Masih Banijamali

In response to the increasing demand for high-performance lightweight magnesium alloys in engineering applications, this research focused on the design and development of a novel quaternary alloy. The effect of adding 1 wt% Ag to the extruded Mg-3Gd-1Zn (GZ31) alloy on its microstructure, mechanical properties, and tribological behavior were thoroughly investigated. A range of advanced characterization techniques, including Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), and laser profilometry, was utilized to elucidate the microstructural changes caused by Ag addition. The results showed that addition of minor Ag led to a grain refinement from ∼4.7 µm to ∼2.3 µm, along with an increase in the volume fraction of second phase particles, notably the emergence of a new Ag-containing phase. These microstructural modifications directly contributed to enhanced mechanical performance, with hardness, yield strength, and ultimate tensile strength increasing by approximately 12 %, 8 %, and 6 % respectively. Besides, the tribological properties in dry sliding conditions were assessed by a pin-on-disc tribometer in normal loads ranging from 5 to 40 N. The Ag-containing alloy exhibited improved wear resistance, with the wear rate reduced by ∼15 % at 20 N, the most substantial reduction recorded over the tested load range. Moreover, the coefficient of friction decreased across all loads, contributing to overall enhanced tribological performance. The wear mechanisms observed in the studied alloys mainly included abrasive and oxidative wear, along with spallation of the generated tribo-oxide layers under higher loads. Therefore, this study basically highlights the role of processing-induced microstructural changes in tailoring mechanical and tribological properties toward the advancement of high-performance magnesium alloy designs.

The present work aims to study the tribological behavior of an extruded ZK60 alloy in the presence of Ce; in a previous study, among ZK60 alloys with different Ce addition rates, an alloy with 3 wt% of Ce was found to exhibit the most promising mechanical (e.g., hardness and strengths) properties, while its wear behavior remained unknown. The results of microstructural examinations by optical and electron microscopes show that Ce addition reduces the grain size from 6.1 to 2.0 μm. Besides, in addition to the precipitates already distributed in the base alloy (Mg₇Zn₃), Ce could promote the formation of a new precipitate (MgZn₂Ce), increasing the total fraction of the precipitates. These microstructural evolutions enhance the strengths of the studied ZK60 alloy, as the yield and tensile strengths increase from 212 to 308 MPa and from 297 to 354 MPa, respectively. A pin on disc tribometer was employed to study the wear behavior of the developed alloy under different normal loads (5, 20, 40, and 60 N). The results show that the base and Ce-added alloys exhibit almost a similar frictional behavior, while the wear resistance of the Ce-added alloy is higher within the load ranges applied: (i) in low load conditions (5 and 20 N), where the abrasive wear is the active mechanism, the precipitates in the Ce-added alloy could enhance the wear resistance. (ii) Under the load of 40 N, oxidative wear is also an operative wear mechanism, leading to a sharp increase in the wear rate of the alloys. In this condition, Ce could provide a protective oxide layer, which could improve the wear resistance of the alloy. (iii) At a load of 60 N, both studied alloys exhibit a similar wear rate due to a severe oxidation condition. Therefore, beyond this loading condition, the microstructural evolutions (e.g., change in precipitation behavior) caused by Ce addition can no longer contribute to the enhancement of wear resistance.

This study aims to develop a novel hot-rolled WE43-B₄Cₚ composite with improved tribological performance for employment in the automotive industry. The pin-on-disc tribometer was used to evaluate the dry tribological behavior of newly developed composite materials containing (0-10) wt.% B₄C under various applied loads. It was observed that increasing B₄C content reduced the friction coefficient and significantly improved wear resistance in composite samples, especially at higher applied loads. With the addition of 10 wt% B₄C, the wear resistance of WE43 alloy was improved by around 25% at low load and 50% at high load regimes. The surface morphology and topography of the wear tracks were examined to identify the dominant wear mechanisms in each wear condition and reinforcement content. The dominant wear mechanisms at low loads were abrasion and slight oxidation, which were switched to adhesion and delamination as the applied load increased and thus to severe plastic deformation under high loads. The superior wear performance of the hot-rolled WE43-10%B₄Cₚ composite was ascribed to improved hardness and strength, as well as increased work hardening capacity of subsurface due to the presence of hard and thermally stable B₄C particles with uniform dispersion and proper bonding to the matrix.

The present study explores the frequency characteristics and critical speeds of rotating functionally graded truncated conical shells stiffened by anisogrid lattice structures. The shell and stiffener structures are transformed into an equivalent conical shell with variable stiffness and density using the smeared method. A dynamic model of the rotating equivalent structure is developed based on the first-order shear deformation theory in order to account for the effects of shear deformation and rotational inertia. By taking centrifugal and Coriolis accelerations and initial hoop tension into account, the motion equations with variable coefficients are derived using Hamilton’s principle and then are solved numerically using the generalized differential quadrature method. The obtained results under different conditions are validated by comparing them with existing data in the literature, and reliable precision is observed. A comprehensive parametric study is conducted on the frequencies of backward and forward travelling waves, with a special focus on critical speeds of the proposed conical structure.