Uceu Fuad Hasan Suhuddin

β Ti-18Mo-xCr alloy has been widely used as an orthopedic implant material because this alloy has the advantage of high strength a lower modulus of elasticity than commercial alloys Ti-6Al-4V, good corrosion resistance. and formability. This research aims to find alloys with high corrosion resistance and low modulus of elasticity and identify the presence of phase β after heat treatment. Ti-18Mo-7Cr is obtained from the melting process using an arc melting furnace followed by heat treatment (solution and aging treatment). To determine the modulus of elasticity using a sonelastic tool and hardness test using Microhardness Vickers. The EIS method was used to determine the corrosion resistance using a 0.9% NaCl solution as a simulated body fluid. The modulus of elasticity owned by the solution treatment alloy tends to be lower than that of the aging alloy. The lowest elastic modulus value and the highest hardness value are found in the Ti-18Mo-7Cr ST850 alloy, which is 91 GPa and 471.42 HV. For corrosion resistance, the aging treatment alloy shows a lower corrosion rate than the solution treatment alloy and is much lower than that of the Ti-6Al-4V alloy. On the other hand, the solution treatment can stabilize the β phase and reduce the corrosion rate due to heating below transus temperature, but aging with a longer holding time can also reduce corrosion resistance more than the corrosion resistance of the solution treatment. The alloy Ti-18Mo-7Cr AT500 has the lowest corrosion rate among the samples in this study, which is 0,0004225 mmpy.

Recycling aluminum chips remains a major challenge in aluminum manufacturing because it is difficult to retain the original quality alloy properties while reducing the carbon footprint and ensuring a sustainable process. This work investigates the microstructural evolution and bonding quality of compacted AA6082 chips processed through friction extrusion/consolidation. The residual material left inside the extrusion container after processing at a high extrusion ratio was analyzed using SEM, EDS, and EBSD to understand bonding mechanisms and microstructure evolution in front of the die. The SEM results show that voids are still present between the chips in the initial compacted material which already shows bonding, while these voids are reducing towards the die interface, particularly related to the present severe plastic deformation. EDS analysis confirms the presence of Al (Fe,Mn)Si intermetallic particles, which break and disperse in the matrix because of shear deformation due to die rotation. EBSD analysis reveals that grains are coarser near the base material, and subdivisions of grains near the die interface are significant because of continuous dynamic recrystallization.

Optimizing the performance and reliability of welding techniques for dissimilar aluminum (Al) to titanium (Ti) is a promising way to establish new applications in aerospace industry. Due to structural weight reduction, lightweight materials can help to minimize fuel consumption and save emissions. Solid-state welding technologies allow short joining cycles and metallurgical changes, residual stresses and severe intermetallic compound formation can be reduced by limited thermal exposure. Besides temperature and plastic deformation, intimate contact plays an important role for diffusion. In this work, AlMgSi alloys with systematic variations of Mg and Si alloying elements, were welded to Ti6Al4V (Ti64) by refill Friction Stir Spot Welding. The focus lays on the effect of Ti64 sheet surface roughness, varied by different surface preparations. Additionally, the influence of the plunge depth, the distance between the tool and the Ti64 sheet surface is analyzed. It was found that a reduced tool to interface spacing has a beneficial influence on joint integrity. Grinding trenches allowed better bonding compared to the pit-like surface structure generated by sandblasting, which led to an increase in mechanical lap-shear properties. Knurling the grinded surfaces resulted in high standard deviation, as most likely not the whole interface area was bonded. However, the partially outstanding properties showed that a beneficial effect can be expected due to mechanical interlocking mechanisms, when sufficient diffusion is ensured.

