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Abstract: Galling, a form of adhesive wear, affects the economics of forming advanced high strength steel (AHSS) in automotive stamping since it results increased die maintenance cost and scrap rate. In this study, the twist compression test (TCT) and finite element (FE) analysis were used to (i) differentiate the performance of galvanized coatings and lubricants, (ii) understand the fundamental aspects of powdering and galling, and (iii) determine the critical interface pressure and temperature that initiate galling or powdering in forming galvanized AHSS. Two galvanized and one bare AHSS and two galvannealed mild steels were tested by TCT using different lubricants. The severity of powdering and galling were ranked to indicate the performance of lubricants and coatings with the D2 tool steel. In all tests, one of the lubricants was more effective in reducing powdering and galling. Among the investigated materials, DP600 HDGI (hot dip galvanized) showed minimum galling, while DP500 HDGI resulted in most severe galling regardless of interface pressure and the lubricant used. Based on FE simulations and measurements, the temperature at the tool–workpiece interface was not found to affect the lubricant viscosity and initiate galling under the investigated conditions. However, the contact pressure at the tool–workpiece interface was found to be significant for the initiation of galling. Furthermore, the tendency for powdering of zinc and galling increased with increasing tool surface roughness. [Copyright &y& Elsevier]

Annealing under an atmosphere with controlled oxygen partial pressure is an effective way for improving reactive wetting during the continuous galvanizing process. Hence, understanding the effects of this annealing step on further manufacturing processes such as welding is essential. The present work has shown that the formation of internal oxides during a controlled atmosphere galvanizing process reduced the resistance and heat input resulted in delaying nugget growth in resistance spot welding, compared to the as-received condition. Furthermore, it was shown that by annealing and subsequent zinc coating, the tensile-shear peak load was decreased under the same welding parameters. The nugget formation mechanism of different surface conditions showed a good correlation with dynamic resistance profiles. • The internal oxides formed during annealing reduced the nugget growth in resistance spot welding. • By annealing and subsequent zinc coating the tensile-shear peak load was decreased under the same welding parameters. • The nugget formation mechanism of different surface conditions showed a proper correlation with dynamic resistance profiles. [ABSTRACT FROM AUTHOR]

In this research work, the optimization of a back-propagation artificial neural network (BPNN) using a new multi-objective bio-inspired algorithm based on squirrels is proposed in order to optimize the main continuous galvanizing process parameters such as the initial cooling rate (CR1), the isothermal holding time at 460 oC (tg), and the final cooling rate (CR2). The computational approach predicts in a satisfactory way the most important mechanical properties including yield strength (YS), ultimate tensile strength (UTS), and elongation at fracture (EL) of cold rolled low carbon DP steels treated under continuous galvanizing thermal cycle conditions. The experimental production of galvanized ultra-high-strength DP steels from cold rolled low carbon sheets with a minimum UTS of 1100 MPa, YS between 550 and 750 MPa, and a minimum elongation of 10% is possible using the proposed methodology. [ABSTRACT FROM AUTHOR]

• This study emphasizes the role of Zn-coating type in weld-brazing of coated high-strength steels. • Novel observations regarding Cu-penetration susceptibility in Zn-coated steels have been reported. • Galvannealed coatings form an Fe-Si inhibition layer that prevents Cu-penetration during weld-brazing. • Galvanized coatings are more susceptible to intergranular Cu-penetration into the steel substrate. • Cu-penetration into the steel could lead to LME susceptibility in largescale industrial applications. Weld-brazing has emerged as a promising alternative to fusion welding for joining Zn-coated advanced high strength steels (AHSSs) due to its lower heat input, reduced Zn burn-off, and elimination of defects like porosity and blowholes. Additionally, the weld-brazing process minimizes HAZ softening, a phenomenon that can affect joint strength. While weld-brazing can potentially eliminate the liquid metal embrittlement (LME) caused by the penetration of molten Zn into grain boundaries (GBs), this study found that galvanized (GI) DP600 steels were more susceptible to intergranular penetration of Cu into the substrate during weld-brazing compared to galvannealed (GA) DP600. Although no Zn-related LME was observed during arc-brazing with Si-Bronze filler, the potential for Cu-related LME cracks to form in GI coated steels may affect the mechanical integrity of the joint. [ABSTRACT FROM AUTHOR]

