Initial micro-galvanic corrosion behavior between Mg_(2)Ca and α-Mg via quasi-in situ SEM approach and first-principles calculation

The initial micro-galvanic corrosion behavior of Mg-30wt%Ca alloy only containing Mg_(2)Ca andα-Mg was studied by immersion testing in a 0.9%Na Cl solution at 37°C.The quasi-in situ SEM and TEM results show that Mg_(2)Ca corroded easier thanα-Mg,indicating that Mg_(2)Ca acted as an anode.The work function(Φ)for Mg_(2)Ca calculated by first-principles is significantly lower compared to that forα-Mg.The Volta potential measured by a scanning Kelvin probe force microscope reveals that the Mg_(2)Ca had a relatively low Volta potential(ψ)value.The lowerΦandψvalues for Mg_(2)Ca indicate a lower electrochemical nobility,which is consistent with the experimental phenomenon.

Galvanic corrosion of AZ31B joined to dual-phase steel with and without Zn layer by ultrasonic and friction stir welding

Galvanic corrosion of AZ31B joined with bare or Zn-coated DP590 steel by ultrasonic spot welding or linear friction stir welding was quantitatively studied by pre-defining anode and cathode in the lap joint samples. Corrosion volume and depth from Mg anode surfaces exposed to 0.1 M sodium chloride solution was analyzed as functions of cathode surface type and welding method. Characterization of as-welded joints was performed to identify any microstructural feature of the bonding zone that could impact galvanic corrosion behavior.COMSOL modeling with modified user subroutine was conducted to simulate the progression of Mg corrosion in the same joint and electrode configurations used for the corrosion experiments. The experimental results indicated that Zn-coated cathode surface can reduce Mg galvanic corrosion significantly as galvanic polarization and cathodic current on Zn-coated surface remained relatively low for Mg in the weld joints.COMSOL modeling described the growth of Mg galvanic corrosion in a reasonable manner but showed limitation by underestimating the corrosion volume as it did not capture self-corrosion.

Boundary Element Method (BEM) Analysis for Galvanic Corrosion of Hot Dip Galvanized Steel Immersed in Seawater

A numerical analysis of galvanic corrosion of hot-dip galvanized steel immersed in seawater was presented. The analysis was based on the boundary element methods （BEMs） coupled with Newton-Raphson iterative technique to treat the nonlinear boundary conditions, which were determined by the experimental polarization curves. Results showed that galvanic current density concentrates on the boundary of steel substrate and zinc coating, and the sacrificial protection of zinc coating to steel substrate results in overprotection of steel cathode. Not only oxygen reduction but also hydrogen reduction could occur as cathode reactions, which probably led up to the adsorption and absorption of hydrogen atoms. Flat galvanized steel tensile sample shows a brittle behavior similar to hydrogen embrittlement according to the SSRT （show strain rate test） in seawater.

GALVANIC CORROSION AND PROTECTION OF GECM/LY12CZ COUPLES UNDER DIFFERENT ATMOSPHERIC EXPOSURE CONDITIONS

Galvanic, compatibility between graphite epoxy composite materials (GECM) and LY12CZ aluminum alloy was evaluated in different atmospheric corrosion environments and by laboratory electrochemical measurements. Open circuit potential electrochemical measurements showed a relatively large potential difference about 1 volt between the GECM and LY12CZ aluminum alloy, and this difference provided the driving force for galvanic corrosion of the LY12CZ aluminum alloy as an anode. Having been exposed for 1, 3 or 5 years in Beijing, Tuandao and Wanning station, GECM/LY12CZ couples showed significant losses of strength and elongation. Protective coatings and non-conductive barriers breaking the galvanic corrosion circuit were evaluated under the same atmospheric corrosive conditions. Epoxy primer paint, glass cloth barriers and LY12CZ anodizing were effective in galvanic corrosion control for GECM/LY12CZ couples.

Galvanic Corrosion Behaviour of HE 20 / MDN 138 ＆ HE 20 /MDN 250 Alloys in Natural Seawater

In view of their excellent mechanical properties, workability and heat treatment characteristics, MDN 138 & MDN 250 have been widely used in missile, rocket and aerospace industries. With light weight and high performance characteristics HE 20 aluminium alloy acts as an important material in defence and aerospace applications. The galvanic corrosion behaviour of the metal combinations HE 20 / MDN 138 and HE 20 / MDN 250, with 1:1 area ratio, has been studied in natural seawater using the open well facility of CECRI's Offshore Platform at Tuticorin for a year. The open circuit potentials of MDN 138, MDN 250 and HE 20 of the individual metal, the mixed potential and galvanic current of the couples HE 20 / MDN 138 and HE 20 / MDN 250 were periodically monitored throughout the study period. The calcareous deposits on MDN 138 and MDN 250 were analysed using XRD. The results of the study reveal that that HE 20 has offered required amount of protection to MDN 138 & MDN 250.

