Effect of heat treatment on microstructure and tensile properties of A356 alloys

Two heat treatments of A356 alloys with combined addition of rare earth and strontium were conducted.T6 treatment is a long time treatment（solution at 535 ℃ for 4 h ＋ aging at 150 ℃ for 15 h）.The other treatment is a short time treatment（solution at 550 ℃ for 2 h ＋ aging at 170 ℃ for 2 h）.The effects of heat treatment on microstructure and tensile properties of the Al-7%Si-0.3%Mg alloys were investigated by optical microscopy,scanning electronic microscopy and tension test.It is found that a 2 h solution at 550 ℃ is sufficient to make homogenization and saturation of magnesium and silicon in α（Al） phase,spheroid of eutectic Si phase.Followed by solution,a 2 h artificial aging at 170 ℃ is almost enough to produce hardening precipitates.Those samples treated with T6 achieve the maximum tensile strength and fracture elongation.With short time treatment（ST）,samples can reach 90% of the maximum yield strength,95% of the maximum strength,and 80% of the maximum elongation.

Microstructure and tensile properties of containerless near-isothermally forged TiAl alloys

Ti-47Al-2Nb-2Cr-0.4（W, Mo） （mole fraction, %） alloy ingot fabricated using vacuum consumable melting was containerless near-isothermally forged, and the high temperature forgeability, microstructure and tensile properties were investigated. The results show that the TiAl ingot exhibits good heat workability during containerless near-isothermally forging process, and there are not evident cracks on the surface of as-forged TiAl pancake with a total deformation degree of 60%. The microstructure of the TiAl ingot appears to be typical nearly-lamellar（NL）, comprising a great amount of lamellar colonies （α2＋γ） and a few equiaxed γ grains. After near-isothermally forging, the as-forged pancake shows primarily fine equiaxed γ grains with an average grain size of 20 μm and some broken lamellar pieces, and some bent lamellas still exist in the hard-deformation zone. Tensile tests at room temperature show that ultimate tensile strength increases from 433 MPa to 573 MPa after forging due to grain refinement effect.

Tensile properties and microstructure of Ti14 alloy after semi-solid forging

Tensile properties of a new α＋Ti2Cu alloy after solid forging at 950 °C and semi-solid forging at 1 000 °C and 1 050 °C were investigated over the temperature range of 20-600 °C. The results reveal that high strength and low ductility are obtained in all semi-solid forged alloys. Tensile properties decrease as the semi-solid forging temperature increases, and cleavage fractures are observed after semi-solid forging at 1 050 °C. The variations in tensile properties are attributed to the coarse microstructures obtained in the semi-solid alloys. It is found that the elevated semi-solid temperatures lead to more liquid precipitates along the prior grain boundaries, which increases the peritectic precipitation and formation of Ti2Cu precipitation zones during re-solidification. Recrystallization heat treatment leads to fine microstructure of semi-solid forged alloys, resulting in improvement of tensile properties.

Effect of slow shot speed on externally solidified crystal,porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

The effect of slow shot speed on externally solidified crystal(ESC),porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM)and laboratory computed tomography(CT).Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg alloy.The AlSi9MnMoV alloy,which was designed with trace multicomponent additions,displays a notable grain refining effect in comparison to the AlSi10MnMg alloy.Refining elements Ti,Zr,V,Nb,B promote heterogeneous nucleation and reduce the grain size of primaryα-Al.At a lower slow shot speed,the large ESCs are easier to form and gather,developing into the dendrite net and net-shrinkage.With an increase in slow shot speed,the size and number of ESCs and porosities significantly reduce.In addition,the distribution of ESCs is more dispersed and the net-shrinkage disappears.The tensile property is greatly improved by adopting a higher slow shot speed.The ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa(increased by 11.52%),and the elongation is enhanced from 3.72%to 6.34%(increased by 70.52%).

