试和用金相显微镜和透射电镜的观察,分析了Yb微合金化对Al-Zn-Mg-Cu-Zr合金再结晶行为和性能的影响.结果表明,在Al-Zn-Mg-Cu-Zr合金中添加微量Yb能形成含Yb的细小弥散相,因此提高T6态合金的再结晶温度,显著提高合金的应力腐蚀抗力和断裂韧性,并略微提高合金的强度和塑性.这些均匀分布于基体上的弥散相能强烈钉扎位错和亚晶界,抑制了再结晶形核,显著抑制了基体再结晶,保持形变回复组织.     

The segregation of elements in high-refractory-content single-crystal nickel-based superalloys

Nickel-based superalloys are complex alloys that contain ten to 15 elements that are widely used in industries where high-temperature strength and corrosion resistance are required. Alloy additions commonly include Cr, Co, W, Ta, Al, Ti, Re, Mo, and, in some alloys, Ru. Each of these additions can affect the as-cast microstructure due to differences in elemental segregation. A better understanding of the effects of typical additions to nickel-based superalloys on the segregation of the elements in the alloy can help identify potential improvements in the processing of current alloys and the development of new alloys. Therefore, the effects of several common alloying additions on solidification segregation and defects were evaluated. In general, an increase in the degree of elemental segregation was observed with increases in each of the elements listed except cobalt and molybdenum. Increased levels of cobalt and molybdenum resulted in reductions in the segregation of most of the elements in the alloy. For more information, contact G.E. Fuchs, University of Florida, Department of Materials Science and Engineering, 116 Rhines Hall, Gainesville, FL 82611, USA; (352) 846-3317; fax (352) 392-7219; e-mail gfuch@mse.ufl.edu.     

Influences of Ca and Y Addition on the Microstructure and Corrosion Resistance of Vacuum Die-Cast AZ91 Alloy

The influences of Ca and Y additions on the microstructure and corrosion resistance of vacuum die-cast AZ91 alloys were investigated by optical microscope,electron scanning microscope,weight-loss test,and electrochemical corrosion experiment.The results indicate that the Ca or Ca and Y additions refined the microstructure and decreased the amount of Mg17Al12 phase on grain boundaries in the alloys.Meanwhile,the addition of Ca and Y led to the formation of network Al2 Ca phase and rod-like Al2 Y phase,improved the corrosion resistance of AZ91 magnesium alloy.Compared with AZ91 alloy,the corrosion rate of AZ91–1.5Ca–1.0Y alloy was decreased to 16.2%,and its corrosion current density was dropped by one order of magnitude after immersion in 3.5 wt% NaCl solution for 24 h.     

Corrosion Resistant Ni-Cr-Mo Alloys

The effects of Cr, Mo and other minor additions (such as Cu and W) on corrosion resistance depends on the environment composition (eg. chloride, nitrate levels) and redox potential. These effects are first discussed in general terms and then specifically with respect to two new alloys, HASTELLOY® alloys C-22 and G-30. The beneficial effects of these elements on corrosion resistance must be balanced against the detrimental effects on thermal stability. High Cr, Mo and W levels can lead to the formation of embrittling intermetallic phases such as sigma and mu. Stability with respect to precipitation of intermetallic and carbide phases is also important from the perspective of fabricability.     

Al-Ti、Al-Ti-C中间合金对AZ91D镁合金组织和性能的影响

研究了Al-5Ti、Al-5Ti-0．25C和Al-8Ti-2C中间合金对AZ91D镁合金的组织、力学性能和耐腐蚀性能的影响。结果表明,添加Al-5Ti中间合金使晶粒粗化,而添加Al-5Ti-0．25C和Al-8Ti-2C中间合金使晶粒细化,Al-8Ti-2C中间舍金的细化效果明显且细化后组织细小均匀;添加Al-5Ti中间合金使合金的力学性能降低,而添加Al-5Ti-0．25C和Al-8Ti-2C中间合金均使合金的拉伸强度和伸长率得到了提高;添加Al-5Ti、Al-5Ti-0．25C和Al-8Ti-2C中间合金均使合金的耐腐蚀性能得到了改善。对于AZ91D合金而言,Al-8Ti-2C中间合金是一种良好的晶粒细化剂。     