The zinc coating layer fracture properties of a galvannealed steel and an electrolytically galvanized steel are analyzed by conducting the in-situ bending test with newly designed samples. It is found that the fracture develops much earlier in the coating layers of the galvannealed steel than that of the electrolytically galvanized steel. Using transmission electron microscope and energy dispersive X-ray spectroscopy, the intermetallic phases of the coating layers are characterized and it is found that the early crack initiation in a galvannealed steel is mainly triggered in the gamma phase. Combining with nanoindentation tests and corresponding simulation, the deformability of intermetallic phases are analyzed to explain the failure behavior of coating layers in the two steels. [ABSTRACT FROM AUTHOR]

• The hydrodynamic influence on faceted crystal growth was clearly observed and evidence was presented in this paper. • An asymmetry of the crystal facets growth was introduced by the melt flow magnitude and direction. • The flow hydrodynamics is able to induce a similar effect to that caused by natural anisotropy in a faceted crystal growth. In this paper we show that the presence of liquid flow around a crystal growing from melt can induce dissymmetry in growth similar to that described by anisotropic interfacial kinetic coefficients. A front tracking interface model based on a cellular automaton approach was applied to the growth of a Fe 2 Al 5 crystal (also known as top dross particle) in a saturated Zn melt at constant temperature. The growth rate was found to be influenced by the intensity of the melt flow and by the direction of the flow with respect to the crystal orientation. The magnitude and the direction of flow modify the diffusion boundary layer, changing the conditions (temperature and concentration) at the facet interface, therefore the mass transfer. We have shown that despite the isotropy of interfacial kinetics, hydrodynamics was able to introduce an anisotropy in the crystal growth similar to the natural anisotropy in interfacial kinetics of the facets. The facets grow rate was found to be strongly dependant on the Reynolds number as well as on the orientation of the crystalline orientation with respect to the flow direction. [ABSTRACT FROM AUTHOR]

• We studied the influence of the flow on the faceted growth of a hexagonal crystal. • A front tracking interface model was used based on a cellular automaton approach. • Faceted growth was found to be faster with the increase of the melt flow velocity. • The flow is forced to contour the growing crystal. • At high velocity magnitude von Karman vortices appear at the back of the crystal. The growth of faceted crystals occurs often in nature and industry, involving often the presence of flow. The growth of faceted crystals is the result of interface kinetics and diffusion phenomenon. The present paper presents a front tracking interface model based on a cellular automaton approach for the simulation of faceted crystal growth. The current model takes into account the interface kinetics and solute transport by diffusion and convection. The propagation of kinks is modelled by differentiating two growth velocities, one normal and one lateral at each face. The positions of the crystal corners are shifted according to growth of adjacent faces. The hydrodynamics is computed with a two-phase model using a penalty method to model the presence of growing obstacles (the crystals). This model was applied in 2D to the growth of hexagonal Fe 2 Al 5 crystals, so called top dross particles, in a saturated liquid at constant temperature. Qualitative comparison was made between simulation and experimental observation of crystal shape and size. The growth rate was found to be strongly influenced by the flow hydrodynamic induced kinetics. [ABSTRACT FROM AUTHOR]

The focus of this ab initio study is the interaction between Fe 2 Al 5 particles and WC surfaces in the hot-dip galvanizing processes. In a first step, we compute surface energies of Fe 2 Al 5 to predict the morphology of the particles. In the next step, the most relevant interfaces between Fe 2 Al 5 and WC are characterized in terms of atomic structure and energetics, where different terminations of the two phases at the interface are considered. Finally, we investigate the effect of Zn on the stability and adhesion of the interface, where we find that low Zn coverages can even increase adhesion, but for high Zn coverages the adhesion drops significantly. Image 1 • Fe 2 Al 5 dross build-up on WC sink coatings was investigated using ab-initio methods. • Fe 2 Al 5 particle shape was predicted based on ab-initio surface calculations. • Interface of Fe 2 Al 5 to WC was constructed and characterized. • Enrichment of Zn along the interface has been investigated. • Adhesion decreases only for large Zn contents at WC- Fe 2 Al 5 interface. [ABSTRACT FROM AUTHOR]