Number Of Thermal Cycles Research Articles

Hot Corrosion Behavior of Plasma-Sprayed WC-CoCr Coatings on AISI 316L Steel Substrate in Na2SO4-25% NaCl Salt Environment

This study investigates the hot corrosion resistance characteristics of plasma-sprayed WC-CoCr coatings deposited on AISI 316L stainless steel. Coated and uncoated samples were exposed to a fused Na2SO4-25%NaCl salt deposit at 700 °C in cyclic conditions for fifty thermal cycles. The corrosion kinetics were determined using a thermogravimetric method. To determine the hot corrosion rate, weight-change measurements were taken after every cycle. X-ray diffraction, energy dispersive spectroscopy, and scanning electron microscopy were performed on samples to examine the hot corrosion characteristics. With a fused salt deposit at 700 °C, the uncoated AISI 316L steel substrate samples experienced faster high-temperature oxidation as compared to coated samples. It was noticed that the uncoated steel substrate gained a little weight during the first few cycles, afterwards as the number of thermal cycles increased, the weight gain followed a linear kinetics. The WC-CoCr coating reduced the weight gain of steel substrate by about 75% in a corrosive salt environment. The plasma-sprayed WC-CoCr coatings had adhesion strength and microhardness of 10.8 ± 2.4 MPa and 410 ± 25 HV0.5, respectively. The hot corrosion-affected coatings displayed slow-scaling kinetics. The oxides of the coatings, formed at the surface were rich in chromium and tungsten. These oxides helped in providing hot corrosion resistance in the corrosive environment as they worked as obstacles to the penetration/diffusion of corrosive elements through coatings. The higher content of tungsten inside the coating promoted WO3 formation, which improved resistance to corrosion at elevated temperatures. Chromium in the coating caused the formation of spinel CoCr2O4 and Cr2O3 the spinel CoCr2O4 that emerged as an intermediate phase also contributes to the maintenance of corrosion resistance. Some oxides such as Fe2O3, FeCr2O4, and CoSO4 were found. Apart from that some traces of Na were also found.

Effects of Welding Parameters on Sigma Phase Precipitation in 25Cr-5Ni-1Mo-2.5Cu-1Mn-0.18N Duplex Stainless Steel

Recently, a new grade of duplex stainless steel, UNS S82551 (25Cr-5Ni-1Mo-2.5Cu-0.18N), has been developed to overcome the drawbacks in super martensitic stainless steel, conventional 22Cr and 25Cr super duplex stainless steels in terms of productivity and cost. The characteristic of the alloy design of UNS S82551 is to use Cu, instead of Mo, to ensure comparable corrosion resistance and strength. In addition, due to the significant decrease in Mo content, UNS S82551 is expected to be less sensitive to sigma phase precipitation during single or multi-pass welding compared with conventional and super duplex stainless steels. There is a trade-off between achieving better properties and avoiding sigma phase precipitation when increasing alloying elements such as Mo, Cr and Cu. In order to utilize the new UNS S82551 steel in industry for welding in a similar manner to conventional and super duplex stainless steels, the prevention of sigma phase precipitation is important. This work investigated the effect of weld thermal cycling on sigma phase precipitation behaviour in UNS S82551 welds. During thermal cycling in the tests, the amount of sigma phase for UNS S31803 and UNS S32750 increased with increasing the number of thermal cycles, and lower cooling rate, but it was not observed for UNS S82551. Based on the isothermal kinetics of sigma phase precipitation, the amount of sigma phase precipitated during thermal cycle can be predicted by applying the additivity rule to the physical model. The area fractions of sigma phase calculated have a good fit to the experimental ones.

Effect of temperature and thermal cycles on the mechanical behavior of sandwich structure with entangled metallic wire mesh

As a novel rigid–flexible heterogeneous material, the sandwich structure with the entangled metallic wire mesh (EMWM) core has obvious advantages on thermo-mechanical performances due to its all-metallic material and structure. Of particular and complexity is the crosslinked microstructure of EMWM core, leading to ambiguous mechanical behaviors of the sandwich structure under gradient temperature and thermal cycles. In the work, the compressive and shear properties of the sandwich structure in different structure directions of the EMWM core were investigated, as well as the thermal cycling failure. The experimental result reveals that the sandwich structure has an excellent compression performance when the temperature below 750 °C. With the temperature increasing, the shear performance of the sandwich structure exhibits a trend from rise to decline. Furthermore, the shear property of the sandwich structure in the transversal direction is better than that in the longitudinal direction. And, the effect of thermal cycle on the failure behaviors (including, the deformation of face-sheet and the delamination of EMWM core) of the sandwich structure was observed. In the number of thermal cycles ranged of 50–200, there are few declinations of the compression and shear performance of the sandwich structure.

