The aging behavior,microstructure and mechanical properties of AlN/AZ91 composite

Microstructure evolution and mechanical properties of the aging treated AlN/AZ91 composites were systematically investigated by optical microscopy(OM),high resolution scanning electron microscopy(HRSEM)with an energy dispersive spectrum(EDS),and high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM).The results show that the higher fracture elongation(14±1%)and ultimate tensile strength(275±6 MPa)were simultaneously obtained in the peak-aged AlN/AZ91 composites.Comparied with AZ91 matrix alloy,the strength was increased by about 44%and the elongation was approximately five times higher,which mainly attributed to the precipitation of nano-sizedγ-Mg_(17)Al_(12)phase and the activation of non-basal slip systems induced by in-situ AlN particles at room temperature.However,the in-situ formation of AlN reinforcements consumed part of Al element in the matrix alloy,which resulted into the volume fraction decreasing ofγ-Mg_(17)Al_(12)precipitates,and then the age hardening and strengthening efficiency were reduced in the AlN/AZ91 composites.On the other hand,the mismatch of thermal expansion coefficient between AlN particles and AZ91 matrix generated high density dislocations around AlN particles,which promoted the precipitation ofγ-Mg_(17)Al_(12)phase,and then the peak aging time and temperature were decreased.

Aging behavior and mechanical properties of 6013 aluminum alloy processed by severe plastic deformation

Structural features, aging behavior, precipitation kinetics and mechanical properties of a 6013 Al–Mg–Si aluminum alloy subjected to equal channel angular pressing （ECAP） at different temperatures were comparatively investigated with that in conventional static aging by quantitative X-ray diffraction （XRD） measurements, differential scanning calorimetry （DSC） and tensile tests. Average grain sizes measured by XRD are in the range of 66-112 nm while the average dislocation density is in the range of 1.20×10^14-1.70×10^14 m^-2 in the deformed alloy. The DSC analysis reveals that the precipitation kinetics in the deformed alloy is much faster as compared with the peak-aged sample due to the smaller grains and higher dislocation density developed after ECAP. Both the yield strength （YS） and ultimate tensile strength （UTS） are dramatically increased in all the ECAP samples as compared with the undeformed counterparts. The maximum strength appears in the samples ECAP treated at room temperature and the maximum YS is about 1.6 times that of the statically peak-aged sample. The very high strength in the ECAP alloy is suggested to be related to the grain size strengthening and dislocation strengthening, as well as the precipitation strengthening contributing from the dynamic precipitation during ECAP.

Creep aging behavior and performance of Al-Zn-Mg-Cu alloys under different parameters in retrogression aging treatment

A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al-Zn-MgCu alloy during regressive reaging. The corresponding creep strain and mechanical properties of samples were studied by conducting creep tests and uniaxial tensile tests. The electrical conductivity was measured using an eddy-current conductivity meter. The microstructures were observed by transmission electron microscopy(TEM). With the increase in regression aging time, the steady creep strain first increased and then decreased, and reached the maximum at 45 min.The steady creep strain increased with the increase in regression aging temperature, and reached the maximum at 200 ℃.The level of steady creep strain was determined by precipitation and dislocation recovery. Creep aging strengthens 7B50-RRA treated with regression aging time at 190 ℃ for 10 min, and the difference in the mechanical properties of alloy becomes smaller. The diffusion of solute atoms reduces the scattering of electrons, leading to a significant improvement in electrical conductivity and stress corrosion cracking(SCC) resistance after creep aging. The findings of this study could help in the application of creep aging forming(CAF) technology in Al-Zn-Mg-Cu alloy under RRA treatment.

Aging Behavior of High Volume Fraction SiC Particles Reinforced 2024Al Composite

2024 Al matrix composite reinforced by SiC particles with 45% volume fraction and 1 um diameter was successfully fabricated by squeeze-exhaust casting method. The aging behavior of SiCp/2024AI composite at four temperatures was investigated and compared to 2024 alloy. It was found that the addition of high volume fraction SiC particles does not alter the aging sequence, but it significantly accelerates the kinetics of precipitation in the composite matrices. Therefore, the aging peak of the composite appears earlier than that of 2024AI alloy. This is attributed to the decrease in the activation energy for the precipitate formation and the increase in the precipitate growth rate due to the high density dislocations in the composite with high volume fraction particles. The high density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.

