Hot tearing mechanisms of B206 aluminum–copper alloy

• The onset temperature of hot tearing in B206 was successfully determined.
• Titanium additions transformed grain structure and eliminated hot tears in B206.
• A novel technique determined the solid phase evolution of α-Al and Al2Cu in B206.
• The onset solid fraction of hot tearing was estimated from α-Al phase evolution.
• Al2Cu phase evolution improved the understanding of hot tearing mechanisms in B206.

In this study, the mechanisms of hot tearing in B206 aluminum alloy were investigated. Castings were produced at three mold temperatures (250 °C, 325 °C and 400 °C) and with two levels of titanium (0.02 wt% and 0.05 wt%) to investigate the effects of cooling rate and grain refinement. A constrained-rod casting mold attached to a load cell was used to monitor the contraction force during solidification and subsequently determine the onset temperature of hot tearing in B206. The corresponding onset solid fraction of hot tearing was estimated from the solid phase evolution of α-Al in B206 using in situ neutron diffraction solidification analysis. Hot tears were found to occur at solid fractions ranging from 0.81 to 0.87. Higher mold temperatures significantly reduced hot tearing severity in B206 but did not alter the onset solid fraction. In contrast, additions of titanium to B206 were effective at eliminating hot tears by transforming the grain structure from coarse dendrites to finer and more globular grains. Finally, in situ neutron diffraction solidification analysis also successfully determined the solid phase evolution of intermetallic Al2Cu during solidification, which in turn, provided a better understanding of the role of Al2Cu in the development of hot tears in B206.