Progression of galling during punching of AA5754 Al sheets with DLC-coated and uncoated steel tools

Abstract

Galling is a commonly observed type of sliding contact-induced damage that occurs as a result of material transfer from the aluminum alloys to the tool surfaces during forming and shaping of aluminum sheets. Progression of galling on uncoated AISI M2 steel tools and tools coated by non-hydrogenated diamond-like carbon (NH-DLC) with amorphous carbon (a-C) structure was investigated during the punching of AA5754-O sheets. Experiments were done either by lubricating aluminum sheets with mineral oil-based lubricant (LUB1), a method commonly used in industry, or by lubricating both the sheet and the punch prior to the initial punching stroke (LUB2). Galling rates were determined using the galling volume per punching stroke (between 20th and 125th strokes) measured using white light interferometry (WLI). Galling rates were lower for LUB2 punching compared to LUB1. In punching with NH-DLC-coated tools using LUB1, the coating was removed from the punch surface after 30 strokes, whereas for LUB2 punching, a negligible amount of aluminum transfer was detected by scanning electron microscopy (SEM) and WLI after 500 strokes, and the coating remained intact.