Experimental study of the thermodynamic properties of high thermal conductivity energy pile

In this paper, high thermal conductivity concrete (containing 4% graphite and 0.6% steel fiber) was prepared as a pile material by a model test. A high thermal conductivity energy pile was produced. The temperature field distribution of the pile and soil, the additional stress of the pile, the soil pressure at the pile end, and the displacement of the pile top were analyzed. The results showed that compared with the thermal conductivity, compressive strength, and flexural strength of ordinary C30 concrete, those of the high thermal conductivity concrete were increased by 30%, 11%, and 9%, respectively. Under load, the additional stress of the pile was large in the middle and small at both ends. After three thermal cycles, the maximum additional tensile and compressive stresses of the pile were 0.48 MPa and −0.58 MPa, respectively. The maximum value of the soil pressure at the pile end decreased with an increase in the number of thermal cycles. Thermal cycles caused cumulative pile top settlement, with a final settlement of 0.26 mm. In practical engineering, the influence of long-term thermal cycles on the safety of buildings should be noted.

Triaxial Test Study on Energy Evolution of Marble after Thermal Cycle

With the increasing requirements for the exploitation of underground resources, the subject of the physical and mechanical properties of rocks under high temperature and pressure needs to be studied urgently. In order to analyze the mechanical and energy characteristics of rocks under different thermal damages and confining pressures (c), a triaxial compression test is performed on 35 marble samples. The effects of thermal damage and high pressure are simulated with different thermal cycles and confining pressures. The results show that as the number of thermal cycles increases, the peak strain of marble gradually rises, but the peak stress and the elastic modulus (E) decrease by a degree, reaching 11.19‰, 39.53 MPa, 4.79 GPa, while there is no confining pressure applied at eight thermal cycles. At this point, the failure mode gradually changes from brittle fracture to plastic failure. When confining pressure rises, peak stress, peak strain, and elastic modulus all show an upward trend, reaching a maximum of 189.45 MPa, 13.39‰, 35.41 GPa, while the sample is undamaged at 30 MPa confining pressure. Moreover, peak stress increases linearly with confining pressure increase. The increased rate of the peak value of the total absorbed energy, elastic strain energy, and dissipated energy all show a convex trend. The dissipated energy gradually increases with the axial strain (ε1) during the rock loading process. The elastic strain energy has an energy storage limit, but the rock fails when the value exceeds the limit. The limit increases first and then decreases with the number of thermal cycles. These results can provide important engineering references for mining underground resources.

Cyclically thermally-activated pile under combined axial/horizontal loads in clay

In this study, the influence of cyclic thermal loading on the mechanical response of an energy pile installed in saturated clay subjected to sustained combined axial/horizontal mechanical loading was investigated using physical modelling. After completion of the soil saturation process and prior to starting the thermo-mechanical loading, the pile fixation was released inducing pile head heave. When the rate of pile head heave became small, the model pile was subjected to compression axial loading of 100 N (i.e. 20% of the estimated ultimate axial load) followed by horizontal loading of 35, 71 and 109 N (corresponding to accumulative pile head horizontal displacements of 4, 7 and 12% of pile diameter) before subsequent 15 heating–cooling cycles. The results indicated that imposing heating–cooling cycles to the pile resulted in irreversible horizontal displacement, accumulating at a reducing rate as the number of thermal cycles increased. By the end of the 15th cycle, the accumulated irreversible horizontal displacement was estimated at 0·57, 1·15 and 1·84% of pile diameter under the horizontal loads of 35, 71 and 109 N, respectively. Reversely, thermally induced pile head axial displacement at the end of the 15th cycle is practically insignificant (smaller than 0·1% of pile diameter).

Thermal cycling effects on the seismic wave propagation coefficients of granite

The seismic wave propagation properties of granite after thermal cycles were experimentally investigated. The granite specimens were subjected to a series of thermal cycles with different thermal cycling temperatures and numbers. Ultrasonic and pendulum impact tests were performed on the granite after thermal cycles. Subsequently, a theoretical study was introduced to explore the wave propagation coefficients of granite after thermal cycles. The effects of the thermal cycling number on the wave attenuation rate, wave velocity, attenuation coefficient, and wavenumber were discussed. The results indicate that the wave velocity and dynamic elastic modulus decrease as the number of thermal cycles increases and that the damage factor increases as the number of thermal cycles increases. However, the variations in wave velocity, dynamic elastic modulus, and damage factor are concentrated mainly in the first thermal cycle. The results further indicate that the wave propagation coefficients, attenuation coefficient, and wavenumber increase as the number of thermal cycles increases. However, they are not significantly influenced by the amplitude and wavelength of impact loading.

