Salt Fog Corrosion Research Articles

Mathematical modelling and development of response surfaces to predict and analyze the salt fog corrosion resistance of friction stir welded AA7075-T651 alloy joints: effect of retrogression and reaging

Mathematical modelling and development of response surfaces to predict and analyze the salt fog corrosion resistance of friction stir welded AA7075-T651 alloy joints: effect of retrogression and reaging

Effect of pH value, chloride ion concentration and salt spraying time on salt fog corrosion resistance of friction stir welded AA7075-T651 alloy joints

Effect of pH value, chloride ion concentration and salt spraying time on salt fog corrosion resistance of friction stir welded AA7075-T651 alloy joints

Mechanical Properties and Pitting Corrosion of Friction Stir Welded Aluminium Alloy 5083 (H321)

In the present work, 6 mm plates of Al-Mg alloy AA5083-H321 was friction welded. Weld microstructures, hardness values and tensile properties were evaluated in the welded condition. Macrostructure studies revealed that the shape of the stir zone is a basin-shaped type and it appeared more like a rectangular box and no macroscopic defect or weakly bonded regions were observed in the weld region, which extended through the full thickness of the plates. There were no noticeable changes in the microstructure compared to the respective unaffected base material and there was not much of difference in the microstructures of the nugget and the base metal. The pitting corrosion results indicate that there was noticeable improvement in the pitting potential values of the welds. The weld nugget region exhibited better pitting corrosion resistance compared to other regions. The base material and the friction stir welded materials are far superior in resistance to salt fog corrosion.

Microstructure and Salt Fog Corrosion of Wrought Mg-Al-Zn and Mg-RE Alloys.

Wrought magnesium alloys have received attention due to their potential application as lightweight materials. However, their use is limited by their poor corrosion resistance. Rare earth additions have the potential to enhance corrosion resistance. The present work included a microstructural investigation and corrosion testing of the alloy WE-43, containing Nd and Y, which was compared against the more conventional compositions of AZ31 and AZ61 alloys. All three alloys exhibited a recrystallized equiaxed structure after hot rolling with the presence of second phases-precipitates. The WE-43 alloy exhibited a better corrosion resistance than AZ31 and AZ61 under salt fog testing, indicated by the lower depth of attack and lower weight loss. The second phases in the microstructure of AZ31 and AZ61 alloys determined their corrosion resistance. The second phases in the AZ31 and AZ61 alloys (based on Al-Mg and Al-Mn phases) were nobler than the Mg matrix and catholically acted, thus sacrificing the Mg matrix. The superior corrosion resistance of WE43 was due to the incorporation of Y in the oxide/hydroxide film. In addition, the second phases in the WE43 consisted of Nd and Y and were less noble than the Mg-matrix. Thus, they acted as anodic sites protecting the Mg-matrix. The above results show the beneficial effect of rare earth additions to wrought Mg alloys towards increased corrosion resistance.

Flake-like ZnAl alloy powder modified waterborne epoxy coatings with enhanced corrosion resistance

Zinc-rich epoxy coatings (ZRECs) have been widely used to protect steel against corrosion because of their excellent corrosion resistance. However, the ZRECs preparation usually used a large amount of Zn powders and organic solvents, which not only wasted resources but also produced a great quantity of volatile organic compounds (VOC). Therefore, it was necessary to develop a method which can prepare epoxy coatings with low Zn content, great corrosion resistance and green environmental protection. In this paper, three different flake metal powders (Zn, ZnAl alloy and ZnAlMg alloy) were used to replace spherical Zn powders to develop environmentally friendly coatings with low pigment content. The coatings were evaluated by salt spray test and electrochemical test. The results show that the use of flake metal powders instead of spherical zinc pigments can enhance the electrical connection between metal particles, prolong the path of corrosive medium infiltration into the coatings, enhance the physical shielding effect of the coatings, and reduce the pigment content by one third. Among them, the ZnAl coatings displayed the best anti-corrosion performance resisting salt fog corrosion for 28 days. In addition, the experimental results show that the self-healing ability of the coatings also plays an important role in the immersion middle and late stages. In short, the waterborne epoxy ZnAl coatings are suitable for large-scale application in harsh environments.

