Dissimilar friction stir welding between polycarbonate and AA 7075 aluminum alloy

In this paper, the effects of process parameters, such as the tool rotational and traverse speeds, on temperature evolution and the microstructural and mechanical properties of dissimilar friction stir welding between 3 mm thick AA 7075 aluminum alloy and polycarbonate (PC) plates were investigated. The tool rotational and traverse speeds were varied from 3 000 to 3 500 rpm and 50 to 150 mm min(-1), respectively. The joint fabricated at 3 250 rpm and 100 mm min(-1) yielded a highest tensile load of 586 N. Microstructural analysis of the stir zone revealed an interlock phenomenon, the transportation of AA 7075 in polycarbonate, and the absence of ceramic-type (carbide, hydride or oxide) compounds. Microhardness (HV) measurement on the weld zone showed an uneven distribution due to the complicated microstructure of the welded joint. The maximum temperatures of 164 degrees C and 66 degrees C were obtained at 3 250 rpm and 100 mm min(-1) at a distance of 5 mm away from the welding centerline in the AA 7075 and PC side, respectively

Employment of fiber laser technology to weld austenitic stainless steel 304 l with aluminum alloy 5083 using pre-placed activating flux

The overlapping welding was carried out in keyhole mode between austenitic stainless steel 304 l and aluminum alloy 5083 using a low power fiber laser in continuous irradiation. The significant content of magnesium as the alloying element with low boiling point and high vapor pressure inside the AA 5083 matrix can induce the spatter formation and depression on surface of the weld beads upon laser beam absorption and temperature growth which can deteriorate the mechanical properties and appearance of the joints. To reduce these defects, a variety of single and multi-components activating fluxes including oxide-based TiO2 and halide-based CaF2 flux powders were pre-placed on the surface of welding material prior to laser welding. The EDX and XRD analyses in addition to microhardness and shear tests were carried out to characterize the joints. The obtained results showed that, the oxide and halide activating fluxes can significantly improve the joints' strength up to 1.48 and 1.85 times in average respectively compared with autogenous joint. It was deduced that the simultaneous effect of significant decrease in joints' surface depression leading to welds' geometry improvement in addition to less formation of interfacial Fe-Al intermetallics, were the major causes for considerable strength improvements. (C) 2015 Elsevier Ltd. All rights reserved

Site diversity mitigation techniques for satellite services for KA-band

Ku and Ka-band are in high-frequency range within the frequency spectrum which is typically from 12 to 18 GHz and 26.5 to 40 GHz respectively. This wide range of frequency offers a huge capacity for satellite broadcasting and broadband applications respectively. In addition to huge capacity, operating at this range of high frequency allows smaller antenna size at consumers’ premise. This is due to the fact that the higher the frequency, the higher the antenna gain thus making it possible to reduce the antenna size to the minimum possible while preserving the required availability. However, operating at high frequency is more susceptible to weather conditions. This is due to the nature of its small signal wavelength where signal power can be absorbed by moisture or water droplets along it transmission paths. It will result in signal impairments thus quality of services. The objective of this research is to study the effectiveness of a mitigation technique called “Site Diversity” in enhancing the service availability for services operating at Ka-band frequency. The data are analyzed using ITU-R site diversity gain model, ITU-R diversity improvement factor mode and Hodge site diversity gain model. Data from two earth station sites, one located in Rawang and the other in Cyberjaya were collected and analyzed within the period of this study. The reference satellite used is MEASAT 5 satellite located at 119-degree east longitude. From the analysis it can be shown that availability of services can be increased up to 99.99% when implement site diversity techniqu

Characterization and microstructural studies of life 5O 8 synthesized by the self propagating high temperature combustion method

LiFe 5O 8 was synthesized by the self-propagating high temperature combustion synthesis using lithium acetate and iron acetate as starting materials and glycine as reductant. The reaction was rapid when the ignition temperature was reached and the product was a light and porous mass of solid material. Analysis using X-Ray powder diffraction and SEM revealed the amorphous nature of the LiFe 5O 8 precursor material. From particle size analysis, the precursor material was much less than 100 nm, but increased upon annealing at 650 °C and 900 °C