Thermal Cycling Aging Research Articles

Effects of Repetitive Freeze-Thaw Thermal Cycles on the In-Plane Effective Thermal Conductivity of a Gas Diffusion Layer in Polymer Electrolyte Membrane Fuel Cells

As the fundamental components of polymer electrolyte membrane fuel cells, the thermal properties of gas diffusion layers (GDLs) play a significant role in influencing their overall heat conduction and management. We have experimentally characterized the temperature dependence of the in-plane thermal conductivity of a commercial carbon paper GDL, including the progressively in-plane thermal degradation of GDLs through a series of repetitive freeze-thaw thermal aging cycles. Even though the thermal properties of carbon fibers are crucial for the thermal performance determination of GDLs, the temperature-dependent in-plane thermal conductivity of pristine GDLs depends mainly on the thermal characteristics of the binder that connects carbon fibers and the polytetrafluoroethylene (PTFE) coated on the microporous layer. The microstructural failure of aged GDLs (breakage of carbon fibers, delamination, adhesive failure of binder, and PTFE cracks) caused by the freeze-thaw thermal aging treatment dominantly affects the in-plane effective thermal degradation at different thermal aging phases. Overall, the breakage of carbon fibers positively contributes, and delamination, adhesive failure of binder, and PTFE cacks negatively contribute to the in-plane effective thermal conductivity of GDLs. In particular, the in-plane thermal conductivity of aged GDLs through 300 cycles reaches a peak.

Comparative study of thermoplastic liner materials with regard to mechanical and permeation barrier properties before and after cyclic thermal aging

Abstract Lightweight pressure vessels of type IV for hydrogen storage consist of a thermoplastic inner liner, commonly from polyethylene or polyamide. The liner is the permeation barrier against the compressed gas and must prevent the formation of cracks, also after temperature changes, for example after refueling processes. In the present work high-density polyethylene, cross-linked polyethylene, polyamide 6 and polyamide 12 were characterized by tensile tests, single notch impact tests and permeations measurements before and after a cyclic thermal aging process. The aging only lead to slight changes of mechanical properties due to post-crystallization, but to a significant decrease of permeation properties. This decrease was contributed to weakened, amorphous regions where chain splitting occurred. Considerable differences in properties resulted from different peroxide cross-linking times of polyethylene at the same temperature. A longer holding time at 200 °C led to an improvement in impact strength by a factor of more than three. However, the permeation properties decreased by about 50 %, indicating that peroxide cross-linking in the melt inhibited the formation of crystalline regions.

Effect of Thermal Cycling Aging on the Surface Microhardness and Roughness of Resin-Infiltrated Enamel Lesions

With the widespread use of resin infiltration, its properties have drawn increasing attention. The objective of this study was to investigate the effect of resin infiltration on the surface microhardness and roughness of enamel lesions after thermal cycling aging. Tooth blocks were made from extracted premolars and placed into a control group, resin-infiltrated group or demineralized group. Before and after the aging procedure, the surface microhardness and surface roughness was measured. Before the aging procedure, the surface microhardness of the control group, resin-infiltrated group and demineralized group was 302.14 (±9.77) HV, 146.62 (±8.22) HV, and 28.85 (±2.21) HV (p 0.001), respectively. After the aging procedure, the surface microhardness of the control group, resin-infiltrated group and demineralized group decreased by 9.42%, 16.59%, and 20.75% ( p 0.001), respectively. Before the aging procedure, the surface roughness of the control group, resin-infiltrated group and demineralized group was 0.29 (±0.04) μm, 0.32 (±0.04) μm, and 0.39 (±0.07) μm (p = 0.009), respectively. After the aging procedure, the surface roughness of the control group, resin-infiltrated group and demineralized group increased by 9.85%, 8.31%, and 17.37% (p = 0.634), respectively. Resin infiltration can improve the surface microhardness and surface roughness of demineralized teeth in an artificial enamel caries model. The treatment also shows good aging resistance after thermal cycling. The infiltrant resin provided a suitable material for early enamel caries.

