A detailed experimental study has been carried out to investigate the zincate immersion deposition process for 99.99%, 6061, and 356-T6 aluminum samples. In particular, the effect of iron and tartrate in the immersion bath, the aluminum surface preparation, and the relationship of the first immersion step to the second immersion step were investigated by chemical, electrochemical (polarization and rest potentials), and surface analytical scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) techniques. Eh-pH diagrams were constructed to determine the most stable zinc, iron, and aluminum species in solution. These diagrams predict that ferrous and ferric ions, as well as aluminum should form stable complexes with tartrate at the typical immersion deposition conditions (Eh -0.9 to -1.0 and pH 14 to 15). Experimentally, tartrate was found to enhance the dissolution rate of aluminum in highly caustic solutions. The addition of ferric chloride to the immersion bath produced coatings that were more crystalline, and also decreased the amount of hydrogen gas evolved in the second immersion step. The deposition of zinc and iron during the second immersion step was considerably less than that during the first immersion step. The second immersion coating became more adherent as the initial surface roughness decreased, and as grain size was increased the second immersion coating became thicker. For increasing grain size the micrographs for the first and second immersion coatings showed that the coatings became more localized. The second immersion coating thickness and morphology were also dependent upon several first immersion variables, such as bath temperature, immersion time and bath composition. Increased dissolution rates of aluminum in the first immersion produced thinner coatings with a finer crystallite growth. Increased bath temperature and increased first immersion time enhanced the dissolution rate of aluminum. The zinc coating slowed the dissolution rate of aluminum. When zinc was absent from the first immersion bath, the aluminum dissolution was much faster and resulted in thinner coatings upon subsequent second immersion. The molar ratio of zinc deposited to aluminum dissolved was a constant value of 1.1 for both first and second immersions; the molar ratio was also constant for the different aluminum substrates examined in this investigation.

Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xvii, 181 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 167-181).

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains xi, 106 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 101-106).

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xx, 272 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 207-208).

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Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains x, 235 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

The use of laser welding in the automotive industry in the past few decades has facilitated joining of hot-dip galvanized (HDG) steel sheets at high production rates and low cost. The recent development of tailor welded blanks (TWB) using laser welding allowed combinations of sheet grades and thicknesses to “tailor” the vehicle part for optimized design, structural integrity and crash performance but more importantly, reductions in weight. Welded blanks are further subjected to stamping or stretch forming prior to final assembly. Unfortunately, both welding and stretch forming cause the galvanized coating to deteriorate, and thereby, undermine the long term corrosion protection. Despite existing publications on zinc coated steel and advances in processing techniques, there is a lack of understanding on the influence of laser welding and stretch forming on the corrosion performance of HDG steel. Hence, the purpose of this study was to determine how welding speed and biaxial strain affect interstitial-free (IF) and high strength low allow (HSLA) steel coupons when they are subjected to continuous immersion and accelerated corrosion tests. The corrosion rates of the coupons were evaluated using electrochemical techniques and gravimetry. Changes in the galvanized coating were characterized using scanning electron metallography. It was observed that, the original zinc layer transformed into the delta and gamma Fe-Zn intermetallic phases locally in the heat affected zone (HAZ) after laser welding. The resulting microstructure was similar to that of a commercially galvannealed coating and exhibited superior corrosion resistance than that of pure zinc. Linear polarization resistance (LPR) measurements revealed that the zinc coating was able to protect a chemically exposed region of steel in 0.1 M NaCl solution. While the Nd:YAG laser welded coupons with narrow HAZs performed equally well as the non-welded ones, diode laser welded coupons, with a wide locally annealed coating in the HAZ, exhibited a decrease in the peak corrosion rate of zinc. Moreover, minimal amounts of rust were observed on the surface of the HAZ after testing. With biaxial strain, welded and deformed coupons generally demonstrated higher peak corrosion rates than that of undeformed welded ones. When subjected to cyclic corrosion testing according to SAE J2334, rust formed in the exposed region after one 24 hour test cycle due to wet-dry conditions. However, zinc corrosion products on the surface provided substantial corrosion resistance to the remaining zinc coating and to the steel substrate. Gravimetric measurements of welded coupons showed a linear increase in weight gain with increased exposed widths of the steel after 30 cycles but biaxial strain further increased the weight gain on deformed coupons. After 60 cycles, the trend became exponential for both welded and deformed coupons. There was a negligible difference between the corrosion performance of IF and HSLA steel. Using X-Ray diffraction and Raman spectroscopy, species of both iron and zinc corrosion products were identified. Without the application of paint coatings, zinc oxide (ZnO), zinc hydroxy chloride (ZnCl2[Zn(OH)2]4), and hydrozincite ([ZnCO3]2[Zn(OH)2]3) were responsible for passivating the surface and reducing the overall corrosion rate of the galvanized coating.

