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In advanced high strength automotive steels, small amounts of diffusible hydrogen can lead to a deterioration of mechanical performances, especially a loss of ductility, in the simultaneous presence of internal stresses and of a sensitive microstructure. In the hot-dip galvanizing process, hydrogen is mainly absorbed during high temperature operations in hydrogen-containing atmospheres before hot-dipping when the solubility of hydrogen in steel is the highest. After hot-dipping, the metallic zinc-based coating can impede hydrogen diffusion out of the metal. As a result, an excess of diffusible hydrogen remains in the steel substrate and can subsequently lead to a possible embrittlement. In this contribution, the effects of the coating nature on the hydrogen diffusion of a 980 MPa dual phase steel (DP980) are investigated. The attention is focused on three Zn-based coating alloys: galvanized (Zn‑0.23%Al), galvannealed (Fe-Zn based on Zn‑0.12%Al) and Zn1.2Al1.2Mg. The hydrogen permeability of the coatings is first assessed through degassing experiments at room temperature and highlights the tightness of all coatings at room temperature. Secondly, cyclic SAE J2334 corrosion testing is performed and enables to highlight a stronger corrosion of GI and GA samples with respect to Zn1.2Al1.2Mg-coated samples, which is however the sole coating that seems to promote a hydrogen uptake during corrosion experiment.

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.

Gas-jet wiping is a widely employed production technology for controlling the final zinc coating thickness on a moving substrate during continuous hot-dip galvanizing. This paper presents an experimental investigation and numerical analysis of a prototype multi-slot air knife, which offers an increase in wiping efficiency relative to the traditional single-slot jet geometry in the continuous galvanizing process. The applicability of the analytical coating weight model of Elsaadawy et al. (Metall Mater Trans B, 38:413-424, 2007) to predict the final coating weight was determined for the multi-slot geometry, where particular focus was devoted to the effect of geometric parameters. Experimental measurements under a variety of knife geometry and process conditions agreed with the coating weight predictions of the analytical model. It was also shown that the air-knife geometric parameters had a significant effect on the pressure profile and shear stress distribution applied by the air knives to the moving substrate. It was determined that the final coating thickness was significantly affected by the auxiliary jet width, Da, where lighter coating weights at higher strip velocities (up to 5.4 pct at Vs = 1.5 m/s) could be achieved by using the multi-slot air-knives prototype vs. the conventional single-slot configuration.

This modeling and optimization study applies a non-linear back-propagation artificial neural network, commonly denoted as BPNN, to model the most important mechanical properties such as yield strength (YS), ultimate tensile strength (UTS) and elongation at fracture (EL) during the experimental processing of hot-dip galvanized dual-phase (GDP) steels. Once the non-linear BPNN is properly trained, the most important variables of the continuous galvanizing process, including initial/first cooling rate (CR1), holding time at the galvanizing temperature of 460 °C (tg) and the final/second cooling rate (CR2), are obtained in an optimal way using an evolutionary approach. The experimental development of GDP steels in continuous processing lines with outstanding mechanical properties (550 &lt, YS &lt, 750 MPa, 1100 MPa &lt, UTS and 10% &lt, EL) is possible by using a combined hybrid approach based in BPNN and multi-objective genetic algorithm (GA). The proposed computational method is applied to the specific design of an actual manufacturing process for the first time.

High-Manganese austenite-containing steels with superior combination of strength and ductility have shown potential for enhancement of passenger safety and body-in-white (BIW) weight reduction. Even though Zn-coated austenitic steels have improved corrosion resistance, they are highly susceptible to liquid metal embrittlement (LME) during welding. The present work is aimed to address LME susceptibility during restrained laser lap joining of high-Mn twinning induced plasticity (TWIP) and medium-Mn transformation induced plasticity (MMn-TRIP) steels. Electron probe micro-analysis (EPMA) results showed that stress-assisted diffusion of Zn into the austenite grain boundaries and further liquid Zn formation by a peritectic reaction lead to grain boundary decohesion. Electron backscatter diffraction (EBSD) results demonstrated that high angle and special grain boundaries are prone to Zn-penetration within the heat-affected-zone (HAZ). Additionally, LME sensitivity was observed to be highly dependent on the magnitude of applied stress.