Multi-physics analysis of the galvanic corrosion of Mg-steel couple under the influence of time-dependent anisotropic deposition film

The anisotropic deposit film formed during the galvanic corrosion can impede the mass transfer of the involved species,thereby affecting the electro-chemical behavior and the evolution of galvanic corrosion.The limitations of experimental studies in the spatial-temporal scales restrict a deeper understanding of the corrosion mechanism,which can be complemented by numerical simulation.A multi-physics coupled model is proposed in this work to systematically investigate the temporal and spatial evolution of galvanic corrosion of the Mg-steel couple with the growing anisotropic deposition layer.By utilizing the multi-physics field coupled technique,various coupled physical-chemical processes underlying the corrosion behavior are built into the model,including chemical reactions,ionic mass transfer in the bulk solution and the deposition layer,interfacial reaction,deposition of corrosion products as well as the morphological transitions caused by metal dissolution and deposition.In particular,the anisotropic deposit film is considered to be a porous layer with a porosity varying in time and space as the corrosion evolves.The predicted corrosion morphology by this model is better than the previous models.The coupled relationship between the electrochemical behavior(e.g.,electrode reaction kinetics,current density,surface potential)and the physical processes(e.g.,ionic transport,geometric evolution of metal surface and film interface)is revealed.The results indicate that a porous deposition layer with a denser inner layer and a loose outer layer is generated,leading to more significant inhibition of mass transfer in the inner layer than the outer layer.The anisotropism of the deposition layer results in a non-uniform conductivity distribution and a discontinuous current density distribution in the electrolyte.The current density on the electrode surface is inhibited by the deposition layer and the variation in the cathode/anode area ratio during the corrosion process.The competition between the transport process and the electrochemical reaction determines the spatial-temporal evolution of the ion concentration.

Galvanic Corrosion of Magnesium Alloy and Aluminum Alloy by Kelvin Probe

Galvanic corrosion on samples of AZ91D magnesium alloy coupled with 2A12 aluminum alloy during neutral salt spray test was investigated.The variations of the surface potential were measured using scanning kelvin probe（SKP）.The results showed that galvanic effect on the corrosion of AZ91D magnesium alloy is closely related to the potential difference between the anodic and cathodic materials.In the initial period,corrosion only occurred in a narrow area at the coupling interface because of the limited distance galvanic current.Then,the corrosion rate of 2A12 aluminum alloy was accelerated due to its poor stability in strong alkali environment,which was attributed to the strong alkalization caused by the corrosion of AZ91D magnesium alloy.With the increase of the potential of 2A12 aluminum alloy as a result of the continuous covering of corrosion products,the potential difference between the two materials was enlarged,which enhanced the galvanic corrosion.

Galvanic corrosion behavior of die cast AZ91D magnesium alloy in chloride solution

: The galvanic corrosion behavior of die cast AZ91D magnesium alloy coupled with H62 brass, 316L stainless steel, A3 steel and LY12 aluminum alloy of different areas in 3.5% NaCl solution was studied. The free corrosion potentials, galvanic potentials and currents of these galvanic couples were measured. The galvanic effects were determined by the mass loss and regression method using three points. The results show that: (1) In these four kinds of couples AZ91D acts as the anode, whose galvanic corrosion behavior is mainly controlled by the cathodic polarization; (2) The free corrosion potentials of these four kinds of couples change a little with time and cathodic/anodic area ratio (CAAR); (3) The galvanic potential of AZ91D/LY12 moves positively with the increase of time and CAAR; (4) The galvanic currents increase with CAAR, but there is difference in the current change between different couples; (5) The anodic dissolution rate of the magnesium alloy increases by 2-3 orders after being coupled with these four kinds of metals and the galvanic effects of these couples have such a relation as γH62> γ316L.S.S>γLY12>γA3.

Computational design of Mg alloys with minimal galvanic corrosion

Formation of galvanic cells between constituent phases is largely responsible for corrosion in Mg-based alloys.We develop a methodology to calculate the electrochemical potentials of intermetallic compounds and alloys using a simple model based on the Born-Haber cycle.Calculated electrochemical potentials are used to predict and control the formation of galvanic cells and minimize corrosion.We demonstrate the applicability of our model by minimizing galvanic corrosion in Mg-3wt%Sr-x Zn alloy by tailoring the Zn composition.The methodology proposed in this work is applicable for any general alloy system and will facilitate efficient design of corrosion resistant alloys.

