Key Engineering Materials Vol. 981

Abstract: Zinc has attracted significant attention in research due to its cost-effective use as an electrodeposited material, effectively protecting various types of steel from corrosion and wear. However, despite its advantages, zinc has limitations in fully guarding steel against corrosion. Recent studies propose that blending zinc with other metals during the coating process can proficiently shield mild steel from deterioration. The motivation for this study stems from recognizing the restrictions of zinc electrodeposition and the limited exploration of zinc multi-facet composite coatings for mild steel. In this study, the electrodeposition technique was employed to apply a coating to mild steel using zinc and nanoparticles of calcium oxide (CaO) and manganese oxide (MnO₂). The coating bath's chemical composition included mass variations of 0-12 g/L for CaO and MnO₂, along with 10 g/L each of boric acid, thiourea, and Na₂SO₄, and 15 g/L of K₂SO₄ and ZnSO₄. The coating process occurred over a twenty-minute period, with a pH of 4.8, voltage set at 3.2V, current density at 1 A/cm², temperature at 47°C, and stirring rate at 200 rpm. Results obtained from the coated mild steel demonstrated that Zn-6CaO-6MnO₂ exhibited the greatest coating thickness at 0.2308 mm, and it showcased impressive corrosion resistance at 2.0618 mm/year. The Zn-CaO-MnO₂ coating displayed a substantial deposit of crystallites in its microstructure, assisted by the presence of manganese, contributing to a smoother surface texture.

Abstract: The extent of deformation in the process of forming body elements affects the amount of thinning of the shaped material, and consequently the possibility of material cohesion loss. In the tests, the size of deformation of the car body elements in the stamping process was determined according to the measurement of the displacement of the measurement points. A measuring grid was applied to the surface of the mat by electrochemical etching. The form with the applied measuring grid was drawing on the production line. Reference point displacement measurements were made with the use of an optical measuring system. The forming limit curve was determined for the CR4 grade steel sheet with a thickness of g = 0.75 mm. The deformation measurement results were related to the forming limit curve to identify the actual deformation level. The results of the deformation measurement allowed to indicate the place and scope of the correction of the shaping tools geometry and process parameters.

Abstract: The fatigue strength of maraging steel, which is an ultra-high-strength steel, is relatively low, compared to that of conventional high-strength steel. The fatigue life of a structure is highly dependent on the surface conditions, because fatigue cracks generally start at the surface of the material. In particular, surface cracks considerably degrade the fatigue limit. To expand the application range of maraging steel, it is necessary to improve the fatigue limit, and render the surface cracks harmless. This study aims to investigate the effect of shot peening (SP) on the fatigue strength of maraging steel with surface cracks. The SP application introduced a compressive residual stress from the specimen surface to a depth of 170 μm, and increased the fatigue limit by 77 %. The estimated crack size that can be rendered harmless, based on fracture mechanics, is (0.170 − 0.202) μm in the range As = (1.0 − 0.1). The intersections of the harmless crack sizes were determined at depth. A semicircular surface crack below this value is harmless in terms of fatigue limit. The usefulness of non-destructive inspection (NDI) and non-damaging technology was evaluated in relation to a_hml, a_NDI, a_25,50, and As. Thus, the SP process can improve the reliability of the maraging steel. Compressive residual stress is the dominant factor to improve fatigue strength and render the surface crack harmless.

Abstract: The aim of this work was to study the microstructure evolution of simulated heat affected zone in mild steel using thermal cycle simulation and it was compared to the heat affected zone in the real welded joint. The optical microscopy, micro-hardness measurements, X-ray diffraction were used as characterization techniques. The microstructures and mechanical properties of the simulated heat affected zone were also determined. The use of the thermal cycle simulation technique revealed in detail the different microstructures in the heat affected zone (HAZ) of the welded joint. Some similarities were observed between the heat affected zone obtained by the thermal cycle simulation technique and the heat affected zone observed in the real welded joint. The thermal cycle simulation technique revealed more details about the microstructure and mechanical behavior of the heat-affected zone. The HAZ microhardness values were lowest hardness in the welded joint. Moreover, the lowest hardness value is obtained for the HAZ simulated at 850°C.

Abstract: In this study, use of adhesive double-sided tape in laser welded ultra-high-strength steel lap joints was evaluated. The test material in the study was abrasion resistant steel (AR400). Optical microscopy was used to investigate macroscopic morphologies of the welds and hardness profiles were measured. Static properties of the joints were evaluated by performing tensile shear strength tests. Fatigue strength of the joints were evaluated by conducting axial fatigue tests. The use of tape resulted in a gap between the welded plates which has several advantages. The gap between the plates markedly increased the width of the weld at the interface of the plates. According to the hardness measurements the hardness of the weld metal was 12% higher compared to the hardness of the AR steel base material. The gap between the plates increased the strength of the joint by up to 20%. The adhesive tape itself did not have a significant effect on the shear strength of the joints. The main advantages of using the tape were a constant air gap and its function as a fastener in welding, so that separate fasteners are not needed.

