What type of indication is associated with a complex aluminum casting having linear indications about halfway around the base?

The correct choice describes a hot tear, which is a type of defect commonly found in complex castings. Hot tears occur when the metal is still solidifying and experiences stress due to thermal contraction, which can lead to cracks. When the casting is cooling, particularly in complex shapes, certain areas may be constrained while others are not. The presence of linear indications around the base suggests that the material was under stress during the cooling phase, causing these characteristic tears.

In contrast, a shrinkage crack typically appears as a more random pattern and occurs in thicker sections where the metal shrinks as it solidifies, but it is not characterized by linear indications. An inclusion refers to foreign material trapped in the metal during casting, which does not create linear indications related to stress and cooling. A lap is a type of surface defect resulting from folding and overlapping of metal during pouring, which is not relevant in this context of stress-related indications.

Therefore, the identification of linear indications halfway around the base most accurately aligns with the characteristics of a hot tear, highlighting the importance of managing thermal stresses during the casting process to prevent such defects.