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.

Zn-coated advanced high strength steels are popular in the automotive industry due to their excellent combination of mechanical strength and ductility as well as superior corrosion resistance provided by the Zn-coating – with hot-dip galvanized and galvannealed coatings being the most popular. Gas metal arc brazing technology is a non-fusion joining method, proposed as an alternative to the gas metal arc welding process due to several advantages: The arc-brazing process delivers significantly lower heat input to the substrate, which minimizes the Zn-coating burn-off leading to higher corrosion protection for the joined parts, and reduces the HAZ softening phenomenon which affects the mechanical integrity of the substrate, while at the same time reduces welding defects such as porosity and blowholes. The strength of an arc-brazed joint depends on the spreading of the molten filler material over the joint to create a bond between the parts as the molten braze solidifies. Existing literature on the subject suggests that heat input is the main driving factor controlling the wettability of the molten braze material with the type of shielding gas used also having an effect. However, the influence of different types of Zn-coatings and their respective surface condition (i.e., clean, or unclean) on the wettability of Cu-based molten braze materials during arc-brazing has not been investigated. The present work investigates the effect of surface morphology of galvanized and galvannealed DP600 steel in the as-received and plasma cleaned conditions on the wettability of molten Si-Bronze (CuSi3Mn1) brazing filler material in the bead-on-plate configuration. The findings of this work clearly demonstrate that the type of coating and its surface condition has a significant effect on the spreading of the molten filler material and on the growth of the intermetallic compound layer at the joint interface and therefore, should be taken into consideration as a factor that can impact the efficacy of an arc-brazed joint.

Fibre laser welds of Fe-0.15C-10Mn-1.5Al medium-Mn transformation induced plasticity (TRIP) steel and its dissimilar combination with high strength low alloy (HSLA) and dual-phase (DP980) steel was assessed with respect to microstructure, microhardness, formability, and tensile properties. The fusion zone (FZ) of the medium-Mn TRIP steel weldment was consist of predominantly martensite with some interdendritic austenite due to high manganese concentration which stabilizes austenite. The FZ of dissimilar combinations to HSLA and DP980 steel consisted of mostly martensite. Microhardness profiles of the medium-Mn TRIP steel showed no indications of detrimental heat-affected zone (HAZ) softening despite the high base metal (BM) hardness (396 HV). Laser welds containing medium-Mn TRIP displayed similar FZ hardness values (413–438 HV). Failure of medium-Mn TRIP laser welds under uniaxial tension occurred adjacent to the FZ where localized strain accumulated. The tensile results showed consistent failure in the weaker BM of dissimilar joints at high joint efficiency (95–100%) with respect to the weaker material of the joint. Biaxial stretch formability of TRIP-TRIP similar welds was determined to be severely limited by the brittle FZ. Strain accumulation in the BM of HSLA and DP980 steel in dissimilar combinations improved formability of laser welded blanks containing medium-Mn TRIP steel. Keywords: Fibre laser welds, Medium manganese TRIP steel, Microstructure, Microhardness, Tensile testing, Formability

Gas-jet wiping using an air knife is an effective hydrodynamic method to control the coating thickness of zinc on a moving steel substrate in the continuous hot-dip galvanizing process. The current generation of single-slot air knives is widely used in the galvanizing industry but has limitations in producing low coating weights at the higher line speeds desired for the current generation of automotive sheet steel products. In this work, a novel configuration of a multiple-slot jet (multijet) air knife is investigated through numerical simulations as an alternative to the traditional single-slot air knife. The aim of this study is to investigate the sensitivity of the coating weight to the pressure and shear stress profiles in order to determine whether there are operating regions that are more robust to air-knife geometry changes. A modified geometry for the multislot air knife is proposed based on computational fluid dynamics results obtained from a parametric study. The effects of different operating conditions such as the main jet Reynolds number (Re m), auxiliary jet Reynolds number (Re a ), and jet-to-wall distances (Z/D) on the final coating thickness were investigated. The results of the modeling showed that by setting the auxiliary jet Reynolds number at a fraction (25%) of the main jet Reynolds number, lighter coating weights can be achieved for higher strip velocities and higher wall-to-jet distances as compared to the single-slot jet design. It is believed that this geometry will provide a robust operating window to enable the prototype design to be employed in the industrial setting.

