Influence of ammonium sulfate on the corrosion behavior of AZ31 magnesium alloy in chloride environment

Electrochemical corrosion of AZ31 magnesium alloy in the NH_(4)^(+)-SO_(4)2−-Cl−environment is studied.Effect of NH_(4)^(+)overshadows that of Cl−as the(NH_(4))_(2)SO_(4) concentration is 0.005 M or higher,yielding an evolution from localized corrosion to uniform corrosion.Acceleration effect of NH_(4)^(+)can be attributed to that(i)NH_(4)^(+)dissolves the inner MgO and hinders the precipitation of Mg(OH)_(2) and(ii)the buffering ability of NH_(4)^(+)provides H+,enhances the hydrogen evolution,and expedites the corrosion process.The latter is demonstrated as the dominant factor with the results in unbuffered and buffered environments.The severe corrosion and hydrogen process in NH_(4)^(+)-containing solution results in a high Hads coverage and yields an inductive loop within the low frequency.Meanwhile,SO_(4)^(2−)is helpful in generating cracked but partially protective corrosion products,while Cl−could broaden the corrosion area beneath the corrosion product.

Structural Design Study of Air-Dropped Unmanned Maritime Mobile Search and Rescue Platforms

In order to improve the efficiency and safety of search and rescue(SAR)at sea,this paper proposes a kind of emergency rapid rescue unmanned craft(air-dropped unmanned maritime motorized search and rescue platform)that can be delivered by a large transport aircraft.This paper studies the structural design scheme of the platform,and the main scale of the platform,the choice of power system and the impact resistance performance are considered in the design process to ensure its rapid response and effective rescue capability under complex sea conditions.Simulation results show that the platform can withstand the impact of air injection into the water and the shipboard equipment can operate normally under the impact load,thus verifying the feasibility and safety of the design.This study serves to improve the maritime search and rescue system and enhance the oceanic emergency response capability.

Roles of pH in the NH_(4)^(+)-induced corrosion of AZ31 magnesium alloy in chloride environment

Corrosion behavior of AZ31 magnesium alloy in NH_(4)^(+)-bearing chloride solution with controlled pH was investigated by weight loss experiment, hydrogen collection, and electrochemical test combined with surface morphology and topography observation. The results show that NH_(4)^(+) and pH of the solution can affect the corrosion of AZ31 magnesium alloy. The existence of NH4+affects the formation and dissolution of corrosion products, which makes the protective effect of the corrosion product layer weaker. The change of pH value not only affects the corrosion mechanism of AZ31, but also alters the concentration of NH_(4)^(+) ions in the solution, which further influences the corrosion product layer of AZ31, and finally makes the corrosion of AZ31 change significantly.

Understanding stress corrosion cracking behavior of 7085-T7651 aluminum alloy in polluted atmosphere

The electrochemical and Stress Corrosion Cracking(SCC)behaviors of 7085-T7651 aluminum alloy in different environments are studied by electrochemical and mechanical testing.The research shows that the type,concentration of the corrosive medium and electrolyte state affect the electrochemical and SCC controlling processes of aluminum alloys.The Thin Electrolyte Layer(TEL)state and the addition of HSO3–increase the corrosion rate and SCC susceptibility.The presence of HSO3–in a corrosive environment can significantly accelerate the corrosion rate and mechanical property degradation,and this effect increases with the increase of HSO3–concentration.Compared with the solution environment,the TEL environment will further aggravate corrosion and mechanical property degradation.With the increase of HSO3–concentration,the pH of the corrosive environment exhibits little change,while the SCC degradation is significantly promoted.This is attributed to the HSO3–induced buffer effect and film-assisted stress effect,yielding the overshadowing effect against solution pH.