Accelerated Thermal Aging Effects on Carbon‐Based Perovskite Solar Cells: A Joint Experimental and Theoretical Analysis

In the search for stable perovskite photovoltaic technology, carbon‐based perovskite solar cells (C‐PSCs) represent a valid, stable solution for near‐future commercialization. However, a complete understanding of the operational device stability calls for assessing the device robustness under thermal stress. Herein, the device response is monitored upon a prolonged thermal cycle aging (heating the device for 1 month up to 80 °C) on state‐of‐the‐art C‐PSCs, often neglected, mimicking outdoor conditions. Device characterization is combined with in‐house‐developed advanced modeling of the current–voltage characteristics of the C‐PSCs using an iterative fitting method based on the single‐diode equation to extrapolate series (RS) and shunt (RSH) resistances. Two temperature regimes are identified: Below 50 °C C‐PSCs are stable, and switching to 80 °C a slow device degradation takes place. This is associated with a net decrease of the device RSH, whereas the RS is unaltered, pointing to interface deterioration. Indeed, structural and optical analyses, by means of X‐ray diffraction and photoluminescence studies, reveal no degradation of the perovskite bulk, providing clear evidence that perovskite/contact interfaces are the bottlenecks for thermal‐induced degradation in C‐PSCs.

Thermal cycling aging of encapsulated phase change material – Compressed expanded natural graphite composite

A paraffin-Compressed Expanded Natural Graphite (CENG) composite encapsulated in aluminium shell has been thermally aged in a packed bed heat storage tank.A hydraulic test bed has been settled in order to impose 8500 thermal cycles where the material underwent a phase change at each cycle. The PCM phase change provokes an expansion of the composite structure that might affect the effective thermal conductivity and then the heat transfer rate of the Thermal Energy Storage (TES). This performance has been monitored all along the cycling test showing a non-significant change in heat transfer rate, despite a delamination of the composite within the capsule. This phenomenon has been explained by the delamination that affects mainly the thermal conductivity in the axial direction while the heat transfer from the PCM to the aluminium shell occurs essentially on the planar direction. Indeed, the thermal conductivity in planar direction is approximatively six times higher than on the axial direction. A DSC analysis on new and aged samples showed that the phase change temperatures remained the same and the latent heat magnitude decreased by less than 10%. A FTIR analysis confirms the chemical stability of the PCM-CENG composite after 8500 cycles.

The effect of thermo-mechanical fatigue on the retentive force and dimensional changes in polyetheretherketone clasps with different thickness and undercut.

PURPOSEEsthetic expectations have increased the use of polyetheretherketone (PEEK) clasps as alternatives to Cr-Co in removable partial dentures (RPDs). The objective of this study was to evaluate the retentive force and dimensional change of clasps with different thickness and undercut made from PEEK by the thermo-mechanical fatigue.MATERIALS AND METHODSPEEK clasps (N = 48) with thicknesses of 1 or 1.50 mm and 48 premolar monolithic zirconia crowns with undercuts of 0.25 mm or 0.50 mm were fabricated. Samples are divided into four groups (C1-C4) and were subjected to 7200 thermal aging cycles (at 5 - 55℃). The changes in the retentive force and dimensions of the clasps were measured by micro-stress testing and micro-CT devices from five measurement points (M1 - M5). One-way ANOVA, paired t-test, two-way repeated ANOVA, and post-hoc tests were used to analyze the data (P < .05).RESULTSThe retentive forces of C1, C2, C3, and C4 groups in initial and final test were found to be 4.389-3.388 N, 4.67 - 3.396 N, 5.161 - 4.096 N, 5.459 - 4.141 N, respectively. The effects of retentive force of all PEEK clasps groups were significant decreased. Thermo-mechanical cycles caused significant dimensional changes at points with M2, M4, and M5, and abraded the clasp corners and increased the distance between the ends of the clasp, resulting in reduced retentive forces (P* = .016, P* = .042, P < .001, respectively).CONCLUSIONThermo-mechanical aging decreases the retentive forces in PEEK clasps. Increasing the thickness and undercut amount of clasps decreases the amount of dimensional change. The values measured after aging are within the clinically acceptable limits.