The present study focused on single and multiple dissimilar joints between DP980 and high-strength low-alloy (HSLA) galvanized steels. The tensile properties of the dissimilar joint between the strong DP980 and the relatively soft HSLA reflected only the properties of HSLA with plastic deformation, and final fracture took place entirely in HSLA. The fatigue properties of the dissimilar joints were more intriguing, with the strong DP980 outperforming at high stress amplitude and the ductile HSLA outperforming at low stress amplitude. For different load amplitudes, fatigue failure occurred in different materials and at different locations. The fatigue strength of DP980 was more negatively impaired by weld defects than that of HSLA.

Thermal sprayed zinc and aluminum alloy coatings provide corrosion protection to steel structures. A new thermal sprayed coating with 1-2% of each Al and Mg shows up to 3 times the corrosion resistance of the conventional Zn and ZnAl alloy coatings. Arc sprayed Zn-Mg-Al alloy wire and three reference materials, Zn, Zn-15%Al and Al-5%Mg, gave coatings 100 - 150 µm thick, using either compressed air or nitrogen as an atomizing gas. Formation of splats in the arc wire spray process is dependent on wire chemistry, temperature and size of the particle prior to impact on the substrate. Splat appearance can be correlations with deposition efficiency of the different materials. Corrosion testing was carried out using electrochemical polarization in artificial sea water and by long-term exposure for two years on Heligoland Island in the North Sea. Of the investigated Zn-based materials, ZnMgAl forms the most stable corrosion product layer which delays the anodic corrosion reaction. At the same time ZnMgAl provides sacrificial protection of damaged, uncoated areas of up to 5 mm. Although Al-based coatings, like AlMg5, provide cathodic protection to steel, they suffer from pitting corrosion which can lead - when undiscovered - to sudden catastrophic failure of the structure.

s Despite numerous studies making an effort to attain a thorough understanding of the liquid-metal-embrittlement (LME) phenomenon, the metallurgical facet of this catastrophic event remains unclear in iron/zinc (Fe/Zn) systems. While it has been frequently reported that the presence of austenite is an essential prerequisite for LME formation, the present study showed that fully ferritic structure is prone to LME phenomenon and has a high susceptibility to LME-cracking which makes it a novel observation adding to a pool of knowledge regarding LME occurrence. The elemental distribution analysis near the LME crack-tip indicated that liquid Zn was not present which confirmed solid-state grain boundary diffusion was a plausible description of LME-cracking. The occurrence of grain dropout as well as a Zn-containing crack in grain boundary without any branches with other cracks showed that grain boundary sensitization has assisted LME-cracking.

Aluminium and magnesium are known for their ability to improve corrosion performance of zinc coatings used for steel protection in automotive applications. To investigate the inhibiting properties of other elements, series of model Zn X, Zn Al X, Zn Mg X and Zn Al Mg X alloys containing 0.2–2 wt% of titanium, mischmetal (mixture of cerium and other lanthanides), zirconium, molybdenum, chromium, boron, gallium, indium, copper, nickel, calcium, manganese and silicon were prepared and their corrosion performance in a cyclic accelerated test and at a marine field site and the ability to provide galvanic protection to steel in defects were characterized. On openly exposed surfaces, none of the investigated elements showed stronger inhibiting effect on atmospheric corrosion than Al and Mg. When exposed to marine climate, it was beneficial to combine Al and Mg. The corrosion stability of Zn Al Mg was further improved by addition of a fourth element. Quaternary Zn Al Mg X alloys outperformed binary Zn X and ternary Zn Al X and Zn Mg X alloys. In average, mass loss was 4-fold higher in confined zones simulating hem flanges. Strong inhibition with Mg and detrimental effects of Al on corrosion in confined zones was found. Several quaternary Zn Al Mg X alloys with improved corrosion stability in both open and confined configurations were identified.

