Fusion Zone (FZ)

Definition - What does Fusion Zone (FZ) mean?

A fusion zone is a section of material that is present after an object has been welded. A fusion zone begins and ends at the portions of the material that have been coalesced, and will have a chemical composition that is a mixture of the substrates being welded together and any additional filler material that may have been used.

Corrosionpedia explains Fusion Zone (FZ)

The fusion zone is often confused with other parts of the anatomy of a weld. The fusion zone is strictly the portion of materials that have undergone melting. The material that has been altered due to the heat of the welding, but not fully melted (the heat affected zone), is not considered the fusion zone.

The fusion zone will be comprised of all the welded materials and any welding filler material (if one was used). However, the fusion zone may not have an equal balance of all the materials that were welded. The amount of each parent material in the fusion zone is known as the percent dilution. The prevalence of one material over another in the fusion zone can vary widely as a result of welding technique, material thickness and material type.

The fusion zone itself is comprised of several parts. The section of the fusion zone that protrudes over top of the base material after welding on the side of the material where welding was initiated is known as the face reinforcement portion of the fusion zone. The portion of material that protrudes on the side of the material opposite of the initial welding is known as the root reinforcement.

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