Undissolved Phase Research Articles

Microstructure Evolution and Mechanical Properties of In Situ TiB2/Al–Zn–Mg–Cu Composites by Electropulsing‐Assisted Solution Treatment

The traditional solution treatment is not completely applicable for in situ TiB2/Al–Zn–Mg–Cu composite due to the influence of TiB2 particles. This study investigates the impact of the electropulsing‐assisted solution (EAS) process on the microstructure evolution and mechanical properties of TiB2/Al–Zn–Mg–Cu composites. The nonuniform microstructure evolution related to the difference in temperature and current density is supported by simulative and experimental results. EAS treatment significantly enhances the degree of supersaturation, allowing phases surrounding TiB2 particles to dissolve without extensive overburning, unlike traditional solution treatments. This improvement is attributed to the reduced thermodynamic barrier and accelerated atomic diffusion, facilitated by both localized and average Joule heating effects and enhanced thermal electron/phonon scattering. Meanwhile, grain size remains stable during the temperature rise induced by EAS treatment. Furthermore, the mechanical properties of composites increase, among which the increase in strength is mainly ascribed to solid–solution strengthening, and the increase in elongation is related to multiple factors referring to TiB2 particles fracture and interface crack between the undissolved phases and matrix. This study provides an approach to achieve an efficient dissolution of phases aggregated with particles and without widespread overburning in particle‐reinforced Al matrix composites via electropulsing techniques.

Microstructure and Mechanical Properties of As-Aged Mg-Zn-Sn-Mn-Al Alloys.

The microstructure and mechanical properties of as-aged Mg-6Zn-4Sn-1Mn-xAl (ZTM641-xAl, x = 0, 0.2, 0.5, 1, 2, 3 and 4 wt.%) alloys are studied in this paper. In terms of microstructure, the results reveal that the addition of Al mainly leads to the formation of the Al8Mn5, Al11Mn4, Al2Mg5Zn2 and Mg32(Al,Zn)49 phases. With increases in the addition of Al, the average grain size first decreases and then increases, while the undissolved phases increase. The average grain size of the ZTM641-0.5Al alloy is the smallest, and the single-aged and double-aged grain size is 14 μm and 12 μm, respectively. As for mechanical properties, with increases in the Al element, the strength decreases, and the elongation first increases and then decreases. The double-aged ZTM641-0.2Al alloy exhibits favorable mechanical properties at room temperature, and the UTS, YS and elongation are 384 MPa, 360 MPa and 9%, respectively. Further, the double-aged ZTM641-0.2Al alloy exhibits the comprehensive mechanical properties at 150 °C, that is, the UTS, YS and elongation are 212 MPa, 196 MPa and 29%, respectively, which is about 45% higher than that of the elongation of ZTM641. The ZTM641-xAl alloys exhibits mixed fracture at room temperature, and, with increases in the addition of Al, the fracture mechanisms of alloys are mixed fracture, ductile fracture and mixed fracture at 200 °C.

Correlation among Composition, Microstructure and Hardness of 7xxx Aluminum Alloy Using Original Statistical Spatial-Mapping Method

The quantitative study of the relationship between material composition, microstructure and properties is of great importance for the improvement in material properties. In this study, the continuous data of elemental composition, recrystallization, hardness and undissolved phase distribution of the same sample in the range of 60 to 150 square millimeters were obtained by high-throughput testing instrument. The distribution characteristics and rules of a single data set were analyzed. In addition, each data set was divided into micro-areas according to the corresponding relationship of location, and the mapping between multi-source heterogeneous micro-area data sets was established to analyze and quantify the correlation between material composition, structure and hardness. The conclusions are as follows: (1) the average size of the insoluble phase in the middle of the two materials is larger than that of the surface, but due to the existence of central segregation, the average area of the T4 insoluble phase showed an abnormal decrease; (2) there was positive micro-segregation of Al, Cr, Ti, and Zr elements, and negative micro-segregation of Zn, Cu, and Fe elements in the recrystallized grains of the T5 middle segregation zone; (3) the growth process of the insoluble phase was synchronous with the recrystallization proportion and the size of the recrystallized grains; (4) the composition segregation and recrystallized coarse grains were the main reasons for the formation of low hardness zone in T4 and T5 materials, respectively.

