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American Society for Testing and Materials

Recent advances in friction-stir welding : Process, weldment structure and properties

The metallurgy of zinc-coated steel

Welding Metallurgy of

Wire-feed additive manufacturing (AM) is a promising alternative to traditional subtractive manufacturing for fabricating large expensive metal components with complex geometry. The current research focus on wire-feed AM is trying to produce complex-shaped functional metal components with good geometry accuracy, surface finish and material property to meet the demanding requirements from aerospace, automotive and rapid tooling industry. Wire-feed AM processes generally involve high residual stresses and distortions due to the excessive heat input and high deposition rate. The influences of process conditions, such as energy input, wire-feed rate, welding speed, deposition pattern and deposition sequences, etc., on thermal history and resultant residual stresses of AM-processed components needs to be further understood. In addition, poor accuracy and surface finish of the process limit the applications of wire-feed AM technology. In this paper, after an introduction of various wire-feed AM technologies and its characteristics, an in depth review of various process aspects of wire-feed AM, including quality and accuracy of wire-feed AM processed components, will be presented. The overall objective is to identify the current challenges for wire-feed AM as well as point out the future research direction.

Wire-feed additive manufacturing of metal components: technologies, developments and future interests

The reaction which occurred between iron panels and Al-Zn baths during hot dipping was investigated. Three baths were studied: 45Al-55Zn, 55Al-45Zn, and 75Al-25Zn (in wt pct) in the temperature range of 570 to 655 °C. The reaction between the iron panel and the Al-Zn bath was very severe and in all cases the iron panel was totally consumed by the bath in less than two minutes. The rapid attack of the iron panels by the Al-Zn baths was attributed to two separate causes depending on growth conditions. First, in some panels the intermediate layer which formed between the iron panel and the molten bath was nonadherent. This resulted in the direct contact of the molten bath with the iron panel at a nonequilibrium interface, which presented a large driving force and little inhibition for the reaction. Second, in panels containing an adherent alloy layer, the layer had channels of liquid Zn which extended from the molten bath to the iron panel. These channels allowed rapid transport of Zn and Al to the iron panel which resulted in a very high reaction rate. The controlling step in the reaction between the iron panel and molten Al-Zn bath was the diffusion rate of Al in the molten bath to the surface of the iron panel. The diffusion coefficient of Al in the molten bath was found to be in the range of 1 × 10-5 to 5 × 10-5 cm2/s. Microstructural, electron microprobe, and X-ray diffraction data are presented to support the above-mentioned mechanisms and conclusions.

The reaction between solid iron and liquid Al-Zn baths

In the galvanizing process, it has been proposed that the grain size of the substrate steel influences the Fe-Zn alloy phase reaction kinetics and growth rate during immersion in the liquid Zn bath. Two grain sizes (nominally 15 and 85 µm) were developed in a decarburized low-carbon (0.005) steel and hot-dipped galvanized in 0.00 wt pct Al-Zn and 0.20 wt pct Al-Zn baths to study the effect of substrate grain size on Fe-Zn phase formation. Uniform attack of the substrate steel occurred in the 0.00 wt pct Al-Zn bath, since an Fe2Al5 inhibition layer did not form. No barrier to nucleation of the Fe-Zn phases exists in this Zn bath, and therefore, the substrate steel grain size had no significant effect on the kinetics of phase growth for the gamma, delta, and zeta phase layers. In the 0.20 wt pct Al-Zn bath, discontinuous Fe-Zn phase growth (outburst formation) occurred due to the initial formation of the Fe-Al inhibition layer. The nucleation of the Fe-Zn phases was significantly retarded in this bath for the large (85 µm) substrate grain size. Whereas outbursts were found in the 15-µm grain size substrate after 10 seconds of immersion time, it required 1200 seconds to nucleate just a few outbursts in the 85-µm substrate. These results support the mechanism that Fe-Al inhibition layer breakdown occurs along fast diffusion paths for Zn in the inhibition layer that correspond to the location of substrate steel grain boundaries where reaction with Fe can occur.

Effect of substrate grain size on iron-zinc reaction kinetics during hot-dip galvanizing

Phosphorous was ion implanted on one surface of a large grain (10 to 20 mm) low-carbon steel sheet in order to study the effect of surface segregation on the formation of Fe-Zn phases during galvanizing Both an Al-free and a 020 wt pct Al-Zn bath at 450 °C were used in this investigation It was found that P surface segregation did not affect the kinetics of Fe-Zn phase growth for the total alloy layer or the individual Fe-Zn gamma, delta, and zeta phase alloy layers in the 000 wt pct Al-Zn baths In the 020 wt pct Al-Zn bath, the Fe2Al5 inhibition layer formed with kinetics, showing linear growth on both the P-ion implanted and non-P-ion implanted surfaces Fe-Zn phase growth only occurred after extended reaction times on both surfaces and was found to directly correspond to the location of substrate grain boundary sites These results indicate that P surface segregation does not affect the growth of Fe-Zn phases or the Fe2Al5 inhibition layer It was shown that in the 020 wt pct Al-Zn bath, substrate grain boundaries are the dominant steel substrate structural feature that controls the kinetics of Fe-Zn alloy phase growth

Effect of phosphorous surface segregation on iron-zinc reaction kinetics during hot-dip galvanizing

Weld overlay coatings for erosion control

Three thermal spray coatings were subjected to high-temperature corrosion experiments to characterize the operative corrosion mechanism(s) and to examine the effects of coating composition and microstructure. Samples were placed in air and sulfur dioxide (SO2) at 600°C for exposure times up to 1,000 h. The ability of a thermal spray coating to protect its substrate effectively was found to depend upon its tendency to form protective oxides and upon the cross-sectional distance from the coating surface to the substrate via fast diffusion paths such as splat boundaries and voids.

Arnold R. Marder

Papers

The reaction between solid iron and liquid Al-Zn baths

Effect of substrate grain size on iron-zinc reaction kinetics during hot-dip galvanizing

Effect of phosphorous surface segregation on iron-zinc reaction kinetics during hot-dip galvanizing

Weld overlay coatings for erosion control

Effects of Thermal Spray Coating Composition and Microstructure on Coating Response and Substrate Protection at High Temperatures