Effects of Artificial Staining and Bleaching Protocols on the Surface Roughness, Color, and Whiteness Changes of an Aged Nanofilled Composite

This study evaluated the surface roughness and color alteration of an aged nanofilled composite exposed to different staining solutions and bleaching agents. Ninety nanofilled composite (Filtek Z350XT, 3M/Oral Care) specimens were submitted to 5,000 thermal cycles and immersed in (n = 30): red wine, coffee, and artificial saliva at 37°C for 48 h. Groups were subdivided according to the bleaching protocol (n = 10) with 20% carbamide peroxide, 38% hydrogen peroxide, or without bleaching - control. Mean surface roughness values (Ra - μm) and color parameters (L*, a*, b*) were measured at baseline (T0), after thermal cycling aging and staining (TS), and after bleaching (TB). Color (ΔE00) and whiteness index (ΔWID) changes were determined after aging and staining (Ts-T0) and after bleaching (TB-TS). The adopted perceptibility and acceptability thresholds of the nanofilled composite were 0.81 and 1.71 ΔE00 units and 0.61 and 2.90 ΔWID units, respectively. Ra was analyzed using mixed models for repeated measurements and L* by the Tukey-Kramer test. The a* and b* values were evaluated by generalized linear models for repeated measures. ΔE00 was tested using two-way ANOVA and Tukey tests, and ΔWID by Kruskal-Wallis and Dunn tests (α = 5%). Ra of all groups decreased after aging and staining (TS, p &amp;lt; 0.05), but increased after bleaching only for groups stained with red wine (TB). Aging and staining decreased the luminosity of the composites, but L* increased after bleaching (p &amp;lt; 0.05). Aging and staining increased a* and b* values, but after bleaching, b* values decreased (p &amp;lt; 0.05). After bleaching, ΔE00 and ΔWID were greater in stained groups at both time intervals, regardless of the bleaching protocol. Stained resin composites exhibited perceptible but unacceptable color (ΔE00 &amp;gt; 1.71) and whiteness (ΔWID &amp;gt; 2.90) changes, regardless of the bleaching treatment performed. Therefore, red wine affected the surface roughness of the aged nanofilled resin submitted to bleaching. Bleaching was unable to reverse the color changes promoted by red wine and coffee on the aged nanofilled composite.

Bond Strength Durability of Adhesive Cements to Translucent Zirconia: Effect of Surface Conditioning

To evaluate the influence of airborne particle abrasion, Piranha acid and hot acid etching on bond strength of zirconia with self-adhesive resin cements after aging. Also, the effect of Silano-Pen treatment on the bond strength of zirconia to resin cements. Thirty-six zirconia blocks were cut, sintered and divided into three groups (n=12); Airborne particle abrasion, Piranha acid, and hot acid etching were then treated with Silano-Pen. Each zirconia block was bonded to its corresponding composite block utilizing either Panavia SA, TheraCem or Panavia F2.0. 360 micro -tensile test bars were obtained and half of them were subjected to 10000 thermal aging cycles. Each microtensile test bar was subjected to microtensile force until debonding. Scanning Electron Microscopic evaluation was performed. There was a significant difference between the surface treatments. Hot acid showed the highest mean bond strength and the lowest was Piranha acid. Panavia SA significantly improved the bond strength compared to TheraCem and Panavia F2.0. The interaction between cement and Silano-Pen was non-significant (p=.067). Under SEM analysis, hot acid treatments showed homogenous granular texture with wide distribution of porous network. Pre-treatment, resin cement, and aging influences the effectiveness of bonding of zirconia. Silano-Pen after hot acid improved the bonding of zirconia.

