Papers by Keyword: Magnesium Alloy

Abstract: The present investigation aims at studying the effect of different tool geometries and process parameters on FSW of thin sheets in AZ31 magnesium alloy. In particular two properly designed tools, with shoulder diameters equal to 8 and 19 mm, were used; each of them was manufactured both in pin and pinless configurations. The effect of the different tool configurations and sizes, and welding parameters on mechanical properties of FSWed joints were analyzed in detail. The results were compared with those obtained on the base material. It was shown that FSWed joints are characterized by strength and ductility values lower than those of base material. Furthermore, the pin tool configuration, with a shoulder diameter of 8 mm, leads to the obtaining of strength and ductility values higher than those provided by the pinless one. A strong beneficial effect is obtained by increasing the shoulder diameter from 8 to 19 mm using the pinless configuration, whilst the FSW with the pin tool is critically affected by the welding conditions. The experimental work was joined to a numerical investigation based on finite element method (FEM) in order to study the material flow occurring during the welding process as well as the distribution of temperature, with the aim to identify a input window of the process parameters within which sound joints can be obtained.

Abstract: Magnesium alloys are light weight and highly recyclable. To use magnesium alloys as parts of products such as automobiles, it is very effective make bosses by using plastic workings because this can reduce material loss and welding for producing parts. The bosses can be produced by a press cylindrical tool with rotation to the surface of the magnesium alloy sheet. To reduce the period of development of the tools in forming condition investigations, numerical simulation with FEM is very useful. FEM technologies have been developed for making bosses with plastic working. Because of the symmetry of the tool, the axisymmetrical FEM is applied as the first step. Bosses were found to increase in height as the friction coefficient increased. To investigate the friction between the tool and the alloy sheets, a ring compression test was conducted. The temperature of the alloy sheets increases as the bosses are formed. Therefore, the compression test was conducted at an elevated temperature. The heat transfer rate also affects the results of the forming simulation. To improve the shape of bosses from the simulation results, 3D simulation was performed. The shape of bosses in the 3D simulation is better than that in the 2D simulation by taking into account the traction at the contact area of the cylindrical tool.

Abstract: Lighter yet stronger magnesium alloys have become very attractive for applications where materials undergo larger strains such as crash events in vehicles and planes, penetration of projectiles in personal body armour and vehicle armours. Excellent combination of light weight and good mechanical properties put magnesium alloys ahead of other structural materials in applications where high specific properties are required. It is well anticipated that magnesium alloys have enormous potential as a whole or a part of protective structures.

Abstract: In order to study the structure-borne sound radiation, statistical energy analysis (SEA) was adopted and an automobile dash was divided into 31 subsystems; the modal density, damping loss factor (DLF) and coupling loss factor (CLF) were acquired, which were the basic parameters of SEA; then dash transmission loss (TL) at the middle and high frequency (MHF) ranging from 100 Hz to 10k Hz was calculated. The most outstanding advantage of SEA was that calculation could be fast done, which was more convenient than FEM (Finite Element Method) and BEM (Boundary Element Method). Finally, a TL experiment was designed to verify the feasibility and reliability of numerical calculation. The 1/3 octave TL curves of the simulation and experiment show a good consistency and the error is engineering permitted, which means SEA simulation possesses high credibility and can guide the engineering research.

Abstract: In order to study the environmental effect on fatigue properties of die-cast magnesium alloys, several fatigue tests were performed for AM50HP and AZ91HP in ambient air, vacuum, engine oil, deionized water and 3.5% NaCl solution. It is found that the S-N curves are steeper in corrosive environment and AM50HP shows a higher sensitivity to the action of 3.5% NaCl solution than AZ91HP. Both alloys do not have endurance limits in 3.5% NaCl solution, whereas endurance limits could be detected in ambient air, which are about 90MPa and 100MPa for AZ91HP and AM50HP respectively. It is also found that FCP rate is substantially increased in corrosion media: the presence of oxygen causes the production of oxide film on the fresh surfaces made during the cyclic loading and the oxide film would restrict the deformation of the matrix beneath the hard film and promote hydrogen embrittlement in the wet condition.

