M. Paramsothy

Toughening mechanisms in Mg/Al macrocomposites: texture and interfacial mechanical interlocking

In this study, two types of new bimetal magnesium/aluminium (Mg/Al) macrocomposites with millimetre-scale Al core reinforcement were fabricated using casting coupled with hot coextrusion. The first macrocomposite was fabricated with an unthreaded Al core while the second one had a threaded Al core. Microstructural characterization revealed Mg texture change and interdiffusion of Mg and Al into each other across the interface in an unbalanced manner. Stress at the bimetal interface was attributed to solid solution formation, thermal expansion mismatch, unbalanced Kirkendall strain, lattice misfit strain and strain localization effects. Results revealed that the presence of the Al core leads to a decrease in strength but an increase in failure strain and toughness (work of fracture ) of Mg. The threaded Al core reduced 0.2%YS and UTS of Mg by 17% and 15%, respectively, and enhanced the failure strain and toughness of Mg by 102% and 73%, respectively. This was 1.4 and 1.6 times less the reduction, and about 6 and 7 times more the increment, when compared with the corresponding changes of 0.2%YS, UTS, failure strain and toughness of the unthreaded macrocomposite, respectively. The toughening mechanisms in bimetal Mg/Al macrocomposites are investigated in this paper.

Improving Compressive Failure Strain and Work of Fracture of Magnesium by Integrating it with Millimeter Length Scale Aluminum

Solidification processing followed by hot coextrusion was used to fabricate a bimetal magnesium/aluminum macrocomposite containing millimeter-scale Al core reinforcement. Microstructural characterization revealed limited interfacial interdiffusion of both metals into each other. Compressive testing revealed that the presence of Al core does not affect 0.2%YS, marginally decreases ultimate compressive strength (UCS), and significantly increases failure strain (115%) and work of fracture (55%) of Mg. The effect of the presence of mm-scale Al core on the compressive properties of the bimetal macrocomposite is investigated in this article.

Processing, Microstructure, and Properties of a Mg/Al Bimetal Macrocomposite

A bimetal magnesium/aluminum (Mg/Al) macrocomposite containing millimeter-scale Al core reinforcement was fabricated via casting and hot-extrusion. Characterization revealed that the Al volume fraction was not uniform along the extruded rod length. Major defects were absent, minimal porosity was present and Mg—Al interfacial integrity was good. The thermal stability of macrocomposite sections was marginally improved when compared to pure Mg. Results revealed that the presence of Al core leads to an improvement in average hardness and stiffness of Mg, and an overall improvement in tensile behavior (beyond 7% Al) assessed using work of fracture (WOF) of Mg. For macrocomposite sections containing more than 7% Al, shift in load bearing from Mg to Al at stress levels corresponding to the plastic deformation zone of Mg was indicated in the stepped tensile stress strain curve. An attempt is made to study the effect of presence of mm-scale Al and its variation on the microstructure and mechanical properties of the bimetal Mg/Al macrocomposite.

Influence of nano-sized carbon nanotube reinforcements on tensile deformation, cyclic fatigue, and final fracture behavior of a magnesium alloy

Magnesium alloy (AZ31) based metal matrix composite reinforced with carbon nanotubes (CNTs) was fabricated using the technique of disintegrated melt deposition followed by hot extrusion. In this research paper, the microstructure, hardness, tensile properties, tensile fracture, high cycle fatigue characteristics, and final fracture behavior of CNTs-reinforced magnesium alloy composite (denoted as AZ31/1.0 vol.% CNT or AZ31/CNT) is presented, discussed, and compared with the unreinforced counterpart (AZ31). The elastic modulus, yield strength, tensile strength of the reinforced magnesium alloy was noticeably higher compared to the unreinforced counterpart. The ductility, quantified both by elongation-to-failure and reduction in cross-section area of the composite was higher than the monolithic counterpart. A comparison of the CNT-reinforced magnesium alloy with the unreinforced counterpart revealed a noticeable improvement in cyclic fatigue life at the load ratios tested. At all values of maximum stress, both the reinforced and unreinforced magnesium alloy was found to degrade the cyclic fatigue life at a lower ratio, i.e., under conditions of fully reversed loading. The viable mechanisms responsible for the enhanced cyclic fatigue life and tensile behavior of the composite are rationalized in light of macroscopic fracture mode and intrinsic microscopic mechanisms governing fracture.

Adding TiC nanoparticles to magnesium alloy ZK60A for strength/ductility enhancement

ZK60A nanocomposite containing TiC nanoparticles was fabricated using solidification processing followed by hot extrusion. The ZK60A nanocomposite exhibited similar grain size to monolithic ZK60A and significantly reduced presence of intermetallic phase, reasonable TiC nanoparticle distribution, nondominant (0 0 0 2) texture in the longitudinal direction, and 16% lower hardness than monolithic ZK60A. Compared tomonolithic ZK60A (in tension), the ZK60A nanocomposite simultaneously exhibited higher 0.2% TYS, UTS, failure strain, and work of fracture (WOF) (+13%, +15%, +76%, and +106%, resp.). Also, compared tomonolithic ZK60A (in compression), the ZK60A nanocomposite exhibited lower 0.2% CYS (-17%) and higher UCS, failure strain, andWOF (+11%, +29%, and +34%, resp.). The beneficial effect of adding TiC nanoparticles on the enhanced tensile and compressive response of ZK60A is investigated in this paper.