Comparison of Designs of Hydrogen Isotope Separation Columns by Numerical Modeling

Mixtures of gas-phase hydrogen isotopologues (diatomic combinations of protium, deuterium, and tritium) can be separated using columns containing a solid such as palladium that reversibly absorbs hydrogen. A temperature-swing process can transport hydrogen into or out of a column by inducing temperature-dependent absorption or desorption reactions. We consider two designs: a thermal cycling absorption process, which moves hydrogen back and forth between two columns, and a simulated moving bed (SMB), where columns are in a circular arrangement. We present a numerical mass and heat transport model of absorption columns for hydrogen isotope separation. It includes a detailed treatment of the absorption–desorption reaction for palladium. By comparing the isotope concentrations within the columns as a function of position and time, we observe that SMB can lead to sharper separations for a given number of thermal cycles by avoiding the remixing of isotopes.

Effect of Thermal Cycling on Microstructure and Mechanical Properties of Cf/SiC–Al Composites

Thermal cycling inevitably affects the microstructure and mechanical properties of composites due to the differences in thermal expansion coefficients (CTEs) of each component. Herein, the evolution of the microstructure and in‐plane compressive properties of Cf/SiC–Al composites after different thermal cycles at different temperature differences are investigated. Moreover, the magnitude and state of residual thermal stress in each component of the composites after thermal cycling are further analyzed by X‐ray diffraction and nanoindentation methods. The results show that with the increase of the temperature difference and the number of thermal cycles, the residual stress in each component gradually accumulates, accompanied by interface debonding and microcracks in the fiber/matrix interface area, which can release part of the residual stress. The evolution of the residual stress and the interface microstructure has a significant effect on the in‐plane compressive strength of the composites. The release of residual stress and the generation of some microcracks are beneficial to the compressive strength, but too many microcracks can reduce the strength.

Magnetic behavior and chaining of strontium ferrite-nylon composite above the melting temperature

To better understand Magnetic Field Assisted Additive Manufacturing (MFAAM) the effect of a magnetic field on the orientation and distribution of magnetic particles in a molten magnetic composite was studied. Vibrating Sample Magnetometer (VSM) measurements were made on Sr-ferrite/PA12 fused deposition modeling filaments of different packing fraction (5 and 40 wt. %). The rotation of the sample’s magnetic moment upon application of a field perpendicular to the easy axis was monitored with a biaxial VSM above the PA12’s softening temperature. The observed magnetic moment transients depend on the temperature, the applied alignment field, the packing fraction, and the initial field-anneal procedure. Longer field-anneals result in larger time constants and seem to induce a hurdle that prevents complete alignment at low temperatures and/or for small fields. Results indicate the molten composite is a non-Newtonian fluid that can support a yielding stress. Scanning Electron microscopy (SEM) images taken on field-annealed samples at 230 °C show strong chaining with little PA-12 left between individual Sr-ferrite particles suggesting that direct particle to particle interaction is the reason for the observed non-zero yielding stress. The melt viscosity of the composite increases with the number of thermal cycles above the melting temperature (Tm). Room temperature (RT) torque magnetometry measurements show that magnetic anisotropy depends on the field annealing process through induced shape anisotropy contributions originating from magnetic particle agglomerates.

Effects of Hygrothermal Environment on Tensile Capacity of Adhesive-injected Anchor Bolt of ALC Panel and ETICS

The connection between the autoclaved lightweight concrete (ALC) and an external thermal insulation composite system (ETICS) is accomplished by anchors. The anchor is consisted of a connector and an anchor bolt, where the anchor bolt is an important force transmission element. Adhesive is used to install an anchor bolt, and significantly improves the anchoring force of the anchor bolt. However, the hygrothermal environment influences the adhesion of the anchor adhesive, which adversely affects the reliability and security of the ALC panel and ETICS connection. To investigate the effect of high temperature and a humid environment on the anchor bonding performance, 5 sets of durability tests were conducted. Each group of 15 specimens was tested for 0, 15, 30, 45, and 60 thermal rain cycles. The test results reveal that, as the number of cycles increased, the tensile capacity of the adhesive-injected anchor bolts decreased, and the capacity's discount factor decreased. The discount factors of the anchor bolt tensile load capacity values after 15, 30, 45 and 60 cycles were 85.5%, 72.1%, 56.2%, and 50.4%, respectively. A prediction model was established based on the relationship between the number of thermal rain cycles and the tensile capacity. Based on the anchor bolt tensile capacity requirements, the model can calculate the number of cycles over which the adhesive-injected anchor bolts need in a hygrothermal environment must be tested, reinforced, and replaced to ensure a good connection between the ALC panel and an ETICS.

