Abstract
An experimental study with an A356-AlSiMgFe alloy was developed to evaluate the microhardness performance in the microstructure resulting of an unsteady-state horizontal solidification process. The Al-7wt%Si-0.3wt%Mg-0.15wt%Fe alloy was elaborated and directionally solidified in a water-cooled horizontal solidification device. In order to experimentally determine the cooling and growth rates (VL and TR, respectively), a thermal analysis was also conducted during solidification. Microstructural characterization by optical microscopy, SEM/EDS elemental mapping and microanalysis of the punctual EDS compositions allowed to observe the presence of an Al-rich dendritic phase (Al(α)) with interdendritic phases second composed of an eutectic mixture: Al(α-eutectic) + Si + Al8Mg3FeSi6(π) + Mg2Si(θ). Furthermore, the dendritic microstructure was characterized by measuring the secondary dendritic spacings (λ2) along the horizontally solidified ingot. Higher HV values were observed within the eutectic mixture.
Highlights
IntroductionIt is known that aluminum-based multicomponent alloys due to their high strength/weight ratio have been considered as one of the most promising materials for application in the automotive and aerospace industries as well as in those referring to electrical and naval engineering[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]
The dendritic morphology has been characterized along the length of the ingot as the microstructure of the primary phase (Alα)
Is obvious that lower VL and TR values have been observed for positions further away from the cooled interface, due to an increasing formation of the solid, which imposes a thermal resistance to the heat extraction by conduction and, as consequence, an increasing profile of λ2 has been observed with the advance of horizontal solidification
Summary
It is known that aluminum-based multicomponent alloys due to their high strength/weight ratio have been considered as one of the most promising materials for application in the automotive and aerospace industries as well as in those referring to electrical and naval engineering[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]. These alloys can be classified as plastic deformation and/or casting alloys. Among these alloys, especially those for casting, are highlighted those containing silicon as the main alloying element. In Al-Si alloys, the addition of some alloying elements (Mg and Cu, as example) increases the strength by solid solution or precipitation hardening[32]. It is highlighted that the Al-(5 to 12)wt%Si casting alloys with addition of magnesium ranging from 0.2 to 0.5 wt% allows the hardening of the matrix by precipitation of second phases, with emphasis to the Mg2Si phase, after solution and artificial aging heat treatments[29,30,31,32]
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