Simultaneous Refinement of Primary Si and Modification of Eutectic Si in A390 Alloy Assisting by Sr-Modifier and Serpentine Pouring Channel Process

Abstract

In this study, A390 alloy was prepared using the combined process of a water-cooled copper serpentine pouring channel (SPC) and strontium (Sr) modifier, in order to simultaneously refine primary silicon (Si) and modify eutectic silicon (Si). The nucleation and growth mechanisms of the Si phase were discussed by morphology analysis and non-isothermal analytical kinetics. The results indicate that the size of primary Si is refined to 25.2–28.5 µm and the morphology of eutectic Si is modified from acicular into fibrous. The serpentine pouring channel process stimulates primary Si nucleation due to chilling effect and has no influence on eutectic Si nucleation. Impacts of Sr-modifier on primary and eutectic Si are similar, including three aspects: (1) poisoning of the nucleation site; (2) decreasing the interface energy between Si phase and liquid; (3) raising the activation energy for diffusion across solid-liquid interface. The content of Sr determines which one of the three aspects mentioned above is the dominant factor to promote or restrain the nucleation and growth of the primary and eutectic Si in hypereutectic Al-Si alloy.

Possibility of Utilization of Gate Geometry to Modify the Mechanical and Structural Properties of Castings on the Al-Si Basis

“…On the basis of the aforementioned and pursuant to the described experiments and expressed mutual relations between the observed and evaluated factors influencing the die casting process and the experiments described in the professional literature [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ], the mutual correlation between the gate structure, the mechanical properties of the casting, its structural composition, and the technological parameters can be expressed as in Figure 8 .…”

“…Eutectic silicon crystallizes during formation of eutectics to a thick plate morphology which is mechanically disadvantageous as the sharp angles concentrate the tension causing breakage when using the casting. Content elements most commonly used are Na, Sr, or Sb because even several hundred ppm of content elements can modify the alloy morphology causing a positively refined fiber structure of the eutectic Si by means of which the structure and mechanical properties of the aluminum alloy on Si basis improve [18][19][20].…”

Enhancing Segregation Behavior of Impurity by Electromagnetic Stirring in the Solidification Process of Al-30Si Alloy

“…To further reveal the growth dynamic process of primary Si in the electromagnetic separation process, the morphologies of the primary Si phase at the side interface were observed by dissolving the eutectic Al-Si matrix, as shown in Figure 5. In the conventional solidification of Al-30Si alloy (Figure 5a), there are numerous growth traces of the island shape and the river pattern in the side interface of the primary Si caused by the uneven solute accumulation in the solid-liquid interface front [30]. With the natural convection was further suppressed by SMF, the morphologies the island shape and the river pattern become increasingly obvious (Figure 5b).…”

Optimization of Heat Treatment Parameters of AlSi7Mg Alloy

“…The modifying effect of strontium is analogous to the impact of correct modification using sodium. Moreover, Sr neutralizes the effect of phosphorus and makes the structure of eutectics more fibrous [ 6 , 17 , 18 , 19 , 20 ]. Such a change in the morphology translates into an essential improvement of mechanical properties, in particular ductility, and facilitates the processes of coalescence and coagulation of silicon in the course of heat treatment.…”