Microstructure and mechanical properties of Co-28Cr-6Mo-0.22C investment castings by current solution treatment

This study examined the impact of current solution treatment on the microstructure and mechanical properties of the Co-28Cr-6Mo-0.22C alloy investment castings.The findings reveal that the current solution treatment significantly promotes the dissolution of carbides at a lower temperature.The optimal conditions for solution treatment are determined as a solution temperature of 1,125°C and a holding time of 5.0 min.Under these parameters,the size and volume fraction of precipitated phases in the investment castings are measured as6.2μm and 1.1vol.%.The yield strength,ultimate tensile strength,and total elongation of the Co-28Cr-6Mo-0.22C investment castings are 535 MPa,760 MPa,and 12.6%,respectively.These values exceed those obtained with the conventional solution treatment at 1,200°C for 4.0 h.The findings suggest a phase transformation of M_(23)C_(6)→σ+C following the current solution treatment at 1,125°C for 5.0 min.In comparison,the traditional solution treatment at 1,200°C for 4.0 h leads to the formation of M_(23)C_(6)and M_(6)C carbides.It is noteworthy that the non-thermal effect of the current during the solution treatment modifies the free energy of both the matrix and precipitation phase.This modification lowers the phase transition temperature of the M_(23)C_(6)→σ+C reaction,thereby facilitating the dissolution of carbides.As a result,the current solution treatment approach achieves carbide dissolution at a lower temperature and within a significantly shorter time when compared to the traditional solution treatment methods.

Temperature variation and solution treatment of high strength AA7050

Temperature variation and solution treatment of high strength aluminum alloy were investigated with temperature data acquisition system,microstructural observation,mechanical properties test,electrical conductivity measurement and differential scanning calorimetry（DSC） analysis.Specimens with two dimensions were employed in the experiment.The results indicate that the specimens with large size undergo low solution temperature and short time,giving rise to the reduction of hardening precipitates.The optimized solution treatments for specimens with dimensions of 25 mm×25 mm×2.5 mm and 70 mm×60 mm×20 mm are（480 ℃,30 min） and（480 ℃,90 min）,respectively.The densities of GP zones and η＇ phases of the small specimen are higher than those of the large specimen,which is consistent with the properties of the alloys.

Effect of solution treatment and aging on microstructural evolution and mechanical behavior of NiTi shape memory alloy

As-received nickel-titanium （NiTi） shape memory alloy with a nominal composition of Ni50.9Ti49.1 （mole fraction,%） was subjected to solution treatment at 1123 K for 2 h and subsequent aging for 2 h at 573 K, 723 K and 873 K, respectively. The influence of solution treatment and aging on microstructural evolution and mechanical behavior of NiTi alloy was systematically investigated by transmission electron microscopy （TEM）, high resolution transmission electron microscopy （HRTEM）, scanning electron microscopy （SEM） and compression test. Solution treatment contributes to eliminating the Ti2Ni phase in the as-received NiTi sample, in which the TiC phase is unable to be removed. Solution treatment leads to ordered domain of atomic arrangement in NiTi alloy. In all the aged NiTi samples, the Ni4Ti3 precipitates, the R phase and the B2 austenite coexist in the NiTi matrix at room temperature, while the martensitic twins can be observed in the NiTi samples aged at 873 K. In the NiTi samples aged at 573 and 723 K, the fine and dense Ni4Ti3 precipitates distribute uniformly in the NiTi matrix, and thus they are coherent with the B2 matrix. However, in the NiTi sample aged at 873 K, the Ni4Ti3 precipitates exhibit the very inhomogeneous size, and they are coherent, semi-coherent and incoherent with the B2 matrix. In the case of aging at 723 K, the NiTi sample exhibits the maximum yield strength, where the fine and homogeneous Ni4Ti3 precipitates act as the effective obstacles against the dislocation motion, which results in the maximum critical resolved shear stress for dislocation slip.

Influence of solution treatment on microstructure and properties of in-situ Mg_2Si/AZ91D composites

The influence of solution treatment on the microstructure and properties of Mg2Si/AZ91D composites fabricated from Mg-SiO2 system via in-situ processing method was investigated.The results show that coarse Chinese script shape Mg2Si phases can be formed by adding SiO2 into AZ91D magnesium alloy with Si content up to 1.5% of the alloy melt.During solution treatment,the morphology and distribution of the coarse Chinese script shape Mg2Si phases are modified.Meanwhile,the β-Mg17Al12 phase is dissolved into the magnesium matrix.With increasing holding time,the coarse Mg2Si phases tend to dissolve,break and spheroidize.After solution treatment at 420 ℃ for 16 h,Mg2Si phases become the finest and relatively well-distributed phase.The tensile strength and elongation are increased by 14.9% and 38.9%,respectively.It is believed that the Mg2Si phases continuously dissolve and break,and finally the spheroidized Mg2Si particles are obtained due to the interface tension of Mg2Si/Mg interface.