Al2O3 Nanoparticle Addition to Commercial Magnesium Alloys: Multiple Beneficial Effects

The multiple beneficial effects of Al2O3 nanoparticle addition to cast magnesium based systems (followed by extrusion) were investigated, constituting either: (a) enhanced strength; or (b) simultaneously enhanced strength and ductility of the corresponding magnesium alloys. AZ31 and ZK60A nanocomposites containing Al2O3 nanoparticle reinforcement were each fabricated using solidification processing followed by hot extrusion. Compared to monolithic AZ31 (tension levels), the corresponding nanocomposite exhibited higher yield strength (0.2% tensile yield strength (TYS)), ultimate strength (UTS), failure strain and work of fracture (WOF) (+19%, +21%, +113% and +162%, respectively). Compared to monolithic AZ31 (compression levels), the corresponding nanocomposite exhibited higher yield strength (0.2% compressive yield strength (CYS)) and ultimate strength (UCS), lower failure strain and higher WOF (+5%, +5%, −4% and +11%, respectively). Compared to monolithic ZK60A (tension levels), the corresponding nanocomposite exhibited lower 0.2% TYS and higher UTS, failure strain and WOF (−4%, +13%, +170% and +200%, respectively). Compared to monolithic ZK60A (compression levels), the corresponding nanocomposite exhibited lower 0.2% CYS and higher UCS, failure strain and WOF (−10%, +7%, +15% and +26%, respectively). The capability of Al2O3 nanoparticles to enhance the properties of cast magnesium alloys in a way never seen before with micron length scale reinforcements is clearly demonstrated.

Enhancing the Performance of Magnesium Alloy AZ31 by Integration with Millimeter Length Scale Aluminium-based Cores

New bimetal magnesium/aluminium macrocomposites containing millimeter-scale Al-based core reinforcement were fabricated using solidification processing followed by hot coextrusion. Two approaches were attempted for enhancing the performance of AZ31: (a) AZ31 shell integration with pure Al core (pure Al core approach) and (b) AZ31 shell integration with AA5052 core (AA5052 core approach), in that order. In the AA5052 core approach eventually, macrointerface width was increased by 2 orders of magnitude (compared to that in the macrocomposite obtained using the pure Al core approach), while stiffness was increased (+36%), 0.2%YS was unchanged and UTS was increased (+14%) (compared to monolithic AZ31). The evolution of the Mg-Al macrointerface and its effect on microstructure and mechanical properties is investigated in this article.

TiC Nanoparticle Addition to Enhance the Mechanical Response of Hybrid Magnesium Alloy

A hybrid magnesium alloy nanocomposite containing TiC nanoparticle reinforcement was fabricated using solidification processing followed by hot extrusion. The nanocomposite exhibited similar grain size to the monolithic hybrid alloy, reasonable TiC nanoparticle distribution, nondominant (0 0 0 2) texture in the longitudinal direction, and 16% higher hardness than the monolithic hybrid alloy. Compared to the monolithic hybrid alloy, the nanocomposite simultaneously exhibited higher tensile yield strength (0.2% TYS), ultimate tensile strength (UTS), failure strain, and work of fracture (WOF) (

Selective Enhancement of Tensile/Compressive Strength and Ductility of AZ31 Magnesium Alloy via Nano-Al2O3 Reinforcement Integration Method Alteration

Two new AZ31 nanocomposites containing Al2O3 nanoparticle reinforcement were fabricated with different reinforcement integration methods using solidification processing followed by hot extrusion. Each nanocomposite had similar composition (Al and Zn contents), microstructure (grain and intermetallic particle sizes, Al2O3 nanoparticle distribution) and hardness. However, the first nanocomposite had better overall tensile properties compared to the second nanocomposite. Also, the second nanocomposite exhibited better overall compressive properties compared to the first nanocomposite. On the whole, the second nanocomposite was more deformable in tension and compression than the first nanocomposite. The effect of reinforcement integration method on the tensile and compressive properties of the AZ31- Al2O3 nanocomposites is investigated in this paper.

Nanoscale Electro Negative Interface Density (NENID) in magnesium alloy nanocomposites: Effect on mechanical properties

In metal matrix composites, particle–matrix interfacial reactions are generally undesirable as this leads to poor interface formation where the particle–matrix stress transfer characteristics are inferior. This is of particular concern regarding magnesium alloy nanocomposites for wide ranging weight critical structural applications. In this study, various magnesium alloy nanocomposites containing Al2O3, carbon nanotube, TiC, or Si3N4 nanoparticle reinforcement were fabricated using solidification processing followed by hot extrusion. Here and for the first time, Nanoscale Electro Negative Interface Density (NENID) quantifies the nanoparticle–alloy matrix interfacial area per unit volume in the magnesium alloy nanocomposite taking into consideration the electronegativity of the nanoparticle reinforcement. We suggest that (1) NENID affects selected mechanical properties in magnesium alloy nanocomposites and (2) there are two joint mechanisms at nanoscale that enable tensile strength and ductility of the alloy nanocomposites to be simultaneously enhanced. We show that NENID indicates the possibility of relatively increased nanoparticle–alloy matrix interfacial reactions occurring while taking into account thermodynamic considerations.