Microstructure and mechanical properties of Al-Alloy with rare earth

• Main Author: Mohammad Diab, Nateg
• Format: Thesis
• Language: English
• Published: 2015
• Subjects: TJ Mechanical engineering and machinery
• Online Access: http://eprints.utm.my/id/eprint/48722/25/NategMohammadDiabMFKM2015.pdf; http://eprints.utm.my/id/eprint/48722/; http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:85087

The development of aluminum alloys is of great interest to many of the industries and biomedical applications, because they provide a high strength to weight ratio, high wear resistance, low density and low coefficient of thermal expansion compared with other materials. These improvements in the field of application make the study of their mechanical behavior of utmost importance. However, these alloys possess some limitations in terms of the interactive effects of additives. Therefore, the present study aims to investigate the influence of the rare-earth, e.g., Lanthanum and yttrium with the amounts of 0.5, 1.0, and 1.5 wt.% on the microstructure and mechanical properties of hypereutectic Al-Si and hypoeutectic Al-Mg alloys. The microscopic observations contain of optical, field emission scanning electron, energy dispersive spectroscopy and X-ray diffraction, and mechanical properties testing, such as tensile, impact, and hardness test were carried out. A good agreement was observed between the results of microstructure and mechanical properties. XRD and EDS results indicate the formation of intermetallic compounds that associated with the modifications, which may play a major cause in improving the mechanical properties. It was also found that the secondary dendrite arm spacing value became smaller with increasing La addition, and decreased slightly from the unmodified 5 µm to 4.1 µm. On the other hand, when the content of La is 1.0%, the iron-rich phases tend to be slender with a size of about 0.5 µm. While with the addition of 1.0 wt.% of Y, the volume fraction of the dendritic phase are tend to decrease along with increase the grain size to 40 µm. The modifications of Al-alloy eutectic structure were improved ductility from 0.7% and 8% to 1.8 and 10.5 with the addition of 1.0 wt.% of La and Y, respectively. However, the addition of 1.0 wt.% of La and Y led to increase the ultimate tensile strength from 100 MPa and 180 MPa to 150 MPa and 200 MPa, respectively. A further addition of La and Y results in a reduction in mechanical properties.