Microstructure and tensile properties of low cost titanium alloys at different cooling rate

Titanium and titanium alloys have several advantages, but the cost of titanium alloys is very expensive compared with the traditional metal materials. This article introduces two new low-cost titanium alloys Ti-2.1Cr-1.3Fe (TCF alloy) and Ti-3Al-2.1Cr-1.3Fe (TACF alloy). In this study, we used Cr-Fe master alloy as one of the raw materials to develop the two new alloys. We introduce the microstructure and tensile properties of the two new alloys from β solution treated with different cooling methods. Optical microscopy (OM), X-ray diffractometry (XRD), and transmission electron microscopy (TEM) were employed to analyze the phase constitution, and scanning electron microscopy (SEM) was used to observe the fracture surfaces. The results indicate that the microstructures consist of β grain boundary and α′ martensite after water quenching (WQ), β matrix and α phase after air cooling (AC) and furnace cooling (FC), respectively. Also, the microstructure is the typical basketweave structures after FC. Of course, athermal ω is also observed by TEM after WQ. The strength increases with decreasing cooling rates and the plasticity is reversed. Because of the athermal ω, the strength and ductility are highest and lowest when the cooling method is WQ. The strength of TACF alloy is higher than the TCF alloy, but the plasticity is lower. The fracture surfaces are almost entirely covered with dimples under the cooling methods of AC and FC. Also, we observe an intergranular fracture area that is generated by athermal ω, although some dimples are observed after WQ.

Effect of synergistic action of ultrasonic vibration and solidification pressure on tensile properties of vacuum counter-pressure casting aluminum alloy

The effect of synergistic action of ultrasonic vibration and solidification pressure on tensile properties of vacuum counter-pressure casting ZL114 A alloys was studied systemically through testing and analyzing the tensile strength and elongation subjected to different ultrasonic powers and solidification pressures. The results indicate that the synergistic action of ultrasonic vibration and solidification pressure can result in the refinement of grains and improvement of tensile properties. Both the highest tensile strength and elongation of aluminum alloy were obtained under synergistic action of 600 W ultrasonic power and 350 kPa solidification pressure. Moreover, the tensile fracture morphology shows obvious ductile fracture characteristics. When the solidification pressure is lower than 300 kPa, the effect of ultrasonic power on tensile strength and elongation is more obvious, but when the solidification pressure is higher than 300 kPa, the effect of solidification pressure on tensile strength and elongation is greater. Meanwhile, the size and morphology of the eutectic silicon were improved significantly by the ultrasonic vibration and pressurized solidification. The strip and massive eutectic silicon phase are completely converted into small short rod-like and evenly distributed Si phases at the grain boundary of primary α-Al.

Microstructures,tensile properties and serrated flow of Al_xCrMnFeCoNi high entropy alloys

Microstructures and mechanical properties of dual-phase AlxCrMnFeCoNi (x=0.4, 0.5, 0.6, at.%) alloys were investigated. Thermomechanical processing leads to a microstructural evolution from cast dendritic structures to equiaxed ones, consisting of face-centered cubic (fcc) and body-centered cubic (bcc) phases in the two states. The volume fraction of bcc phase increases and the size of fcc grain decreases with increasing Al content, resulting in remarkably improved tensile strength. Specifically, the serrated flow occurring at the medium temperatures varies from type A+B to B+C or C as the testing temperature increases. The average serration amplitude of these Al-containing alloys is larger than that of CoCrFeNiMn alloy due to the enhanced pinning effect. The early small strain produces low-density of dislocation arrays and bowed dislocations in fcc grains while the dislocation climb and shearing mechanism dominate inside bcc grains. The cross-slip and kinks of dislocations are frequently observed and high-density-tangled dislocations lead to dislocation cells after plastic deformation with a high strain.