Advanced high strength steels (AHSS), specifically dual phase (DP) steels, are extensively used to reduce the weight of vehicles. Fiber laser welding (FLW) has been shown to provide welds with superior mechanical properties made at high welding speeds. Galvannealing (GA) and galvanizing (GI) coated sheet steels are extensively used for auto bodies to improve corrosion resistance. As such, the effect of coating type on the microstructure, mechanical properties and fatigue properties of FLW similar joints of DP980 was assessed. There existed spherical tempered martensite in the GA coated DP980 base metal (BM), most likely caused by the galvannealing process. Coating type did not present a noticeable effect on the microstructure of the welded zones. The GI coating, however, could evaporate violently during welding, resulting in high concavity and other welding defects which negatively affect the high-cycle fatigue property. Measures to mitigate the negative effects of the GI coating were discussed. Keywords: Coating, Fiber laser welded, DP980, Similar joints, Fatigue

The focus of this ab initio study is the interaction between Fe2Al5 particles and WC surfaces in the hot-dip galvanizing processes. In a first step, we compute surface energies of Fe2Al5 to predict the morphology of the particles. In the next step, the most relevant interfaces between Fe2Al5 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.

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 phase transformation kinetics under continuous cooling conditions for intercritical austenite in a cold rolled low carbon steel were investigated over a wide range of cooling rates (0.1&ndash, 200 ∘ C/s). The start and finish temperatures of the intercritical austenite transformation were determined by quenching dilatometry and a continuous cooling transformation (CCT) diagram was constructed. The resulting experimental CCT diagram was compared with that calculated via JMatPro software, and verified using electron microscopy and hardness tests. In general, the results reveal that the experimental CCT diagram can be helpful in the design of thermal cycles for the production of different grades of dual-phase&ndash, advanced high-strengh steels (DP-AHSS) in continuous processing lines. The results suggest that C enrichment of intercritical austenite as a result of heating in the two phases (ferrite&ndash, austenite) region and C partitioning during the formation of pro-eutectoid ferrite on cooling significantly alters the character of subsequent austenite phase transformations.

Metallic zinc coatings are well established and recognized as the most cost-effective corrosion protection available for steel structures. Zinc coatings protect steel from atmospheric, marine and in-soil exposure conditions, and can be applied either by hot dip galvanizing or by thermal spraying. Hot dip galvanizing involves the full immersion of the steel into a bath of molten zinc, ensuring complete coverage over all surfaces. However, some structures can be too large to be galvanized. Zinc thermal spray involves projecting drops of liquid zinc onto the surface of the steel using compressed air. With thermal sprayed zinc coatings, there is no size limitation to the part to be coated, and the technology is fully portable, allowing easy field applications. Whether applied by galvanizing or thermal spraying, zinc coatings are fully compatible and steels coated by either method can be incorporated into one structure with no concerns. Zinc coatings provide decades of maintenance free service and case studies of hot dip galvanized and zinc thermal sprayed steel structures will be presented.

Author(s): Naulleau, P; Anderson, C; Chao, W; Goldberg, K; Wojdyla, A; Bhattarai, S; Neureuther, A; Goodwin, F; Neisser, M | Abstract: With the slipping of the insertion node for extreme ultraviolet lithography, demands on resist resolution have increased further stressing sensitivity requirements. A variety of resists, both chemically amplified and not, have been developed meeting resolution needs, but falling short on sensitivity and line-width roughness (LWR). Note that resolution is an absolute mandatory requirement, the true tradeoff that must be considered is between sensitivity and contact hole printing is a crucial application for extreme ultraviolet lithography and is particularly challenged by resist sensitivity due to inherent inefficiencies in darkfield contact printing. Checkerboard strong phase shift masks have the potential to alleviate this problem through a 4× increase in optical efficiency. The feasibility of this method is demonstrated using the SEMATECH-Berkeley Microfield Exposure Tool pseudo phase shift mask configuration and preliminary results are provided on the fabrication of an etched multilayer checkerboard phase shift mask.

Corrosion of reinforcing steel bar is a significant cause of concrete failure, caus- ing expensive repairs and premature structure replacements. Galvanizing provides proven cor- rosion protection for reinforcing steel significantly extending the life of concrete bridge struc- tures. Whether applied by the traditional batch hot dip process or the new continuous galvaniz- ing process, zinc coatings protect reinforcing steel both as a barrier coating and as a sacrificial anode. The properties of galvanized reinforcing steel and its contribution to improvement of concrete performance of bridges will be presented together with the status of related product standards.

