Comparison among chemical and electromagnetic stirring and vibration melt treatments for Al–Si hypereutectic alloys

Abstract

A comparison among the microstructure refinement between chemical treatment and electromagnetic stirring and vibration (ESV) for the 390 Al–Si hypereutectic alloys is presented. The use of melt treatments assisted by chemical (i.e. P and Sr) modifiers for Al–Si hypereutectic alloys are limited to reduce in size the primary Si particles by the multiplication of active nuclei sites (Si agglomerates). This limits the coarsening effect of the primary Si particles in the liquid state. This paper shows the microstructures of ESV melt treated of Al–Si hypereutectic alloys; such microstructures show that ESV melt treatments are effective in the liquid and semi-solid states. In this paper are presented microstructures of ESV melt treated samples at temperatures as high as 130 °C above the liquidus. ESV treatments applied at temperatures of 100 °C above liquidus or higher have a limited effectiveness in Si modification by promoting the formation of feathered-like primary Si particles. ESV treatments are more effective when applied at temperatures close to liquidus (i.e. 620 °C for the 390 Al–Si alloy), under this condition ESV treatments can successfully modify primary Si particles transforming them into “ eutectic-like” particles. The resulting microstructure shows primary Si free microstructures with similar appearance to a Sr modified Al–Si hypoeutectic microstructure. The use of combined ESV and chemical treatments further refining the microstructure of the Al–Si hypereutectic alloys. In the present paper, the Si modification level was quantified using the silicon modification level (SiML). Thermal analysis results show good agreement with microstructure refinement, showing a correlation of R 2 = 0.89.