The effect of ultrasonic melt treatment (UST) on the microstructure of hypereutectic Al-17 wt.% Si alloys was investigated. UST applied to a melt at a temperature range of 750 - 800 °C refines the primary Si dramatically but has little influence on the grain size of primary Al. The solidification behaviour was characterised by thermal analysis and a mechanism responsible for the primary Si refinement was suggested. Whilst UST has no effect on the grain refinement, a significant increase in the matrix hardness as well as the tensile strength in the as cast condition is possibly associated with solid solution hardening. Detailed microstructure analysis was carried out and characteristics of the intermetallic formation in the Al-17 wt.% Si alloys were further discussed in the view point of Cu solubility in the Al matrix, which is considered to increase with UST.
Hot working behavior of an aluminum alloy matrix composite reinforced with TiC particulates was investigated by a high temperature compression test. Power dissipation maps were constructed using a dynamic material model and the deformation mechanism was investigated by means of an EBSD analysis. The interrelationship between the microstructure evolution and the efficiency of power dissipation was derived and the roles of TiC particles and other constituent phases in determining processing maps were further discussed.
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