Which of the following processes might result in excess heat during thermite welding?

Excess heat during thermite welding can occur during the preheating process. Preheating is an important step in thermite welding as it involves warming the base metal to a certain temperature before the actual welding process begins. This helps to reduce the temperature difference between the molten weld metal and the base metal, promoting better fusion and reducing the risk of thermal shock. However, if the preheating is excessive, it can lead to overheating of the base metal, which can create challenges such as warping, distortion, or even degradation of material properties.

In contrast, charging refers to the process of preparing and applying the thermite mixture, which is focused on ensuring the reactants are correctly positioned for the reaction. Notching involves creating grooves or indentations to aid in the alignment of the metals being welded, which does not inherently produce heat. Alignment is the process of positioning the pieces to ensure proper fit-up prior to welding, and while important for the welding process, it does not contribute to generating excess heat. Thus, preheating stands out as the process most likely associated with creating excess heat in thermite welding.