Microstructure and corrosion evolution of additively. Stresscorrosion cracking of highstrength aluminum alloys. Aluminum alloys most often associated with stresscorrosion cracking in actual service are 2014, 2024, 2219, 7075, 7079, and 7178 alloys, and cast alloys of ternalloy 7, 40e, 195, and 220 compositions. Selecting aluminum alloys to resist failure by fracture. However, aluminum alloys have a high strengthtoweight ratio. Corrosion fatigue and stress corrosion tests have been done on aluminium 5% magnesium4% zinc alloy in two conditions of heattreatment, i. Out of eight series of aluminium alloys, 2xxx, 5xxx and 7xxx aluminium alloys are susceptible to scc. Residual stress is produced by initial metal forming and welding operations although a good welding procedure will avoid this problem by properly annealing the heated area. The alloys comprising of 42 45% nickel will not be attacked in this. G47 test method for determining susceptibility to stresscorrosion cracking of 2xxx and 7xxx aluminum alloy products ics code ics number code 77. Degradation related to pits, intergranular or general corrosion can be measured by.
Highstrength aluminum alloys are of considerable importance in our technologically advanced society. A major part of the paper is devoted to the results of the latest alloy development. The stress corrosion susceptibility defined as the reciprocal of failure time has been investigated as a function of alloyenvironment system, isothermal aging treatment, microstructure, applied tensile stress, and temperature using smooth and. High strength aluminum alloys of dramatically increased stress corrosion. Stress corrosion cracking results from the conjoint action of three components. Stress corrosion cracking is not instantaneous, so time is a factor in its occurrence. These aluminum alloys can be difficult to arc weld without encountering problems during andor after welding. The susceptibility to stresscorrosion cracking is believed to be due to networks of dislocations which are produced during the solution heat treatment of precipitation hardening alloys. Aluminium specifications, properties, classifications. As shown in figure 1, we can see that with the increase in znmg ratio, the time at which the alloy reaches the peak hardness gradually increases.
For example, copper and its alloys are susceptible to ammonia compounds, mild steels are susceptible to alkalis and stainless steels are susceptible to chlorides. Of these, 5xxx and 6xxx alloys offer medium torelatively high strength, good corrosion resis tance, and are generally so tough that fracture toughness is rarely a design consideration. Aluminium is most commonly alloyed with copper, zinc, magnesium, silicon, manganese and lithium. Stress corrosion cracking scc is a progressive fracturing that occurs in metals as a result of the combined influence of tensile stress and a corrosive environment. In these high strength 7xxx aluminium alloys, scc plays a vital factor of. The stress corrosion cracking scc behaviour of aluminium alloys has been studied for the past five decades and is still a research area of high interest due to the demand for higher strength aluminium alloys for fuel saving. A generalized theory of stress corrosion of alloys, in symp. Probability is discussed in relation to its role of predicting the stress corrosion cracking of cu metals. It should not be confused with the term stress corrosion cracking which is an anodic cracking mechanism. Some examples of stress corrosion cracking in service are described. Corrosion behavior of inconel 625 heanjia super metals. The corrosion resistance of aluminum is dependent upon a protective oxide film. Atmospheric stress corrosion cracking of a superplastic 7475 aluminum alloy j. Perhaps the bestknown application is in the aerospace.
The objective of the present study is to determine the threshold stress level of stress corrosion cracking scc in aa7075t651 aluminium alloy. The tensile stresses necessary to initiate stresscorrosion cracking may be either 1. Stress corrosion cracking scc is the cracking induced from the combined influence of tensile stress and a corrosive environment. Structural failure due to scc can be very unpredictablefailure could occur after as little as a few hours of exposure, or the equipment could continue to function normally for. The scope of the journal includes the latest developments in areas of corrosion.