Experimental investigation of the effect of thermal cycling on the thermomechanical properties of three rock varieties for high temperature thermal energy storage

During the past years “rock batteries” have become increasingly relevant for the storage of renewable energy sources, such as wind and solar energy, because of their economic and ecological advantages with respect to previously more common materials for thermal energy storage (TES) such as salt. In rock-based TES systems, thermal energy is stored in packed-bed rock using air as heat transfer fluid. We investigated three different rock types with respect to changes in thermomechanical properties after different numbers of thermal cycles, Ruhr sandstone (Oberste quarry in Dortmund - Germany), basalt (commercial MTV basalt) and Calanca gneiss. Cylindrical samples were heated to 800°C within 11,5 h before temperature was kept constant for another 30 min and then decreased within 11,5 h. Samples were thermomechanically investigated before thermal treatment, and again after 1, 3, 7 and 15 cycles. Additionally, two samples of each rock type were subjected to a thermal cycle with a maximum temperature of 450°C and to 1000°C, respectively, at a heating/cooling rate corresponding to that of the samples heated to 800°C. Samples were characterised with respect to ultrasound wave velocity, bulk density, thermal conductivity, thermal diffusivity, uniaxial compressive strength, splitting tensile strength, mineral content (X-ray powder diffraction) and microstructure (thin section analysis). Samples of basalt could not withstand the standard heating rate. The samples crushed into small pieces also when heating rates were reduced and at a maximum heating temperature of 800°C. For sandstone and gneiss, the ultrasound wave velocity, bulk density, thermal conductivity, thermal diffusivity, uniaxial compressive strength and splitting tensile strength decreased systematically with increasing number of cycles, while the maximum reduction occurred after the first cycle and the relative reduction was similar between both rocks. Microstructural analysis indicated an increase in crack density and minor mineralogical changes upon heating. Both rocks, Ruhr sandstone and Calanca gneiss, appear suitable for TES, but Calanca gneiss is less suitable for temperatures above 800°C due to a significant reduction in bulk density and uniaxial compressive strength when heated to 1000°C. Also, its anisotropy and anisotropic response to heating can lead to preferred flow paths of the heat transfer fluid. Ruhr sandstone maintains a high uniaxial compressive strength of about 100 MPa even after 15 cycles while thermal capacity was only slightly reduced or even increased, and can be recommended for use in high temperature TES. This study is the outcome of a research-oriented teaching program at Ruhr-University Bochum within the Geoscience curriculum for students with focus on Engineering Geology. Student authors (Fränzer to Thomas) are listed in alphabetical order.

Ponašanje materijala X10CrMoVNb9-1 prilikom ponovljenog termičkog tretmana tokom montaže

The paper presents comparative test results of X10CrMoVNb9-1 steel collector samples. The influence of repeated heat treatment on the properties of the material was investigated, and the samples underwent a different number of thermal cycles. This material is most often used for pipes and pipe connections resistant to high pressures and temperatures. Steel is characterized by high thermal strength properties, which is why it is used in thermal power plants for superheater pipes, collectors as well as for high pressure steam pipes. It can be used even at high temperatures up to 600°C. The aim of this paper is the behaviour of the material during repeated heat treatment, which often occurs during the installation of the pipeline, and is caused by the repair of defects in the welded joint, incorrect installation of the pipeline and similar procedures.