Effect of fusion welding processes on tensile properties of armor grade, high thickness, non-heat treatable aluminium alloy joints

AA5059 is one of the high strength armor grade aluminium alloy that finds its applications in the military vehicles due to the higher resistance against the armor piercing (AP) threats. This study aimed at finding the best suitable process among the fusion welding processes such as gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) by evaluating the tensile properties of AA5059 aluminium alloy joints. The fracture path was identified by mapping the low hardness distribution profile (LHDP) across the weld cross section under tensile loading. Optical and scanning electron microscopies were used to characterize the microstructural features of the welded joints at various zones. It is evident from the results that GTAW joints showed superior tensile properties compared to GMAW joints and this is primarily owing to the presence of finer grains in the weld metal zone (WMZ) and narrow heat-affected zone (HAZ). The lower heat input associated with the GTAW process effectively reduced the size of the WMZ and HAZ compared to GMAW process. Lower heat input of GTAW process results in faster cooling rate which hinders the grain growth and reduces the evaporation of magnesium in weld metal compared to GMAW joints. The fracture surface of GTAW joint consists of more dimples than GMAW joints which is an indication that the GTAW joint possess improved ductility than GMAW joint.

Effect of trace Sc and Zr on aging behavior and tensile properties of 2618 alloy

The aging behavior of 2618 (Al Cu Mg Fe Ni) alloy added trace Sc and Zr was studied by Vicker’s hardness measurement at 200 and 300 ℃, and the tensile properties(yield strength, ultimate tensile strength and elongation) of alloys were measured at 20, 200, 250 and 300 ℃. The microstructures were observed by using optical microscope, SEM and TEM. It was found that the addition of Sc and Zr to 2618 alloy resulted in a uniform distribution of fine coherent Al 3(Sc,Zr) precipitates which had obvious aging hardening effect and made the S’ phase precipitate more homogeneously. The strength of alloy increased at ambient and elevated temperature without a decrease of ductility because of the precipitation strengthening and thermal stability of Al 3(Sc,Zr) particles. The ductile fracture of alloy occurred by microviod nucleation, growth and coalescence, so the microvoid coalescence was the dominant fracture mechanism. Al 3(Sc,Zr) particles could inhabit the recrystallization process of alloy 2618.

Effect of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn alloys

The effects of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn(wt.%)alloys were investigated by X-ray diffractometry(XRD),optical microscopy(OM),scanning electron microscopy(SEM)and tensile test.It is found that,as-cast Mg-8Li-3Al-(1,2,3)Sn alloys consist ofα-Mg+β-Li duplex matrix,MgLiAl2 and Li2Mg Sn phases.Increasing Sn content leads to grain refinement ofα-Mg dendrites and increase in content of Li2MgSn phase.During hot extrusion,complete dynamic recrystallization(DRX)takes place inβ-Li phase while incomplete DRX takes place inα-Mg phase.As Sn content is increased,the volume fraction of DRXedα-Mg grains is increased and the average grain size of DRXedα-Mg grains is decreased.Increasing Sn content is beneficial to strength but harmful to ductility for as-cast Mg-8Li-3Al-(1,2,3)Sn alloys.Tensile properties of Mg-8Li-3Al-(1,2,3)Sn alloys are improved significantly via hot extrusion and Mg-8Li-3Al-2Sn alloy exhibits the best tensile properties.

Effects of La addition on the microstructure and tensile properties of Al-Si-Cu-Mg casting alloys

The effects of La addition on the microstructure and tensile properties of B-refmed and Sr-modified A1-1 1Si-1.5Cu-0.3Mg cast- ing alloys were investigated. With a trace addition of La （0.05wt%-0. lwt%）, the mutual poisoning effect between B and Sr can be neutral- ized by the formation of LaB6 rather than SrB6. By employing a La/B weight ratio of 2：1, uniform microstructures, which are characterized by well refined ct-A1 grains and adequately modified eutectic Si particles as well as the incorporation of precipitated strengthening intermetal- lics, are obtained and lead to appreciable tensile properties with an ultimate tensile strength of 270 MPa and elongation of 5.8%.

