Laser joining for different materials between 1050 aluminum alloy sheet of 1 mm thickness and polypropylene sheet of 2 mm thickness using a newly developed insert sheet was studied. The diode laser-irradiation to the polypropylene side was carried out in air. The effects of the aluminum surface state on the joining properties were examined. The joining strength increased with the increase in aluminum surface area except for the surface with the intense ruggedness. It was found that the chemical condition of aluminum surface treated with the acid or alkaline solution strongly affected the joining strength rather than the surface roughness.
With the rapid development of electronic devices, internal heat generation in these devices becomes significantly denser. Accordingly, their thermal management becomes increasingly important for stable operation. For the performance improvement of heat dissipation in limited installation spaces, passive two-phase cooling technique using water is applied. Instead of water, using a more volatile substance as the working fluid is advantageous in many aspects. For instance, the higher volumetric capacity that is the product of vapor density and latent heat of vaporization allows compactness, while higher boiling heat transfer coefficient can extend the stable operation conditions under heavy loads of the electronic devices. In this study, a gravity-driven cooling circuit known as thermosyphon using refrigerants R134a, R1234ze(E), and R1234ze(Z) is experimentally investigated. The experimental thermosyphon successfully kept the heating block temperature simulating electronic devices below 80 °C at heat fluxes up to 1400, 1250, and 1110 kWm-2 with R134a, R1234ze(E), and R1234ze(Z), respectively. Furthermore, using a super-hydrophilic boiling surface fabricated by laser irradiation, the heat flux was extended to 1600, 1400, and 130 kWm-2 , respectively. The experiment demonstrated that using the selected volatile fluids and super-hydrophilic surfaces could be a beneficial method for cooling electronic devices.
Thixomolded magnesium products have been applied as an alternative for plastic moldings in body frames for electronic equipments. AZ91D magnesium alloy chips are ordinarily used for thixomolding process. The carbon nanoparticle was fixed in the magnesium chip surface in order to improve the castability of thixomolding process. The manufacture of magnesium-carbon alloy is not easy, because carbon does not have the wettability for magnesium. However, the magnesium alloy chips fixed carbon nanoparticles make it possible to produce the magnesium-carbon alloy by thixomolding process. Since the fluidity of the magnesium alloy chip with carbon nanoparticle was improved in comparison with the AZ91D magnesium alloy chip, thin thickness molding became possible. In addition, mechanical properties of the thixomolded magnesium alloy made of the magnesium alloy chips fixed carbon nanoparticle were also improved.
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