Materials Science Forum Vol. 1195

Abstract: Surface defects in hot-rolled steel slabs, particularly EN 10025-2 S235JR, are commonly addressed through manual flame scarfing. However, variability in operator technique and uncontrolled parameters often lead to inconsistent results. This study investigates the effects of inner oxygen nozzle length and scarfing path width using Taguchi experimental design and Response Surface Methodology. Key performance metrics—slag mass, removal depth, and processing time—were analysed. Results show that longer nozzles combined with narrower paths minimize slag without sacrificing efficiency. Regression models (R² > 0.95) validated by MATLAB simulations confirmed strong predictive accuracy. The findings offer a statistically optimized approach to improve surface treatment consistency, presenting a practical framework for enhancing manual scarfing operations in steel manufacturing.

Abstract: The cold forming of A 240 TP 304L stainless steel, as used in pressure vessel dish heads, introduces significant plastic deformation and internal stress-strain, which can lead to microstructural defects like hairline cracks. While plasma cutting is an efficient fabrication method, it creates a Heat-Affected Zone (HAZ), where thermal effects can obscure the stress-strain state, making it difficult to accurately identify defects. The study compared two methods for identifying the HAZ boundary: hardness measurements and magnetic measurements. Hardness measurements proved to be an unreliable method for defining the HAZ boundary, as the hardness values at the edges of the specimen showed insignificant and inconsistent differences compared to the central region. This is likely because the rapid heating from plasma cutting did not allow sufficient time for grain relaxation. In contrast, the magnetic measurement method proved to be a highly effective and relevant approach. Microstructural deformation resulting from shear forces during metal forming and plasma cutting causes a shift in the steel’s properties from paramagnetic to weakly ferromagnetic. This change creates a distinct magnetic remanence signature that clearly differentiates the HAZ from the parent material. Therefore, the induced magnetic property serves as a reliable, indirect indicator for the HAZ boundary. The non-contact and non-destructive nature of this magnetic measurement technique makes it a superior alternative to traditional methods that are often destructive, such an involve sectioning, or may fail to detect subsurface defects that are not visible during an inspection. This method holds significant potential for application in the manufacturing industry to enhance quality control and ensure the integrity of A 240 TP 304L stainless steel components.

Abstract: This study investigates the mechanical properties and microstructure of dissimilar welds between AISI 304 and Duplex 2550 using GTAW and SMAW processes with filler metals ER309 and E309-16. The weld joint exhibited a tensile strength of 508.7 MPa, lower than AISI 304's minimum of 515 MPa and Duplex 2550's 760 MPa, primarily due to the heat-affected zone (HAZ). Significant differences in hardness were observed, with the weld metal averaging 194.8 HV, compared to 181.9 HV and 229.9 HV for the HAZ of AISI 304 and Duplex 2550, respectively. Charpy tests indicated reduced impact energy and absorption in the weld metal and HAZ compared to the base metal. XRD analysis revealed the formation of intermetallic phases, including chi (χ), sigma (σ), and carbides in the weld metal, which compromised mechanical properties and corrosion resistance.

Abstract: Welding ferritic stainless steel to copper is well known to be challenging because of the large mismatch in their thermal conductivities and metallurgical behaviors. Dissimilar joints are required in a range of energy, automotive, and metallurgical applications. In this study, TIG welding of SS 409 to copper C11000 was performed using ERNiCr-3 (Ni-based) and ER70S-G (Mn-based) filler metals under controlled DCEN conditions to evaluate their mechanical and microstructural performance. Tensile testing, microhardness mapping, and microstructural observations using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS) were performed after the welding process. The results show that the joints welded with ERNiCr-3 exhibited a higher ultimate tensile strength, reaching approximately 220 MPa, along with an elongation of approximately 10%. In comparison, ER70S-G joints achieved a tensile strength of approximately 160 MPa and exhibited lower ductility, with an elongation of approximately 6%. A smoother hardness transition across the weld interface was observed for ERNiCr-3, whereas ER70S-G produced a more localized hardness peak close to the fusion boundary. SEM-EDS analysis indicated sound fusion for both filler metals, with limited formation of interfacial compounds. Based on these results, ERNiCr-3 remains the preferred filler when a higher mechanical performance is required. However, ER70S-G can be considered a practical and economical alternative to TIG-welded SS 409–Cu C11000 joints in applications where moderate strength is sufficient.

Abstract: This study develops a generalized regression neural network (GRNN) model to analyze the effectiveness of cryogenic machining compared to dry and wet machining. The model was trained using datasets derived from face milling experiments on SS316 stainless steel, involving variations in spindle speed, feed rate, and depth of cut, with surface roughness (Ra) as the measured output. Cryogenic machining consistently produced lower Ra values, as confirmed by Interval Plot analysis. The GRNN model accurately predicted Ra, achieving low Mean Absolute Percentage Error values (2.31% for training and 2.05% for testing), along with high coefficients of determination (R² = 0.9957 for training and 0.9956 for testing). The GRNN model was then utilized for sensitivity analysis and response surface analysis. Perturbation-based sensitivity analysis identified the machining technique as the most influential parameter. Response surface analysis further confirmed the superiority of cryogenic machining across all parameter settings.