Effects of solution treatment on microstructure and mechanical properties of Al-9.0Zn-2.8Mg-2.5Cu-0.12Zr-0.03Sc alloy

Effects of additions minor contents of 0.03%Sc and 0.12%Zr and solution treatment on microstructure and mechanical properties of Al-9.0Zn-2.8Mg-2.5Cu alloy were studied by metallographic microscopy, differential thermal analysis （DSC） and transmission electron microscopy （TEM）, in order to obtain high-performance Al alloys. The minor additions of Sc （less than 0.1%） were carried out. The results show that with the additions of 0.03% Sc and 0.12% Zr, the petaloid Al3（Sc,Zr） precipitated phases occur in Al-9.0Zn-2.8Mg-2.5Cu alloy, and Al3（Sc,Zr） particles obviously hinder the recrystallization of Al-9.0Zn-2.8Mg-2.5Cu alloy during homogenizing and extruding processes due to their strong pinning effect on dislocation. Multi-stage solution is better than single solution, for it can avoid recrystallization of Al-9.0Zn-2.8Mg-2.5Cu alloy with the minor contents of Sc （less than 0.1%）. The proper solution treatment is （420 °C, 3 h）＋（465 °C, 2 h） under which Al-9.0Zn-2.8Mg-2.5Cu-0.12Zr-0.03Sc alloy obtains a tensile strength of 777.29 MPa and a elongation of 11.84%.

Microstructure evolution of Mg-9Gd-2Er-0.4Zr alloy during solid solution treatment

Microstructure evolution of the cast Mg-9Gd-2Er-0.4Zr alloy during solid solution treatment at temperature of 460-520 ℃ for 3-12 h was investigated by using optical microscope（OM）,scanning electron microscope（SEM） and transmission electron microscope（TEM）.The results indicated that the grain size and the shape of second phase were obviously changed with time and/or temperature going on.At 460 ℃ for 3 h,the morphology of the Mg5（GdEr） phase was changed into fragmentized island morphology and the volume faction of the phase decreased.After solution solid treatment at 460 ℃ for 6 h,the Mg5（GdEr） phase was already completely dissolved,but some cuboid-shaped RE-rich phase precipitated.As the temperature increased,the morphology of the Mg5（GdEr） phase was transformed into the same morphology as that at 460 ℃ for 6 h.It was suggested that the microstructure evolution of the alloy during the solid solution treatment was concluded as follows：Mg5（GdEr） eutectic phase→Gd/Er atom diffusing into matrix→spheroidic Mg5（GdEr） phase→cuboid-shaped RE-rich phase→grain boundary immigration.

Effect of solution treatment and artificial aging on microstructure and mechanical properties of Al-Cu alloy

In order to achieve good mechanical properties of Al-Cu alloys such as high strength and good toughness,precipitation hardening and artificial aging treatment were applied.As defined by the T6 heat treatment,the standard artificial aging treatment for Al-Cu alloy followed heat treatments of solution treatment at 510-530 ℃ for 2 h,quenching in water at 60 ℃ and then artificial aging at 160-190 ℃ for 2-8 h.The effects of solution treatment and artificial aging on the microstructure and mechanical properties of Al-Cu alloy were studied by optical microscopy（OM）,scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDS）,transmission electron microscopy（TEM） and tensile test.The results of solution treatment indicate that the mechanical properties of Al-Cu alloy increase and then decrease with the increase of solution temperature.This is because the residual phases dissolve gradually into the matrix,and the fraction of the precipitation and the size of the re-crystallized grain increased.Compared to the solution temperature,the solution holding time has less effect on the microstructure and the mechanical properties of Al-Cu alloy.The artificial aging treatments were conducted at 160-180 ℃ for 2-8 h.The results show that the ultimate tensile strength can be obtained at 180 ℃ for 8 h.Ultimate tensile strength increased with increasing time or temperature.Yield strength was found as the same as the ultimate tensile strength result.

