Defects in Metal Material Forming Processing, Part 5

Defects in metal forming processes can arise due to various factors, including material properties, process parameters, and environmental conditions. Here are some common defects associated with metal forming:

Blistering

After processing or annealing, the surface of the product will have strip-shaped or bubble-shaped bulges distributed along the processing direction. After cutting, it is a cavity. This bulge is called blistering.

Blisters are mostly strip-shaped, with smooth surfaces, elongated along the processing direction. After cutting, the inner wall is bright metal color, and some are accompanied by oxides or other inclusions. Bubbles are mostly symmetrically distributed on both sides, and are more obvious in thinner plates, strips or thin-walled tubes.

The main reasons for blistering are: defects such as pores and shrinkage holes in the ingot; improper furnace atmosphere control and excessive furnace temperature during billet annealing; poor matching between the ingot and the extrusion barrel and extrusion pad during tube and bar extrusion, or excessive lubrication of the extrusion barrel and piercing needle, unclean cleaning of the extrusion barrel, and cracks in the piercing needle.