Die galling or pick up failure is produced by progressive adhesion of aluminum the die surface producing irregular tensile forces in the die reduction cavity. The high pressure generated and the sesulting frictional forces have caused localized welding of the metal to the die.
Die galling in aluminum is a surface-related problem. The nature and thickness of the aluminum-oxide layer formed during
and subsequent to hot rolling is directly related to the severity
of galling.It can be theorized that layers of oxide which form at
high temperatures inhibit the occurrence of galling.This is due to the fact that porous oixde acts ar a lubricant carrier during
drawing.On the other hand, the absence of oixde will subject the surfaces to metal-to-metal contact promoting galling by welding.