The evolution of microstructure and mechanical properties during high-speed direct-chill casting in different Al–Mg₂Si in situ composites

Dong-tao Wang，Hai-tao Zhang，Lei Li，Hai-lin Wu，Ke Qin，Jian-zhong Cui

Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University

摘 要：The effect of high-speed direct-chill（DC） casting on the microstructure and mechanical properties of Al–Mg₂Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg₂Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy（FE-SEM） and transmission electron microscopy（TEM）. The results revealed that an increase of the casting speed substantially refined the primary Mg₂Si particles（from 28 to 12 μm）, the spacing of eutectic Mg₂Si（from 3 to 0.5 μm）, and the grains of AA6061 alloy（from 102 to 22 μm）. The morphology of the eutectic Mg₂Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg₂Si phase and the grains in the Al–Mg₂Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg₂Si composites and AA6061 alloy billets.

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