Casting Defects in Transition Layer of Cu/Al Composite Castings Prepared Using Pouring Aluminum Method and Their Formation Mechanism

Abstract

Abstract In this study, Cu/Al composite castings were prepared using the pouring aluminum method, and the casting defects in the transition layer and their formation mechanism were investigated. Shrinkage cavities, shrinkage porosities, and cracks were easily formed in the transition layer, and the thickness of the transition layer was uneven after recombination of the solid Cu and liquid Al. Shrinkage cavities easily formed within the α + eutectic (α + CuAl2) phase, and cracks mainly appeared within the Cu9Al4 and CuAl2 phases. The transition layer with uneven thickness and irregular shape readily formed where the metals solidified last during the solidification; the difference in density between solid Cu and liquid Al, as well as the natural convection in the melt, were responsible for these irregular shapes. As the metals shrunk, shrinkage cavities and porosities formed without external melt feeding. Cracks formed in the Cu9Al4 and CuAl2 phases and at the Cu9Al4/CuAl2 and CuAl2/eutectic (α(Al + CuAl2) interfaces during the solid shrinkage process after the solidification was complete.