The effect of crack tip environment on crack growth behaviour of a low alloy steel at cathodic potentials in artificial seawater

The environment at crack tip and its effect on the crack growth behaviour of low alloy steel-E690 steel were studied at cathodic potentials in artificial seawater.The results showed that the micro environment at crack tip and crack growth behaviour were related to the electrochemical reactions at crack tip,which were affected by the stress state and applied potentials.The crack tip environment was acidified under cyclic loading,resulting from the crack tip anodic dissolution reaction and corresponding hydrolysis reaction.Because of the hydrogen evolution and the inhibited anodic dissolution inside the crack,the crack tip p H increases as the cathodic potential decreases.The effect of cathodic potentials on the electrochemical reactions caused the variation of the hydrogen content,which influenced the crack growth rate because the crack growth behaviour was controlled by hydrogen embrittlement mechanism.This resulted in a fact that with the negative decrease of potential,the crack growth rate first decreased and then increased,with the minimum rate at-0.75 V.And the crack growth path exhibited transgranular fracture.

New insights into the mechanism of localised corrosion induced by TiN-containing inclusions in high strength low alloy steel

This work investigated the chemical and electrochemical mechanisms of localised corrosion triggered by CaS·xMgO·y Al_(2)O_(3)·TiN complex inclusions in high strength low alloy steel(HSLAS)under a simulated marine environment.Special focus was given to the role of the TiN portion of the inclusion on the initiation and growth of the corrosion pits.The thermodynamic process of pitting initiation was investigated by Gibbs free energy,Pourbaix diagram and first principle calculation.Localised corrosion is mainly induced by inclusions and triggered by dissolution of adjacent distorted matrix.Chemical dissolution of CaS portion in CaS·xMgO·y Al_(2)O_(3)·TiN complex inclusion creates an acidic aggressive environment that accelerates the further dissolution of inclusion and matrix.Galvanic coupling effect between TiN inclusion and matrix is directly verified.TiN covered with a TiOfilm acts as the cathodic phase in galvanic corrosion,although it has a lower Volta potential than the matrix.This is an unusual correlation with the scanning Kelvin probe force microscopy result,which has been explained for this special system.

Mechanistic study of ammonium-induced corrosion of AZ31 magnesium alloy in sulfate solution

The influence of NH4+ions on the corrosion behavior of AZ31 magnesium alloy was investigated by immersion test,hydrogen evolution,electrochemical methods and morphology observation.The results demonstrate the acceleration effect of NH4+on corrosion of AZ31 magnesium alloy due to the disruption of protective MgO film in NH4+-containing solution.The loose and cracked corrosion products of AZ31 magnesium alloy in NH4+-containing solutions are mainly composed of(Mg0.833Al0.167)(OH)2(CO3)0.083·0.75H2O and Mg5(CO3)4(OH)2·5H2O.When the NH4+concentration is lower than 0.01 M,knife-cut like corrosion occurs in some active area of the surface due to the partial dissolution of MgO layer.As the NH4+concentration is increased to 0.1 M,the MgO layer is completely disrupted,resulting in the occurrence of uniform corrosion.Both cathodic and anodic reactions are accelerated by NH4+ions,while the effect of original pH values on the reaction kinetics can be neglected in NH4+-containing solutions.

Corrosion Evolution of High-Strength Aluminum Alloys in the Simulated Service Environment of Amphibious Aircraft in the Presence of Chloride and Bisulfite

The corrosion evolution of 2024-T351 and 7075-T651 aluminum alloys in the thin electrolyte layer(TEL)and wet-dry alternating cycle(WDAC)environment is studied in this work.The results show that in the TEL environment,the competitive effect between H+that accelerates corrosion reactions and deposition of aluminum sulfate that impedes corrosion attacks exists during the corrosion exposure.The difference is that with increasing HSO_(3)^(-),subsurface intergranular corrosion on 2024-T351 is promoted to form exfoliation corrosion eventually and the degree of exfoliation corrosion begins to decrease because the blocking effect of aluminum sulfate exceeds the expediting effect of H+.For 7075-T651,the corrosion area and the corrosion diameter decrease gradually,which is attributed to the HSO_(3)^(-)-enhanced deposition of corrosion products and their blocking effect.In the WDAC environment,the corrosion processes of 2024-T351 and 7075-T651 are the acidic dissolution of the matrix during the soaking phase.When the HSO_(3)^(-)concentration is high enough(0.1 M),the inhibiting effect of aluminum sulfate becomes the dominant factor.