Showing papers by "Arnold R. Marder published in 1994"

Interfacial layer development in hot-dip galvanneal coatings on interstitial free (IF) steel

Abstract: During the annealing of hot-dip galvanized coatings on interstitial free (IF) steel, an interfacial layer was found to develop and grow at the steel/coating interface. The interfacial layer followed a three-step growth process in which there was initial rapid growth up to a thickness of approximately 1.0 µm, followed by a period of essentially no growth with continued zinc and iron interdiffusion into the coating, and finally renewed growth at long time (60 second) anneals. The interfacial layer did not inhibit zinc and iron interdiffusion or the development of the Fe-Zn alloy layer. Coating iron content increased rapidly before the interfacial layer grew to a thickness of 1.0 µm, however, once the coating reached a total iron content in excess of 11.0 wt pct, interfacial layer growth became active and coating iron content increased only slightly with continued annealing. Although powdering of the coating as evaluated by a 60 deg bend test was generally found to increase with an increase in interfacial layer thickness, particularly in excess of 1.0 µm, no definitive relationship between interfacial layer thickness and powdering was found. The thickness of this interfacial layer, however, can be used as an indicator of formability performance.

Structure of as-deposited iron-zinc coatings from chloride bath

Abstract: The iron content, phase constitution, and microstructure of electrodeposited iron-zinc alloy coatings deposited from chloride baths were investigated. It was found that the iron content of the coatings varied with the current density used during processing and that coatings containing 6 to 13 wt pct Fe consisted of nonequilibrium phases, η andG. η phase, hexagonal close-packed (hcp) zinc supersaturated with iron to about 8 wt pct Fe, contained nanometer-size crys-tals divided by 30-nm-wide growth steps. Within the growth steps, an amorphous phase was present. TheG phase, a body-centered cubic (bcc) phase similar to equilibrium γ phase, existed as equiaxed 30- to 80-nm-wide grains in 10 and 13 wt pct Fe coatings. It is suggested that the microstructure of higher iron content coatings resulted from a recovery/polygonization process.

Effect of annealing upon decomposition of electrodeposited iron-zinc alloy coatings

Abstract: As-deposited electrodeposited iron-zinc alloy coatings containing η phase, decompose upon heating through a sequence of metastable phases. The h c p η phase transforms to b c c G, or Г-like phase via a rapid diffusional phase transformation in the vicinity of 150 °C. For bulk iron contents of 8–13 wt%, η transforms to 100% G phase. The G phase subsequently transforms at 240 °C to ς′ phase, which in turn transforms to δ or Г1 phase near 300 °C by depletion of iron from the surrounding matrix. The decomposition process may be driven by supersaturation of η with iron.

η to G phase transformation in electrodeposited iron-zinc alloy coatings

Abstract: Theη toG phase transformation in electrodeposited iron-zinc alloy coatings is a rapid diffusional phase transformation occurring in the nanometer-scale microstructure of the coatings. Iron-supersaturated zinc, orη phase, undergoes a decomposition process to an iron-deficient Γ-like, orG, phase at temperatures near 150 it°C. The phase transformation is preceded by a polygonization process, driven by strain energy and/or supersaturation in the material. TheG phase nucleates on boundaries within theη phase and grows into 30- to 80-nm equiaxed grains. The activation energy for the transformation varies with iron content, which may indicate that solute effects influence boundary diffusion of zinc.