Combined Effects of Ultrasonic Melt Treatment and Cu/Mg Solute on the Microstructure and Mechanical Properties of a Hypoeutectic Al-7Si Alloy

Quantitative approach to realization of ultrasonic grain refinement of Al-7Si-2Cu-1Mg alloy

“…The quantitative approach suggested in the present work may also account for other controversial results 4,5,17 regarding grain refinement by UST. Zhang et al .…”

“…They suggested that ultrasonic cavitation accelerated the SiO 2 reduction reaction, increasing the number density of MgAl 2 O 4 particles and their wettability, while acoustic streaming dispersed the active nuclei throughout the melt 20 . As mentioned above, in our previous study 5 , although a relatively a large number of MgAl 2 O 4 particles formed in the melt due to the relatively higher Mg content (1wt.%) in the Al-7Si-2Cu-1Mg alloy, grain refinement did not occur, so it is necessary to clarify the reason and it is thought to be suitable for the purpose of this study. Thus, the Al-7Si-2Cu-1Mg alloy was used in this study.…”

“…17 reported that the grain refinement efficiency decreases with increasing melt temperature for UST applied to Al-9Si-3Cu alloy. In addition, in our recent study 5 , UST at about 100 °C above the liquidus temperatures of hypoeutectic Al-Si alloys with Cu and Mg additions was found to increase the grain size, although a large number of MgAl 2 O 4 particles were observed to be well wetted and finely dispersed. The above research works suggest that the increase in the grain size is possibly due to de-agglomeration of particle by UST, inducing decrease in size of inoculant particles for α-Al, which increases the required undercooling for nucleation.…”

“…The grain refinement of aluminum and its alloys has long been approached since it involves such benefits as reduced segregation, enhanced feeding of liquid in the mushy zone, and reduced or better-dispersed porosity; thus has been often achieved through the addition of nucleant particles 1 . Besides inoculation, various liquid metal processes including mechanical shearing 2 , ultrasonic melt treatment 3–5 and subsequent rapid solidification have been suggested to enhance the heterogeneous nucleation by evenly distributing the nuclei particles as well as triggering nucleation of α-Al grains with substantial undercooling.…”

“…Meanwhile, Mg is often added to Al alloys to improve the mechanical properties while its addition always causes the formation of MgO and MgAl 2 O 4 oxides in the alloy melt 5,18 . Fan et al .…”