Salt-Fog Corrosion Behavior of GCr15 Steels Treated by Ultrasonic Strengthening Grinding Process

In this paper, the corrosion resistance of four GCr15 steel samples has been investigated. Three samples were initially surface-treated by ultrasonic shot peening (USP), a dry ultrasonic strengthening grinding process (DUSGP), and a wet ultrasonic strengthening grinding process (WUSGP), respectively, while another one was only polished. Then, all the processed samples were subjected to salt spray corrosion. Sample properties, such as capacitance arc, self-corrosion potential (Ecorr), self-corrosion current density (Icorr), corrosion morphology, and corrosion products were analyzed. Results show that the sample treated by WUSGP has the best corrosion resistance, which can be attributed to the high dislocation density, small grain size, needle-like and lath-like shape of martensite content formed in the treatment, which hinders Cl− from eroding the matrix. The obtained corrosion pits and cracks in Sample WUSGP show a width of approximately 1.4 µm and 2.1 µm, respectively, degrading 78% and 75% compared to polishing. The possible corrosion mechanism of the samples has been discussed. The findings denote that the treatment fused ceramic balls, strengthened liquid, and corundum in USP could be an efficient method to improve the corrosion resistance of some mechanical parts.

A SUSTAINABLE APPROACH TO IMPROVEMENT OF CORROSION PROTECTION COATINGS FOR STEEL STRUCTURES

Corrosion is a primary factor compromising the safety and service life of steel structures. Corrosion protection coatings are generally employed for protection of the steel structures that are exposed to different aggressive environments. This research evaluated the use of biobased ion exchangers as a sustainable means of improving corrosion protection coatings.
 Two base polymer coatings (vinyl and coal-tar epoxy) were considered. The following types and dosages of biobased ion exchangers were evaluated in these coatings: (i) strong-base ion exchange cellulose in OH, PO4, SiO3, BO3, NO2, SO4 and NO3 forms at 1% by weight of resin; (ii) weak-acid starch citrate ion exchanger in H form at 1 wt.%; and (iii) strong-base ion exchange cellulose in OH form at 2 wt.%. In addition, a strong-base ion exchange resin in OH form was considered at 1 and 2 wt.% as control. Different coating formulations were evaluated based on the outcomes of salt-fog corrosion, moisture resistance, pull-off strength, and abrasion resistance tests. The introduction of certain biobased ion exchangers in protective coatings was found to be an effective means of achieving improved levels of corrosion resistance, adhesion capacity, moisture stability and abrasion resistance.

Evaluation of Conversion Coatings Without Hexavalent Chromium for Aerospace and Defense Applications

Conversion coatings containing hexavalent chromium are currently used in aerospace and defense manufacturing on various aluminum alloys to provide corrosion protection and enhanced adhesion of subsequent coatings. However, hexavalent chromium is toxic to humans with negative health effects from acute and chronic exposure. Regulatory mandates have accelerated a global effort to replace hexavalent chromium-containing materials because of their toxicity. A consortium was established to evaluate safer conversion coating materials, including the chemical processing of the surfaces prior to applying the conversion coatings. Four conversion coatings without hexavalent chromium were compared against a hexavalent chromium-based conversion coating for the following tests: coating weight, electrical contact resistance, paint adhesion, bare and painted neutral salt fog corrosion tests, painted SO2 salt fog corrosion test, and painted outdoor beachfront corrosion test. The test results for the four conversion coatings without hexavalent chromium were encouraging since several candidates exceeded some of the specification requirements or consortium expectations. In particular, the Socosurf TCS/PACS conversion coating performed well in the coating weight, electrical contact resistance, paint adhesion, and corrosion tests. The results of this evaluation provide significant progress toward providing a replacement material for a traditionally hexavalent chromium material application on aluminum.

Welding studies on dissimilar magnesium alloys for improving corrosion behaviour

Dissimilar friction stir and tungsten inert gas between Magnesium alloys AZ31B and ZM21 plates with a thickness of 5 mm was performed. The friction stir welding tool is rotated at 2100 rpm under a constant transverse speed of 140 mm/min. A salt fog corrosion test is used to determine weldments' material losses and corrosion behavior in various zones using different welding processes for magnesium alloys like AZ31B and ZM21, which use friction stir welding (FSW) tungsten inert gas (TIG) welding. AZ31B weldment area is more susceptible to corrosion than ZM21. Both welds' macro and microstructures are analyzed to understand the metallurgical characteristics of the two different welds. Taguchi L9 orthogonal design improves process parameters for both the FSW and TIG welding processes. The rotating speed, tool shape, and axial load are the input process parameters for FSW, while the welding speed is kept constant. By single goal optimization, the maximum tensile strength of the dissimilar joints is 208 MPa. FSW welds of Dissimilar Magnesium alloys AZ31B and ZM21 were successfully manufactured with no defects.