Effect of Zn/Mg Ratio on Microstructure and Properties of Cold Extruded Al-xZn-2.4Mg-0.84Cu-0.2Zr-0.25Ti Aluminum Alloy

The effect of various Zn/Mg ratios on the microstructure and properties of cold extruded Al-xZn-2.4Mg-0.84Cu-0.2Zr-0.25Ti aluminum alloys was investigated. The microstructure analyses showed that as the Zn/Mg ratio increased from 3.46 to 3.84 and to 4.04, the recrystallization degree and the undissolved phase gradually increased. Moreover, with the increasing Zn/Mg ratio, the grain size of the alloy was refined, and the dislocation strengthening effect firstly increased and then decreased. The mechanical test results showed that as the Zn/Mg ratio increased from 3.46 to 3.84 and to 4.04, the tensile strength and hardness of the cold extruded Al-xZn-2.4Mg-0.84Cu-0.2Zr-0.25Ti alloy firstly increased and then decreased. The alloy with lower Zn/Mg ratio exhibited better capacitor characteristics, surface protection and corrosion resistance.

Effect of red mud proportion on the strength and microstructure of ferrosialate based geopolymer mortar

This paper studies the effect of various red mud proportions on the strength and microstructural changes in theferrosialate geopolymer mortar. The optimum percentage of red mud (RM) has to be found with respect to the molarity ofSodium hydroxide (NaOH) to maintain the suitable alkalinity of the mixture for maximum strength gain. This percentagehas been found to be between 20 and 30% RM proportions. From XRD micrographs, it has been found that the crystallinitypercentage increased with the increase in red mud content. For oven-cured samples, SEM images showed that, till the redmud replacement reaches 20%, any increase in the red mud leads to denser microstructure and a decrease in intensity ofunreactive particles. Beyond that, samples displayed a higher number of undissolved phases. Whereas, for ambientcuringspecimens, this limit is found to be 30%. Synergy has to be found among the red mud content, curing type and curingtemperature for optimum results. Ferrosialate geopolymer samples has shown 53.34% higher maximum compressivestrength than sialate geopolymer samples. The oxide ratios of SiO2/Al2O3 = 4.0 to 4.3, Na2O/SiO2 = 0.15 to 0.17 andFe2O3/Al2O3 = 0.27 to 0.37 have found to be limits for favouring maximum strength gain.

Microstructure and properties of a new Al–Cu–Mg–Zn–Zr–Ti heat resistant aluminum alloy

The effects of adding Ti with 0, 0.47 and 0.89 (wt%) on the microstructure and properties of the new Al-2.87Cu-3.83Mg-2.91Zn-0.2Zr-xTi cold extruded heat-resistant aluminum alloy materials are studied. The results show that after cold extrusion, 480 °C × 2 h solution treatment and 120 °C × 12 h aging, with the increase of Ti content, the internal undissolved phase of the alloy increase, grain refine, room temperature strength and heat resistance also improved. The alloy with 0.89Ti has the highest strength, and its hardness and electrical conductivity are 160.8HV and 23.56% IACS, respectively. Compared with the alloy without Ti, the tensile strength at room temperature is increased by 73.08 MPa, reaching 471.55 MPa, and the elongation after fracture is 16.67%. The peak value of hot compression at 250 °C increase by 86.57 MPa, reaching 326.66 MPa. At the same time, the alloy also has good resistance to intergranular corrosion, and the maximum intergranular corrosion depth is 146.31 μm.

