Effects of processing parameters on the refinement of primary Si in A390 alloys with a new Al–Si–P master alloy

In this study, a new Al–17Si–2.5P master alloy has been successfully prepared to refine primary Si in hypereutectic A390 alloys. By means of electron probe microanalyzer (EPMA), a large number of AlP particles can be found in the Al–17Si–2.5P master alloy. An orthogonal L₉(3³) test was designed to investigate the integrated effects of refining factors including phosphorus addition level, melting temperature and holding time, and subsequently to optimize the processing parameters. It is found that under the optimized conditions, i.e., phosphorus addition of 375 ppm, melting temperature of 800 °C, and holding time of 30 min, the average sizes of primary Si can be most remarkably decreased from 116 μm to 14 μm with sphere-like morphology. Meanwhile, the Brinell hardness and tensile strength can be significantly increased by 14.1 and 27.8%, respectively. In addition, thermal analysis is also performed with differential scanning calorimeter (DSC) to analyze the solidification process of Al–18Si alloys.