Aging behavior of nano-SiC_p reinforced AZ61 magnesium matrix composites

The mechanical properties of magnesium matrix composties can be further improved by aging treatment. To study the aging behavior of SiC particles reinforced AZ61 magnesium matrix composites fabricated by ultrasonic method, an investigation has been undertaken by means of Vickers hardness measurement, scanning electron microscopy （SEM） and energy spectrum analyzing apparatus. The box-type heat treatment furnace was used in the study. The results showed that no discontinuous cellular precipitation is observed at the grain boundaries in the magnesium matrix of the composite while the MglTAI12 preferentially precipitates in the matrix. The time to reach the peak hardness for AZ61 alloy or SiCp/AZ61 magnesium matrix composites is reduced with the increase of aging temperature. At the same temperature, the composite exhibit an accelerated aging manner but lower aging efficiency, compared with the unreinforced matrix alloy. The microhardness of the composite is higher than that of the unreinforced matrix alloy, because that the SiC particles distributes homogeneously in the matrix alloy under the ultrasonic processing condition.

Effect of Er on Aging Behavior of 1420 Alloy

Effect of trace rare earth Er addition on the aging behavior of 1420 alloys was studied using hardness testing. Precipitation behavior during aging was investigated by electron microscopy transmission. It is found that small amounts of Er can modify the aging behavior of 1420 alloy, for example, improve the hardness and shift peak aging time. All those results may be attributed to the increase of diffusion coefficient of Li atom in the Al matrix added with Er. As a consequence, rate of nucleation and growth of δ′ (Al_3Li) was promoted; the Al_3Er particles act as preferential sites for the nucleation and growth of δ′, which in turn results in the presentation of more composite particles.

Aging Behaviors of Silicone Rubber Composite Materials under Outdoor Environment

We investigated the aging effect on the chemical structure of silicone rubber composite materials under outdoor environment. The variations of low molecular weight siloxanes in silicone rubber were probed by gas chromatography-mass spectrometry during the degradation process. The experimental results indicate that a series of cyclic siloxanes exist in both the virgin and aged silicone rubber samples, while the additional low molecular weight siloxanes（hexamethyl cyclotrisiloxane） only appear in the aged samples. Meanwhile, the total amounts of low molecular weight siloxanes in the aged samples are much less than those in the virgin ones. The loss of low molecular weight siloxanes is induced by the chain scission and depolymerization.

Aging Behavior of As-Extruded Ti Particles Reinforced VW94 Composites

The ageing behavior of as-extruded Ti_(P)/VW94 composites was investigated.The peak hardness of the composites increases compared to the matrix alloy and the 5%Ti_(P)/VW94 composite presents the highest peak hardness of 148.7 HV after aging for about 50 h.However,the hardness increments first decrease and then slightly increase with increasing Ti particle content due to the introduction of high-density dislocations by Ti particles.

Influence of Li addition on mechanical property and aging precipitation behavior of A1-3.5Cu-1.5Mg alloy

The influence of Li addition on mechanical property and aging precipitation behavior of Al-3.5Cu-1.5Mg alloy was investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM） and high resolution transmission electron microscopy（HRTEM）.The results show that the tensile strength can be significantly improved with the slightly decreased ductility and the form of fracture morphology is converted from ductile fracture into ductile/britde mixed fracture by adding 1.0%Li.Besides,the peak aging time at 185 ℃ is delayed from 12 to 24 h and the main precipitation phase S（Al2CuMg） is converted into S＇（Al2CuMg）＋δ（Al3Li）,while the formation of S＇（Al2CuMg） is delayed.