Effect of Zn/Mg ratio on T6 state microstructure and properties of Al-xZn-2.6Mg-0.94Cu-0.2Zr-0.8Ti cold extruded aluminum alloy

The effects of 3.76, 3.98 and 4.22 Zn/Mg ratios on the T6 State Microstructure and properties of Al-xZn-2.6Mg-0.94Cu-0.2Zr-0.8Ti cold extruded aluminium alloy were studied by means of metallographic structure analysis, insoluble phase analysis, XRD analysis, hardness and electrical conductivity test, tensile property test and corrosion test. The results show that when the ratio of Zn/Mg increases from 3.76 to 4.22, the grain size of the alloy tends to grow, the recrystallization degree increases, the amount of undissolved phases increases, and the dislocation strengthening decreases slightly under solid solution at 450 °C × 2 h + 460 °C × 2 h + 470 °C × 2 h and aging treatment at 120 °C × 24 h. And the tensile strength at room temperature and elongation after fracture decrease gradually, and the intergranular corrosion resistance also decreases gradually. Therefore, the optimum composition of this experiment should be Al-9.74Zn-2.59Mg-0.94Cu-0.195Zr-0.83Ti (corresponding to the ratio of Zn/Mg 3.76), with room temperature tensile strength of 727.77 MPa, post-break elongation of 5.1%, and general intergranular corrosion resistance.

Effect of Ti content on microstructure and properties of Al-9.9Zn-2.6Mg-0.91Cu-0.2Zr-xTi aluminum alloy

The effects of different Ti contents of 0, 0.34 wt% and 0.81 wt% on the microstructure and properties of hot extruded Al-9.9Zn-2.6Mg-0.91Cu-0.2Zr-xTi alloy were studied by means of metallographic analysis, XRD analysis, hardness and conductivity test, tensile property test and corrosion test. The results show that the addition of Ti in the alloy can inhibit recrystallization and grain growth, and can refine the grain obviously when the solid solution treatment is 450 °C × 2 h + 460 °C × 2 h +470 °C × 2 h and aging treatment is 120 °C × twenty four h. When the content of Ti varies in the range of 0–0.81 wt%, with the increase of Ti content, the number of undissolved phases increases and dislocation strengthening increases. However, the electrical conductivity of the alloy decreases gradually, and the hardness and room temperature tensile strength first basically remain unchanged and then decrease (the strength of the alloy decreased from 740.05 MPa to 738.5 MPa and then to 700.09 MPa). The elongation of the alloy decreases slightly after fracture, and the intergranular corrosion resistance increases first and then decreases. With the increase of Ti content, the peak stress of hot compression of the alloy increases first and then decreases at 250 °C. Therefore, considering the properties, the optimum composition of the experiment is Al-10.2Zn-2.59Mg-0.92Cu-0.184Zr-0.34Ti. Its room temperature tensile strength is 738.5 MPa, and the elongation after fracture is 7.5%, and the peak thermal compression stress at 250 °C is 357.4 MPa(Increase by 48% compared with Ti-free alloys).

Effect of solution and aging system on microstructure and mechanical properties of 7000 series aluminum alloy produced by powder metallurgy

Different solid solution treatments (G1, G2, G3) and aging treatment were performed on the 7000 series aluminum alloy prepared by powder metallurgy (PM). The phase analysis and microstructure observation of the alloy material were carried out using metallographic microscope (MM), x-ray diffraction (XRD) analyzer and scan electron microscope (SEM). Hardness, electrical conductivity and the compressive mechanical properties of the alloy were measured. The results show that the size and quantity of the undissolved phase in the 7000 series aluminum alloy gradually decrease with the increase of the highest temperature of solid solution and the total solid solution time. When the highest temperature of solution rises to 470 °C (G2), the amount of undissolved phase in the alloy decreases slowly; As the solid solution temperature increases, the hardness of the alloy gradually increases under the aging treatment at 121 °C. The alloy under G3 solid solution has the highest hardness after 15 h aging, and the peak value is 227.5HV. With the increase of solution temperature, the electrical conductivity of aluminum alloy decreases gradually after aging. With the increase of solid solution temperature and solid solution time, the compressive strength value of the alloy after the aging increases first and then decreases. The compressive strength of alloy under G2 solid solution process reaches a maximum of 675.15 MPa, and its fracture strain is 7.73%.