G47 test method for determining susceptibility to stress corrosion cracking of 2xxx and 7xxx aluminum alloy products ics code ics number code 77. Corrosionpedia what is stress corrosion cracking scc. Service experience and current research, technical report afmltr67329, in proc. This new second edition serves as a goto reference on the complex subject of stress corrosion cracking scc, offering information to help metallurgists, materials scientists, and designers determine whether scc will be an issue for their design or application. Metallurgical and materials transactions a, 1996, 27. The localised corrosion caused by pitting, even from the early stages of corrosion in wrought aa7075t6, can initiate fatigue cracks in the presence of cyclic stressleading to the failure of. Aluminum and its alloys are divided into two broad classes, castings and wrought or mechanically worked products. Susceptible alloys, especially steels, react with hydrogen sulfide, forming metal sulfides and atomic hydrogen as corrosion byproducts. Environmentally assisted cracking of aluminum alloys in chloride. Copperaluminium alloys are commonly known as aluminium bronzes.
Protection of metals and physical chemistry of surfaces 54. Sulfide stress cracking ssc is a form of hydrogen embrittlement which is a cathodic cracking mechanism. Pdf stress corrosion cracking behaviour of 7xxx aluminum. Many engineering applications demand employment of joining processes for making components of desired size, shape and geometry. Stress corrosion cracking of aluminum alloys ubc library. This chapter brings out the general understanding of the scc mechanisms and the critical metallurgical issues affecting the scc behaviour of aluminium alloys. Small additions of chromium, titanium, zirconium, lead, bismuth and nickel are also made and iron is invariably present in small quantities. Pure aluminum is a fairly ductile material with low tensile strength, but highstrength alloys can have tensile strengths of up to 690 mpa 100 ksi furthermore, aluminum retains its strength at extremely low temperatures, which makes it a good material for use in. The impact of scc on a material usually falls between dry cracking and the fatigue threshold of that material. Stress corrosion cracking scc of austenitic stainless. Stress corrosion cracking behaviour of 7xxx aluminum alloys.
An extensive failure analysis shows how many service failures occurred in the industry and what kind of alloys and stresses led to initiation and propagation of stress corrosion cracks which caused these service failures. For example, it has been found that such dislocations in the 7075 t6 alloy are formed during the quenching from the solution heat treatment temperature. Stresscorrosion cracking in aluminum alloys is characteristically intergranular. In general, the residual strength decreases with increasing scc sensitivity. The versatility of aluminium makes it the most widely used metal after steel. The stress corrosion behaviour of precipitation hardened al9mg, al22zn and al3mg6zn alloys has been studied in aqueous environments and ethanol. Nickel and nickel base alloys are normally resistant to chloride stress corrosion cracking as compared to stainless steels. The postulated mechanisms for stress corrosion cracking of. Alloys 7079t6, 7075 t6 and 2024 t3 contributed to more than 90% of the service failures of all highstrength aluminum alloys.
Stresscorrosion tests on highstrength aluminum alloy. Speci m ens ofthe othermaterials were pitted, but no. It is also lighter than steel, with only onethird the density. Stresscorrosion cracking in high strength steels and in titanium and aluminum alloys by defense technical information center. Enhancing the stress corrosion cracking resistance of a. Pdf stress corrosion cracking behaviour of 7xxx aluminum alloys. The corrosion properties of aluminum and its alloys.
They offer a combination of properties such as high strength, hardness, corrosion resistance and wear resistance. There are over 300 wrought alloys with 50 in common use. The specifications, properties, classifications and class details are provided for aluminium and aluminium alloys. Even though aluminium alloys melt at lower temperatures than steels, they require higher heat inputs for welding due to their higher thermal conductivity. The most common type of stress corrosion cracking in stainless steels occurs in chloride environments, which will be the focus of. Gearing corrosion 32 p279, 1975 the technical advice and recommendations made in this product data sheet should not be relied or acted upon without conducting your own further investigations, including. Electrochemical noise evaluation and statistical analysis during stress corrosion cracking scc of aluminium alloy 7075t6 has been investigated in 3. Evaluating stress corrosion cracking behaviour of high strength. Effect of znmg ratios on microstructure and stress. The latter is subdivided into heattreatable and nonheattreatable alloys, and into various forms produced by mechanical working. The mechanical properties of 5083h1 and 7075t6 in sl orientation are. An extensive failure analysis shows how many service failures occurred in the aerospace industry over a ten year period and what kind of alloys and stresses led to initiation and propagation of stress corrosion cracks which caused these service failures.