Tensile properties and fracture behavior of Ti_2AlNb based alloys at room temperature

The tensile mechanical properties and fracture behaviors of Ti 22Al 20Nb 7Ta alloys were studied at room temperature. Three typical microstructures of Ti 2AlNb based alloys were obtained by combination of thermal mechanical processing and heat treat ment. They are: 1) lath mixture of O + B 2 with remaining β grain boundaries and α 2 phase; 2) equiaxed O phase in B 2 matrix; 3) fine lath mixture of O + B 2 without remaining β grain boundaries. It is shown that the microstructure obviously affects the tensile properties of Ti 2AlNb based alloys. The microstructure of fine lath mixture of O + B 2 without remaining β grain boundaries has good combination of yield stress and ductility, while the microstructure with lath mixture of O + B 2 with remaining β grain boundaries and α 2 phase has low yield stress and elongation. The fracture mode was also controlled by the microstructure of Ti 2AlNb based alloys. By means of SEM, it was found that the dominated fracture mode of microstructure with lath mixture of O + B 2 with remained β grain boundary and α 2 phase was intergranular, and the fracture mode of the other two microstructures was mainly transgranular.

Tensile properties of as-deformed 2A50 aluminum alloy in semi-solid state

Tensile properties of as-deformed 2A50 aluminum alloy were investigated in the high temperature solid and semi-solid states. The results show that temperature has almost no effect on the maximum tensile stress between 500 ℃ and 530 ℃, and the maximum tensile stress decreases rapidly when the temperature is above 532 ℃. The ductility decreases with increasing temperature and has an obvious fall when the temperature is above solidus temperature. This alloy almost has no ductility above 537 ℃, and cannot sustain tensile stress above 550℃. A brittle temperature range in which this alloy is prone to form microcracks was derived. The relation between microstructure, fraction solid and tensile properties were also investigated by examining the metallograph and fracture surface morphology of tested specimens, which could provide reference for forecasting the microcracks in this alloy occurring in semi-solid processing.

Relationship among microstructure,mechanical properties and texture of TA32 titanium alloy sheets during hot tensile deformation

The relationship among microstructure,mechanical properties and texture of TA32 titanium alloy sheets during hot tensile deformation at 800℃was investigated.In the test,the original sheet exhibited relatively low flow stress and sound plasticity,and increasing the heat treatment temperature resulted in an increased ultimate tensile strength(UTS)and a decreased elongation(EL).The deformation mechanism of TA32 alloy was dominated by high angle grain boundaries sliding and coordinated by dislocation motion.The coarsening of grains and the annihilation of dislocations in heat-treated specimens weakened the deformation ability of material,which led to the increase in flow stress.Based on the high-temperature creep equation,the quantitative relationship between microstructure and flow stress was established.The grain size exponent andαphase strength constant of TA32 alloy were calculated to be 1.57 and 549.58 MPa,respectively.The flow stress was accurately predicted by combining with the corresponding phase volume fraction and grain size.Besides,the deformation behavior of TA32 alloy was also dependent on the orientation of predominantαphase,and the main slip mode was the activation of prismaticslip system.The decrease of near prism-oriented texture in heat-treated specimens resulted in the enhancement of strength of the material.

EFFECT OF HEAT TREATMENTS ON TENSILE PROPERTIES AND MICROSTRUCTURE OF 2195 ALLOY

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Effect of partial recrystallization on microstructure and tensile properties of NiFeCoCrMn high-entropy alloy

To obtain a balance between strength and ductility in NiFeCoCrMn high-entropy alloy, the degree of dislocation strengthening was tuned via partial recrystallization during traditional thermomechanical processing(cold rolling and recrystallization). The tensile properties in each state were then examined. Significant improvements in uniform elongation and work hardening rate, with decrease in yield strength and ultimate tensile strength, are associated with increase in the recrystallized fraction, i.e., reductions in the degree of strain hardening. In particular, recrystallized fractions of 37% and 74% are obtained by annealing at 650 ℃ for 10 min and 15 min, respectively, which results in yield strengths of 1003 MPa and 742 MPa and uniform elongations of 4% and 24%, respectively. The strengthening is due to the unrecrystallized grains with a high density of dislocations, whereas the ductility benefits from the presence of recrystallized strain-free grains.

