Effect of constitution for Al-Mg₂Si alloys on surfacial quality of extruded Al-Mg₂Si alloys in industrial scale

Effect of precipitate state of Mg₂Si as well as Si content in Al-Mg₂Si alloys on the reduction of a die-line defect on the surface of extruded products was investigated in industrial scale. The solid product was extruded by 1500 us ton direct extrusion press at billet temprature 460°C, ram speed 9-13 mm/s and extrusion ratio 66.5. When Si content is low and a large amount of coarsened Mg₂Si is present in the alloy after homogenization at 400°C for 2 h, the extruded samples have bright smooth surface and nonbright rough surface. When a microscopic Mg₂Si is present in the alloy after homogenization at 200°C for 2 h, the extruded samples have high-quality surface with only nonbright and uniform surface roughness. When Si content is high and a large amount of coarsened Mg₂Si is present in the alloy after homogenization at 400°C for 2 h, the extruded samples have poor-quality surface with a tearing defect. However, when a microscopic Mg₂Si is present in the alloy, which is caused by a widely used homogenizing method or after homogenization at 200°C for 2 h, the samples extruded at ram speed 9-13 mm/s have high-quality surface with only nonbright and uniform surface roughness.