Corrosion and Electrochemical Behavior of Zn-Cu-Ti Alloy Added with La in 3% NaOH Solution

The corrosion mechanism of Zn-Cu-Tialloy added with La in 3% NaOH solution was investigated by electrochemicaltesting and SEM observation.Polarization curves manifested that the overallcorrosion kinetics of alloys are under anodic control.The anodic passivation of the Zn-Cu-Tialloy is remarkably improved by the addition of La.Because La can effectively improve the hydrogen evolution/oxygen reduction over-potentialof alloy elements,and the rare earth oxide film plays an important role in insulation that can strengthen the dielectric properties of Zn-Cu-Tialloy,the corrosion resistance of Zn-Cu-Tialloy is made significantly better by adding a trace amount of La.The improvement of corrosion resistance is not positively correlated with the adding amount of La to alloy.The Zn-Cu-Ti-0.5La alloy displays the best corrosion resistance behavior.The corrosion form of the alloys mainly belongs to a selective corrosion and the main solid corrosion products are Zn（OH）_2 and ZnO.

Chi Phase after Short-term Aging and Corrosion Behavior in 2205 Duplex Stainless Steel

Correlation between pitting corrosion behavior and chi（ χ ）phase formed after a short-term aging（5,10 and 15 min）at 850 ℃ of 2205 duplex stainless steel（DSS）was investigated using potentiodynamic polarization tests,optical microscopy,and scanning electron microscopy equipped with energy-dispersive spectrum system.Results showed that after aging for 5min,the χ phase initially precipitated at ferrite grain boundaries,developed and then became linked with prolonging aging time.The χ phase was rich in Cr and Mo,resulting in formation of depleted zones nearby.The χ phase could reduce corrosion resistance of DSS and slightly influence its stability,but the specimens still displayed the capacity for repassivation.Some lines of evidence showed that stable pitting corrosion initiated at the boundaries of precipitates.The χ phase was selectively corroded during the first stage of corrosion and then the depleted zones nearby were attacked.In addition,the grain size and volume of precipitates also affected pit nucleation and progress,and suitable size and distribution of χ phase could aggravate pit initiation at precipitate boundaries.The χ phase with considerably low volume fraction and small size was not sensitive position for pit initiation.

Enhancing mechanical properties and corrosion resistance of nickel-aluminum bronze via hot rolling process

The mechanical properties and corrosion behavior of as-cast, as-annealed and hot-rolled nickelaluminum bronze(NAB) alloy(Cu-9 Al-10 Ni-4 Fe-1.2 Mn, all in wt.%) in 3.5 wt.% Na Cl solution were investigated. The results show that annealing introduces a large number of k phases to precipitate in the k phase. However, after further hot rolling, the original continuous k phases are spheroidized and dispersed, increasing the strength, hardness, and elongation of the alloy. In addition to the enhanced mechanical properties, the corrosion resistance of the NAB samples is also improved significantly by hot rolling, as revealed by the mass loss measurements, electrochemical impedance spectroscopy(EIS), and cross-sectional corrosion morphology. Selective phase corrosion occurs by the preferential corrosion of the k phase, which acts as an anode to the k phases, and the uncorroded k phases are retained in the corrosion product film. The interfaces between the k phases and the surrounding corrosion products become discontinuous caused by the spheroidization of k phases, reducing the corrosion of the substrate by the corrosive medium via the channels. As a result, the corrosion rate and the maximum local corrosion depth of the hot-rolled NAB sample are greatly reduced.

Selection and Characterization for Corrosion Control

In a recent study by the National Association of Corrosion Engineers （NACE）, the global cost of corrosion was estimated to be US$ 2.5 trillion, equivalent to 3.4% of the global Gross Domestic Product [htto：//imtacact.nace.org/]. The prevention practices could save between study found that implementing the best corrosion 15%-35% of the cost of damage. One of the important measures to reduce the corrosion damage is using an appropriate material. Selection of a suitable material according to corrosivity of the service environment is essentially important in battle against industrial corrosion. Corrosion detection, damage characterization and surface analysis are critical approaches to fundamental understanding of the root cause and detailed mechanism of corrosion. They lay a foundation for prevention and mitigation of material corrosion in service environments. A technical breakthrough in these fields may result in significantly widened applications of traditional and emerging materials.