Effects of Pb and Cu additives on microstructure and wear corrosion resistance behaviour of PM Al–Si alloys

Abstract

The wear and wear corrosion resistance behaviour of Al–20Si–XPb–YCu (X=0–10 wt-%, Y=0–3 wt-%) alloys fabricated by a powder metallurgy (PM) technique and subsequent heat treatments were evaluated by a block on ring tribotest. The microstructure of all aluminium alloys was observed by optical microscopy and scanning electron microscopy with X-ray energy dispersive spectroscopy. The effects of applied potentials and environments including dry air and 3.5 wt-%NaCl aqueous solution were studied. The results of microstructure analysis indicated that Pb exhibited a bimodal distribution in the Pb containing alloys, and Cu particles become to form the intermetallic phase CuAl₂. Furthermore, the hardness rises significantly for both Pb and Cu containing alloys only after solid solution quenching treatment. The wear and corrosion results showed that the addition of both lead and copper would improve the wear resistance but lead to a higher corrosion rate whereas heat treatment had a beneficial effect of reducing the corrosion rate of most alloys with the exception of Al–Si alloy. Furthermore, by comparison of all alloys after heat treatment, the wear corrosion resistance of Al–Si alloy was inferior to the other alloys; consequent additions of Pb and Cu further improved its wear corrosion resistance. Moreover, at an anodic potential, the wear corrosion rate and current density of both Al–Si and Al–Si–Cu alloys containing particle Pb decrease significantly owing to a corrosion product layer composed of Al, O and Pb elements.     

A combined mapping process for the development of platinum-modified Ni-based superalloys

Heat-resistant Ni-based alloys have been used extensively for components in turbine engines for the past 50 years. Platinum group metal (PGM) alloying additions (i.e., platinum and iridium) have been found in past studies to increase the oxidation and the hot corrosion performance of Ni-based alloys. The basis for this investigation was to develop a PGM-modified superalloy having high-temperature strength, thermal stability, and excellent oxidation/hot corrosion performance.     

Entwicklung verbesserter Bleiwerkstoffe für den Chemie-Apparatebau–II: Korrosionsprüfung

Improvements in lead alloys for chemical plants – II: Corrosion testing Within the scope of a R&D programme concentrated on the development of finegrained lead alloys for chemical plants, the corrosion resistance of various lead alloys has been tested in boiling H₂SO₄. The anti-corrosive properties of copper-alloyed lead, which were unstable in a 70% H₂SO₄, could be stabilized by a grain refinement of the casting with selenium, i. e. the corrosion resistance was improved and rendered more uniform. Further additions of tin and palladium still doubled the corrosion resistance. Small amounts of silver (0.01%) had a positive, but not decisive effect. In a 50% H₂SO₄, additions of tin have already an effect similar to that of selenium, whereas palladium does not further increase this positive influence. Additions of tellurium had different effects. The corrosion resistance of alloys containing 4% Sb, which is satisfactory in a 50% H₂SO₄, is deteriorated by an increased As-content. Measurements of the current density and potential revealed a nearly completely suppressed active current peak for Pb-4% Sb as well as lead alloyed with slight amounts of nickel; besides, both alloys showed, mainly in a 70% H₂SO₄, a rising corrosion loss with passing time. It may accordingly be supposed that in both cases the oxygen reduction was decisive for passivation, whilst with the other alloys under the aerating conditions used the hydrogen reduction was the most important cathodic reaction.     

Effect of molybdenum additions on the microstructures and corrosion behaviours of 316L stainless steel-based alloys

Alloys were made by alloying 5, 10, 15, 17.5 and 20?wt-% Mo with Type 316L stainless steel. Sigma phases containing 21–29?wt-% Mo formed along the austenite grain boundaries with the addition of 5?wt-% Mo and increased with additions up to 15?wt-% Mo, but they decreased with further additions. Laves phases containing 33–40?wt-% Mo co-precipitated at additions of 10?wt-% Mo which increased with further Mo increases. The corrosion resistance, assessed by potentiodynamic polarisation in a 10?mM NaCl solution adjusted to pH 4, increased relative to Type 316L for alloys made with 5 and 10?wt-% added Mo, but decreased with further additions due to preferential corrosion of the Laves phase. The alloy made with 10?wt-% added Mo had the highest corrosion resistance due primarily to the high Mo content of the austenite.     

