Using Recycled Materials for Semi- Solid Processing of Al-Si-Mg Based Alloys

In order to reduce CO2 emission and energy consumption, more recycled secondary materials have to be used in foundry industry, especially for Al-Si-Mg based alloys for semi-solid processing. In this paper, Al-Si-Mg based alloys with the addition of recycled secondary materials up to 30 % (10, 20, 30 %, respectively) have been produced by semi-solid processing. The solidification microstructure was investigated using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, computed tomography (CT) was also used to elucidate the size, size distribution, number density, volume fraction of porosities. It was found that with the addition of the recycled secondary materials up to 30 %, there is no significant effect on the solidification microstructure in terms of the grain size and the shape factor of primary α-Al and the second α-Al. More importantly, the morphology of eutectic Si can be well modified and that of the Fe-containing phase (π-AlSiMgFe) can be tailored. Furthermore, with increasing recycled secondary materials, at least another two important issues should also be highlighted. Firstly, more TiB2 particles were observed, which can be due to the addition of Al-Ti-B grain refiners for the grain refinement of recycled secondary materials. Secondly, a significant interaction between Sr and P was also observed in the recycled secondary materials. The present investigation clearly demonstrates that Al-Si-Mg based alloys with the addition of recycled secondary materials at least up to 30% can be used for semi-solid processing, which may facilitate better sustainability.

EFFECTS OF INJECTION SPEED ON MECHANICAL PROPERTIES IN HIGH-PRESSURE DIE CASTING OF MG-RE ALLOY

In this study, in order to clarify the unknown physical properties of the Mg-Al-Th-RE alloy, the relationship between the injection conditions and the internal porosities and the mechanical properties exerted by the solidification microstructure were investigated. The obtained cast samples were investigated using X-ray CT internal measurements, tensile tests, Vickers hardness tests and solidification microstructure observations. The flow simulation and the X-ray CT analysis results showed that the porosity volume increased as the injection speed increases. The higher injection speed also affected the metal microstructure to become denser, which leads to a higher material strength and hardness. The eutectic phases quickly formed because of the shorter filled and cooled time. Therefore, the growth of the primary phase α-Mg was suppressed. On the other hand, it was considered that the material strength and hardness were greatly reduced by the coarse primary phase.