Effect of Superheat on Hot Tearing Susceptibility in Re-melted 6061 Aluminum Alloy

This experiment aimed to evaluate the susceptibility of re-melted 6061 aluminum alloy to hot tearing by focusing on how variation in superheat affected both cooling rate and thermal stress during solidification. To achieve this goal, an instrumented constrained rod casting (CRC) method was used to record the cooling and stress curves. Additionally, hot tearing was analyzed considering different casting designs and feeding mechanisms. Fracture surfaces resulting from hot tearing was examined using scanning electron microscopy (SEM). The experiment found that increasing the superheat in re-melted 6061 aluminum alloy led to a decrease in cooling rate and slowed the solidification process. This scenario occurred due to the reduction in the temperature gradient between the molten metal and the mold, an increase in the time required for mold to absorb heat, as well as changes in the nucleation and crystal growth mechanisms. Consequently, the average load recorded during solidification increased due to heat, thermal contraction, and microstructural changes that increased thermal stress. It was also observed that higher superheat widened liquid-solid phase range, and also increased susceptibility to hot tearing. Finally, all these factors contributed to the increase in hot tearing during solidification process.