Investigation of surface cracking of hot-extruded AA7075 billet

Abstract Extrudability of AA7075 is determined by tearing occurring through extrusion conditions by extrusion limit diagram relating to temperatures and speeds. Extruded parts were observed for tearing appearance and analyzed elements. As results, localization of melting by local heat generated by friction coupled with tension stress and zinc-segregated concentration stimulates tearing sensitivity. Furthermore, at small grain region, zinc-segregated concentration is well scattered without tearing. Therefore, an attempt to control microstructure in die by a newly-developed twist-groove porthole die is proposed to induce large severe deformation in die leading to grain refinement reducing tearing sensitivity to accelerate speed in hot extrusion.