Cracking Behavior Induced by Shear Deformation Revealed on In Situ Observation in Semisolid Cu–0.1 mass% Fe–P Alloys with P Contents of 0.03–0.15 mass%

In situ observation was employed to elucidate shear-induced cracking in semisolid Cu–0.1 mass% Fe–P ternary alloys and to clarify the role of phosphorus content in crack formation. During shear deformation, crack formation in Cu–0.1 mass% Fe–P alloys with estimated solid fractions ranging from 0.94 to 0.99 depended strongly on the phosphorus content. Cracking occurred at the phosphorus content range of 0.09–0.15mass%, whereas no cracking occurred at the range of 0.03–0.06mass%. Semisolid deformation is generally governed by either grain deformation or grain rearrangement. Phosphorus addition shifts this balance toward grain rearrangement rather than grain deformation, leading to cracking due to insufficient melt flow between solid grains. Because the solid fractions during shear deformation were comparable, the effect of phosphorus is attributed to its dissolution into the solid grains, which modifies their mechanical properties and promotes grain rearrangement.