Continuous Partial Discharges Analysis During Automated Thermal Cycle Aging Experiment

This work presents an experiment proposal for continuous partial discharge analysis during an automated thermal cycle experiment for hydro generator stator coils/bars. It is an innovative approach because we propose to perform partial discharges test and thermal cycle experiment simultaneously, while they are usually performed individually. We developed an automated test bench that allows performing data acquisition throughout the experiments. We decided to force different coil failures during the tests to observe any changes in the partial discharges trend. First, we changed the thermal cycle temperature limits, and this led to coil overheating before an electrical failure occurred in the insulation. Later, we applied a voltage that was higher than the rated for the coil, which led to a faster electrical failure. The partial discharges trend changed moments before the electrical fault, and the system was able to identify such change. Our preliminary results show that the continuous analysis of partial discharges trends might lead to better maintenance planning by identifying the moment when the hydro generator aging gets critical.

Microtensile Bond Strength Between Self-Adhesive Resin Cements and Resin Based Ceramic CAD/CAM Block

Purpose: The objective of this study is to evaluate and compare the microtensile bond strength (μTBS) of four different self-adhesive resin cements to a resin-based ceramic CAD/CAM block, at the baseline, and after subjecting them to 5,000 thermo-cycles.Materials and Methods: Four self-adhesive dual-cured resin cements; G-CEM LinkAce (GC EUROPE, Leuven, Belgium), RelyX U200 (3M ESPE, Seefeld, Germany), Maxcem Elite (Kerr, CA, USA), TheraCem (Bisco, Schaumburg, USA) were applied to Cerasmart CAD/CAM blocks (GC EUROPE, Leuven, Belgium). CAD/CAM blocks were sectioned into sticks and subjected to µTBS tests at 24 hours, and the other half were subjected to tests after 5000 thermo-cycles. The data were tested by one-way variance analysis (p&lt;0.05). Results: The highest bond strength values were observed in TheraCem, followed by G-CEM LinkAce and RelyX U200, respectively (p&lt;0.05). At the baseline, G-CEM LinkAce, RelyX U200, and Maxcem Elite showed statistically similar results. After 5,000 thermal-cycles, a significant decrease was observed in the bond strength values of G-CEM LinkAce (p&lt;0.05). Conclusion: Between the adhesive cements used in the study, TheraCem showed the highest micro-tensile bond strength values both in the baseline (24h) results, and after the 5,000 thermal-cycle aging procedures.

Structural health monitoring of metal-to-glass\u2013ceramics penetration during thermal cycling aging using femto-laser inscribed FBG sensors

Maintaining the mechanical strength and hermetic reliability of metal-to-glass–ceramics electrical penetration assembly (MTGC-EPA) is a key concern for ensuring the pressure boundaries of nuclear power plants. The transient temperature change caused by power adjusting or accidents in High Temperature Reactor Pebble-bed Modules may affect the structural health of sealing glass–ceramics, even leading to radiation leakage. To evaluate whether the function could survive temperature variations during the service life, thermal cycling aging experiments were imposed to MTGC-EPA. A grating length-mismatched sensing method to monitor the residual strain, an important factor of glass–ceramics structural health, was demonstrated in real-time by femto-laser inscribed fiber Bragg grating (FBG) sensor during the curing process and thermal cycling aging. Scanning electron microscope (SEM) and leakage rate tests were carried out to obtain the comparisons of microstructure and hermeticity before and after the thermal cycling. The residual strain showed a slight growth trend with thermal cycles repetition and it persisted a high value (~ 4,000 με) reflected by both Bragg wavelength shift and spectrum shape. The grating length mismatched single FBG embedded in glass–ceramics was feasible to demodulate the temperature and strain simultaneously, and the embedded FBG method achieved the structural health monitoring of MTGC-EPA during thermal cycling aging with good accuracy and reliability. Combining with the results of SEM and leakage rate detecting, the structural health of MTGC-EPA was demonstrated to be capable to endure the severe thermal conditions in nuclear reactors.