Abstract: Friction stir welding (FSW) has risen to prominence recently due to its ability to join alloys having low weldability such as magnesium alloys. This paper aims to enhance mechanical properties of FSW joints of AZ31B-H24 by varying pin profiles. In this work, four different tool pin profiles were investigated, namely cylindrical, conical, square, and triangular. The FSW processes were conducted at tool rotation speed of 1500 rpm and tool traveling speed 30 mm/min. Afterwards, several experimental works were conducted, i.e. microstructure observations, hardness measurements, tensile tests, and fatigue crack growth rate (FCGR) tests combined with scanning electron microscopy (SEM) fractographic study. Results showed that the square pins produced the best FSW joints with the ultimate tensile strength (UTS), typically of 212.3 MPa respectively. Fractographic analysis showed that the fracture occurred in weld nugget zone (WNZ) close to advancing side (AS). It seemed that the high strength of FSW joints produced by the square pin was likely attributed to the proper frictional heat and material flow which gave the best dynamic recrystallization in WNZ. The present investigation also revealed that FSW joint under the the square pin had better fatigue performance than AZ31B-H24 base metal as indicated by its lower FCGR.

Abstract: The growth of the electronics industry highlights the need for lead-free solder materials that balance environmental safety and performance. This study examines the effect of Zn addition on Sn-0.7Cu-1.5Ag solder alloys containing 7, 8, and 9 wt.% Zn. The alloys were synthesized through melting and solidification, followed by characterization using SEM-EDX, DSC, Vickers hardness, wettability, and density tests. Results indicate that Zn promotes the transformation of Ag₃Sn into SnZn₃ phases, which dominate with higher Zn levels. The melting point decreased from 223.19 °C to 221.27 °C with a narrower transition range, suggesting improved thermal properties. However, Zn reduced wettability (7.43 mm² to 5.87 mm²), density (7.33 g/ml to 6.49 g/ml), and hardness (16.1 Hv to 15.4 Hv). Overall, Zn addition lowers the melting point but compromises mechanical strength and spreading ability, indicating the need for optimization to achieve reliable solder performance.

Abstract: Activated Tungsten Inert Gas (A-TIG) welding is widely used to enhance penetration in aluminum alloys; however, inconsistent weld performance is often reported even when similar active-flux chemistries are applied. This indicates that factors beyond flux composition alone influence weld stability, highlighting the importance of understanding flux delivery during welding. The scientific objective of this study is to clarify how solvent characteristics govern active-flux transport, surface retention, and weld pool response in A-TIG welding of Aluminum 5083-H116. Rather than optimizing flux chemistry, this work focuses on isolating the solvent effect using a TiO₂–SiO₂ active-flux system dispersed in methanol–isopropanol solvent mixtures. A-TIG welding experiments were carried out under identical welding parameters and flux chemistry, while varying the solvent composition. Weld penetration depth, penetration-to-width ratio, microhardness distribution, and grain structure were evaluated to assess the metallurgical response. The results show that solvent composition significantly influences penetration behavior, with penetration depth varying from approximately 3.5 mm to 5.0 mm and the penetration-to-width ratio increasing by up to 30% under more stable solvent conditions. Microhardness in the weld metal ranged between 70 and 90 HV, accompanied by observable differences in grain morphology. More stable flux retention associated with methanol-rich solvent mixtures produced smoother penetration profiles and finer, more uniform grains, whereas higher isopropanol content tended to result in less stable penetration and coarser grain structures. These findings provide new understanding that solvent selection plays a governing role in A-TIG welding by controlling flux transport and arc–pool interaction. The study extends conventional flux-centric A-TIG knowledge and offers a practical framework for improving weld stability and reproducibility in aluminum alloy welding through solvent-controlled flux delivery.

Abstract: This study investigates the coupled influence of vibration frequency and mold temperature on the solidification behavior and mechanical performance of recycled aluminum derived from automotive wheel scrap. Investment casting was conducted at mold temperatures ranging from 150 to 350 °C while applying mechanical vibration at frequencies between 100 and 250 Hz. Hardness testing, tensile characterization, optical metallography, and multi-scale SEM analysis were employed to evaluate the evolution of microstructure and defects under varying thermo-mechanical conditions. The results show that mechanical properties exhibit a non-linear dependence on vibration frequency, with an optimum window at 100–150 Hz where dendrite fragmentation, eutectic segmentation, and reduced microporosity contribute to enhanced hardness and tensile behavior. Frequencies above 150 Hz induce turbulent melt flow, promoting pore clustering and intermetallic agglomeration that significantly degrade strength. Mold temperature further modulates these effects, where temperatures above 300 °C suppress vibrational refinement due to reduced thermal gradients and grain coarsening. The combined findings demonstrate that microstructural refinement in recycled aluminum can only be achieved when vibration and thermal conditions are simultaneously optimized. This work establishes a clear processing window for vibration-assisted casting of recycled aluminum and provides practical guidance for industrial remelting operations targeting improved sustainability and mechanical reliability.