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.
Highlights
A390 aluminum alloy is a common specification of American aluminum alloys with hypereutectic silicon content and has several characteristics of good wear resistance, low density and thermal expansion coefficient
The base alloy used in this study was a commercial A390 alloy with a chemical composition given in Table 1
The addition of Sr leads to an increase of 2.64 to 9.06 ◦ C and a decrease of respectively, suggesting that Sr restrains the primary Si nucleation and promotes the eutectic Si
Summary
A390 aluminum alloy is a common specification of American aluminum alloys with hypereutectic silicon content and has several characteristics of good wear resistance, low density and thermal expansion coefficient. These properties have significant meaning to the automobile industry for the production of fuel-efficient vehicles using light-weight components such as connecting rods, pistons, air conditioner compressors, cylinder liners and engine blocks [1]. In traditional casting processes, the primary Si particle can exhibit several morphologies—such as star-like and plate-like morphologies—whereas the eutectic Si is generally coarse acicular in unmodified alloys, which can lead to premature crack initiation and fracture in tension and deteriorating mechanical properties [2]. The refinement of primary Si and modification of eutectic Si are crucial for improving mechanical properties and wear resistance
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