Abstract
This paper studied the relationship between the residual amount of Sr and the morphology of the eutectic Si phase in A356 obtained through different modification treatment processes; additionally, the cooling rates of molds were studied. The eutectic Si phase revealed a satisfactory modification effect at residual Sr amounts above 0.01 wt % in A356 alloys cast using an iron mould. Complete modification of the eutectic Si phase could be achieved at a Sr additive amount 0.03 wt % in an A356 melt. The addition of higher amounts of Sr (~0.04–0.06 wt %) did not improve the modification effect. With the addition of 0.06 wt % Sr into A356 alloy melt and holding at 750 °C, the anti-fading capacity of Sr modification effect could be sustained for 120 minutes. More Sr is needed to obtain a good modification of eutectic Si for an A356 alloy cast using a sand mold.
Highlights
Exhibiting excellent mechanical properties at both room and high temperatures, as well as high corrosion and wear resistance, among other advantages, cast Al-Si alloys are extensively used in auto, aerospace, weaponry, and other industries [1,2]
When 0.02% of Sr was added, the eutectic Si phase underwent the desired modification, as its morphology changed from bulky acicular to fibrous
The results of the direct-reading spectrometer indicated that, in constitutional samples cast with an aluminum melt with initial Sr quantities of 0.02%, 0.03%, 0.04%, 0.05%, and 0.06%, the residual amounts of Sr were 0.011%, 0.019%, 0.029%, 0.039%, and 0.044%, respectively. These results suggest that the eutectic Si phase could achieve the desired modification effect at Sr residual amounts above 0.011%
Summary
Exhibiting excellent mechanical properties at both room and high temperatures, as well as high corrosion and wear resistance, among other advantages, cast Al-Si alloys are extensively used in auto, aerospace, weaponry, and other industries [1,2]. The unmodified eutectic Si phase presented in Al-Si alloys usually exists in a plate-like form incorporated into an aluminum matrix. For this reason, the treatment of cast Al-Si alloy melts usually requires modification treatments to improve the mechanical properties (especially plasticity) [3,4,5]. Lots of research and practice shows that during the modification treatment of cast Al-Si alloys of the same grade, different additive amounts of Sr (ranging from 0.01% to 0.06%)
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