Study of galvanic corrosion and mechanical joint properties of AZ31B and carbon-fiber–reinforced polymer joined by friction self-piercing riveting

A new testing methodology was developed to quantitively study galvanic corrosion of AZ31B and thermoset carbon-fiber–reinforced polymer spot-joined by a friction self-piercing riveting process.Pre-defined areas of AZ31B in the joint were exposed in 0.1 M NaCl solution over time.Massive galvanic corrosion of AZ31B was observed as exposure time increased.The measured volume loss was converted into corrosion current that was at least 48 times greater than the corrosion current of AZ31B without galvanic coupling.Ninety percent of the mechanical joint integrity was retained for corroded F-SPR joints to 200 h and then decreased because of the massive volume loss of AZ31B。

Effect of 1,2,4-triazole on galvanic corrosion between cobalt and copper in CMP based alkaline slurry

Cobalt has become a new type of barrier material with its unique advantages since the copper-interconnects in the great-large scale integrated circuits （GLSI） into 10 nm and below technical nodes, but cobalt and copper have severe galvanic corrosion during chemical-mechanical flattening. The effect of 1,2,4-triazole on Co/Cu galvanic corrosion in alkaline slurry and the control of rate selectivity of copper and cobalt were investigated in this work. The results of electrochemical experiments and polishing experiments had indicated that a certain concentration of 1,2,4-triazole could form a layer of insoluble and dense passive film on the surface of cobalt and cop- per, which reduced the corrosion potential difference between cobalt and copper. Meantime, the removal rate of cobalt and copper could be effectively controlled according to demand during the CMP process. When the study optimized slurry was composed of 0.5 wt% colloidal silica, 0.1%vol. hydrogen peroxide, 0.05 wt% FA/O, 345 ppm 1,2,4-triazole, cobalt had higher corrosion potential than copper and the galvanic corrosion could be reduced effectively when the corrosion potential difference between them decreased to 1 mV and the galvanic corrosion current density reached 0.02 nA/cm2. Meanwhile, the removal rate of Co was 62.396 nm/min, the removal rate of Cu was 47.328 nm/min, so that the removal rate ratio of cobalt and copper was 1.32 ： 1, which was a good amendment to the dishing pits. The contact potential corrosion of Co/Cu was very weak, which could be better for meeting the requirements of the barrier CMP.

Microstructure induced galvanic corrosion evolution of SAC305 solder alloys in simulated marine atmosphere

Motivated by the increasing use of Sn-3.0 Ag-0.5 Cu(SAC305)solder in electronics worked in marine atmospheric environment and the uneven distribution of Ag3Sn and Cu6Sn5 intermetallic compounds(IMCs)inβ-Sn matrix,comb-like electrodes have been designed for in-situ EIS measurements to study the microstructure induced galvanic corrosion evolution of SAC305 solder in simulated marine atmosphere with high-temperature and high-humidity.Results indicate that in-situ EIS measurement by comb-like electrodes is an effective method for corrosion evolution behavior study of SAC305 solder.Besides,the galvanic effect between Ag3Sn IMCs andβ-Sn matrix can aggravate the corrosion of both as-received and furnace-cooled SAC305 solder as the exposure time proceeds in spite of the presence of corrosion product layer.Pitting corrosion can be preferentially found on furnace-cooled SAC305 with larger Ag3Sn grain size.Moreover,the generated inner stress during phases transformation process with Sn3O(OH)2Cl2 as an intermediate and the possible hydrogen evolution at local acidified sites are supposed to be responsible for the loose,porous,cracked,and non-adherent corrosion product layer.These findings clearly demonstrate the corrosion acceleration behavior and mechanism of SAC305 solder,and provide potential guidelines on maintenance of microelectronic devices for safe operation and longer in-service duration.

A new method to determine the synergistic effects of area ratio and microstructure on the galvanic corrosion of LAS A508/309 L/308 L SS dissimilar metals weld

The synergistic effects of area ratio and microstructure on the galvanic corrosion of A508/309 L/308 L dissimilar metals weld(DMW)are studied by a multi-analytical approach.It was demonstrated that decreasing the anode/cathode surface area ratio obviously enhances the corrosion rate of A508,both locally and globally.Deeper analyses of the AFM results enabled quantitative comparison of the corrosion behaviour of the different surface constituents.It was revealed that in the galvanic interaction of the DMW,the grain refined region corrodes most,followed by the partial grain refined region and base metal matrix of the A508,respectively.The electrochemical localization index(LI)estimation method and AFM analysis both confirmed the presence of a mixed(localized and uniform)corrosion phenomenon occurring on the surface of the A508 anode metal in the galvanic interaction of the dissimilar metals.Finally,the degree of synergism equation was utilized to describe the synergistic effects of anode/cathode area ratio and the microstructure of the samples on the galvanic corrosion of LAS A508/309 L/308 L SS DMW.

