Abstract
The influence of superheat treatment on the microstructure and dynamic mechanical properties of A357 alloys has been investigated. The study of microstructure was performed by optical microscope. Dynamic mechanical properties (storage modulus, loss modulus and damping capacity) were measured by the dynamic mechanical analyzer (DMA). Microstructure showed coarser and angular eutectic Si particles with larger α-Al dendrites in non-superheated A357 alloy. In contrast, finer and rounded eutectic Si particles together with smaller and preferably oriented α-Al dendrites have been observed in superheated A357 alloy. Dynamic mechanical properties showed an increasing trend of loss modulus and damping capacity, meanwhile a decreasing trend of storage modulus at elevated temperatures for superheated and non-superheated A357 alloys. The significant improvement of damping capacities has been observed at lower temperatures range (50 to 277 °C) and higher temperatures range (278 to 380 °C) in non-superheated A357 alloy and superheated A357 alloy, respectively. The high damping capacity of superheated A357 alloy has been ascribed to the grain boundary damping at elevated temperatures.

Key words
A357, melt superheat treatment, grain boundary damping

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