Friction Stir Extrusion (FSE), Direct Extrusion (DE) and Indirect Extrusion (IE) are all valid processes for the production of round profiles. However, differences and similarities between them have yet to be analyzed by the scientific community, since with the same geometry, each technology instills specific properties to the extruded product. In this context, the present work proposes an in-depth analysis via QForm UK Finite Element Method (FEM) software of the effect that each process has on a AA6061 extruded wire. Various combinations of rotational speed (200, 400, 600 rpm), feed rate (1, 2, 3, 4 mm/s) and pre-heating temperature (450, 500°C) were analyzed to assess differences and similarities between FSE, DE and IE. The feedstock material for FSE was chosen to be powder, while a solid billet was used for conventional extrusion.

Optimizing the mechanical properties of aluminum to titanium welds is crucial to establish applications for dissimilar lightweight structures in the aerospace industry. In this context, solid-state welding technologies have proven effective in terms of short joining cycles, allowing the combination of cost-effective production and structural weight optimization. However, metallurgical effects between aluminum and titanium in the joint interface are still not completely understood due to differences in physical as well as chemical characteristics. In this study, aluminum alloy 6013 was welded to Ti6Al4V by refill Friction Stir Spot Wel ding, including systematic variations of Mg and Si alloying element content in the used AA6013 sheets. In total five different Al alloys were welded to the titanium to investigate the influence of Mg and Si during processing. Apart from the material selection, the weld strength is mainly influenced by the intermetallic compound thickness at the interface, which in turn primarily depends on the exposed temperature cycle. Consequently, major interest during this study was given on the temperature evolution, interfacial features and the global mechanical properties.

Refill friction stir spot welding (refill FSSW) is a solid-state joining technique that enables dissimilar welding between aluminum and steel alloys with minimal intermetallic compound (IMC) formation. Previous studies have focused on the interfacial mechanical performance of such joints, limited attention has been given to the localized corrosion behavior of the aluminum surface after welding, particularly in relation to microstructural evolution. This study investigates the effect of refill FSSW on the localized corrosion resistance of the aluminum surface in dissimilar joints with DP600 steel, since the Al side is typically the exposed surface in automotive service conditions. Emphasis is placed on the correlation between microstructural changes induced by the welding thermal cycle, such as grain refinement and precipitate coarsening, and localized corrosion behavior. The welded samples were characterized by optical and scanning electron microscopy, Vickers hardness measurements and potentiodynamic polarization techniques. Corrosion tests revealed a slight reduction in corrosion resistance in the stir zone compared to the base metal, mainly attributed to Mg₂Si coarsening. Pit initiation sites were associated with Al(Fe, Mn)Si and Mg₂Si precipitates. These findings offer new insights into the corrosion mechanisms acting on the aluminum surface of refill FSSW joints, supporting the development of more corrosion-resistant dissimilar structures.

The refill friction stir spot welding (refill FSSW) process is an innovative solid-state spot-welding method, which has evolved from the concept of friction stir welding. Compared to riveting, the process has the advantage of avoiding stress concentration by eliminating holes. In addition, weight can be saved compared to riveting as no additional material is needed. However, the fatigue strength of refill FSSW joints under cyclic loading is still not satisfactory. To address this challenge, laser shock peening (LSP) is investigated as an innovative residual stress engineering technique to improve the fatigue performance of refill FSSW AA2024-T3 joints. Two application scenarios are investigated, one investigating the LSP technique as a complementary manufacturing process to the refill FSSW technology, and the other investigating the LSP technique as a repair process for damaged joints. The fatigue test results showed that the application of the LSP treatment can significantly improve the fatigue behaviour of the refill FSSW overlap joints. In terms of Basquin fatigue strength, the LSP treatment resulted in an improvement by a factor of 1.51 and 2.82 for the one- and two-sided LSP-treated specimens, respectively. The life of specimens with refill FSSW joints that had been specifically pre-damaged by stopping the fatigue test at approximately 51%, 75% and 83% of the number of cycles to the Basquin fatigue strength, applying LSP treatment and continuing the fatigue test was also significantly extended. The results of this study show that LSP is a very effective technique for significantly extending the fatigue life of refill FSSW joints. Therefore, the combination of these two manufacturing processes, refill FSSW and LSP, represents a promising technology for industrial companies that require high fatigue performance for their structural components.