Microstructure and Mechanical Properties of Oxide-Dispersion Strengthened Al6063 Alloy with Ultra-Fine Grain Structure

Abstract

The microstructure and mechanical properties of the ultra-fine grained (UFG) Al6063 alloy reinforced with nanometric aluminum oxide nanoparticles (25 nm) were investigated and compared with the coarse-grained (CG) Al6063 alloy (~2 lm). The UFG materials were prepared by mechanical alloying (MA) under high-purity Ar and Ar-5 vol pct O 2 atmospheres followed by hot powder extrusion (HPE). The CG alloy was produced by HPE of the gasatomized Al6063 powder without applying MA. Electron backscatter diffraction under scanning electron microscopy together with transmission electron microscopy studies revealed that the microstructure of the milled powders after HPE consisted of ultra-fine grains (>100 nm) surrounded by nanostructured grains (<100 nm), revealing the formation of a bimodal grain structure. The grain size distribution was in the range of 20 to 850 nm with an average of 360 and 300 nm for Ar and Ar-5 pct O 2 atmospheres, respectively. The amount of oxide particles formed by reactive mechanical alloying under the Ar/O 2 atmosphere was~0.8 vol pct, whereas the particles were almost uniformly distributed throughout the aluminum matrix. The UFG materials exhibited significant improvement in the hardness and yield strength with an absence of strain hardening behavior compared with CG material. The fracture surfaces showed a ductile fracture mode for both CG and UFG Al6063, in which the dimple size was related to the grain structure. A mixture of ductile-brittle fracture mode was observed for the UFG alloy containing 0.8 vol pct Al 2 O 3 particles. The tensile behavior was described based on the formation of nonequilibrium grain boundaries with high internal stress and dislocation-based models.

Microstructure, strengthening mechanisms and hot deformation behavior of an oxide-dispersion strengthened UFG Al6063 alloy

“…A uniform distribution of second phase and reinforcement particles in the matrix was seen. As reported elsewhere [12,13], energy dispersive X-ray spectroscopy and selected area diffraction (SAD) patterns showed that the particles are AlFeSi (α and β), Al 8 Mg 3 FeSi 2 , and Mg 2 Si precipitates. The reinforcement particles were determined to be Al 2 O 3 with an average size and volume fraction of approximately 25 nm and 0.8%, respectively.…”

Strain‐Induced Dissolution and Precipitation of Secondary Phases and Synergetic Stengthening Mechanisms of Al–Zn–Mg–Cu Alloy during ECAP

“…Considering various strengthening mechanisms separately, the formula of the overall yield stress can be written as follows where σ 0 is the Peierls–Nabarro stress, σ 0 = 10 MPa, σ gs is the stress related to grain boundary strengthening, σ ss is the stress related to solid solution strengthening, σ Or is the stress related to Orowan strengthening (due to the presence of secondary phases), σ d is the stress related to dislocation strengthening.…”

Sintering Behavior of Nanocrystalline Al6063 Powders Prepared by High-Energy Mechanical Milling

“…This might be ascribed to the high defect density (e.g. dislocations and grain boundaries) and large specific surface area of the MM powder particles that could provide an additional driving force and promote the densification during sintering [37]. According to Fig.…”