Microstructure and properties of AZ31 with an Al/Si-enriched surface layer fabricated through thermochemical treatment
| Autor: | Michał Cieślik, R. Mola |
|---|---|
| Rok vydání: | 2019 |
| Předmět: |
010302 applied physics
Materials science Scanning electron microscope Analytical chemistry 02 engineering and technology Surfaces and Interfaces General Chemistry 021001 nanoscience & nanotechnology Condensed Matter Physics Microstructure 01 natural sciences Surfaces Coatings and Films Phase (matter) 0103 physical sciences Volume fraction Materials Chemistry Surface layer 0210 nano-technology Powder mixture Eutectic system Solid solution |
| Zdroj: | Surface and Coatings Technology. 374:201-209 |
| ISSN: | 0257-8972 |
| Popis: | The surface enrichment of AZ31 magnesium alloy with Al and Si was achieved using the thermochemical treatment method. The experiments involved heating AZ31 in contact with an Al + Si powder mixture. Two mixtures acting as the source of diffusion elements were tested: 80% Al + 20% Si and 50% Al + 50% Si. The heat treatment of the AZ31 in the Al + 20% Si mixture was performed at three different temperatures: 435, 445 and 455 °C. As the best results were obtained at 445 °C, this temperature was used to heat AZ31 in contact with the Al + 50% Si mixture. The surface modification of AZ31 was attributable to the diffusion processes taking place at the substrate/powder reactive interface. The microstructure of the alloyed layers was characterized using an optical microscope (OM) and a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). An X-ray diffractometer (XRD) was employed to determine the phase composition. The examinations showed that the modified surface layer produced from the Al + 20% Si powder mixture was continuous and had uniform thickness (400–450 μm). The Al/Si-enriched layer was mainly composed of a eutectic, i.e., an Mg17Al12 intermetallic phase and a solid solution of Al in Mg, and unevenly distributed Mg2Si phase particles. The use of the Al + 50% Si powder mixture resulted in the formation of a thinner, continuous layer (about 200 μm) with a much higher volume fraction of the Mg2Si phase. In this case, the layer had a more uniform structure; the particles of the Mg2Si phase were evenly distributed over the eutectic matrix. Due to the presence of hard phases, i.e., Mg2Si and Mg17Al12, both types of Al/Si-enriched surface layers had much higher hardness than the AZ31 substrate. The tribological tests revealed that the alloyed layers had very good wear resistance under dry sliding conditions. Because of the higher volume fraction of the Mg2Si phase particles, the layer fabricated from the Al + 50% Si powder mixture had higher hardness and wear resistance than the layer fabricated from the mixture containing 20% Si. |
| Databáze: | OpenAIRE |
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