How is fusion welding defined?

Fusion welding is defined as the process of joining metals by melting and fusing them together. This involves applying sufficient heat to bring the base metals to their melting point, allowing them to intermingle and solidify as a single joint once cooled. This method is fundamental to many welding techniques, such as arc welding, MIG welding, and TIG welding, where the creation of a continuous, strong, and permanent bond between the metals is critical.

The other methods listed – mechanical fastening, room temperature joining, and adhesive joining – do not involve melting the base materials and therefore do not fall under the category of fusion welding. Mechanical fasteners rely on physical means to hold pieces together, while joining at room temperature involves techniques that do not generate the necessary heat to achieve fusion. Adhesives also create bonds without melting the base metals, rather utilizing chemical properties to adhere surfaces together. Thus, option A accurately captures the essence of fusion welding as a process based on melting and fusing metals.