Fatigue Cycles and Performance Evaluation of Accelerating Aging Heat Treated Aluminum Semi Solid Materials Designed for Automotive Dynamic Components

The A357-type (Al-Si-Mg) aluminum semi solid casting materials are known for their excellent strength and good ductility, which make them materials of choice, preferable in the manufacturing of automotive dynamic mechanical components. Semi-solid casting is considered as an effective technique for the manufacturing of automotive mechanical dynamic components of superior quality performance and efficiency. The lower control arm in an automotive suspension system is the significant mechanical dynamic component responsible for linking the wheels of the vehicle to the chassis. A new trend is to manufacture this part from A357 aluminum alloy due to its lightweight, high specific strength, and better corrosion resistance than steel. This study proposes different designs of a suspension control arm developed, concerning its strength to weight ratio. Furthermore, this study aims to investigate the effect of accelerating thermal aging treatments on the fatigue life of bending fatigue specimens manufactured from alloy A357 using the Rheocasting semi-solid technology. The results revealed that the multiple aging cycles, of WC3, indicated superior fatigue life compared to standard thermal aging cycles. On the other hand, the proposed designs of automotive suspension control components showed higher strength-to-weight ratios, better stress distribution, and lower Von-Mises stresses compared to conventional designs.

Impact of Aging on Mechanical Properties of Thermally Conductive Gap Fillers

Abstract Thermal interface materials (TIMs) are an important component in electronic packaging, and there is a concerted effort to understand their reliability when used under various environmental load conditions. Previous researchers have investigated gap fillers and other types of TIMs to understand their performance degradation under loading conditions such as thermal cycling and thermal aging. Most of the study in the literature focuses on studying the changes in thermal properties, and there is a lack of understanding when it comes to studying the mechanical behavior of TIMs. Degradation of mechanical properties is the cause for the loss in thermal performance and is critical during TIM selection process. Moreover, mechanical properties such as modulus and coefficient of thermal expansion (CTE) are critical to assess performance of TIMs using finite element analysis (FEA) and potentially save time and money in the evaluation and selection process. Due to the very soft nature of TIMs, sample preparation is a challenging part of material characterization. In this paper, commercially available TIMs are studied using testing methods such as thermomechanical analyzer (TMA), dynamic mechanical analyzer (DMA), and Fourier infrared spectroscopy (FTIR). These methods are used to characterize the material properties and study the changes in properties due to aging. In this work, the followings are presented: impact of filler content on the mechanical properties, sample preparation method for curable TIM materials with specified thicknesses, and impact of thermal aging on mechanical properties.

Laser-Aided Enamel Conditioning: A Comparison of Microleakage Under Brackets Following Different Aging Procedures

Objective: To evaluate microleakage under the orthodontic adhesives applied following two version of erbium:yttrium aluminum garnet (Er:YAG) laser-aided enamel conditioning after thermal and thermomechanical simulators. Materials and Methods: A comparative analytical study based on metal braces bonded on the enamel of extracted teeth ( n = 160) etched with acid, Er:YAG laser and Er:YAG laser with an X-Runner handpiece, and self-etch adhesives. An arch wire was ligatured to samples which were embedded in acrylic blocks by two with periodontal ligaments. The specimens were subdivided into two groups: those aged with thermal cycling and thermomechanical aging procedures. The samples were immersed in basic fuchsin solution (0.5%) for 24 h. Buccolingual sections were performed on the mesial and distal wings of the braces. The color penetration at the gingival and occlusal margins of the adhesive-bracket and enamel-adhesive was evaluated under a stereomicroscope. The median and mean values of microleakage in both groups were evaluated with Kruskal–Wallis and Mann–Whitney U tests ( P &lt; .05). Results: The highest microleakage was recorded in the gingival part of the samples aged with the thermomechanical aging procedure ( P = .001). The amount of microleakage generally increased in the samples subjected to thermomechanical loading, but the only significant difference was recorded in the gingival part in each four different conditioning methods. Conclusion: Microleakage of the phosphoric acid-etched groups was recorded with lower values for both aging methods. Thermomechanical aging should be included to microleakage studies due to increased microleakage on gingival side for all etching groups.