Effect of interrupted aging on mechanical properties and corrosion resistance of 7A75 aluminum alloy

The effects of interrupted aging on mechanical properties and corrosion resistance of 7A75 aluminum alloy extruded bar were investigated through various analyses,including electrical conductivity,mechanical properties,local corrosion properties,and slow strain rate tensile stress corrosion tests.Microstructure characterization techniques such as metallographic microscopy,scanning electron microscopy(SEM),and transmission electron microscopy(TEM)were also employed.The results indicate that the tensile strength of the alloy produced by T6I6 aging is similar to that produced by T6I4 aging,and it even exceeds 700 MPa.Furthermore,the yield strength increases by 52.7 MPa,reaching 654.8 MPa after T6I6 aging treatment.The maximum depths of intergranular corrosion(IGC)and exfoliation corrosion(EXCO)decrease from 116.3 and 468.5μm to 89.5 and 324.3μm,respectively.The stress corrosion factor also decreases from 2.1%to 1.6%.These findings suggest that the alloy treated with T6I6 aging exhibits both high strength and excellent stress corrosion cracking resistance.Similarly,when the alloy is treated with T6I4,T6I6 and T6I7 aging,the sizes of grain boundary precipitates(GBPs)are found to be 5.2,18.4,and 32.8 nm,respectively.The sizes of matrix precipitates are 4.8,5.7 and 15.7 nm,respectively.The atomic fractions of Zn in GBPs are 9.92 at.%,8.23 at.%and 6.87 at.%,respectively,while the atomic fractions of Mg are 12.66 at.%,8.43 at.%and 7.00 at.%,respectively.Additionally,the atomic fractions of Cu are 1.83 at.%,2.47 at.%and 3.41 at.%,respectively.

Accelerated Aging Behaviors and Mechanism of Fluoroelastomer in Lubricating Oil Medium

The aging behaviors and mechanism of fluoroelastomer(FKM)under lubricating oil(FKM-O)and air(FKM-A,as a comparison)at elevated temperatures were studied from both physical and chemical viewpoints.The obvious changes of mechanical and swelling performances indicate that the coupling effect of lubricating oil and temperature causes more serious deterioration of FKM-O compared to that of FKM-A.Meanwhile,much stronger temperature dependence of both bulk properties and micro-structures for FKM-O is found.Three-stage physical diffusion process is defined in FKM-O due to the competition between oil diffusion and elastic retraction of network.FTIR results reveal that the dehydrofluorination reaction causes the fracture of C-F bonds and produces a large number of C=C bonds in the backbone.The coupling effect of oil medium and high temperature could accelerate the scission of C=C bonds and generate a series of fragments with different molecular sizes.The TGA results,crosslinking density Ve,and glass transition temperature Tg derived from different measurements coherently demonstrate the network destruction in the initial stage and the simultaneous reconstruction occurring at the final stage.The newly formed local network induced by reconstruction cannot compensate the break of the original rubber network and thus only provides lower tensile strength and thermal stability.

Sintering effect on electrical properties and pulse aging behavior of(V_2O_5-Mn_3O_4-Er_2O_3 )-doped zinc oxide varistor ceramics

The effect of sintering temperature on microstructure, electrical properties, and pulse aging behavior of （V2O5-Mn3O4-Er2O3）-doped zinc oxide varistor ceramics was systematically studied. When the sintering temperature increased, the average grain size increased from 6.1 to 8.7μm and the sintered density decreased from 5.52 to 5.43 g/cm3. The breakdown field decreased from 3856 to 922 V/cm with an increase in the sintering temperature up to 900 °C, whereas a further increase to 2352 V/cm at 925 °C. The nonlinear coefficient increased pronouncedly from 4.6 to 30.0 with an increase in the sintering temperature. The varistor ceramics sintered at 850 °C exhibited the best clamping characteristics, with the clamp voltage ratio of the range of 2.22-2.88 for pulse current of 1-25 A. The varistor ceramics sintered at 925 °C exhibited the strongest stability, with %ΔE1 mA/cm2=-8.8% after applying the multi-pulse current of 25 A.

