Q1: Thermit welding is categorised as the __________ welding.

ANS:B - fusion

Fusion, in the context of welding, refers to the process of melting base metal and, often, a filler material to form a weld joint. Here's an explanation of fusion welding:

1. Melting of Base Metal: Fusion welding involves heating the base metal of the workpieces to the point where it becomes molten. This typically requires raising the temperature of the metal above its melting point. The heat source used in fusion welding processes can vary depending on the specific welding technique, but it is typically generated by electrical arcs, flames, lasers, or other methods.
2. Formation of Weld Pool: As the base metal melts, it forms a molten pool or puddle at the joint interface. This weld pool is where the fusion of the workpieces occurs. The size and shape of the weld pool can be controlled by adjusting welding parameters such as heat input, travel speed, and welding technique.
3. Addition of Filler Material (if needed): In some fusion welding processes, a filler material may be added to the weld pool to enhance the joint strength or fill gaps between the workpieces. The filler material is typically in the form of a consumable electrode, wire, or rod that melts and mixes with the molten base metal to form the weld bead.
4. Solidification and Solid-State Bonding: After the welding process is complete, the molten metal in the weld pool cools and solidifies, forming a solidified weld bead that joins the workpieces together. During solidification, the molten metal undergoes phase transformation from liquid to solid, creating a metallurgical bond between the welded components.
5. Post-Weld Heat Treatment (if needed): In some cases, post-weld heat treatment may be performed to relieve residual stresses, refine the microstructure, or improve the mechanical properties of the weld joint.

Fusion welding processes are widely used in various industries for joining metals and alloys, ranging from structural welding in construction to precision welding in aerospace and automotive applications. These processes offer versatility, allowing for the welding of a wide range of materials and component geometries, and they can produce strong and durable weld joints when performed correctly.