Abstract: The anisotropic effects on the mechanical response of AZ31B sheet at high strain rates have been analyzed. The experimental results indicate that the stress-strain behaviour of the alloy is highly anisotropic and rate sensitive. However, anisotropy of the mechanical properties of the alloy is less significant at higher strain rates. Under tensile loading, the anisotropic behaviour of the alloy is less significant as compare to its behaviour under compression. In both compression and tensile loading the alloy shows significant rate sensitivity as compare to quasi-static strain rates but at higher rates it is less significant. The maximum stress is observed to reach nearly 600 MPa for transverse direction impact. The tension-compression asymmetry is observed in the alloy.

Abstract: This paper presents a new fabrication process for producing magnesium alloy components via metal injection moulding (MIM). Here, four kind of feedstock with 62, 64, 66 and 68% powder loading were prepared by a mixture of gas atomized ZK60 magnesium alloy powder with a resin consisting of palm stearin and low density polyethylene. The rheological investigation of the feedstock was carried out and the optimal powder loading was determined. The optimal powder loading feedstock was then injected by screw type injection moulding machine. The effects of injection moulding parameters on the physical and mechanical properties of green compacts were evaluated. The results showed that injection moulding of a feedstock containing 64% magnesium alloy was possible at high barrel temperature and pressure.

Abstract: Hydrogen storage is a key enabling technology for the advancement of hydrogen and fuel cell power technologies in transportation, stationary, and portable applications. The hydrogen transport from surface to the core of the metal powder particles is an important step during a hydrogenation reaction. Therefore, the hydrogen desorption kinetics are required for a complete understanding of the hydrogenation mechanism. In this present work, Mg-Ni-Nb systems were synthesized by mechanical alloying under optimized milling parameters (milling speed, milling time). The structural evolution (nanostructure, formation of intermetallic phases, etc) during ball milling was studied by X-ray diffraction. The activation energy of the mechanical alloyed powders was studied for Mg-Ni-Nb systems. Hydrogenation and dehydrogenation studies were carried out and understood the hydrogen interaction with Mg based alloys.

Abstract: The present study emphasizes the effect of addition of sodium citrate (C₆H₅Na₃O₇.2H₂O) and sodium tungstate (Na₂WO₄.2H₂O) to a silicate based electrolyte system on the corrosion behavior of PEO treated ZM21 magnesium alloy. The phase composition of the as-developed coating was evaluated by X-ray diffraction (XRD) analysis, while its surface morphology, thickness and elemental distribution were observed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Potentiodynamic polarization tests were done in 3.5 wt% NaCl solution to analyze the corrosion behavior of the ceramic coatings in simulated marine environment. The results of XRD showed that the phase composition of all coatings comprised of Mg₂SiO₄ and MgO irrespective of the additive used. In addition to Mg, Si and O, the presence of W, C in EDS spectrum indicated that these elements were incorporated into the coating from the electrolyte system containing tungstate and citrate. The corrosion test results revealed that the PEO coatings obtained in tungstate containing electrolyte solution showed higher corrosion resistance than those formed in citrate containing electrolyte solution.

Abstract: AZ31B magnesium alloy were irradiated by a high current pulsed electron beam (HCPEB) device with pulse times 10, 15 and 20 respectively. The morphology of the surface and cross-section of modified layer were investigated by optical microscope. The corrosion resistance of modified layer were tested by EG&G M273 potentiostat in 5% NaCl solution. Wear resistance were tested by HRS-2 high speed reciprocation frictional testing machines. The results indicated that magnesium alloy surface hardness obviously enhances, the wear volume reduces 7%, the corrosion resistance also improves obviously after electron beam processing.