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Hot-dip galvanized panels of low-carbon (LC) and interstitial-free (IF) steels were produced in a laboratory simulator with an average coating mass of 60 g/m 2 . Three pot aluminum levels were used, viz., 0.10 pct (by wt), 0.15 pct, and 0.18 pct. Metallography, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize coating and base steel microstructures. Wet chemical analysis and scanning transmission electron microscopy (STEM) were employed for compositional analyses. The aluminum content of the melt was found to be the predominant factor influencing the distribution of Al in the coating. At 0.18 pct melt aluminum, Al is partitioned between the aluminide inhibition layer at the coating-steel interface (ϳ80 pct) and the zinc overlay (ϳ20 pct). At 0.15 pct, it is partitioned among the aluminide layer (ϳ75 pct to 80 pct), zinc-iron (FeZn 13 , ) intermetallic layer (ϳ5 pct to 15 pct), and the coating overlay (ϳ10 pct). At 0.10 pct, the aluminum is divided almost equally between the overlay and the zinc-iron intermetallics. At the two lower aluminum levels is the distribution marginally influenced by the steel grade. The was found to not preferentially nucleate at the ferrite grain boundaries. When both the aluminide and occurred at the coating-steel interface, the particles appeared near discontinuities and thinner regions in the aluminide layer. The coating, relative to the melt, is enriched in aluminum because of its concentration in the aluminide and in the zinc-iron intermetallics. This enrichment increases with melt aluminum through an increase in the aluminum content of the aluminide layer and not of its thickness. In addition, a few tens-of-nanometers-thick layer enriched in aluminum, oxygen, and iron is observed on the outer surface of all coatings. The aluminum content in this layer also increases with an increase in the melt aluminum, but it contributes negligibly to the coating's content because of its extreme thinness.

A major consideration in autobody application of coated sheets is paint performance on electrogalvanized coatings. This paper describes a study in which a number of electrogalvanized coatings, including Zn, 9%Ni-Zn, 13%Ni-Zn, and 18%Fe-Zn, were characterized for composition, structure, and phosphatability and compared for paint performance in accelerated corrosion tests. Metallographic examination and microanalysis of scribe cross sections were conducted to understand the mechanisms of cosmetic corrosion. Results indicate that paint creep-back is determined by two interrelated factors, namely, (1) anodic dissolution of the coating and (2) metal coating/e-coat interfacial failure. The relative importance of these factors in relation to test conditions and the coating characteristics is examined, and approaches to improve cosmetic corrosion performance of electrogalvanized coatings are discussed.sentative materials from the zinc alloy group, namely, 9%Ni-Zn, 13%Ni-Zn, and 18%Fe-Zn coatings were also inciuded in the study.

Effect of specimen orientation, heat treatment and applied potential on the stress corrosion susceptibility of magnesium AZ61 (Mg‐6.3% Al‐0.5% Zn‐0.20% Mn) alloy in an aqueous 3.5% NaCl + 2% K2CrO4 solution at room temperature was investigated. Stress corrosion times to failure were measured at different values of initial stress intensities using single edge (pre) cracked sheet tensile specimens and a modified tensometer. It was observed that while the specimen orientation has a significant effect on the measured values of stress corrosion threshold stress intensity, KIscc, the effect of varying the quench rate during heat treatment was minimal. Polarization measurements both in stressed and unstressed conditions, failed to reveal any significant effect of the applied stress intensity on the anodic polarization behavior of the alloy. However, measurements made under four different potentiostatic conditions showed a considerable increase in stress corrosion times to failure of the alloy. The results, together with fractographic observations of fractured specimen are discussed in terms of the mechanisms of stress corrosion cracking, in magnesium alloys.

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