Role of Grain Refinement in the Hot Tearing of Cast Al-Cu Alloy

The effects of grain refinement on hot tear formation and contraction behavior in a modified Al-Cu alloy 206 (M206) have been studied. The experiments were conducted using a newly developed mold which could simultaneously measure the contraction force/temperature during solidification for a restrained casting, and thereby could be used to investigate hot tear formation. Quantitative information on crack initiation and propagation was obtained by analyzing load measurement data. Al-Ti and Al-Ti-B master alloys were added to the melt to refine the grains to obtain grains ranging from columnar dendritic to equiaxed dendritic and globular structures. Effects of grain structure and grain size on hot tearing susceptibility were investigated. The correlations between microstructure evolution in grain-refined castings at various levels and hot tear formation were determined and discussed. Grain refinement was found to have a complex effect on load onset. Hot tearing tendency was significantly affected by both grain size and grain morphology as reflected by the measured data.