Microstructure, electrical and dielectric properties, and aging behavior of ZPCCA varistor ceramics with Er_2O_3 doping

The microstructure, electrical and dielectric properties, and DC-accelerated aging of the ZPCCA （ZnO-Pr6O11-CoO- Cr203-A1203） ceramics were investigated with various contents of Er203. The ceramic phases consisted of a bulk phase of ZnO grains, and a minor secondary phase of mixture of Pr6O11 and Er203. The increase of the content of doped Er203 increased the densities of sintered pellet from 5.66 to 5.85 g/cm3, and decreased the average grain size from 9.6 to 6.3 μm. With the increase of the content of doped Er203, the breakdown field increased from 2390 to 4530 V/cm, and the nonlinear coefficient increased from 28.4 to 39.1. The sample doped with 0.25 mol.% Er203 exhibited the strongest electrical stability; variation rates for the breakdown field measured at 1.0 mA/cm2, and for the non-ohmic coefficient were -3.4% and -23,8%, respectively, after application of a stress of 0.95 Eu/125 ℃/24 h.

Aging behavior and precipitate characterization of Zn-rich Al-Zn-Mg-Cu alloys with various Mg and Cu contents

Four Zn-rich Al-Zn-Mg-Cu alloys with different Mg and Cu contents were fabricated by spray deposition.The effects of Mg and Cu contents on the aging behaviors of the whole precipitation process of the alloys were systematically investigated.The results show that the primary precipitates in the under-aged and peak-aged alloys are GPⅡ and η'phases;no GPⅠ zones were observed.During aging,the dissolution driving force of the precipitates increases with increasing Mg content;therefore,the volume fraction of precipitates in the grain interior and the area fraction of precipitates at the grain boundary increase obviously,which contributes to a considerable improvement in yield strength and decrease in plasticity of the high Mg content alloys.Cu content has no apparent effect on the size and volume fraction of precipitates.However,a higher Cu content can effectively prevent coarsening and transformation of precipitates,which is beneficial to maintain the peak aging state of the alloys.This research provides a basis for the composition optimization of the rapid-solidified highly alloying Al-Zn-Mg-Cu alloys.

Effect of forging temperature on the microstructure,subsequent aging precipitation behavior,and mechanical properties of Mg-Gd-Y-Zr-Ag alloy

The deformation mechanism,microstructure evolution,and precipitation behavior of a Mg-8.9Gd-1.8Y-0.5Zr-0.2Ag(wt.%)alloy multi-directionally forged at three different temperatures were investigated.As the forging temperature increases,the particle-stimulated nucleation(PSN)effect diminishes as the num-ber of dynamic precipitates decreases,pyramidal slip is activated,grain boundary migration accelerates,and continuous dynamic recrystallization(CDRX)dominates.The microstructures varied greatly,although fine-grained structures were formed at all different forging temperatures.Competitive precipitation be-tween dynamic precipitate growth,dislocation-induced precipitation,and homogeneous precipitation was observed after aging treatment.Among them,the medium temperature(748 K)forged and aged alloy ex-hibits the best mechanical performance,with an ultimate tensile strength of 436 MPa,and elongation of 16.3%.The calculation indicates that the mixed precipitation structure containing theβprecipitate band provides a 35%higher strengthening contribution than the typical homogeneously distributed precipi-tates.The formation of precipitation-free zones(PFZs)ensures that aging will not cause a dramatic de-crease in ductility,which provides a reference for the industrial preparation of high-performance wrought Mg-Gd series alloys.

Effect of aging on microstructure of Mg-Zn-Er alloys

The effect of aging on microstructure of Mg-Zn-Er alloys at 473 K was investigated using hardness measurement,scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The results indicated that both Mg3.8Zn1.5Er and Mg5Zn2.0Er alloys exhibited visible age-hardening effect,especially the latter alloy.Microstructure analysis showed that,after being aged,lots of fine MgZn2 phases with hexagonal structure were found in the α-Mg matrix.Comparing with Mg3.8Zn1.5Er alloy,the accelerated hardenin...

