Microwave material processing is a novel energy efficient technology with improved mechanical properties, minimized defects and economical and environmental advantages making it a convenient application for various types of materials. Although, microwave interaction with matter has been largely investigated and published in food processing, ceramics and chemistry, no particular work has been involved in collecting the interactions of microwaves with metals and placing a special emphasis on their interaction with metals and metal-based formulations, and here resides the aim of the review: consolidating the fundamentals of microwave heating applications as a time and energy saving application and addressing its various applications and mechanisms with metal interactions seeking a more sustainable environment. This review reports the latest literature findings on microwave processing fundamentals and highlights the advanced technological improvement applied on metals in this field. It focuses on the relevant industrial applications related to the development of microwave technology on metals and its possible future processing in this specific scope of investigation.

Microwave dielectric heating: Applications on metals processing

https://www.mri.psu.edu/sites/default/files/file_attach/204.pdf

Effect of microwave and conventional heating on sintering behavior and properties of Al-Mg-Si-Cu alloy

Nanocrystalline bulk materials are desirable for many applications as they combine mechanical strength and specific electronic transport properties. Our bottom-up approach starts with tailored nanoparticles. Compaction and thermal treatment are crucial, but usually the final stage sintering is accompanied by rapid grain growth which spoils nanocrystallinity. For electrically conducting nanoparticles, field activated sintering techniques overcome this problem. Small grain sizes have been maintained in spite of consolidation. Nevertheless, the underlying principles, which are of high practical importance, have not been fully elucidated yet. In this combined experimental and theoretical work, we show how the developing microstructure during sintering correlates with the percolation paths of the current through the powder using highly doped silicon nanoparticles as a model system. It is possible to achieve a nanocrystalline bulk material and a homogeneous microstructure. For this, not only the generation of current paths due to compaction, but also the disintegration due to Joule heating is required. The observed density fluctuations on the micrometer scale are attributed to the heat profile of the simulated powder networks.

http://iopscience.iop.org/article/10.1088/0957-4484/22/13/135601/pdf

From nanoparticles to nanocrystalline bulk: percolation effects in field assisted sintering of silicon nanoparticles.

Mechanical and physical properties of sintered aluminum powders

The effect of the addition of elemental Mg, Sri and Pb on the sintering of impressed prealloyed 2124 and 6061 powder has been investigated. Despite being sintered at a temperature that resulted in similar to20 vol.% liquid phase, high density was possible only upon the addition of similar to1% elemental Mg as well as trace amounts of Sri or Pb. Additions of Mg facilitated oxide disruption, while Sri and Pb segregated to the liquid phase, where they reduced the liquid's surface tension, thus improving sintering. (C) 2002 Elsevier Science B.V. All rights reserved.

On the sintering of uncompacted, pre-alloyed Al powder alloys

The present powder metallurgy production route for sintered aluminum alloy parts is based on the liquid phase sintering of premixed powder compacts. This paper presents the results of a study of an alternative net shape powder processing route, using vacuum degassing, compaction and sintering of a prealloyed 6061 Al powder. The compacting conditions were varied to determine their effects on the green density and green strength of the compacts prepared from the as-received and degassed powders. Using the same compacting conditions, the compacts prepared from the degassed powder were sintered at three different temperatures within the melting range of the alloy to determine the effect of this parameter on sintered density and tensile properties. The degassing was found to increase the green density, and the transverse rupture strength of green compacts was a factor of two greater for the degassed powder. Furthermore, the tensile properties of the degassed and sintered powder compacts were higher than those of equivalent alloys prepared for blended powders and comparable to the tensile properties achieved via degassing and hot extrusion of the prealloyed 6061 Al powder.

S. Pelletier

Papers

Sintered 6061 al prealloyed powder : Processing and mechanical behavior