Abstract: In the present work, a cellular automata finite element model (CAFE) was developed to model the ductile-brittle transition of a Grade A ship plate steel. Therefore, ductile and brittle cellular automata (CA) arrays of cells were created in the model to integrate material data at microstructural level, along with the ductile and brittle fracture processes. Microstructural data was analysed with Weibull distributions and incorporated in CAFE model using random number generators, along with ductile and brittle fracture parameters. Ductile fracture was modelled with Rousselier damage model; hence damage model parameters were calibrated with experimental data. Brittle fracture was modelled with Beremin model, and four different cleavage particles, found in a Grade A ship plate steel, were incorporated in CAFE model in order to model a competition of particles nucleating microcracks of critical size in the damage regions of Impact Charpy tests and four-point double-notch bend tests performed at low temperature. The mechanical properties the plate steel was measured in the transition region and incorporated in CAFE model, along with ductile-brittle transition rules. The present CAFE model was able to simulate distributions of microcracks in the notch region of four-point double-notch bend models (in the transition region), which correlated with experimental data. CAFE model was also able to simulate microvoids in the notch region of Charpy specimens along with the load-displacement Charpy curve for room test temperature, with very good agreement with experimental data. Once CAFE model was validated at micro and structural level, it was applied to model the typical scatter of impact Charpy energy values in the transition region of Grade A ship plate steel with good agreement with the measured ductile-brittle transition curved of the plate steel. Keywords: cellular automata, finite element modelling, ductile-brittle transition, damage modelling.

Abstract: The article presents some new theoretical and experimental solution of a scientific and applied problem of technological support for vibratory centrifugal processing of complex-profiled parts in a bulk abrasive environment. This solution aims to increase productivity while ensuring the desired quality of the processed surfaces. The authors have developed a mathematical model that describes the action of abrasive particles on the surface of the parts, taking into account the parameters of the granular abrasive medium based on Voigt’s law. This allows the description of dynamic processes in the processing environment for a wide range of material types. The natural frequencies of oscillations of the processed medium layer have been determined, which depend on the amplitude of its vibrations for different densities of soft and hard materials of the processed medium and the medium with linear-elastic properties. The methodology includes the use of test equipment to conduct experimental research on the process, which involves determining changes in specific metal removal rates and surface roughness using the frequency converter Altivar 71 with the PowerSuite v.2.5.0 software.

Abstract: The demand for structural lightweight in a variety of industries, particularly the automobile industry, has driven the development of heat-free die-cast aluminum alloys with excellent properties. Utilizing lightweight materials, such as Al-Si alloys has several benefits, including higher overall performance in automobiles and other industries, increased heat resistance efficiency, decreased emissions, and reduced weight. The purpose of this study is to modify the microstructure and enhance the mechanical properties of high-pressure die-casting (HPDC) AlSi10MnMg foundry alloy by incorporation of TiB₂ and Sc without any heat treatment. The results showed that the HPDC process significantly refines the grain structure and AlSiMnFe intermetallic compounds, transforming the eutectic morphology from sharp to rounded, and 93% enhancement in elongation at the optimum content (0.018 wt.%) of TiB₂. While the hardness of the alloy was improved by 15.7% with the addition of 0.03wt.% TiB₂. TiB₂ incorporation refines the grain structure and AlSiMnFe phases, while depressing externally solidified crystals (ESCs). The HPDC process refines Al₃Sc phases as well as AlSiMnFe phases while increasing yield strength due to Al₃Sc strengthening effects. After 0.5wt.% Sc addition in 0.018wt.% TiB₂-AlSi10MnMg alloy, the YS, and EL reached the maximum of 196MPa and 9.93% respectively.

Abstract: Waste eggshell powders with a particle size of less than 0.315 μm were surface treated with vinyltrimethoxysilane. XRD, FT-IR, BET and SEM analyses were used to determine the surface characteristics of eggshells before and after silane treatment. The preparation of films of unplasticized suspension polyvinyl chloride with untreated and silane-treated eggshells was done by co-precipitation of solutions from cyclohexanone. The tensile properties of obtained films containing vinyltrimethoxysilane-treated eggshell powders were investigated and analyzed relative to the compositions with untreated powders.