Two surfaces P and Q are to be joined together. In which of the given joining operation(s), there is no melting of the two surfaces P and Q for creating the joint?

The correct options are Brazing and Adhesive bonding.

To understand why these joining operations do not involve the melting of the two surfaces to be joined (surfaces P and Q), let us analyze each of the given options:

1. Brazing:
Brazing is a thermal joining process in which a filler metal is heated above its melting point (but below the melting point of the base metals P and Q) and distributed between the closely fitted surfaces by capillary action. Since the temperature of the operation is kept below the melting points of surfaces P and Q, the base metals themselves do not melt during the joining process.

2. Adhesive bonding:
Adhesive bonding is a non-thermal joining method that uses a chemical substance (an adhesive) to join surfaces P and Q. The process relies on chemical adhesion and physical cohesion at the interface between the adhesive and the surfaces. There is absolutely no heating or melting of the parent surfaces P and Q required to establish the joint.

3. Arc welding and Spot welding (Why they are incorrect):
In contrast to brazing and adhesive bonding, welding processes (both arc welding and spot welding) are fusion joining operations. They work by applying intense heat to melt the base metals at the joint interface (surfaces P and Q), allowing them to fuse together upon cooling, often with the addition of a filler material.

Therefore, only Brazing and Adhesive bonding result in joining without melting the two parent surfaces P and Q.