Abstract
Abstract The aluminum alloy AA 6351 is a precipitation hardened alloy of the Al-Mg-Si system, additionally containing Mn and Fe. In this study, the microstructural characterization during processing of a thick wall extruded AA 6351 tube was carried out. Several complementary techniques for microstructural characterization were used, such as polarized light optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, backscattered electron diffraction, X-ray diffraction, hardness and electrical conductivity measurements. The main characteristics of the grains and precipitates were analyzed. After solidification, the presence of a relatively homogeneous grain distribution with an average diameter of about 100 µm and an intermetallic phase with elongated morphology rich in Al, Fe, Mn and Si was observed. During extrusion, the initial grain size was reduced to about one-fifth of the initial diameter and the elongated phase, probably a-Al(Fe,Mn)Si, was fractured and redistributed and the resulting fragments were aligned in the extrusion direction. A peripheral coarse grain zone was detected and analyzed near the outer and inner surfaces of the tube.
Highlights
Aluminum alloy 6351 is a precipitation hardened alloy of the Al-Si-Mg system, containing about 2.5 mass % of solute
No systematic study on the microstructural evolution during tube extrusion of 6351 aluminum alloy has been found in the technical literature
Samples taken from the center and near the billet surface were analyzed using polarized light optical microscopy (PLOM) and scanning electron microscopy (SEM)
Summary
Aluminum alloy 6351 is a precipitation hardened alloy of the Al-Si-Mg system, containing about 2.5 mass % of solute. The occurrence of a peripheral coarse grain zone (PCG) in extruded aluminum profiles is a relatively frequent event (Van Geertruyden et al, 2005) (Eivani; Zhou; Duszczyk, 2016). This zone is a surface defect that has negative consequences on mechanical strength, fatigue strength, machinability, corrosion resistance, resistance to stress corrosion cracking, anodized surface quality, aesthetic appearance, and susceptibility to formation during the subsequent plastic deformation of a superficial defect known as orange peel. No systematic study on the microstructural evolution during tube extrusion of 6351 aluminum alloy has been found in the technical literature
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