Corrosion and wear resistant WC17Co-TC4 composite coatings with fully dense microstructure enabled by in-situ forging of the large-sized WC17Co particles in cold spray

Although cold spray is a potential alternative to produce high quality Ti-based coatings due to its low process temperature, the cold sprayed Ti or Ti-based alloys usually exhibit a porous microstructure and thus cannot provide effective corrosion protection for the substrate and behave poor wear resistance. In this work, an additional forging/hammering effect for the Ti alloy coatings was introduced by mixing large-sized WC17Co particles into TC4 powder. During spraying, the impact of the large-sized WC17Co particles could plastically deform the deposited TC4 particles and therefore in-situ densify the deposited TC4 coating layer. The embedded WC17Co particles would help to improve the wear resistance of the coating. The effect of WC17Co content in the feedstock powder on microstructure, corrosion and wear performance of the coatings was examined. The porosity of WC17Co-TC4 composite coatings was reduced from 16 % to below 0.5 %. The composite coatings possessed excellent corrosion protection to substrates and the 80 vol.% WC17Co-TC4 composite coating showed the best corrosion resistance. As compared with the pure TC4 coating, the corrosion rate was reduced by 100 times and no corrosion production was observed at coating/substrate interface even after 1000 h salt-fog corrosion test. An increasing trend was detected in wear resistance with the proportion of WC17Co in the feedstock. The 80 vol.% WC17Co coating performed 10 times wear resistance higher than the pure TC4 coating. It is attempted to provide a new approach to develop corrosion and wear resistant Ti and Ti alloy coatings by cold spray.

The durability of flexible eddy current array (FECA) sensors in harsh service environments

Sensors for structural health monitoring (SHM) need to be permanently integrated on structures and withstand the harsh service environments, which has been a big challenge for the application of SHM in aircrafts. This paper focuses on the durability of flexible eddy current array (FECA) sensors in harsh service environments of aircrafts, including vibration environment and several typical exposed environments. First, a kind of FECA sensor is illustrated and its integration method is proposed. Moreover, in order to study the durability of the sensor in vibration environment, the modal analysis is performed by the finite element method. According to the simulation results, the durability experiment in vibration environment is carried out under the fourth order vibration mode, which makes the sensor suffer the harshest vibration loads. During the vibration experiment, output signals of the sensor keep stable and the sensor is well bonded to the structure, which shows the integrated sensor has high durability in vibration environment. Finally, the durability of integrated sensors is separately tested in three exposed environments, including salt fog corrosion environment, fluid immersion environment, as well as hygrothermal and ultraviolet-radiation environment. After these environmental exposure experiments, all sensors are well bonded to structures and can effectively monitor fatigue cracks, which shows great durability. Therefore, FECA sensors can survive in harsh service environments of aircrafts, which provides important support for the engineering applications of FECA sensors.

Investigation on corrosion behavior of cryogenically treated friction stir welded AA5083

The aluminum alloy 5083 is widely used as a structural material in marine applications due to very good corrosion resistance and low temperature mechanical properties. Friction stir welding, being a solid state process, offers several benefits over the traditional fusion welding processes. In this study, 10 mm thick AA5083–H321 plates were successfully friction stir welded and the welds were investigated for corrosion behavior using salt fog corrosion tests. The friction stir welds exhibited more corrosion rate compared to that of the base material. However, the corrosion rate was observed to decrease with increase in time of exposure. The cryogenic treatment was found to improve corrosion resistance of the base material and the welds. Furthermore, the corrosion rate increases with decrease in pH value of the salt solution. By and large, it is determined that the cryogenic treatment advantageously effects the corrosion behavior