Electrolyte composition and galvanic corrosion for ruthenium/copper electrochemical mechanical polishing

Electrochemical mechanical polishing(ECMP)is a new and highly promising technology.A specific challenge for integrating Ru as barrier in Cu interconnect structures is the galvanic corrosion of Cu that occurs during ECMP.To mitigate the problem,the benzotriazole(BTA)and ascorbic acid(AA)were chosen as selective anodic and cathodic inhibitors for Cu and Ru,respectively.The optimization of electrolytes at different pHs including BTA,hydroxyethylidenediphosphoric acid(HEDP),and AA were investigated using electrochemical methods.The Ru/Cu removal rate and the planarization efficiency during Ru/Cu ECMP can be approximated using electrochemical measurements of the removal rate,with and without surface abrasion.Chemical systems that exhibit a 1:1 selectivity between the barrier layer and copper would be ideal for the barrier removal step of ECMP.Optimized slurry consists of 20.0 wt%HEDP,0.5 wt%BTA,and 0.3 wt%AA at pH 2.2.Using the optimized slurry,the selectivity of Ru to Cu is near 1.Electrochemical measurements of open circuit potentials,potentiodynamic polarization,and impedance spectroscopy were performed to investigate the galvanic corrosion between ruthenium and copper.

Effects of Electroplated Coatings on Corrosion Behavior of Ti-1023/30CrMnSiA Galvanic Couple

Galvanic corrosion behavior of Ti-1023 titanium alloy coupled 30CrMnSiA steel was investigated in 3.5% NaCl solution. Particular attention was given to the effect of three different electroplated coatings on corrosion behavior of the galvanic couple. Galvanic corrosion test was conducted on Ti-1023 titanium alloy which coupled Ni-electroplated 30CrMnSiA, Zn-electroplated 30CrMnSiA, Cd-electroplated 30CrMnSiA and bare 30CrMnSiA, respectively. Corrosion properties including open circuit potential （Eoc）, galvanic corrosion potential （Eg）, and galvanic corrosion current （lg） were monitored. Corrosion morphology was observed by optical microscope （OM） and corrosion mechanism was analyzed and discussed. The results show that the three electroplated coatings improve the corrosion resistance of the anode in different magnitudes. Ni-electroplated 30CrMnSiA and Cd-electroplated 30CrMnSiA coatings are found to be least susceptible to galvanic corrosion when coupled Ti-1023 titanium alloy. Zn-electroplated 30CrMnSiA is moderately susceptible to galvanic corrosion. But the bare 30CrMnSiA is highly susceptible to galvanic corrosion in corrosive environment.

GALVANIC CORROSION BETWEEN GRAPHITE EPOXY COMPOSITE MATERIALS AND LY12CZ ALUMINUM ALLOY

The electrochemical approach was used to show the nature of the galvanic corrosion when graphite epoxy composite materials(GECM)were coupled to LY12CZ aluminum alloy. An open circuit potential difference of one volt was obtained in 3.5% NaCl solution between GECM and LY12CZ. Corrosion current data (zero impedance technique) indicated that there was serious corrosion at GECM/LY12CZ couple.When GECM/LY12CZ couples were exposed to ASTM salt spray and alternate immersion condition, fiber glass cloth and H06-2 epoxy primer paint were effective methods for preventing galvanic corrosion.The slow strain rate test (SSRT) showed that GECM increased the LY12CZ stress corrosion crack growth rate.

Inhibition of galvanic corrosion in Al/Cu coupling model by synergistic combination of 3-Amino-1,2,4-triazole-5-thiol and cerium chloride

Asynergistic inhibition study was carried out on an aluminium/copper galvanic coupling model in neutral aerated NaCl solution using scanning vibrating electrode technique(SVET).The approach allows the simulation of the local micro-galvanic cells of AA2024-T3 obtained from the potential difference between the intermetallic particles(IMPs)and the aluminium matrix.The inhibition effect of CeCl3 and 3-Amino-1,2,4-triazole-5-thiol(ATAT)was demonstrated by the reduction in the galvanic current density over Al and Cu surfaces.An improved inhibition from positive synergistic effect was revealed by the combination of the two inhibitors after 24 h of immersion,with the best inhibition recorded for Ce1.5ATAT3.5.Scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS)and time of flight secondary ion mass spectrometry(ToF-SIMS)were used to characterize the Ce-and ATAT-based complex film formed and to illustrate the mechanism of inhibition.

