Al-Mg-Si 系合金の熱間押出におけるピックアップ欠陥発生メカニズム

6000 series aluminum alloys are used in a variety of fields including architectural materials. Many of these products are hollow shapes extruded using a port-hole die. In extrusion processes with complex cross-sectional geometries and extrusion conditions with high productivity, grain-like sloughing defects called pick-up often occur irregularly on the surface of the extruded material, which is a problem that degrades productivity and surface quality of the product. In this research, we focused on the structural change inside the port-hole die and the growth process of pick-up on the die-bearing surface, and investigated the effect of the change of material flow by the port-hole mechanism and the difference of alloying elements on the growth process. The number of pick-up was found to increase with increasing ram stroke during hot extrusion. The addition of more magnesium (Mg) to the billet increased the extrusion load and the number of pick-up. In addition, Mg was preferentially deposited on the die-bearing surface and the deposits of pick-up that occurred were MgO. Oxidation of the die bearing surface and control of the die-aluminum interface are important to control pick-up.