Papers by Author: Muralidharan Paramsothy

Abstract: Currently, long period stacking/ordered phases (LPSO phases) are known to reinforceMg97Y2Zn1 type Mg-RE alloys. The LPSO phases are composed of a solid solution of Y and Znatoms placed orderly in long periods along the Mg basal plane. Also, an efficient way to strengthena polycrystalline material is to reduce its grain size. This increases the density of grain boundarieswhich impede the flow of dislocations. In many of the LPSO forming solidification processed Mg-RE alloys, the common practice is to solutionize the ingot, quench in warm water, hot extrude andthermally age. While this practice is suitable for obtaining high strength Mg-RE alloys, itconveniently employs the common idea in conventional metallurgy of fine intermetallicstrengthening while refining the grain size to within the micron regime. In this work, an alternativemethod involving boride nanoparticle addition to obtain a selected solidification processed ultrahighstrength (tensile yield strength > 400 MPa) Mg-RE alloy is discussed. Here, LPSO phaserather than fine intermetallic formation while retaining grain size under the micron regime ishighlighted.

Abstract: Carbon nanotube (CNT) reinforced magnesium alloy (AZ31)-based composite was fabricated using the technique of solidification processing followed by hot extrusion. In this paper is presented and briefly discussed the conjoint influence of reinforcement and processing on microstructural development, microhardness, tensile deformation and final fracture behavior of the magnesium alloy composite and comparisons made with the unreinforced alloy (AZ31). The interactive influences of the CNT reinforcement and processing in governing engineering stress versus engineering strain response and tensile properties is neatly presented and discussed. The macroscopic fracture mode and intrinsic microscopic mechanisms governing quasi-static deformation and fracture behavior of both the CNT reinforced and unreinforced magnesium alloy is both elaborated and rationalized in light of the specific role played by presence of reinforcing phase in the magnesium alloy metal matrix, intrinsic microstructural effects and nature of loading.

Abstract: Carbon nanotubes (CNT)-reinforced magnesium alloy (AZ31) was fabricated using the technique of solidification processing followed by hot extrusion. Test specimens of both the composite and the unreinforced alloy were cyclically deformed at two different load ratios spanning tension-tension loading (R = 0.1) and fully-reversed tension-compression (R= -1) loading under total stress amplitude-control. A comparison of the CNT reinforced magnesium alloy with the unreinforced counterpart revealed well over two hundred percent improvement in cyclic fatigue life at load ratio of 0.1 and about two-hundred and fifty percent improvement in the high cycle fatigue life under conditions of fully-reversed loading [R= -1.0]. At all values of maximum stress, the high cycle fatigue response of both the reinforced and unreinforced magnesium alloy was found to degrade at the lower load ratio (-1.0). The synergistic and interactive influences of reinforcement and processing on microstructural development, cyclic fatigue life and kinetics governing fracture behavior are presented and briefly discussed.

Abstract: 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.

Abstract: New bimetal magnesium/aluminium macrocomposites containing millimeter-scale Al based core reinforcement were fabricated using solidification processing followed by hot coextrusion. The initial macrocomposite consisted of a combination of pure Mg shell and pure Al core. Some problems encountered with the macrocomposite were Mg and Al grain coarsening, an inadequate Mg-Al interface (macrointerface) and consequent reduction in strength, compared to monolithic Mg. To rectify these problems, three approaches were taken in the following order primarily to widen (strengthen) the Mg-Al interface: (a) pouring of pure Al at 900°C (higher temperature approach), (b) pure Mg shell substitution with AZ31 shell (single substitution approach) and (c) pure Mg shell and pure Al core substitution with AZ31 shell and AA5052 core, respectively (double substitution approach). The evolution (strengthening) of the Mg-Al interface and its effect on microstructure and mechanical properties in each macrocomposite is investigated in this paper.