The effect of secondary phase on corrosion behaviors of the titanium–zirconium–molybdenum alloy

As the range of applications for molybdenum and its alloys has expanded,the corrosive environment for molybdenum alloys has become more demanding.In the past,the content of doping elements has been studied to investigate their infl uence on the corrosion performance of titanium–zirconium–molybdenum(TZM)alloys.In this paper,it is considered that the second phase in the alloy is the main factor aff ecting the corrosion performance of TZM alloys.By comparing the corrosion behavior of molybdenum metal and TZM alloy,the eff ect of the secondary phase on corrosion behaviors of TZM alloy has been investigated.The results show that the second phase reduces the corrosion resistance of the TZM alloy.The potential of the second phase is 73.7 mV higher than that of the Mo matrix,which contributes to the formation of microscopic electric couples.Under the action of microscopic electric couples,pitting corrosion is preferentially formed at the interface between the second phase and the matrix,which accelerates the corrosion of the matrix.This paper provides a theoretical basis for the application of TZM alloys in corrosive environments.

Construction of Fe/Ag galvanic couple by mechanochemical in-situ reduced Ag to accelerate the degradation of Fe-based implant

Orthopedic applications of Fe have been hindered by the insufficient degradation rate.Alloying with noble elements(such as Ag,Au,and Pt)to generate galvanic couples is a feasible approach.However,the direct preparation of homogenous alloys by mechanical alloying or metallurgy is difficult because of the differences in strength,density,and toughness.In this study,Ag_(2)O was selected as the precursor phase for incorporation into Fe to achieve a homogeneous distribution of Ag,which was then reduced in situ to Ag via a mechanochemical reduction reaction during mechanical alloying.The composite powders were printed as implants by selective laser melting,where a fast cooling rate contributed to the retention of the phase distribution of the obtained powder.The electrochemical tests showed that the Fe-Ag_(2)O implant had a high corrosion current density(21.88±0.12μA/cm^(2))and instantaneous corrosion rate(0.23±0.05 mm/year).Moreover,the implant exhibited a faster degradation rate(0.22 mm/year)than Fe(0.15 mm/year)and Fe-Ag(0.21 mm/year)after immersion for 28 d.The acceleration mechanism of the implant could be attributed to the uniformly distributed Ag particles triggering many galvanic couples with the Fe grains,which was confirmed by the observation of the corrosion surface.In addition,the composite implants exhibited good biocompatibility and antibacterial properties.

Fatigue Crack Arrest in Mild Steel via Iron Electroplating

In this work, electrochemical plating treatments were applied to ASTM A36 steel specimens to study the efficiency and limitations of this method for arresting fatigue crack propagation. Electroplated iron was deposited onto the crack surfaces using a circuit in which Swedish Iron served as the anode in a solution of Ammonium Iron(II) Sulfate Hexahydrate. The iron ions were driven into fatigue cracks that were formed within ASTM E399 compact tension specimens. This work showed that an iron-plating treatment operated at 20°C can arrest fatigue crack propagation for a significant period of cycles. The propagation re-initiation lives that resulted ranged from 11,000 to 230,000 cycles. As observed in prior work, the propagation re-initiation life correlated strongly to the magnitude of the stress intensity factor range that was applied during cycling. As this stress intensity increased, the propagation re-initiation life decreased. Repeated treatments on the same crack provided extended service lives by as much as 370,000 cycles or 60% of the entire fatigue life of the component. Future work may show that re-application of the treatment, when conducted prior to crack re-initiation, could further extend the service life indefinitely. The Correia crack closure model was modified to provide an empirical expression for predicting the crack re-initiation life of the treated component. Interestingly, highly effective arrest behavior was still observed for cracks that were loaded to stress intensity factors of only 3 - 6 <img src="Edit_f69af9cd-e908-4aef-8ccb-3b1f36e16d08.png" alt="" />during the treatment but then subjected to 20 <img src="Edit_5ddb9cae-23ad-442d-8e6c-63b5e1d99a0f.png" alt="" /> during cyclic loading. Galvanic corrosion of the plated material exposed to simulated seawater was estimated to be 3 mpy. Future work will examine the use of less active plating alloys and the possibility of applying effective treatments into cracks that are in an unloaded state.