Micro‐Mechanical Behavior of an Exceptionally Strong Metal Matrix Nanocomposite Processed by High‐Pressure Torsion

Abstract

This research describes the micro-mechanical behavior of an Al-Mg alloy system synthesized from two separate commercial Al-1050 and ZK60 alloys through the application of high-pressure torsion (HPT) for five turns at room temperature. The essential mechanical characteristics of the alloys are observed at the corresponding phases in a multi-layered structure at the disk center but the edge contains a metal matrix nanocomposite (MMNC) exhibiting an apparent plastic instability and decreasing strain rate sensitivity under strain rates of 10 À4 À10 À3 s À1 . The results demonstrate a significant opportunity for using HPT processing to prepare new alloy systems involving a wide range of MMNCs.

Micro-mechanical and tribological properties of aluminum-magnesium nanocomposites processed by high-pressure torsion

“…The disk after 20 turns by HPT gives a gradient-type microstructure where the central region towards a radius of r ≈ 2.5 mm shows a multi-layered formation of Al-rich and Mgrich phases while the outer region at r > 2.5 mm reveals a complete mixing of these two phases. Using conventional analysis [20][21][22], the outer region showing a mixture of Al and Mg phases has an estimated equivalent von Mises strain of ~230-460 due to torsional straining and the consequent gradient structure is consistent with results reported earlier for disks processed up to 10 HPT turns [14][15][16].…”

“…It should be noted also that there was no evidence for any plastic instability in both MMNCs at the disk edges after HPT for 20 turns and after PDA whereas a plastic instability was observed earlier in an Al-Mg system after HPT for 5 turns [16]. This apparent dichotomy is probably due to the higher volume fractions and the homogeneous distributions of the hard and fine phases of the intermetallic compounds within the matrix after higher numbers of HPT turns as in the present study.…”

“…The significance of postdeformation annealing (PDA) on the microstructure was investigated together with the mechanical properties in the nanocomposite region of the Al-Mg system after HPT. The study of PDA was specifically aimed to demonstrate the improvement in plasticity and the increase in the strain rate sensitivity in the synthesized Al-Mg hybrid system after HPT for 20 turns where an Al-Mg system after 10 turns demonstrated low ductility and a decreased strain rate sensitivity [16]. The results confirm the feasibility of using HPT processing in the preparation of new alloy systems and of incorporating PDA for an enhancement in the essential mechanical properties in the processed alloy systems.…”

“…However, this study described only the computational calculation of the distribution of equivalent stress in the processed disk using a finite element method and there was no detailed microstructural analysis of the processed disk. Recently, the bonding of separate Al and Mg disks was processed through HPT by stacking a set of two disks for up to 20 turns [13] and stacking three disks for 5-10 turns [14][15][16] for producing bi-layered and multi-layered structures, respectively, in an Al-Mg system through HPT at RT. In particular, the earlier studies focused on determining the strengthening mechanisms [14], the fast diffusivity of Mg in Al matrix [15] and the plastic instability [16] of the Al-Mg system from the bonding of three disks.…”

“…Recently, the bonding of separate Al and Mg disks was processed through HPT by stacking a set of two disks for up to 20 turns [13] and stacking three disks for 5-10 turns [14][15][16] for producing bi-layered and multi-layered structures, respectively, in an Al-Mg system through HPT at RT. In particular, the earlier studies focused on determining the strengthening mechanisms [14], the fast diffusivity of Mg in Al matrix [15] and the plastic instability [16] of the Al-Mg system from the bonding of three disks. It is important to note that there has been no report on the tribological properties of this newly synthesized metal system fabricated from solid metals through the application of HPT.…”