Microstructure and tensile properties of as-extruded Mg-Sn-Y alloys

The microstructure and tensile properties of the Mg-1.0%Sn-xY(x=1.5%,3.0%,3.5%,atom fraction)alloys extruded indirectly at 350℃ were investigated by means of optical microscopy,scanning electron microscopy and tensile test.The mean grain sizes ofα-Mg matrix in the three extruded alloys are 6,8 and 12μm,respectively,slightly increasing with the addition of Y. The relationship between microstructure and strength was discussed in detail.The results show that the addition of Y has little effect on the grain refinement of the as-extruded Mg-Sn based alloys above.The only MgSnY phase is detected in the Mg-Sn-1.5%Y alloy, and the Sn3Y5 phase in the Mg-Sn-3.5%Y alloy,whereas both of them simultaneously exist in the Mg-Sn-3.0%Y alloy.The particle shape of MgSnY and Sn3Y5 phase,inherited from the solidification,has little change before and after hot extrusion.Mg-Sn-3.0%Y alloy has the highest ultimate tensile strength(UTS),305 MPa,by over 50%compared with that of the other two alloys.

Effects of microstructure on tensile properties of AA2050-T84 Al−Li alloy

The effect of microstructure evolution on the tensile properties of 2050 Al-Li alloy thick plate aged at 150 ℃ with 80 mm in thickness(t) was studied from a microstructural perspective. Scanning electron microscope, optical microscope, transmission electron microscope and X-ray diffractometer were used to explore the surface(t/6), interlayer(t/3) and center(t/2) thickness layer of this alloy. Results show that the secondary phases on grain boundaries, precipitates and textures vary depending on the thickness location. The precipitation strengthening has a stronger influence on the alloy along the rolling direction than the transverse direction from the under-aged to the peak-aging condition;however, its effect on the anisotropy is insignificant. The higher Taylor factor(M) value caused by stronger β fiber rolling textures and the intergranular phases is the main reason that leads to the highest strength at the t/2 position along the rolling direction. The M-value has a limited change at different thickness layers along the transverse direction, which causes the same tensile strength.

Effect of ECAP on microstructure and tensile properties of A390 aluminum alloy

The purpose of the present research is to determine the tensile strength and elongation of the A390 alloy processed by ECAP and to reveal the relationship between the microstructure and tensile properties. Optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for microstructural analysis of the samples. The results of the mechanical testing showed that the ultimate tensile strength (UTS) increased from 142 MPa for the as-cast sample to 275 MPa for the sample after the third ECAP pass. Increasing the ECAP passes up to 4 led to a remarkable enhancement of elongation compared with the as-cast sample. It was found that the improvement of strength and ductility of A390 alloy with increasing the number of ECAP passes was attributed to the homogenous distribution of particles, reduction of particle size, and elimination of voids especially adjacent to the primary silicon particles. The results of fractography demonstrated that when the number of ECAP passes increased to 4, the uniform round dimples formed and the relatively brittle as-cast sample transformed to a ductile alloy.

Modifying microstructures and tensile properties of Mg-Sm based alloy via extrusion ratio

Microstructure and tensile properties of a Mg-Sm-Zn-Zr alloy with various extrusion ratios(ERs)of 6.9,10.4 and 17.6 were systematically investigated.It was identified that,greater ER increased dynamic recrystallization(DRX)fraction and coarsened DRX grains,which further suggests weakened basal fiber texture for the studied alloy.This is mainly due to the rising temperature from massive deformation heat when hot-extrusion.As a result,greater ER corresponds to a decreased strength but improved ductility.Finally,transmission electron microscopy(TEM)observations reveal that the dominant intermetallic phase,Mg_(3)Sm,is metastable,and it will transform into Mg_(41)Sm_(5)during extrusion with high-ER.This transformation leads to the accumulation of surplus Sm and Zn atoms,which induces the precipitation of Sm Zn_(3)phase at the surface of Mg_(41)Sm_(5)matrix.