Effect of Zr on undissolved phases and carbide precipitation in Ti microalloyed low-carbon steel

The undissolved phases and carbide precipitation in Ti and Ti–Zr microalloyed low-carbon steels were investigated by scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectrometry. At 1225 °C, the replacement of Ti by Zr formed Zr2CS and (Zr, Ti)N (the Ti/Zr atomic ratio is 0.11) and reduced the consumption of Ti. At 925 °C, it was identified that TiC phases were precipitated at first and Zr was incorporated into the TiC lattice in the subsequent precipitation process, which promoted the precipitation of titanium carbide. The calculation of the interaction coefficient between Ti, C, N and Zr showed that Zr reduced the activity of Ti and C and increased the activity of N in the iron matrix. Therefore, with the addition of Zr, the solubility of Ti was increased, and the consumption of Ti was reduced at high temperature in Ti microalloyed low-carbon steel. The thermodynamic calculation of carbide precipitation transformation showed that the replacement of Ti by Zr increased the nucleation driving force and the nucleation rate of titanium carbide, while the critical core size and the critical nuclear energy were reduced. As the holding time was extended, the Zr/Ti atomic ratio increased and the size of the precipitates also increased. When the Zr/Ti atomic ratio reached a certain level, the size of the precipitates did not increase with further increase in atomic ratio. When the Zr/Ti atomic ratio in (Ti, Zr)C was 0.05–0.17, (Ti, Zr)C was the most stable carbide and the easiest to nucleate at 925 °C. There was more of the (Ti, Zr)C phase than TiC at 925 °C after 50 and 100 s, and the time to complete the coarsening behavior of (Ti, Zr)C was shorter than that of TiC.

Study on The Process of Hydrogen Steel 12Cr2Mo1VR Rolling and Heat Treatment

In order to research the heat treatment process of hydrogen 12Cr2Mo1VR steel, the small furnace of 50 kg was smelted and rolled. The influence of cooling rate on the microstructure of steel was studied, and the quenching and tempering process of heat treatment was explored. It is found that the austenitizing temperature of heat treatment should be above 875°C in order to obtain better solid solution strengthening effect and avoid two coarsening caused by undissolved phase after quenching. In order to avoid serious M6C phase with coarse coarsening in tempering, the tempering temperature should be higher than 706°C. After comparing the impact properties and tensile properties of different heat treatments, two heat treatment systems were further contrasted, and 970°C WQ + 710°C AC was selected as the best heat treatment system.

Electrochemical behavior of Inconel 718 fabricated by laser solid forming on different sections

Microstructural analysis and electrochemical behavior of Inconel 718 fabricated by laser solid forming on horizontal section (HS) and vertical section (VS) were investigated. The electrochemical results show that the corrosion resistance on HS and VS have no difference in 10 wt.% NaNO3 solution. However, HS possesses lower surface products resistance at low current densities due to the tube-like distribution of secondary phases. Besides, their higher current efficiencies at low current densities are mainly attributed to the undissolved phases being flushed away by the flowing electrolyte. The fast detachment rates of secondary phases at high current densities improve the surface quality.