Bond strength to ZLS ceramics at different etching times and cementation protocols after aging

Objective: To assess the influence of 5% hydrofluoric acid etching time (ET), cementation protocol (CP), and thermal cycling (TC) aging on the microshear bond strength (µSBS) of zirconia-reinforced lithium silicate ceramic (ZLS) to adhesive resin cement. Material and Methods: Ten VITA Suprinity® ceramic blocks were cut in 120 slices (1.4 mm thickness) and randomly assigned to 12 groups (n = 10) according to the combination of factors (2x3x2 design): etching time (20 or 30 s), cementation protocol (silane + universal adhesive + resin cement; universal adhesive + resin cement; silane + resin cement) and thermal cycling (cycled or no-cycled). RelyX Ceramic Primer and Scotchbond™ Universal Adhesive were used respectively as silane (S) and universal adhesive (Ua). Ceramic surface was etched, and the cementation protocol performed on the delimited bonding area. Then, resin cement (RelyX™ Ultimate Cement [Rc]) cylinders were bonded and light cured. After, specimens were stored in deionized water at 37°C for 7 days and subjected to the µSBS test. Results: Data passed the normality test and three-way ANOVA analysis showed statistical difference (p&lt;0.01) for isolated; double (ET/TC) (p&lt;0.05), and triple (p&lt;0.05) factor interactions. Conclusion: The combination 30s etching-Ua-Rc presented higher adhesive bond strength after thermal aging.

Quality Index Charts of Al-Si-Mg Semi Solid Alloys Subjected to Multiple Temperatures Aging Treatments and Different Quenching Media.

The use of quality index charts is considered as an effective mean for evaluating the mechanical performance of Aluminum alloys for industrial engineering applications. The current study was carried out to investigate the influences of multiple-interrupted temperatures aging and quenching media (water versus air) on the quality index performance and precipitations evolution of A357 Aluminum semi solid alloys. Regarding the lack of similar investigations applied on such alloys, the quality index charts were generated for Al-Si-Mg semi solid castings based on its tensile properties. These charts are used to determine the quality index, in MPa, as a simple mean for compromising the strength and ductility together in one value using the Drouzy model. The multiple temperatures aging cycles were applied to improve the quality index values of Al-Si-Mg semi solid alloys for enhancing its characteristic and performance to resist the mechanical failures relating to automotive dynamic parts. The evolution of Mg2Si hardening precipitates, formed for specific thermal aging cycles, was investigated using transmission electron microscopy (TEM). The results obtained in this work revealed that the optimum quality index values were obtained by the application of T6-thermal under-aging treatment cycles. The regression models, using a statistical design of experiments, indicated that the optimum strength and high-quality index values were obtained by the application of interrupted thermal aging cycles, mainly C2,3-T6/T4/T7 conditions.

Evaluation of Nanostructured Coatings for the Protection of Apuan Marble Stone

Nowadays the use of multifunctional nanomaterials has significantly increased with interesting applications for the cultural heritage conservation sector, leading to the definition and use of products with innovative properties. Therefore, a preliminary validation of the performances and behavior over time of these treatments becomes an unavoidable key point for a correct use of these products before being applied to historical materials, in order to avoid irreparable damage over time. In this direction, the aim of this study was to evaluate the effectiveness of the treatment with multifunctional nanostructured products on Apuan marble. The focus of the work was to test methods to accelerate aging, in order to simulate different environmental agents of degradation to which marble in historical buildings can be exposed. Stone samples were examined after exposition to high temperature cycles in a muffle furnace, treatments in saline solution, cycles of thermal shock and aging by SO2 action in presence of humidity. After each artificial aging cycle, changes in appearance were noted and chemical-physical properties were measured in order to compare differences between fresh and treated samples. The protective qualities of the coatings were evaluated using the following tests: contact angle; photocatalytic properties by methylene blue degradation tests; photodegradation kinetics of pollutants under UVA irradiation. Before and after the treatments, scanning electron microscopy equipped by microanalysis detector (SEM-EDS) was also used to evaluate changes in the surface morphology of the samples. The results showed effects of degradation in the rock samples due to aging after each test and all the products applied to the sample surface seemed to be very efficient in relation to their functions.