Seismic Behavior of Reinforced Concrete Frame Joints in Coastal Atmosphere

The study aims to research the influence of salt fog corrosion cycles on seismic performance of reinforced concrete (RC) frame beam‐column joints in coastal atmosphere. Based on low cyclic loading tests of six RC frame beam‐column joint specimens, this study analyses the failure patterns, hysteresis loops, load carrying capacity, displacement, backbone curves, and energy dissipation capacity of corrosion‐damaged RC frame beam‐column joints. The effect of salt fog corrosion cycles and axial compression ratios are tested repeatedly. The results show that with the same level of axial compression of the frame joint specimens, as the increase of salt fog cycles, the strength, ductility, energy dissipation, bearing capacity, and deformation capacity of joints degenerated to different degrees． When the corrosion level is the same, the stiffness degradation appeared to be more apparent as the increase of axial compression ratio. Then, the behavior degeneration rule of the RC frame beam‐column joints is analyzed and formed according to the results of the test; the degeneration restoring force models of corroded RC frame beam‐column joints is formed and verified based on Clough’s three‐line degenerate restoring force model and the introduction to cyclic degeneration index. The results show that the restoring force model can better describe the hysteresis characteristics of the beam‐column joints of corroded RC frames. The research is a theoretical reference for the seismic analysis of the RC frame structure affected by coastal atmospheric environment.

Salt-fog corrosion behavior of C/SiC and its effect on ablation resistance

Carbon fiber-reinforced silicon carbide (C/SiC) composites are significantly important candidates for thermal protection materials. The corrosion mechanism of C/SiC composite materials is the basis of their optimization and application. In this study, structural evolution of C/SiC composites fabricated by chemical vapor infiltration was investigated in the salt-fog storage environment. Furthermore, the effect of salt-fog on their ablation behaviors under oxyacetylene flame environment was studied. The ablation morphologies and corrosion mechanisms of C/SiC composites were analyzed and discussed. The results indicated that silica layer with size of c.a. 20 nm was formed on the surface of composite. The extent of corrosion in salt fog was limited, and it had little effect on the ablation behavior of the C/SiC composites, as well on the tensile strength and bending strength.

Use of a blast coating process to promote adhesion between aluminium surfaces for the automotive industry

ABSTRACTThe influence of surface roughness on adhesive bond strength for aluminium to aluminium bonding is investigated. firstly, the effect of varying surface roughness is investigated using grit-blast surface preparation. this is then compared to a novel ambient temperature blast coating technique known as coblast which, using a co-incident blast stream of abrasive and coating media, simultaneously removes a surface’s native passivation layer while depositing an active epoxy primer coating on the newly-exposed reactive metal surface. a range of al2o3 abrasive media with particle sizes from < 13 m to < 1200 m were used to prepare the varying surface roughness profiles. characterisation techniques such as surface profilometry, sem, edx, x-ray diffraction and light microscopy were used to investigate the level of coating coverage along with the degree of plastic deformation induced in the substrate as a result of the coating procedure. in addition, a modified lap shear test was conducted along with salt fog corrosion testing. results indicate that replacement of the grit-blast treatment with the epoxy coblast coating gives cohesive failure and an increase in lap shear strength of up to 15% before corrosion testing and up to 36% after 240 hours in a salt fog chamber.

Corrosion properties of low carbon steel prepared by submerged friction stir processing

Submerged friction stir processing (SFSP), that is, the entire process was carried out underwater, was successfully conducted on low carbon steel. The microstructure, electrochemical corrosion, and salt fog corrosion properties of SFSP low carbon steel were investigated. The results indicated that phase transformation and dynamic recrystallization occurred during SFSP and finally resulted in a dual phase fine grain microstructure in the processed zone (PZ), which consisted of ferrite and homogenous martensite phase. The grain size of ferrite was refined to 5.7 µm, and the width of martensite phase was 650 nm, respectively. In addition to changing the microstructure of low carbon steel, SFSP could also affect its corrosion property. SFSP samples exhibited better resistance against electrochemical corrosion and salt fog corrosion than BM samples. The reason was that, grain refinement and martensite formation induced by SFSP were conducive to forming dense protective layer, which effectively hindered the electrochemical corrosion and salt fog corrosion of the SFSP low carbon steel.