Effects of Mg and Cu on microstructures and properties of spray-deposited Al-Zn-Mg-Cu alloys

As important aeronautics and astronautics materials, the Al-Zn-Mg-Cu alloys have been fabricated by spray deposition. The effects of Mg and Cu on the microstructures and mechanical properties were systematically investigated. The S (Al2MgCu) and θ (Al2Cu) phases exist in equilibrium solidification conditions, but they were not found in the rapid solidification conditions due to the change of solidification paths and phase components during the spray deposition process. The volume fraction of the secondary phases/precipitates increases with increasing Mg content, which leads to the improvement of yield strength as well as to raise tendency of intergranular fracture. Undissolved phases can be promoted by increasing Cu content in the Mg-rich (∼2.65 wt% Mg) alloys. Furthermore, Cu has weak effects on yield strength but plays a positive role in maintaining the peak strength value of the alloys in overaged condition. The alloy with a medium (Mg+Cu) content shows superior overall properties: the ultimate tensile strength (UTS), yield strength (YS) and elongation can reach values of 812 ± 3 MPa, 780 ± 3 MPa and 7.0 ± 0.7%, respectively.

Quantification of Vanadium Precipitates after Reheating Slab Steel by Synchrotron X-Ray Absorption Spectroscopy (XAS)

High Strength Low Alloy (HSLA) steels or microalloyed steels are developed in order toimprove the strength and toughness compared with conventional carbon steels. During the reheatingprocess at 1250-1300 °C for a few hours, the furnace consumes large amount of energy, and the slabsuffers from thick oxide scale. This results in significant mass loss. The long reheating time ensuresmaximum dissolution of the microalloying elements, which must be kept to precipitate duringcooling at the end of the hot rolling process. To minimise the reheating time and save the energyconsumption, this research studied the dissolution kinetics of vanadium in HSLA steel. Vanadium isa main microalloying element added to provide higher strength mainly by precipitation hardening. Itis supposed to be dissolved readily according to the solubility limit. The samples were reheated to1200 °C and 1250 °C for 0, 10, 30, and 60 s. After that the fraction of vanadium dissolved in the solidsolution and the remaining undissolved phases of VC, CN, and V(C,N) were measured bysynchrotron XAS. As soon as the sample reaches as low temperature as 1200 °C, a large atomicfraction of 0.878 of vanadium can be dissolved in the solid solution.

합금원소 첨가 및 열처리 공정 제어를 통한 Al-7Si-0.35Mg 주조재 합금의 기계적 특성 향상

Improvement of the mechanical properties of a commercial aluminium casting alloy, A356, was achieved through an optimised combination of alloying elements, modification, and heat treatment. 0.7 wt.% Cu and an additional 0.2 wt.% Mg were added to an Al-7Si-0.35Mg alloy for strengthening at both room and elevated temperatures, whilst a subsequent decrease in the ductility was compensated for by the modification of eutectic Si by Sr addition at a level of up to 110 ppm. It was found that the dissolution of Cu-rich or Mg-rich phases could be maximised by solid-solutionising an alloy with 40 ppm Sr at <TEX>$530^{\circ}C$</TEX>, increasing the tensile and yield strengths to 350 MPa and 297 MPa, respectively, with a reasonably high strain of 5% after peak-aging at <TEX>$210^{\circ}C$</TEX>. Further addition of Sr up to 110 ppm is, however, more likely to interfere with the dissolution of the Cu-rich or Mg-rich phases during solid solution treatment, resulting in a slight decrease in both tensile and yield strengths at room temperature. Besides the Cu addition, such undissolved phases, on the other hand, may contribute to elevated temperature strength at <TEX>$200^{\circ}C$</TEX>.

Tailored Mg and Cu contents affecting the microstructures and mechanical properties of high-strength Al–Zn–Mg–Cu alloys

