Using high-pressure torsion to process an aluminum–magnesium nanocomposite through diffusion bonding

Abstract

Disks of commercial Al-1050 and ZK60A alloys were stacked together and then processed by conventional high-pressure torsion (HPT) through 1 and 5 turns at room temperature to investigate the synthesis of an Al-Mg alloy system. Measurements of microhardness and observations of the microstructures and local compositions after processing through 5 turns revealed the formation of an ultrafine multi-layered structure in the central region of the disk but with an intermetallic b-Al 3 Mg 2 phase in the form of nano-layers in the nanostructured Al matrix near the edge of the disk. The activation energy for diffusion bonding of the Al and Mg phases was estimated and it is shown that this value is low and consistent with surface diffusion due to the very high density of vacancy-type defects introduced by HPT processing. The results demonstrate a significant potential for making use of HPT processing in the preparation of new alloy systems.

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].…”

“…Thus, for the MMNC in the Al-Mg system immediately after HPT for 20 turns, the decreasing plasticity demonstrated by the reduced strain rates is reasonable because of the interaction of a significant number of dislocations introduced during HPT with the very rapid Mg solutes within the Al matrix. The rapid diffusivity of Mg atoms is a key process for the diffusion bonding of Al and Mg in producing the Al-Mg system though HPT [14,15] and a recent review described the acceptance of the fast atomic mobility during SPD by recognizing the significant increase in the vacancy concentration through SPD processing [60].…”

“…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.…”

Intermetallics formed at interface of ultrafine grained Al/Mg bi-layered disks processed by high pressure torsion at room temperature

“…the AJ62/AlSi17Cu4Mg engine block fabricated by die casting [1]. Mg/Al composites have been fabricated by friction stir welding [2], twin roll casting [3], roll cladding [4], co-extrusion [5], accumulative roll bonding (ARB) [6] and high pressure torsion (HPT) [7,8]. Amongst the Mg/Al composites fabricated through these techniques, a substantial variation in bonding quality and intermetallics formed at the interface is found.…”