Formation of Phases and Microstructures in Al-8Si Alloys with Different Mg Content.

Ni Tian,Liang Zuo,Guangdong Wang,Chuncheng Liu,Kun Liu,Gang Zhao,Yiran Zhou

doi:10.3390/ma14040762

Ni Tian, Liang Zuo + Show 5 more

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https://doi.org/10.3390/ma14040762

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Abstract

Mg-containing high-silicon aluminum alloy is a heat-treatable aluminum alloy that is now widely used in the aerospace and automotive industries because of its high specific strength, high wear resistance and corrosion resistance, low thermal expansion coefficient, and low cost. More attention has been paid to optimizing the microstructure to increase the performance of this type of aluminum alloy. In the present work, the solidification processes of Mg-free and Mg-containing (0.33–1.32%) Al-8Si alloys were analyzed by the experimental results combined with the thermodynamic calculation. The results showed that α-Al, Si, and Al5FeSi were in the Mg-free Al-8Si alloy ingots, while the Al5FeSi phases in alloys with Mg additions were transformed into π phases (Al8Mg3FeSi6) by the reaction L+Al5FeSi→α-Al+Si+Al8Mg3FeSi6. There was a binary eutectic reaction of L→α-Al+Al5FeSi when the Mg content exceeded 0.51% and the Fe content was higher than 0.17%. With the increase of Mg content, the volume of Mg2Si was gradually increased while the divorced eutectic phenomenon of the quaternary eutectic structure (α-Al+Si+Mg2Si+Al8Mg3FeSi6) was weakened and the eutectic structure was significantly refined.

Highlights

Al-Si alloy is widely used in the aerospace and automotive industries because of its high specific strength, wear resistance and corrosion resistance, low thermal expansion coefficient, and excellent castability that is incomparable to other aluminum alloys [1,2,3,4]
To improve the strength and plastic toughness of Al-Si alloy, the Mg content added to this type of alloy is generally no more than 1.5% to ensure that the solid solubility of Mg2Si in Al does not reach the upper limit of solubility, which is 1.85%, and avoid the appearance of a coarse primary Mg2Si phase
The fixed direct chill casting (DCC) parameters, including the casting temperature, casting speed, cooling rate, and the casting pressure, were used to cast the experimental alloys in the current work to focus on the effect of Mg content on the type, morphology, size, and quantity of the second phases in Al-8Si alloy

Summary

Introduction

Al-Si alloy is widely used in the aerospace and automotive industries because of its high specific strength, wear resistance and corrosion resistance, low thermal expansion coefficient, and excellent castability that is incomparable to other aluminum alloys [1,2,3,4]. Al-Mg2Si binary eutectic cells with regular morphologies have flake-like Mg2Si surrounded by α-Al. Wu et al [14] studied the effects of Cu on the microstructure and mechanical properties of Al-14.5Si-0.5Mg alloy, and it is reported that the Fe-containing phases in the alloy were β-Al5FeSi when the Cu content was 4.65% but were converted to Al8Mg3FeSi6 with a Cu content of 0.52%. The fixed direct chill casting (DCC) parameters, including the casting temperature, casting speed, cooling rate, and the casting pressure, were used to cast the experimental alloys in the current work to focus on the effect of Mg content on the type, morphology, size, and quantity of the second phases in Al-8Si alloy. The solidification process of the phases and microstructures in Al-8Si aluminum alloys with different Mg contents were analyzed in combination with the phase diagram and thermodynamic analysis to provide the experimental understanding on optimizing the composition and improving the overall performance of Mg-containing Al-Si alloy

Materials and Methods

Effect of Mg Content on the Microstructure of DC-Casted Al-8Si Alloy

Effect of Mg Content on the Phases of DC-Casted Al-8Si Alloy

Effect of Mg Content on the Solidification Behavior of DC-Casted Al-8Si Alloy

Conclusions