Study on Rolling Defects of Al-Mg Alloys with High Mg Content in Normal Rolling and Cross-Rolling Processes.

This study investigated defect formation and strain distribution in high-Mg-content Al-Mg alloys during normal rolling and cross-rolling processes. The finite element analysis (FEA) revealed the presence of wave defects and strain localization-induced zipper cracks in normal cold rolling, which were confirmed by the experimental results. The concentration of shear strain played a significant role in crack formation and propagation. However, the influence of wave defects was minimal in the cross-rolling process, which exhibited a relatively uniform strain distribution. Nonetheless, strain concentration at the edge and center regions led to the formation of zipper cracks and edge cracks, with more pronounced propagation observed in the experiments compared to FEA predictions. Furthermore, texture evolution was found to be a crucial factor affecting crack propagation, particularly with the development of the Goss texture component, which was observed via electron backscattered diffraction analysis at bending points. The Goss texture hindered crack propagation, while the Brass texture allowed cracks to pass through. This phenomenon was consistent with both FEA and experimental observations. To mitigate edge crack formation and propagation, potential strategies involve promoting the formation of the Goss texture at the edge through alloy and process conditions, as well as implementing intermediate annealing to alleviate stress accumulation. These measures can enhance the overall quality and reliability of Al-Mg alloys during cross-rolling processes. In summary, understanding the mechanisms of defect formation and strain distribution in Al-Mg alloys during rolling processes is crucial for optimizing their mechanical properties. The findings of this study provide insights into the challenges associated with wave defects, strain localization, and crack propagation. Future research and optimization efforts should focus on implementing strategies to minimize defects and improve the overall quality of Al-Mg alloys in industrial applications.

Microstructure and Mechanical Properties of Commercially Pure Ti/Steel Joint Brazed by Zr-Ti-Ni Amorphous Filler Metal.

In this study, the characteristics of commercially pure titanium (hereinafter referred as CP-Ti)/Steel joints, brazed with Zr-Ti-Ni amorphous filler metal were analyzed. The effects of brazing temperature and time on the microstructure and joining strength of the CP-Ti/Steel joints were investigated. It was observed that Ti diffused into stainless steel substrate formed a brittle reaction zone, which contained intermetallic compounds, such as τ (Ti5Cr7Fe17), (Fe, -Ni)Ti, and FeTi, observed at the joint interface. As the brazing temperature and time increased, the width of the reaction layer in the joint was observed to increase. To suppress the oxidation of the substrates, the experiment was conducted at a cooling and heating speed of 100 °C/min, under a vacuum of 5×10-5 torr. The joining strength was observed to be significantly affected by the brazing conditions, such as temperature and duration time. The shear strength test showed that the strength increased for 15 min and then sharply decreased. This was attributed to the formation of brittle intermetallic compounds, like (Fe, Ni)Ti. The joint brazed at 880 °C for 15 min showed the maximum joining strength, of 216 MPa.

Brazing Characteristics and Bonding Strength of Pure Titanium Joints Brazed with Low-Melting Temperature Zi-17Ti-22Ni Filler Metal.

The brazing characteristics and bonding strengths of pure titanium joints are evaluated for joints brazed with Zr-17Ti-22Ni filler. Vacuum brazing was conducted at temperatures between the melting temperatures of the filler metals and the beta-transition temperature of pure titanium at 3 MPa of pressure for 5 min. Fracturing of the pure titanium joint brazed at 1,093 K occurred before yielding during the tensile tests owing to the presence of a serious segregation region containing harder and more brittle [Ti, Zr]2Ni intermetallic compounds. In contrast, in pure titanium joints brazed at and above 1,113 K, fracturing occurred at the base metal. The yield strengths of the samples brazed at 1,113 K-1,133 K were estimated to be in the range of 320-350 MPa and the ultimate tensile strengths likewise ranged from 350 to 380 MPa. The strength of pure titanium brazed at 1,153 K decreased rapidly. The results of this study show that the optimum temperature to ensure good performance after the brazing of pure titanium with Zr-17Ti-22Ni as a filler metal ranges from 1,113 K to 1,133 K.

Microstructural and Mechanical Characteristics of A356 Alloys as a Function of Mn Content and Cast Thickness.

In this study, the changes in the microstructural characteristics and mechanical properties of A356 alloys as a function of Mn content and cast thickness were evaluated using structural analysis and tensile tests. Five different A356+x%Mn alloys were prepared by casting in molds of different thicknesses followed by solid solution treatment at 813 K for 195 min and aging treatment at 423 K for 120 min. It was confirmed that the secondary dendrite arm spacing (SDAS) increased with increasing thickness of the cast sample, whilst, for a given thickness, the addition of small amounts of Mn resulted in a decrease of the SDAS. Mn contents of 0.05-0.15% resulted in ~7-9% improvements in the spheroid ratio of the primary Si particles compared to that of the commercial A356 alloy. Further, the spheroid ratio of the primary Si particles obtained in the thin cast samples were higher than that obtained in the thick cast samples. In particular, the addition of small amounts of Mn was also effective in suppressing the formation of the needle-like beta Al-Fe-Si intermetallic compound. The yield and tensile strengths of the thinner cast samples were higher than those of the thicker cast samples. Finally, Mn contents of 0.05-0.15% resulted in enhanced yield and tensile strengths, but Mn content ≥0.1% resulted in decreased elongation.

Evaluation of the Hot Workability of Commercially Pure Ti Using Hot Torsion Tests.

Optimum processing conditions were obtained by evaluating the hot working behavior of commercially pure Ti using hot torsion tests. Hot torsion tests were conducted at temperatures ranging from 800 °C-1000 °C and strain rates ranging from 0.1-10 s-1. The flow curves show that the peak stress increases as the temperature decreases and the strain rate increases. The optimum processing conditions were derived by comparing the processing and activation energy maps. The microstructure was characterized based on various regions of the processing map. The activation energy for plastic deformation was obtained using the constitutive equation. The activation energy differs depending on the constituent phases.