High strength low alloy (HSLA) and dual-phase DP980 (UTS P 980 MPa) steels were joined using fiber laser welding in similar and dissimilar materials combinations. The welded joints were characterized with respect to microhardness and tensile properties at three different temperatures: � 40 C, 25 C, and 180 C. Tensile properties of the welded joints were compared to those of the base metal (BM) obtained under similar conditions. A good correlation was found between the welded joints and the BM in relation to the tensile properties obtained at the different temperatures. A general trend of increase in the yield strength (YS), the ultimate tensile strength (UTS) and energy absorption (EA) with decreasing temperature was observed; however, work hardening coefficient was not altered and insignificant scatter was observed in case of the elongation. However, in the DP980 steel, dynamic strain ageing was observed only in the BM.

The main process variables to produce galvanized dual phase (DP) steel sheets in continuous galvanizing lines are time and temperature of intercritical austenitizing (tIA and TIA), cooling rate (CR1) after intercritical austenitizing, holding time at the galvanizing temperature (tG) and finally the cooling rate (CR2) to room temperature. In this research work, the effects of CR1, tG and CR2 on the ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) of cold rolled low carbon steel were investigated by applying an experimental central composite design and a multivariate regression model. A multi-objective optimization and the Pareto Front were used for the optimization of the continuous galvanizing heat treatments. Typical thermal cycles applied for the production of continuous galvanized AHSS-DP strips were simulated in a quenching dilatometer using miniature tensile specimens. The experimental results of UTS, YS and EL were used to fit the multivariate regression model for the prediction of these mechanical properties from the processing parameters (CR1, tG and CR2). In general, the results show that the proposed multivariate model correctly predicts the mechanical properties of UTS, YS and %EL for DP steels processed under continuous galvanizing conditions. Furthermore, it is demonstrated that the phase transformations that take place during the optimized tG (galvanizing time) play a dominant role in determining the values of the mechanical properties of the DP steel. The production of hot-dip galvanized DP steels with a minimum tensile strength of 1100 MPa is possible by applying the proposed methodology. The results provide important scientific and technological knowledge about the annealing/galvanizing thermal cycle effects on the microstructure and mechanical properties of DP steels.

DP980 dual phase and high strength low alloy (HSLA) steels were welded, using fibre laser, with varying amounts of concavity to determine its effects on the tensile and fatigue properties. Higher concavity, 25 to 35%, was observed to reduce the tensile strength of the DP980 welds, while not affecting the tensile strength of HSLA welds. All welds exhibited lower fatigue resistance compared to their base metals. However, DP980 welds with higher concavity (25 to 35%) exhibited even lower fatigue resistance while HSLA welds showed similar performance regardless of changes in concavity. Concavity could be minimised by reducing welding power and increasing the welding speed.

Formability of laser welded blanks (LWBs) was measured in the biaxial stretch forming mode using the limiting dome height (LDH) test. High strength low alloy steel and two dual-phase (DP600 and DP980) steels were used for fabricating LWBs. The failure location and the LDH values of the formed blanks were correlated to the hardness across the welds. The effects of weld line position and geometry on the formal- ity was evaluated by investigating LWBs with three different weld line positions (0, 15 and 30 mm offsets from the blank center) for both linear and curvilinear geometry. The formability was found to be depen- dent on the weld line position and increased when the weld was located farther from the blank center due to more uniform strain developed during LDH tests. Interestingly, weld line geometry was observed to have a stronger influence on the formability DP600 steel. In addition to weld line position and geom- etry, heat affected zone softening was observed to be the dominant factor in controlling the formability of all the DP980 LWBs and the curvilinear welds of DP600 with failure consistently occurring in the region with more severe softening.

