The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

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

Light metallography, x-ray diffraction, scanning electron microscope (SEM), (EMPA), and scanning transmission electron microscope (STEM) were used to study the microstructural characteristics of 55 w/o Al—Zn-Si (Galvalume) hot-dip coatings on steel Processing variables of coating thickness and dip time were studied and a thin foil sample preparation technique involving ion beam thinning for the STEM evaluation of coating cross sections was developed The spangled coating surface was comprised of a fine dendritic network, and correlations between dendrite arm spacing and spangle size with coating thickness have been made The overlay, or solidified bath, consists of grains of A1-rich dendrites along with Zn-rich interdendritic zones EMPA in conjunction with TEM imaging showed that these Zn-rich interdendritic regions had a heavy concentration of precipitates Selective etching of the overlay revealed a forest of Si particles which grew out from the alloy layer The alloy layer was studied using the EMPA and STEM and it was found that up to five intermetallic phases were present after long dip times

The microstructure of 55 w/o Al—Zn—Si (Galvalume) hot dip coatings

Electrodeposition from a sulfamate bath has been used to produce single layer and discretely stepped electro-composites consisting of a metallic nickel matrix with second phase alumina (α-Al2O3) particles. Light optical microscopy (LOM), scanning electron microscopy (SEM), quantitative image analysis (QIA), and micro-indentation techniques were used to characterize the deposits. As previously seen, an increase in bath particle loading and decrease in plating current density increased the volume percent of alumina incorporated into the coating, with a maximum of 40 vol % being attained. For samples deposited above 1 A/dm2, a direct relationship between the alumina volume percent and coating hardness was seen due in part to the related decrease in interparticle spacing (IPS) at the higher vol %. However, the strengthening mechanism of the electro-composites may be more complex with both the metallic nickel grain structure and IPS being factors, as seen for samples deposited at 0.5 A/dm2. The incorporation of alumina into the electrodeposited nickel was also observed to affect the as-plated surface structure of the coating. Due to the particles inhibiting the formation of pyramidal features found on the surface of pure nickel electrodeposits, the electro-composite surfaces were observed to be relatively flat. Also, structure within the metallic nickel matrix appeared due to rapid growth of the nickel coating around the inert particles when plated at high current densities. In addition, discretely layered functionally graded materials were produced without alterations to the original deposition procedure of the single layer deposits. It was found that the various processing stages needed to produce the stepped coatings did not affect the structure or properties of the individual layers, when compared to that of the corresponding single-layered electro-composites.

Characterization of single and discretely-stepped electro-composite coatings of nickel-alumina

The undercooling required for eutectic nucleation was measured using differential scanning calorimetry for Al-Zn alloys containing 2–8 wt% Al. While an average undercooling of only 0.25°C was required for the nucleation of Zn by proeutectic Al, an undercooling of 4.0°C was necessary for the nucleation of Al by primary Zn. The non-reciprocal nucleation characteristics of this system results in the formation of Zn halos around proeutectic Al dendrites and a difference in the eutectic structure when comparing hypo- to hypereutectic alloys in terms of interlamellar spacing, second phase volume fraction, and eutectic morphology.

Nucleation characteristics and microstructure in off-eutectic Al-Zn alloys

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.

Arnold R. Marder

Papers

The microstructure of 55 w/o Al—Zn—Si (Galvalume) hot dip coatings

Characterization of single and discretely-stepped electro-composite coatings of nickel-alumina

Nucleation characteristics and microstructure in off-eutectic Al-Zn alloys

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

The effect of second phase volume fraction on the erosion resistance of metal-matrix composites