Effects of grain refinement and residual elements on hot tearing in aluminum castings

In the present work, some investigations have been carried out on hot tears in the Al-1 wt.% Sn alloy, with the objective of preventing hot tearing in aluminum castings. Al-1Sn alloy is extremely prone to hot tearing due to its long freezing range and is an ideal model for studying hot tearing. Experiments were conducted with varying grain refiner (Al-5Ti-1B) percent and pouring temperature. Grain refiner was added to the melt up to 3.0% by weight, which is the conventional limit for grain refiner addition. However, it was found that the maximum addition of grain refiner could not prevent hot tearing, which contradicts the conclusions of some earlier researchers. A mathematical model developed from the experimental data (using regression analysis) has indicated that, among all the constituents present in the Al-1Sn alloy, tin highly increases hot tearing tendency, whereas titanium in the grain refiner decreases hot tearing tendency. The model has also indicated that iron, which is the common impurity in commercial aluminum, reduces hot tearing. Based on the aforesaid model, further experiments were conducted with the addition of iron, which has resulted in complete elimination of hot tearing. Microstructural analysis was carried out using a scanning electron microscope (SEM). The leaf-like structure containing the Al-Sn-Fe-rich phase held the adjacent grains together and thus prevented hot tearing.