Effects of single and multi-stage solid solution treatments on microstructure and properties of as-extruded AA7055 helical profile

The effects of single-stage solution treatment(SST),enhanced solution treatment(EST),high-temperature pre-precipitation(HTPP)and multi-stage solution treatment(MST)on the microstructure,mechanical properties and corrosion resistance of the as-extruded 7055 aluminium alloy(AA7055)helical profile were investigated using differential scanning calorimetry(DSC),optical microscopy(OM),scanning electron microscopy(SEM),electron back-scattered diffraction(EBSD)and transmission electron microscopy(TEM).It was observed that EST and MST could promote the dissolution of the second-phase particles compared with the traditional SST,and the intergranular phases were distinctly discontinuously distributed after HTPP and MST.There was obvious difference in the main texture type and texture strength for the alloy after different solid solution treatments.HTPP could improve the corrosion resistance of the alloy by regulating the intergranular phases,but the mechanical properties were severely weakened.While the good corrosion resistance of the alloy could be obtained by MST without obvious strength loss.As a result,the MST is an ideal solid solution treatment scheme for AA7055.

Microstructure evolution of modified die-cast AlSi10MnMg alloy during solution treatment and its effect on mechanical properties

To optimize the solution treatment process of a modified high-pressure die-cast AlSi10MnMg alloy, the influence of the solution treatment on the microstructure, mechanical properties and fracture mechanisms was studied using OM, SEM, EBSD and tensile test. The experimental results suggest that the solution treatment could be completed in a shorter time at a temperature much lower than the conventional practice. Surface blistering could be avoided and substantial strengthening effect could be achieved in the following aging process. Prolonging solution treatment time and elevating solution temperature would be meaningless or even harmful. The rapid evolution of eutectic silicon during solution treatment, especially at the early stage, affected the way of interaction among α-Al grains during plastic deformation, and changed the ultimate mechanical properties and fracture mode.

Microstructural evolution during solution treatment of thixoformed AM60B Mg alloy

The microstructural evolution and kinetic characteristics were studied during solution treatment of AM60B Mg alloy prepared by thixoforming. The results indicate that the microstructural evolution includes two stages： the first stage involves rapid dissolution of eutectic β （Mg 17 Al 12 ） phase, homogenization and coarsening, and the second stage is regarded as normal grain growth consisting of primary α-Mg particles （primary particles） and secondary α-Mg grains （secondary grains）. In the first stage, the dissolution completes in a quite short time because the fine β phase can quickly dissolve into the small-sized secondary grains. The homogenization of Al element needs relatively long time. Simultaneously, the microstructure morphology and average grain size obviously change. The first stage sustains approximately 1 h when it is solutionized at 395 ℃ Comparatively, the second stage needs very long time and the microstructure evolves quite slowly as a result of low Al content gradient and thus low diffusivity of Al element after the homogenization of the first stage. The growth model of primary particles obeys power function while that of the secondary grains follows the traditional growth equation in the first stage. In the second stage, both of the primary particles and secondary grains behave a same model controlled by diffusion along grain boundaries and through crystal lattice.

Effect of solution treatment time on plasticity and ductile fracture of 7075 aluminum alloy sheet in hot stamping process

The effect of solution treatment time on the post-formed plasticity and ductile fracture of 7075 aluminum alloy in the hot stamping process was studied.Tensile tests were conducted on the specimens subjected to the hot stamping process with different solution treatment time.The digital image correlation(DIC)analysis was used to obtain the strain of the specimen.Based on the experiments and modeling,the Yld2000-3d yield criterion and the DF2014 ductile fracture criterion were calibrated and used to characterize the anisotropy and fracture behavior of the metal,respectively.Furthermore,the microstructure of specimens was studied.The experimental and simulation results indicate that the 7075 aluminum alloy retains distinct anisotropy after the hot stamping process,and there is no obvious effect of extending the solution treatment time on the material anisotropy.However,it is found that a longer solution treatment time can increase the fracture strain of the aluminum alloy during the hot stamping process,which may be related to the decrease of the second-phase particles size.