The aim of this study was to evaluation the microstructure and fatigue properties of welded joints made with fiber laser welding (FLW) on a high strength low alloy (HSLA) and dual-phase (DP980, UTS ⩾ 980 MPa) steel in similar and dissimilar material combinations. The fusion zone (FZ) consisted of martensite, and the heat affected zone (HAZ) contained some newly formed martensite and partially tempered martensite on the DP980 steel side. A characteristic asymmetric hardness profile across the dissimilar HSLA–DP980 welded joint was observed. While a soft zone occurred on the DP980 side, it was absent on the HSLA side. Inside the FZ two hardness sub-regions were observed due to the difference in the alloying elements between two steels along with the fast cooling during FLW. The presence of soft zone on the DP980 side had no effect on the tensile properties, since the lowest hardness value in the soft zone was still higher than that of the HSLA base metal (BM). A joint efficiency of 97–100% was achieved with respect to the HSLA. The strain to failure of the dissimilar HSLA–DP980 welded joints was significantly (∼threefold) higher than that of the similar DP980–DP980 welded joints. Although the fatigue strength of the dissimilar HSLA–DP980 welded joints was lower than that of DP980–DP980 welded joints, it was equivalent to that of HSLA–HSLA welded joints. Failure occurred in the BM on the HSLA side in the tensile tests and fatigue tests at high cyclic stress levels, where yielding occurred. At the intermediate and lower cyclic stress levels, fatigue failure occurred in the weld area due to the higher sensitivity to the weld concavity.

The state of knowledge of formation of the galvanneal coating on continuous process lines is reviewed. Influences of materials and process variables on phase makeup that are key to achieving acceptability are reviewed. Current targets for key process variables are then described, followed by a consideration of the most frequent galvanneal coating quality issues and their causes. New developments in roll texturing for temper rolling of galvanneal are then described.

The study was aimed at evaluating the microstructure and mechanical properties of high-speed fiber laser welded high strength low alloy (HSLA) and DP980 dual-phase steel joints with varying weld geometries. Fusion zone (FZ) consisted of martensitic structure, and heat-affected zone (HAZ) contained newly-formed martensite in both steels and partially tempered martensite in DP980. While HAZ-softening was present in DP980, it was absent in HSLA. A distinctive ‘‘suspension bridge’’-like hardness profile with the FZ hardness as a ‘‘pylon’’ appeared in the fiber laser welded joints. Both HSLA and DP980 joints showed a superior tensile strength, with a joint efficiency of 94–96% and 96–97%, respectively, despite a reduced elongation in DP980 joints. Fatigue strength was higher in DP980 joints than in HSLA joints at higher stress amplitudes, but had no obvious difference at lower stress amplitudes. DP980 multiple linear welds exhibited a larger scatter and lower fatigue strength. Fatigue failure of HSLA joints occurred in the base metal at a stress amplitude above 250 MPa, and at weld concavity at a lower stress amplitude below 250 MPa. Fatigue crack in DP980 joints initiated predominantly from the weld concavity at both high and low levels of stress amplitudes.

The aim of this study was to identify the effect of fiber laser welding (FLW) on the microstructure, hardness, tensile properties and fatigue performance of high-strength (UTS ≥ 980 MPa) DP980 dual-phase steel with single linear and multiple linear joint geometry. While FLWed joints showed tempered martensite at the outer heat-affected zone (HAZ) which caused softening in the welds, a lower extent of martensite tempering and higher hardness value were observed in the narrower HAZ of the FLWed joint than in the wider HAZ of the diode laser welded (DLWed) joint due to a higher power density, faster welding speed, lower heat input, and faster cooling rate. A characteristic “suspension bridge”-like hardness profile with the fusion zone (FZ) hardness as a “pylon” appeared in the FLW due to the formation of almost fully martensitic structure in the FZ. Despite the lower ductility after FLW, a joint efficiency of about 96–97% was achieved with the yield strength essentially unchanged. At higher stress amplitudes, fatigue life of the FLWed joints was equivalent to that of BM, but at lower stress amplitudes no direct improvement in the fatigue resistance was observed due to the presence of soft zone and weld concavity. Multiple linear welds appeared to increase the probability of premature dynamic fatigue failure at lower stress amplitudes as a result of increasing number of weld concavities and soft zones. Fatigue crack initiation occurred from the specimen surface where the weld concavity met with a soft zone, and crack propagation was mainly characterized by the typical fatigue striations along with secondary cracks.

