Prevention of seizure in extrusion of aluminium alloy billet by dies having textured surface

Abstract

Seizure occurring in extrusion of an aluminium alloy billet was prevented by texturing the die surface. A liquid lubricant is entrapped in micro pockets produced on the textured surface, and is flowed out during extrusion to prevent the lubricant film breakdown. TiCN-based cermet and WC-Co dies having high anti-seizure property were employed, and the dull micro pockets were formed on the die surface by shot peening and polishing processes. The anti-seizure property was evaluated from single extrusion and repeated extrusion of an A5056 aluminium alloy billet using a liquid lubricant containing a sulphur additive. Although the roughness of the textured surface was about one order of magnitude larger than that of the polished surface, the anti-seizure property is considerably higher, whereas the difference in extrusion load between both surfaces was comparatively small. It was found that the TiCN-based cermet die having the textured surface has a high anti-seizure property. Keywords: Lubrication, Extrusion, Aluminium, Seizure, Micro pocket, Textured surface