Corrosion behavior of 2024 Al-Cu-Mg alloy of various tempers

Corrosion behavior of 2024 Al-Cu-Mg alloy of different tempers was assessed by potentiodynamic polarization studies in 3.5% NaCl solution, 3.5% NaCI＋I.0% H2O2 solution and 3.5% NaCl solution at pH 12. Polarization curves showed shifting of corrosion potential （φPcor） towards more negative potential with increasing ageing time and shifting of φcorr in the positive direction with the addition of H2O2 in NaCl solution. Polarization curves in 3.5% NaCl solution at pH 12 exhibited distinct passivity phenomenon. Optical micrographs of the corroded surfaces showed general corrosion, extensive pitting and intergranular corrosion as well. Cyclic potentiodynamic polarization curves exhibited wide hysteresis loop and the mode of corrosion attack confirmed that the alloy states are susceptible to pit growth damage. Attempts were made to explain the observed corrosion behavior of the alloy of various tempers in different electrolytes with the help of microstructural features.

Effect of Li addition on mechanical properties and ageing precipitation behavior of extruded Al-3.0 Mg-0.5 Si alloy

The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-resolution transmission electron microscopy(HRTEM)images.The results show that the tensile strength of the Li-containing alloy can be significantly improved;however,the ductility is sharply decreased and the fracture mechanism changes from ductile fracture to intergranular fracture.The elasticity modulus of the Li-containing alloy increases by 11.6%compared with the base alloy.The microstructure observation shows that the Li addition can absolutely change the precipitation behavior of the base alloy,andδ′-Al_(3)Li phase becomes the main precipitates.Besides,β′′-Mg_(2)Si andδ′-Al_(3)Li dual phases precipitation can be visibly observed at 170℃ ageing for 100 h,although the quantity ofδ′-Al_(3)Li phase is more thanβ′′-Mg_(2)Si phase.The width of the precipitate-free zone(PFZ)of the Li-containing alloy is much wider at the over-ageing state than the base alloy,which has a negative impact on the ductile and results in the decrease of elongation.

Effects of process parameters on mechanical properties and microstructures of creep aged 2124 aluminum alloy

A series of tests were carried microstructures of 2124 aluminum alloy in increase of aging time, temperature and low-to-peak-to-low manner. No significant out to investigate the effects of process parameters on mechanical properties and creep aging process. The results show that creep strain and creep rate increase with the applied stress. The hardness of specimen varies with aging time and stress in a effect of temperature on hardness of material is seen in the range of 185-195 ℃. The optimum mechanical properties are obtained at the conditions of （200 MPa, 185 ℃, 8 h） as the result of the coexistence of strengthening S＂ and S＇ phases in the matrix by transmission electron microscopy （TEM）. TEM observation shows that applied stress promotes the formation and growth of precioitates and no obvious stress orientation effect is observed in the matrix.

Microstructure and mechanical properties of as-cast Mg-8Li-xZn-yGd(x=1,2,3,4;y=1,2) alloys

The as-cast Mg-8 Li-xZn-yGd(x=1 2, 3,4;y=1,2;wt.%)alloys were prepared in a vacuum induction furnace and their microstructure and mechanical properties were investigated. The results show that the increase of Zn content results in the volume fraction of W-phase(Mg3 Zn3 Gd2) increasing while that of Mg3 Gd phase decreasing. The strength of Mg-8 Li-xZn-1 Gd alloys is improved with the increase of Zn content,which is ascribed to the second phase strengthening of fine strip-like W-phase and the solid solution strengthening of Zn element.For Mg-8 Li-4 Zn-yGd alloys,the increase of Gd content leads to the appearance of coarse and discontinuous net-like W-phase, which decreases the strength. The Mg-8 Li-4 Zn-1 Gd alloy exhibits an optimum comprehensive performance with the yield strength, ultimate tensile strength and elongation of 154.7 MPa, 197.0 MPa and 12.4%, respectively. In addition,the aging behavior of the typical alloys was also investigated.