The Micro-Shear bond strength of different cements to commercially pure titanium.

BackgroundThe most appropriate luting agent for attaching the prefabricated Ti-based insert of hybrid abutments to its ceramic component has not yet been determined. This study was done aimed at examining the micro-shear bond strength (μSBS) of different cements to commercially pure titanium (Cp Ti).Material and MethodsA total of 100 milled cubes of Cp Ti was airborne-particle abraded using 250 μm aluminum oxide particles. Specimens were then divided into 5 groups (n=20) according to the type of resin cement used: (1) Panavia F.2, (2) Rely X U200, (3) Panavia SA LUTING Plus, (4) GC Fuji I, and (5) GC FujiCEM 2. After 24h storage, half of the samples were subjected to 5000 cycles of thermal aging. Next, the bonded samples were tested in the micro-shear mode. Data (MPa) were analyzed using a two-way ANOVA and the post hoc Tukey test (α=0.05). After debonding, each sample was examined for the failure mode classification.ResultsThe highest μSBS value in the study cements was obtained for Panavia F.2 cement (P<0.001) with no significant difference with Rely X U200 (P=0.07). The μSBS values of both GI-based cements were significantly lower than those of resin cements. Thermal aging decreased the μSBS values of all groups (P=0.003) significantly. The mainly occurred failure mode in all groups was the adhesive feature.ConclusionsResin cements demonstrated acceptable bonding to Cp Ti, yet Gl-based cements did not. From among the cements examined, Panavia F.2 can be considered as the best option for bonding to Ti. Key words:Bond strength, Glass ionomer, Hybride abutment, Resin cement, Titanium.

Thermal cycling aging effects on the tensile property and constitute behavior of Sn–3.0Ag–0.5Cu solder alloy

Thermal cycling aging effects on the tensile property of Sn–3.0Ag–0.5Cu solder alloy are investigated experimentally and theoretically. Solder specimens were tested at temperature ranges from 77 to 293 K and 77–398 K with different cyclic numbers. Thermal cycling optimizes the microstructure of solder and causes dislocation, which can enhance both tensile strength and plasticity of solder material. It is observed experimentally that the plasticity of Sn–3.0Ag–0.5Cu solder alloy is strongly time dependent, higher cycle number leads to an increase of plastic strain. A unified creep plasticity constitutive model is developed by modifying the drag strength and taking the effects of temperature and cycling number into account. A new material damage parameter is proposed to consider the temperature effect during the treatment, which is incorporated into the developed model to describe the mechanical behavior of Sn–3.0Ag–0.5Cu solder under thermal cycling. The numerical predictions agree well with the experimental results of Sn–3.0Ag–0.5Cu solder alloys, it shows the developed constitutive model can describe the mechanical properties of Sn–3.0Ag–0.5Cu solder under thermal cycling with reasonable accuracy.

Influence of Thermal Aging Parameters on the Characteristics of Aluminum Semi-Solid Alloys

The current study aimed at analyzing the response of semisolid A357 aluminum alloys to unconventional thermal treatment cycles of T4/T6/T7 conditions. The mechanical, electrical, and microstructural characterizations of such semisolid alloys were investigated. The microstructure evolutions of Fe-intermetallic phases and strengthening precipitates were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The mechanical failure of such semi solid A357 aluminum alloys, used for suspension automotive parts, is mostly related to cracking issues which start from the surface due to hardness problems and propagate due to severe load variations. For these reasons, the multiple thermal aging cycles, in this study, are applied to enhance the mechanical properties and to have compromised values compared to those obtained by standard thermal treatments. The results obtained in this work indicate that the heat treatment of this alloy can be optimized. The results showed that the optimum characteristics of A357 semisolid alloys were obtained by applying thermal under-aging cycle, interrupted thermal aging cycles and a T7/T6 two steps aging treatment condition. The electrical conductivity and electron microscopy were applied in this study to analyze the characteristics of hardening phases formed due to different aging cycles applied to the alloys investigated.