engleski

The impact of melt retention time on the strontium modification efficiency

The modification of eutectic (αAl+βSi) phase is frequently performed during processing of aluminum-silicone (Al-Si) based foundry alloys leading to a structural transformation of the eutectic βSi phase from a course plate to a fine fibrous morphology. The morphological refinement of the brittle eutectic βSi phase improves ductility, tensile strength, and elongation. This research was performed to estimate the influence of melt retention time on strontium (Sr) modification efficiency. For this purpose, the AlSi12 alloy with eutectic composition was produced and processed by the addition of AlSr10 master alloy. The samples for chemical, mechanical and microstructure analysis were taken with melt retention time of 20 min, 40 min and 80 min. The results of chemical composition analysis indicated the decrease in Sr content with the increase in melt retention time. Despite appropriate addition of AlSr10 master alloy during melt processing, the sufficient amount of Sr was not achieved. The poor Sr recovery was a result of the subsequent addition of chemical degassing agents. The reaction between Sr and degassing agents led to the gas entrapment in the melt. Consequently, the highest gas index and most severe porosities were found in sample with retention time of 20 min. By prolonging the melt retention time to 40 min and 80 min, both gas index and porosities were reduced. The fully modified eutectic (αAl+βSi) phase morphology was only obtained in sample with retention time of 20 min. After melt retention time of 40 min the unmodified plate-like eutectic βSi phase particles were found. Additional prolongation of melt retention time to 80 min led to the coarsening of eutectic βSi phase particle. The plate-like eutectic βSi phase particles were located near the primary αAl dendritic network and surrounding the primary βSi phase particles. This phase distribution suggests that the transformation of the primary αAl dendritic network is followed by solidification of unmodified eutectic βSi phase particles.

AlSi12 alloy ; Strontium Eutectic modification ; Modification efficiency

nije evidentirano