Influence of the modification of iron-bearing intermetallic and eutectic Si on the mechanical behavior near the solidus temperature in Al-Si-Cu 319 cast alloy

The mechanical behavior near the solidus temperature in Al-Si-Cu 319 cast alloys was studied in both the solid and semisolid states. Mn and Sr were introduced to modify the iron-bearing intermetallic from platelet beta-Fe to Chinese script alpha-Fe and the eutectic Si particles from a flake to fibrous shape, respectively. During the high-temperature tensile tests, the strength and ductility of the alloys decreased with increasing temperature and liquid fraction. The mechanical behavior at a given temperature near the solidus was mainly controlled by iron-bearing intermetallics and eutectic Si particles. In both the solid and semisolid states, the high-temperature mechanical properties are improved due to the modification of the iron-bearing intermetallics from platelet beta-Fe to Chinese script alpha-Fe by Mn addition, while they are further enhanced by the simultaneous modification of the iron-bearing intermetallics and eutectic Si particles by the combined additions of Mn and Sr. The fracture surfaces of the tensile samples under solid and semisolid conditions were examined to study the crack initiation and propagation. The susceptibility to hot tearing for the alloys with different microstructures is discussed.