Effects of solution treatment and aging process on microstructure refining of semi-solid slurry of wrought aluminum alloy 7A09

A new method was exploited using solution treatment and aging process as a pretreatment in preparing semi-solid slurry with fine microstructure before isothermal treatment of wrought aluminum alloy 7A09.Parameters of pretreatment were optimized by orthogonal experiment design and proper precursor was prepared.The evolution of microstructure of semi-solid slurry during isothermal treatment was analyzed and the mechanism of microstructure refining was discussed.The result of orthogonal experiment design shows that the optimum parameters are 462 ℃for solution temperature,40min for solution time,132 ℃for aging temperature and 14 h for aging time.Microstructure of isothermal treatment is fine,homogenous,with globular solid grains and a solid fraction between 50%and 70%,which is qualified for later semi-solid forming process.Mechanism of microstructure evolution includes the agglomeration ofα-phase and Ostwald ripening.Precipitations prepared by solution and aging treatment prevent the grains from coarsening and promote the grain ripening to globular shape.

Effect of solution treatment on corrosion characteristics of biodegradable Mg-6Zn alloy

A binary Mg-6Zn biodegradable alloy was solution treated to evaluate the effects of resulting microstructure changes on the alloy＇s degradation rate and mechanisms in-vitro. The treatment was conducted at 350 °C for 6-48 h. Optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction were used to analyze the as-cast and treated samples. Immersion and electrochemical tests were performed in simulated body fluid at 37 °C to assess the samples corrosion resistance. To confirm the results of the corrosion tests, p H measurement was carried out. It is found that over 24 h solution treatment dissolves intermetallic phases in matrix and produces an almost single phase microstructure. Decreasing the intermetallic phases results in lower cathode/anode region ratios and lowers corrosion rates. The results of the electrochemical and mass loss tests reveal that extended solution treatment improves the corrosion resistance of the alloy. The results also show that solution at 350 °C for 24 h enhances the corrosion resistance of the as-cast alloy more than 60%. In addition, decreasing intermetallic phases in the microstructure accompanied a lower p H rise reduced corrosion rate. Solution treatment is suggested as a corrosion improving process for the application of Mg-Zn alloys as biodegradable implant materials.

Influence of solution treatment on microstructure,mechanical and corrosion properties of Mg-4Zn alloy

The solution treatment parameters,mechanical properties and corrosion behavior of binary Mg-4Zn alloy were investigated.The results showed that after the solution treatment at 335℃ for 16 h,Mg-4Zn alloy had an ultimate tensile strength of 184.13 MPa and elongation of 9.43%.Furthermore,the corrosion resistance was evaluated by electrochemical measurements and immersion tests in 3.5%NaCl solution.The results revealed that the corrosion current density of the solution treatment Mg alloy was 11.2µA/cm^(−2),it was lower than 15.8µA/cm^(−2) for the as-cast Mg alloy under the same conditions,which was greatly associated with the micro-cathode effect of the second phases.

Effects of solution treatment on mechanical properties and microstructures of Al-Li-Cu-Mg-Ag alloy

Mechanical properties and microstructures of Al-Li-Cu-Mg-Ag alloy after solution treatments were investigated by means of optical microscopy （OM）, tensile test, hardness measurement and electrical conductivity test, differential scanning calorimetric （DSC）, energy dispersive X-ray （EDX）, scanning electron microscopy （SEM） and transition electron microscopy （TEM）, respectively The results show that both tensile strength and hardness increase first and then decrease with temperature at constant holding time of 30 min with maximum strength and hardness appearing at 520 ℃. Tensile strength, hardness and elongation of samples treated at 520 ℃ for 30 min are 566 MPa （σb）, 512 MPa （σ0.2）, HB 148 and 8.23% （δ）, respectively. There are certain amount of fine T1 （AI2CuLi） phase dispersing among AI substrates according to TEM images. This may result in mixed fracture morphology with trans-granular and inter-granular delamination cracks observed in SEM images.

Effect of solid solution treatment on in vitro degradation rate of as-extruded Mg-Zn-Ag alloys

The degradation behaviors of the as-extruded and solution treated Mg-3Zn-xAg(x=0,1,3,mass fraction,%)alloys,as well as as-extruded pure Mg,have been investigated by immersion tests in simulated body fluid(SBF)at37°C.The as-extruded Mg-Zn(-Ag)alloys contained Mg51Zn20and Ag17Mg54.While the quasi-single phase Mg-Zn(-Ag)alloys were obtained by solution treatment at400°C for8h.The quasi-single phase Mg-Zn(-Ag)alloys showed lower degradation rate and more homogeneous degradation than corresponding as-extruded Mg alloys.Degradation rate of solid-solution treated Mg-3Zn-1Ag and Mg-3Zn-3Ag was approximately half that of corresponding as-extruded Mg alloy.Moreover,the degradation rate of solid-solution treated Mg-3Zn and Mg-3Zn-1Ag was equivalent to that of as-extruded pure Mg.However,heterogeneous degradation also occurred in quasi-single phase Mg-Zn-Ag alloys,compared to pure Mg.So,preparing complete single-phase Mg alloys could be a potential and feasible way to improve the corrosion resistance.