The use of laser welding in the automotive industry in the past few decades has facilitated joining of hot-dip galvanized (HDG) steel sheets at high production rates and low cost. The recent development of tailor welded blanks (TWB) using laser welding allowed combinations of sheet grades and thicknesses to “tailor” the vehicle part for optimized design, structural integrity and crash performance but more importantly, reductions in weight. Welded blanks are further subjected to stamping or stretch forming prior to final assembly. Unfortunately, both welding and stretch forming cause the galvanized coating to deteriorate, and thereby, undermine the long term corrosion protection. Despite existing publications on zinc coated steel and advances in processing techniques, there is a lack of understanding on the influence of laser welding and stretch forming on the corrosion performance of HDG steel. Hence, the purpose of this study was to determine how welding speed and biaxial strain affect interstitial-free (IF) and high strength low allow (HSLA) steel coupons when they are subjected to continuous immersion and accelerated corrosion tests. The corrosion rates of the coupons were evaluated using electrochemical techniques and gravimetry. Changes in the galvanized coating were characterized using scanning electron metallography. It was observed that, the original zinc layer transformed into the delta and gamma Fe-Zn intermetallic phases locally in the heat affected zone (HAZ) after laser welding. The resulting microstructure was similar to that of a commercially galvannealed coating and exhibited superior corrosion resistance than that of pure zinc. Linear polarization resistance (LPR) measurements revealed that the zinc coating was able to protect a chemically exposed region of steel in 0.1 M NaCl solution. While the Nd:YAG laser welded coupons with narrow HAZs performed equally well as the non-welded ones, diode laser welded coupons, with a wide locally annealed coating in the HAZ, exhibited a decrease in the peak corrosion rate of zinc. Moreover, minimal amounts of rust were observed on the surface of the HAZ after testing. With biaxial strain, welded and deformed coupons generally demonstrated higher peak corrosion rates than that of undeformed welded ones. When subjected to cyclic corrosion testing according to SAE J2334, rust formed in the exposed region after one 24 hour test cycle due to wet-dry conditions. However, zinc corrosion products on the surface provided substantial corrosion resistance to the remaining zinc coating and to the steel substrate. Gravimetric measurements of welded coupons showed a linear increase in weight gain with increased exposed widths of the steel after 30 cycles but biaxial strain further increased the weight gain on deformed coupons. After 60 cycles, the trend became exponential for both welded and deformed coupons. There was a negligible difference between the corrosion performance of IF and HSLA steel. Using X-Ray diffraction and Raman spectroscopy, species of both iron and zinc corrosion products were identified. Without the application of paint coatings, zinc oxide (ZnO), zinc hydroxy chloride (ZnCl2[Zn(OH)2]4), and hydrozincite ([ZnCO3]2[Zn(OH)2]3) were responsible for passivating the surface and reducing the overall corrosion rate of the galvanized coating.

Zn redukcija iš šarminių elektrolitų vyksta per tarpinę oksido/hidroksido fazės susidarymo stadiją. Dalis oksidinių junginių gali būti neredukuojami, todėl terptis į metalinę dangą. Impulsinės elektrolizės taikymas Zn dangų nusodinimui yra vienas iš būdų modifikuoti metalo struktūrą ir tuo pačiu pagerinti dangų korozinį atsparumą. Nemetalinių intarpų kiekis impulsine elektrolize nusodintose Zn ir jo lydinių dangose nėra tyrinėtas. Nemetalinių intarpų kiekis buvo nustatytas dangų anodinio tirpinimo Na2SO4 + Na2 EDTA tirpale ir Rentgeno fotoelektronų spektroskopijos metodais. Nustatyta, kad oksidinių intarpų kiekis impulsine elektrolize nusodintose Zn ir Zn-Ni dangose buvo didesnis, lyginant su nuolatinės srovės dangomis, taip pat į Zn dangas, lyginant su lydinių, įsiterpia daugiau oksidinių junginių. Nuolatine srove nusodintose Zn dangose ZnO kiekis yra didesnis už Zn(OH)2, tačiau impulsinė elektrolizės taikymas didina hidroksido kiekį dangoje. Nuolatine srove nusodintose Zn-Ni dangose oksido ir hidroksido intarpų kiekiai yra panašūs, tuo tarpu impulsinė elektrolizė ženkliai padidina hidroksido kiekį dangoje. / Electrodeposition process of Zn in alkaline solutions occurs through oxide/hydroxide phase formation, which under certain conditions could not be totally reduced and therefore formation of non metallic (oxide/hydroxide) inclusions can take place. Pulse plating of metal coatings is widely used as the method for metal structure modification in order to enhance the corrosion resistance of Zn and Zn alloy coatings, however the amount of inclusions in pulse plated Zn and Zn-Ni coatings was not investigated up to date. The amount of non-metallic inclusions was determined from anodic dissolution curves, obtained in Na2SO4 + Na2 EDTA solution and from X-ray photoelectron analysis of the sample surfaces after Ar ion sputtering. The amount of the oxide phase in Zn and Zn-Ni coatings was determined to be higher in the pulse plated coatings with respect to direct current ones, while in Zn coatings this amount was also higher with respect to the alloy. The amount of ZnO in the inclusions of direct current plated Zn coatings is higher than that of Zn(OH)2, however, application of pulse deposition increases the amount of the latter compound. Oxide and hydroxide amounts in the direct current plated Zn-Ni coatings are similar, meanwhile, the pulse plating increases significantly the amount of hydroxide phase.

This diploma thesis discusses laser cutting and the consecutive surface treatment of cut parts. The theory of laser cutting is described in the first part of this thesis, including laser history and the laser emergence principle. Cut parameters and the influence of the laser cutting on the material are described later on. The next part describes the laser cutting technological possibilities and other laser technology utilization options are outlined. In the last theory part, metal surface treatment used in the experiment is covered. Coating thickness is evaluated in the practical part of this thesis, as well as roughness, microhardness, chemical microanalysis and metalography. The evaluation of the results achieved, and optimal surface treatment execution suggestions are addressed in the last part of this thesis.