Ever since the Bronze Age, metals have been cast in different shapes for different applications. Smooth surfaces that are resistant to corrosion are crucial for many of the present-day uses of cast metals, ranging from bio-implants to automotive parts.
Optical microscope cross-sections of the alloy surface show that increases in laser beam overlap during processing reduces the number of small cracks (top left, 25% overlap; top right, 50%; bottom left, 75%; and bottom right, 90%).
Copyright : © 2013 Elsevier
Yingchun Guan, from the A*STAR Singapore Institute of Manufacturing Technology (SIMTech) and her co-workers have shown how different laser-processing methods improve metal surfaces and protect them against corrosion1.
Laser processing involves scanning a high-intensity laser beam multiple times across the surface of a metal. Each scan by the laser beam ‘writes’ a track in the surface, which partially melts the metal. Consecutive tracks can overlap — the degree to which affects how well the melting caused by these tracks will smooth the surface of the metal. The scanning speed can also affect the surface melt.
Guan and co-workers investigated how different degrees of overlap between the tracks affect the surface properties of AZ91D — a common magnesium alloy. “AZ91D is the most widely used magnesium alloy for the production of high-volume components for the automotive, electronics and telecommunications industries,” Guan explains.
By examining cross-sections of AZ91D samples post-melt, the researchers found that the greater the degree of overlap between the tracks, the fewer the number of small cracks that developed during solidification (see image). According to Guan, this finding should be considered when processing metals destined for exposure to fluids, such as those that will be used in bio-implants.
The researchers also detected alterations in the alloy’s composition through changes in the degree of laser-track overlap. Melted magnesium evaporates more readily than aluminum, and as the degree of laser-track overlap increased, it changed the composition of the alloy — particularly in the larger areas of melt. Theoretical calculations by Guan and her co-workers described these kinetics accurately.
According to the team’s model, a greater level of overlap provided a greater amount of heat, which improved the convection of the metals within the molten liquid and yielded a more homogeneous surface. Electrochemical tests by the team also confirmed that the more homogeneous the surface of a material, the more resistant it was to corrosion.
The team’s approach, particularly the theoretical model, is applicable to assess laser processing of other alloys and compounds, Guan notes. As the surface structures affect not only the mechanical and chemical properties but also the electronic, thermal and optical parameters, these findings will be of relevance to metals used in a variety of applications.
The A*STAR-affiliated researchers contributing to this research are from the Singapore Institute of Manufacturing Technology
ReferenceGuan, Y. C., Zhou, W., Li, Z. L. & Zheng, H. Y. Influence of overlapping tracks on microstructure evolution and corrosion behavior in laser-melt magnesium alloy. Materials & Design 52, 452–458 (2013).
New manufacturing process for SiC power devices opens market to more competition
14.09.2017 | North Carolina State University
Quick, Precise, but not Cold
17.05.2017 | Fraunhofer-Institut für Lasertechnik ILT
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems Holding GmbH about commercial use of a multi-well tissue plate for automated and reliable tissue engineering & drug testing.
MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
21.09.2017 | Physics and Astronomy
21.09.2017 | Life Sciences
21.09.2017 | Health and Medicine