Damage mechanism and heat transfer characteristics of limestone after thermal shock cycle treatments based on geothermal development

Since coal and petroleum resources are facing depletion, geothermal resources that can be stably mined for a long time are increasingly valued, especially hot dry rock (HDR). However, thermal shock damage of rock is an unavoidable problem in the development of HDR. The effects of thermal shock fatigue on the physical and mechanical properties and heat conduction of limestone are analyzed in this paper. The limestone is subjected to 1–5 heating and cooling cycles at 100 °C–500 °C. The L* a* b* values, P-wave velocity, thermal conductivity, and tensile strength of the treated limestone are obtained. The experimental results show that the P-wave velocity, thermal conductivity, and tensile strength of limestone decrease with an increase in the temperature for a constant number of thermal cycles. When the temperature is constant, the wave velocity, thermal conductivity, and tensile strength of the limestone decrease with an increase in the number of heating and cooling cycles. In addition, the numerical simulation indicates that the heat treatment temperature, the number of cycles, and the heat transfer time have significant effects on the internal heat transfer of the limestone. Changes in the calcite crystal structure due to fatigue after multiple thermal shocks can lead to cracks between crystals, significantly affecting the physical and mechanical properties of limestone. This study provides insights into the damage characteristics and heat transfer behavior of limestone under thermal shock fatigue, as well as theoretical support for the development of geothermal carbonate reservoirs.

Effect of Multiple Thermal Cycles on the Microstructure and Mechanical Properties of AISI 1045 Weldments.

AISI 1045 medium carbon steel sheets having 10 mm thickness were subjected to the shielded metal arc welding process with three, five, and seven passes. The variations in the microstructure due to multiple thermal cycles in the heat-affected zone (HAZ), base metal (BM), and fusion zone (FZ) have been investigated and correlated with measured mechanical properties. Upon comparing fracture mechanics and mechanical properties with microstructural observations, it is elucidated that samples become ductile by increasing the number of thermal cycles which can be attributed to the transformations in the ferrite morphology in the HAZ. Based on mechanical, microstructural, and fracture analysis, it is concluded that post-weld heat treatment can be avoided if the number of passes during welding is increased.

Explaining the origin of the orientation of the front transformation in spin-transition crystals

Preferred orientations of the macroscopic high-spin (HS) low-spin (LS) interfaces appearing in spin transition molecular crystals during their phase transitions are explained through the study of a generalized 3D version of the electroelastic model accounting for an anisotropic change of the lattice parameters, $a, b$, and $c$ at the transition. The investigations are performed at 0 K by analyzing the energy landscape of a lattice made of two HS and LS phases, separated by a tilted interface with variable orientation, $\ensuremath{\theta}$ as a function of the anisotropy ratio, $\ensuremath{\lambda}=\frac{\mathrm{\ensuremath{\Delta}}b}{\mathrm{\ensuremath{\Delta}}a}=\frac{\mathrm{\ensuremath{\Delta}}b}{\mathrm{\ensuremath{\Delta}}c}$, where $\mathrm{\ensuremath{\Delta}}x={x}_{\mathrm{HS}}\ensuremath{-}{x}_{\mathrm{LS}}$ is the lattice misfit along $x\phantom{\rule{4pt}{0ex}}(\phantom{\rule{0.16em}{0ex}}=a,b,c)$ direction between HS and LS states. For large $\ensuremath{\lambda}<0$, the $\ensuremath{\theta}$ dependence of the relaxed total elastic energy depicts a symmetric double-well structure with two stable positions, ${\ensuremath{\theta}}_{\mathrm{min}}$, and an unstable orientation ${\ensuremath{\theta}}_{\mathrm{max}}={90}^{\ensuremath{\circ}}$. Beyond a critical value, ${\ensuremath{\lambda}}_{C}^{\ensuremath{-}}<0$, only one minimum subsists at $\ensuremath{\theta}={90}^{\ensuremath{\circ}}$, thus recalling the behavior of an order parameter of a 2nd order phase transition. On increasing $\ensuremath{\lambda}$, this minimum survives until a second threshold value ${\ensuremath{\lambda}}_{C}^{+}>0$ above which, the elastic energy recovers a double well configuration with two new preferential interface orientations, highlighting the existence of a re-entrant phenomenon. We demonstrate that the behavior of ${\ensuremath{\theta}}_{\mathrm{min}}$ versus $\ensuremath{\lambda}$ follows the same universality class as that of a second-order phase transition, for which we calculate the critical exponents $\ensuremath{\beta}$ and $\ensuremath{\nu}$ through a finite size scaling analysis. Overall, these investigations reveal that in switchable molecular solids with anisotropic unit cell deformation between the LS and HS states, there exists a stress-free interface orientation ensuring their integrity upon a large number of thermal cycles or loads during their practical utilization

Research on thermal fatigue failure mechanism of BGA solder joints based on microstructure evolution

SAC305 (Sn-3.0 %Ag-0.5 %Cu) BGA (ball grid array) solder joints were subjected to thermal cycling. As the number of thermal cycles increased, the thickness of IMCs (intermetallic compounds) increased accordingly. The interface evolutions of the BGA-chip and BGA-PCB (printed circuit board) interfaces were different. On the chip side, the main component of the IMCs was (Cu,Ni)6Sn5, which might form a fine network crack structure with the Ni layer under thermal stress. On the PCB side, Pb particles and the IMC Cu6Sn5 showed a weak ability to coordinate the relative deformation. Grain boundary cracks were easily generated at the BGA-PCB interface and developed into transcrystalline cracks, leading to a high failure rate.