The influence of microstructure on surface phenomena: Rolled zinc

A series of rolled zinc (Zn) alloys, all with purity exceeding 99.7%, have been shown to have material losses due to corrosion spanning an order of magnitude during field exposure trials. In order to explain these large variations in corrosion performance, the influence of alloying additions and microstructure has been investigated. Corrosion rates were found to increase with increasing alloying additions of copper (Cu) and, depending upon its distribution, titanium (Ti). The influence of grain size was investigated using a series of heat-treated rolled zinc specimens. Binary Zn-Ti and Zn-Cu alloys were used to study the independent influences of Ti and Cu on zinc corrosion. An increased understanding of the influence of Cu:Ti ratios has been developed and an approach to optimise the corrosion resistance of rolled zinc materials has been proposed.     

The influence of zirconium additions on the corrosion of magnesium

Sixteen custom binary Mg–Zr alloys and four commercial Zr-containing Mg-alloys were used to investigate the role of Zr on the corrosion of Mg. Mg–Zr alloys were manufactured with a range of different Zr concentrations. It was observed that the Mg–Zr alloys with a smaller mean Zr particle size had more Zr dissolved in solid solution. Both the Zr in solid solution and in metallic particle form were observed to have a deleterious effect on the corrosion rate of Mg. However, this deleterious effect is less pronounced to effect in alloys with multiple alloying additions.     

Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

Due to their excellent corrosion resistance, iron aluminum alloys are currently being considered for use as weld claddings in fossil fuel fired power plants. The susceptibility to hydrogen cracking of these alloys at higher aluminum concentrations has led researchers to examine the effect of chromium additions on the corrosion resistance of lower aluminum alloys. In this work, three iron aluminum alloys were exposed to simulated coal combustion environments at 500 and 700 °C for short (100 h) and long (5000 h) isothermal durations. Scanning electron microscopy was used to analyze the corrosion products. All alloys exhibited excellent corrosion resistance during short term exposures. For longer test times, increasing the aluminum concentration improved alloy corrosion resistance. The addition of chromium to the binary iron aluminum alloy prevented the formation iron sulfide and resulted in slower corrosion kinetics. A general classification of the scales developed on these alloys is presented.     

Untersuchungen über das Korrosionsverhalten von Zirkoniumlegierungen. III. Untersuchungen an Zirkonium-Titan-Legierungen

Investigations into the corrosion behaviour of zirconium alloys III. Investigations on zirconium titanium alloys Investigations on zirconium alloys containing up to 4OO% titanium and, eventually, up to 10% Nb or Mo and small amounts of Fe, Ni and Cr (together 1.5% maximum) have revealed that titanium increases the dissolution power of zirconium for other alloying elements without tending to form two-phase structures. As to corrosion behaviour the better alloys are somewhat superior to other alloys. While titanium impairs the corrosion resistance of pure zirconium with respect to boiling mineral acids (20% HCl, sulphuric or nitric acids) titanium additions up to 10% of improve the corrosion behaviour of ZrNb and ZrMo alloys; alloys of the type Zr10Nb10Ti or Zr10Ti10Ta are comparable, with respect to the corrosion resistance, to pure zirconium. The scaling resistance of zirconium passes through a minimum at a five to ten percent Ti and arrives at its maximum value with 40% Ti. Further improvements may be obtained by addition of 10% Nb.     

Effect of Mg Additions and Thermal Treatment on Corrosion Properties of Al–Li–Cu-Base Alloys

An investigation on the corrosion and electrochemical behavior of experimental and industrial semifinished items of Al–Li–Cu–base alloys offers possibilities of increasing the corrosion resistance of aluminum–lithium alloys by alloying and an nontraditional thermal treatment. Magnesium added in a concentration of no more than 0.4% leads to a improvement of the corrosion and mechanical characteristics of the alloy, whereas increasing its concentration up to 1.0% deteriorates all the corrosion characteristics. An investigation of the effect of the cathodic additions of Zr, Mn, and Mn + Cr shows that the corrosion properties are nonchanged by substitution of Mn or Mn + Cr for Zr. The resistance to general corrosion, exfoliation corrosion, and corrosion cracking is enhanced by a nontraditional artificial aging.