The term stresscorrosion refers to the occurrence of crack formation caused by. Stress corrosion cracking of components made of aluminium alloy welds may be influenced by the prior postweld heat treatment, phase transformations microconstituents in the weld metal andor heat affected zone and the residual stresses that develop during welding. The stress corrosion cracking scc of aluminum alloys is a welldocumented phenomenon, but there is considerable disagreement in the scientific literature as to what mechanism causes it. These problems are usually associated with cracking, most often, hot cracking and on occasion, stress corrosion cracking scc. Various methods for the prevention of stress corrosion cracking are discussed. Hardness and conductivity in relation with the znmg ratio of the alloy. The improved stress corrosion cracking resistance of the lowcu containing alznmgcu aluminum alloy subjected to stepquench and aging heat treatment is mainly attributed to grain boundary precipitates with high cu content, large size and discontinuous distribution. These alloys are a range of copperbased alloys in which.
Stress corrosion cracking of aluminum alloys springerlink. The paper contains most of the results of stress corrosion tests with aluminum. Stress corrosion cracking behaviour of 7xxx aluminum. However, there is a general agreement that for aluminum the electrochemical factor predominates and the electrochemical theory continues to be the basis for developing aluminum alloys and tempers resistant to scc. The 5xxx alloys provide good resistance to stress corrosion in marine atmospheres and good weld ing characteristics. Stress corrosion cracking of aluminum alloys total materia. Standard classification of resistance to stresscorrosion. Reducing the susceptibility of alloys, particularly aluminium alloys, to stress corrosion cracking.
The stress corrosion cracking scc behaviour of aluminium alloys has been studied for the past five decades and is still a research area of high interest due to the demand for higher strength. Stress corrosion cracking scc is a common issue with many specialty alloys. Aluminum is one of the most prevalent metallic elements in the solid portion of the earths crust, comprising approximately 8%. The aluminum alloys that fall into this difficulttoweld category can be divided into different groups.
Aluminum alloys that contain appreciable amounts of soluble alloying elements, primarily copper, magnesium, silicon, and zinc, are susceptible to stresscorrosion cracking scc. T6 aging operations on aluminium alloy 7075 result in high strength of this alloy and fine and uniform distribution of t6precipitates of secondary phases in the network, for which the preparations stages are. Copper alloys stress corrosion cracking austral wright. Stress corrosion cracking scc is degradation of mechanical properties under the combined action of stress and corrosive environment of the. Aluminum alloys that contain appreciable amounts of soluble alloying elements, primarily copper, magnesium, silicon, and zinc, are susceptible to stress corrosion cracking scc. Stress corrosion cracking stress corrosion cracking scc is a phenomenon found in various materials, notably in metal alloys. It is always present in a combined form, usually a hydrated oxide, of which bauxite is the primary ore. Stress corrosion cracking scc is degradation of mechanical properties under the. The required tensile stresses may be in the form of directly applied stresses or in the form of residual. The advantageous effect of nickel on limiting the stress corrosion cracking in boiling 42% mgcl2 is observed. Scc is often associated with chlorides, but can also occur with caustics and other corrosive media.232 475 1471 46 1425 582 536 1642 813 956 331 1152 832 1054 661 725 1134 1485 1137 1144 764 927 622 1107 122 147 1051 913 164 600 1557 694 405 538 704 908 883 234 1230 318 1164 696 1301 380