Thermomechanical volume change behavior of deep-water sediment

Understanding the thermomechanical behavior of deep-water sediment is essential for the safety design of deep-water engineering structures. In this study, a series of temperature-controlled oedometer tests was conducted to explore the volume change behavior of the deep-water sediment sampled from the South China Sea. The experimental results showed that for the normally consolidated specimens, the thermal volume change was independent of the effective vertical stress and decreased with the increasing number of thermal cycles. The thermal volume change was closely related to the recent stress history. The contractive volumetric strain decreases and the expansive one increases with increasing OCRs under heating conditions. Under the reloading conditions, the overconsolidated specimens during heating show contractive behavior and the magnitude of the contractive volumetric strain depends on the reloading path. The thermal volumetric strain induced by secondary consolidation plays a main role on the deformation of the normally consolidated or reloaded specimens under heating conditions. A reloading index is proposed to characterize quantitatively the thermal volumetric strain of the overconsolidated specimens under heating conditions simply and effectively when the reloading stress is lower than the yield stress.

Experimental and Computational Investigation for Accelerated Testing and Characterization of Next-Generation Steam Turbine Rotors

Abstract A unique set of test protocols is developed to evaluate new materials for high-temperature and pressure applications (>700 °C and 310 bar) in next-generation thermal power plants. These protocols employ accelerated testing processes to provide a realistic estimate of a component’s life under actual field operating conditions. A state-of-the-art experimental facility to characterize turbine rotors for advanced ultra-supercritical conditions was commissioned at Bharat Heavy Electricals Limited, India. An alloy rotor mounted inside the test chamber is subjected to cyclic thermal and mechanical stresses at elevated temperatures for a predetermined number of thermal cycles to estimate its creep and fatigue life. Cyclic thermal and mechanical loads are applied by sequentially exposing rotors rotating at high speed to transient heating, steady-state soaking, and transient cooling. These transient heating and cooling processes are carefully designed to achieve specific temperature gradients inside the rotor bulk. The rotor is heated in a vacuum by thermal radiation from heater coils. In contrast, rotor cooling is accomplished by circulating relatively cold nitrogen gas through the chamber. Preliminary findings from accelerated tests are reported here. Two computational fluid dynamics (CFD) models were developed to support the transient heating and cooling experiments. Good agreement is observed between CFD simulations and measurements, validating the approach presented. This facility, established under a clean energy research initiative, plays a vital role in reducing the time and cost involved in finding suitable alloy materials, thus advancing the development of ultra-efficient thermal power plants.

Thermal cycles behavior and microstructure of AZ31/SiC composite prepared by stir casting

In the present work, the effect of thermal cycles on the physical and thermal properties of AZ31 alloy and AZ31/5wt%SiC and AZ31/10wt%SiC composites was investigated. Samples were prepared using the stir casting method and then subjected to precipitation hardening. Thermal cycles were done for as-cast and aged samples with V-shaped notch under 300, 600, and 900 heating and cooling cycles at 150 and 350 °C. The crack length (CL) was evaluated using optical microscope (OM), scanning electron microscope (SEM), and energy-dispersive scanning electron (EDS) analysis. Also, density, porosity, thermal expansion coefficient of the samples were evaluated. X-ray diffraction (XRD) analysis was employed to assess the phases present in the material. The results demonstrated that by increasing the number of thermal cycles up to 600 at 150 °C and 350 °C, the porosity and density of the as-cast and aged AZ31 alloy decreased and increased, respectively; however, the density and open porosity were remained constant for the composite samples. The crack's length enlarged with increasing the thermal cycles from 300 to 600 µm at 150 °C and 300 to 900 µm at 350 °C. It was found that the reinforcement and precipitates prevented the rapid growth of the crack in the magnesium matrix. All in All, composite and the aged samples demonstrated better thermal fatigue resistance compared with that of the unreinforced alloy and as-cast samples, respectively.