Effect of casting temperature on halo in the solidification microstructure of direct-chill casting Al-16.5Si-4.5Cu-0.6Mg-0.1Zr alloys

Abstract

The effect of casting temperature on the halo structure of direct-chill (DC) casting Al-16.5Si-4.5Cu-0.6Mg-0.1Zr alloys was investigated. The results indicated that the microstructure consists of fine primary Si, α-Al dendrite halo, and fine fibrous coupled eutectic structure, Al2Cu, and Al8FeMg3Si6 phase. The formation of halos was systematically analyzed. The temperature gradient at the solid–liquid interface front played an essential role in the development and growth of the halo. As the casting temperature elevated, the temperature gradient of the solid–liquid interface front increased, the solid–liquid interface became stable, the α-Al dendrite halo was less developed, the number of large-sized Si atomic clusters in the melt decreased and the growth of primary Si was inhibited.