Martensitic or complex phase steels are leading candidates for automotive impact management applications. However, achieving high strengths while obtaining high quality coatings via continuous galvanizing is a challenge due to cooling rate limitations of the processing equipment and selective oxidation of alloying elements such as Cr, Mn, and Si adversely affecting reactive wetting. The galvanizability of a CrMnSi steel with a target tensile strength above 1250 MPa was investigated within the context of the continuous galvanizing line. The continuous cooling transformation behavior of the candidate alloy was determined, from which intercritical and austenitic annealing thermal cycles were developed. The evolution of substrate surface chemistry and oxide morphology during these treatments and their subsequent effect on reactive wetting during galvanizing were characterized. The target strength of 1250 MPa was achieved and high quality coatings produced using both intercritical (75% γ) and austenitic (100% γ) annealing using a conventional 95%N2–5%H2, −30°C dew point process atmosphere and 0.20 wt% dissolved (effective) Al bath, despite the presence of significant Mn and Cr oxides on the substrate surfaces. It is proposed that complete reactive wetting by the Zn(Al, Fe) bath was promoted by in situ aluminothermic reduction of the Mn and Cr-oxides by the dissolved bath Al.

Creep tests were performed at 295 and 373 K on a cryogenically ball-milled Zn–4.5Al alloy. Creep tests on the as-milled microstructure having an average grain size of 260 nm showed clear signs of a threshold stress. The same material after a targeted heat treatment showed no signs of a threshold stress for the same alloy with an average grain size of 510 nm. In both cases stress exponent ( n ) values close to 1 and activation energies close to that of grain boundary diffusion were noted. Potential causes of the threshold stress are proposed as being a nanocrystalline oxide dispersion or non-uniform solute segregation, each of which could potentially interfere with grain boundary vacancy transfer mechanisms.

Carbon contamination is a significant issue with extreme ultraviolet (EUV) masks because it lowers throughput and has potential effects on imaging performance. Current carbon contamination research is primarily focused on the lifetime of the multilayer surfaces, determined by reflectivity loss and reduced throughput in EUV exposure tools. However, contamination on patterned EUV masks can cause additional effects on absorbing features and can affect the printed images. In this work, various carbon contamination experiments were performed to study the impact between contamination topography and observed imaging performance. Lithographic simulation using calculated aerial images and experimentally determined resist parameters was performed and compared to the printing results to estimate the allowed carbon thickness with critical dimension compensation applied to the mask.

Panels coated by hot dipping with zinc (HDG), Zn–5Al (Galfan) and Zn–1.5Al–1.5Mg coatings at different thicknesses were phosphated and painted on an industrial line. Crevice panels with non-painted bare parts modelling conditions in hem flanges, reference panels with open surfaces and formed non-painted panels were exposed to a cyclic accelerated automotive test. Zn–Al–Mg coatings with the thickness of 10 µm provided similar or even better protection than HDG and Galfan at 20 µm in both confined and open configurations. In comparison to 10-µm HDG, the Zn–Al–Mg coating delayed red rust appearance in crevices by a factor of 2 and the maximal depth of corrosion in the steel substrate was by 42% lower. Confined areas were more corroded than open surfaces. For HDG, the time to red rust appearance dropped by 50–75%, corrosion attack in steel was from 3.5 to 7 times deeper and mass gain was about 2.3 times higher in crevices than on open surfaces. Corrosion of Zn–Al–Mg may be more affected by local environmental conditions created by the crevice configuration than for HDG. Red rust appearance on formed panels of 20-µm Galfan, 7-, 10- and 14-µm Zn–Al–Mg was delayed to 10-µm HDG by a factor of 2.8, 3.5, 3.8 and >4.5, respectively. No adverse effect of forming was noticed. The results indicate that 2- to 3-fold reduction of the coating thickness for Zn–Al–Mg alloy coatings in comparison to traditional HDG may be possible without compromising the corrosion performance.

The mechanical properties of Zn–4 wt% Al casting alloys are compared after various processing methods including sand casting, die-casting, and high energy cryogenic ball milling. For the cast structures there is an increase in strength when transitioning from a coarse sand casting microstructure to a finer grained thin-section die-casting. This is in contrast to a decrease in strength and increase in ductility seen when the cast structure is broken up by high energy cryogenic ball milling to a uniform ultra-fine grain scale. The ultra-fine grained structures produced by cryogenic ball milling subjected to a range of isothermal heat treatments follow the Hall–Petch behavior over the range of grain sizes studied.