Effects of solution treatment on microstructure and tensile properties of as-cast alloy 625

Effects of solution treatment between 1050 and 1250℃on microstructure and tensile properties of as-cast alloy 625 were investigated.The microstructure and solidification characteristics of the alloy were studied by SEM,EDS,EPMA and DTA.The results showed that the solidification sequence of the alloy should be written as L→L+γ→L+γ+MC→L+γ+MC+γ/Laves→γ+MC+γ/Laves.After solution treatment at 1225 and 1250°C,incipient melting of Laves phase was observed.The ultimate tensile strength decreased monotonically with the increase of solution treatment temperature,and the yield strength had no significant variation.The elongation increased slightly at first and then reached a minimum value at 1250°C.The fracture mechanism changed from transgranular mode to intergranular mode after solution at 1250°C for the reason that numerous Laves phases melted at grain boundaries and microcracks nucleated in the molten pool.The suitable solution treatment temperature of this alloy was 1200°C.

Effects of Solution Treatment Time and Sr-Modification on Microstructure and Mechanical Property of Al-Si Piston Alloy

The purpose of this paper was to investigate the effects of solution treatment time and Sr-modification on the microstructure and property of the Al-Si piston alloy.It was found that as-cast microstructures of unmodified and Sr-modified Al-Si alloys consisted of a coarse acicular plate of eutectic Si,Cu_3NiAl_6 and Mg_2Si phases in theα-Al matrix but different in size and morphology.Both size and inter-particle spacing of Si particles were significantly changed by increasing the solution treatment time.After a short solution treatment,the coarse acicular plate of the eutectic Si appears to be fragmented.Fully modified microstructure of Sr-modified alloy can reduce the solution treatment time compared to unmodified alloy.The maximum of a peak hardness value is found in the very short solution treatment of both Al-Si piston alloys.Compared to 10 h solution treatment,the solution treatment of 2-4 h is sufficient to achieve appropriate microstructures and hardness. The short solution treatment is very useful to increase the productivity and to reduce the manufacturing cost of the Al-Si piston alloys.

Microstructural evolution of direct chill cast Al-15.5Si-4Cu-1Mg-1Ni-0.5Cr alloy during solution treatment

Heat treatment has important influence on the microstructure and mechanical properties of Al-Si alloys. The most common used heat treatment method for these alloys is solution treatment followed by age-hardening. This paper investigates the microstructural evolution of a direct chill （DC） cast AI-15.5Si-4Cu-1Mg-1Ni-0.5Cr alloy after solution treated at 500, 510, 520 and 530℃, respectively for different times. The major phases observed in the as-cast alloy are a-aluminum dendrite, primary Si particle, eutectic Si, AITCu,Ni, AIsCu2MgsSi6, Al15（Cr, Fe, Ni, Cu）4Si2 and AI2Cu. The AI2Cu phase dissolves completely after being solution treated for 2 h at 500℃, while the eutectic Si, Al5Cu2Mg5Si6 and Al15（Cr, Fe, Ni, Cu）4Si2 phases are insoluble. In addition, the Al7Cu4Ni phase is substituted by the Al3CuNi phase. The a-aluminum dendrite network disappears when the solution temperature is increased to 530℃. Incipient melting of the Al2Cu-rich eutectic mixture occurrs at 520℃, and melting of the AIsCu2MgsSi6 and Al3CuNi phases is observed at a solution temperature of 530℃. The void formation of the structure and deterioration of the mechanical properties are found in samples solution treated at 530℃.

Preparation of a single-phase Mg-6Zn alloy via ECAP-stimulated solution treatment

The solution of the intermetallic phase and the homogenization of composition are important for Mg alloy biomaterials.A single-phase Mg-6Zn alloy with the average grain size of about 20μm was prepared by ECAP processed for six passes at 320°C.It indicated that the ECAP could significantly promote the process of solid solution in Mg-Zn alloy.The results showed that complete dissolution of the intermetallic phase improved the corrosion resistance of Mg-6Zn alloy in 0.9%NaCl solution by turning the corrosion behavior into uniform corrosion and increased the hardness in combination with its smaller grain size.