Effect of homogenization treatment on the pick-up defect on the surface of extruded 6063 aluminum alloy

The microstructures of as-cast and homogeneous alloys were analyzed by metalloscope, scanning electron microscope and X-ray diffraction. The effect of homogenization treatment on the pick-up defect on the surface of extruded 6063 aluminum alloy were investigated. The results show that as-cast alloy consists of supersaturated α-Al solid solution and non-equilibrium eutectic phase in network structure which uniformly distributes along grain boundaries. The non-equilibrium eutectic is composed of Mg₂Si phase and β-AlFeSi phase. During the process of homogenization treatment, the non-equilibrium eutectic structure broke and dissolved, and the acicular β-AlFeSi phase transformed to spherical α-AFeSi phase. A large number of pick-up defects were observed on the surface of extruded alloy without homogenization treatment. The non-equilibrium eutectic phase disappeared and the number of pick-up defects decreased gradually with the increase of holding time of homogenization treatment at 570 ℃. In conclusion, the proper homogenization treatment of 6063 alloy is at 570 ℃ for 6h.