Kerosene-fuelled high velocity oxy-fuel (HVOF) spray of Ti2AlC MAX phase powders

Kerosene-fueled high velocity oxy-fuel (HVOF) spray was employed to deposit commercial Ti2AlC MAX phase powders onto Inconel 600 substrates. After optimizing three process parameters including flow rates of kerosene and oxygen as well as spray distance, a dense Ti2AlC coating with a very low decomposition was obtained. Using Rietveld phase analysis of the X-ray diffraction pattern, the weight percentage of Ti2AlC in the coating was determined to be 53.0%, which is not only far better than the coating deposited by plasma spray, but also is comparable with the optimum Ti2AlC coatings sprayed by H2-fueled HVOF and cold spray. This optimized Ti2AlC coating was further analyzed by a variety of techniques to probe its surface chemistry, morphology, cross-sectional microstructure, mechanical properties and salt fog corrosion resistance.

Single microcapsules containing epoxy healing agent used for development in the fabrication of cost efficient self-healing epoxy coating

Abstract In this study, to reduce the size significantly, a number of microcapsules were prepared to apply in situ encapsulation method with poly(urea-formaldehyde) (PUF) as the shell material and epoxy resin (EPL 1012 R ) as the core substance. Upon that, a systematic investigation was done on the properties of microcapsules affected by the synthesis procedure. In their optimum state, the synthesis parameters were concluded to exhibit the following properties: viscosity of oil phase of 15–25 (mPa.s), initial pH = 4, emulsifier of sodium dodecyl benzene sulfonate (SDBS) and 0.5 (wt.%) content for the emulsifier. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA) were applied to study morphology, chemical structure, mean size, size distribution and thermal properties of the resulting microcapsules. The morphological study showed the microcapsules prepared by SDBS (0.5 wt.%) are of spherical nature with few adhesions and the average diameter 2.13 (μm) for encapsulation of epoxy resin. The yield and core content for those microcapsules were determined 50 (wt.%) and 54 (wt.%), respectively. Investigating the microcapsules’ chemical structure revealed successful encapsulation of the epoxy resin in PUF shell and the results were confirmed by thermal analysis. Self-healing performance of the coatings containing epoxy-microcapsule was evaluated by salt fog corrosion test by ASTM B117 and eventually showed excellent corrosion resistance in scratched coatings confirming self-healing properties. Furthermore, electrochemical tests were employed for quantitative investigations of self-healing performance of the coating which confirmed the salt fog corrosion results.

Tribological Behavior of Aluminum Slurry Coating on 300M Steel

Al slurry coatings, an alternative of Cd coating to protect against corrosion in the aerospace industry, are currently being explored to satisfy the stringent technology and safety requirements for aeronautical applications. The results of salt fog corrosion exposure, fluid corrosion exposure (immersion), humidity resistance, electrical conductivity, galvanic corrosion, embrittlement, and fatigue indicate that Al slurry coatings can be used as an alternative of Cd coatings. However, the tribological property of Al slurry coatings has still not been investigated. Two types of aluminum slurry coatings on 300M steel were produced using the innovative technological process and characterized by scanning electron microscope, nanoindentation tests, and adhesion tests. The H/E and H 3/E 2 ratios of the two-layer Al slurry-coated sample were almost four times higher than the Cd-Ti plating-coated sample. The dry wear test results show that the friction coefficient of the two-layer Al slurry coating independently from the load was lower than the Cd-Ti plating. The width of the wear track of the two-layer Al slurry coating was significantly narrower, only 62% of the Cd-Ti plating wear scar. Compared to the Cd-Ti plating, an excellent wear resistance of the two-layer Al slurry coating can be attributed to its high resistance to plastic deformation and good load-bearing capacity. The results indicate that the two-layer Al slurry coating is an excellent alternative to Cd coatings in the aerospace industry.

Plasma spray of Ti2AlC MAX phase powders: Effects of process parameters on coatings' properties

Plasma spraying was employed to spray commercial Ti2AlC MAX phase powders onto Inconel 600 substrates. Effects of different process parameters, including arc current, flow rates of primary Ar, secondary H2 and carrier Ar, powder feedrate, spray distance as well as presence of cooling air on the backside on the substrate were systematically screened by evaluating the content of Ti2AlC in the coating through X-ray diffraction and Rietveld phase analysis. The highest content of the remaining Ti2AlC in the coating was achieved to be 26.0%. The coating with 26.0wt% of Ti2AlC was further analyzed by a variety of techniques to probe its surface chemistry, morphology, cross-sectional microstructure, mechanical properties and salt fog corrosion resistance.