The effects of systematic variation of Mg and Cu contents (Mg: ~1.5, 2.0, and 2.5, Cu: ~1.5, 2.0, 2.5, and 2.9wt%) on the microstructures and mechanical properties of high-Zn (8.5wt%) Al–Zn–Mg–Cu alloys are investigated. Fracture toughness is experimentally approached by the Kahn tear test. Results showed that, under same ageing condition, the conductivity, hardness, strength and toughness of the designed alloys are primarily determined by Mg content: the higher the Mg content, the higher the hardness and strength, but the lower the conductivity and toughness. Increasing Cu content can produce a similar phenomenon, but with weak effects compared with Mg. The experiments and thermodynamic/kinetic simulation indicate that, increasing Mg/Cu content can improve the volume fraction of matrix precipitates, so as to improve the strength and hardness, and the effects of Mg are stronger than Cu. Additionally, increasing Mg content can somewhat reduce the sizes of the matrix precipitates especially in overaged condition, which is also good for the strength and hardness. However, with increasing Mg content the area fraction of the grain boundary precipitates (GBPs) and the yield stress contrast between grain interiors and precipitate free zones (PFZs) at grain boundary can be increased greatly, consequently promoting intergranular fracture and decreasing toughness. For the alloys with low/middle Mg content (e.g., 1.5/2.0wt%), increasing Cu content will improve the yield stress contrast between grain interiors and PFZs as well as the recrystallization degree, so that intergranular fracture will be promoted for toughness reduction. For the alloys with high Mg content (e.g., 2.5wt%), the increased undissolved phases induced by high Cu content will promote fracture at/near coarse constituent particles, favoring further toughness reduction.

Optimization of the Solution Heat Treatment of Rheo-High Pressure Die Cast Al-Cu-Mg-Ag 2139 Alloy

This paper investigates the optimization of the solution heat treatment parameters of the rheo-high pressure die cast (R-HPDC) 2139 aluminium alloy. Differential Scanning Calorimetry (DSC) and optical microscopy were used to investigate the incidence of incipient melting and therefore determine suitable solution heat treatment temperatures. A three-step solution heat treatment where the alloy was heat treated from 400°C to 513°C using controlled heating conditions and held at 513°C for 2 hours and finally heated up from 513°C to 525°C and held there for 16 hours was done. R-HPDC is known to produce surface liquid segregation and when processing the alloys these areas are most prone to incipient melting. The applicability of a single (525°C for 16h) and three-step solution heat treatments on the R-HPDC 2139 aluminium alloy was also investigated. A single-step solution heat treatment results in incipient melting, whereas this is mostly eliminated using the three-step solution heat treatment. However, a high volume fraction of undissolved phases remain in the liquid segregated areas, even after the three-step solution heat treatment.

Effect of Aging on Super-Elastic Response of a Polycrystalline FeNiCoAlNbB Shape Memory Alloy

This study reports the effect of aging duration on the super-elastic response of Fe-30%Ni-18%Co-10.5%Al-2%Nb-0.15%B (at.%) poly-crystals in compression. The aging temperature was 600°C and the aging durations were 20h, 45h, 60h and 72h, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) were used in the work. The results show that with prolonging the aging duration, the super-elastic strain rises firstly and then descends. The super-elastic strain reaches the maximum 10.5% when the aging duration is 60h. The crisis stress for stress-induced martensite (σM) has no obvious changes, being about 250MPa when the aging duration is between 20h and 60h. But σM increases markedly when the aging duration prolongs to 72h. The hardness of the specimens changes in the same way as the superelastic strain, and reaches the maximum of 497HV10 when the aging duration is 60h. During the aging process, two factors react. One is the decomposing and reducing in size of the undissolved phase (σ). The other is the formation of the precipitation phase (γ'). Nb can dissolve into the matrix phase (γ) adequately and promote the formation of γ'. The combination of the two factors improves the strength and superelasticity of the specimens till the over-aging arises corresponding to the 72h aging duration.

Effects of samarium on microstructure and mechanical properties of Mg–Y–Sm–Zr alloys during thermo-mechanical treatments

Microstructure and mechanical properties of Mg–4Y–xSm–0.5Zr (x = 1, 4, 8) alloys during thermo-mechanical treatments were investigated in this study. Mg–4Y–4Sm–0.5Zr alloy exhibits higher tensile strength but lower elongation than Mg–4Y–1Sm–0.5Zr alloy during the thermo-mechanical treatments. Large amount of intermetallic phases still remained at grain boundaries in Mg–4Y–8Sm–0.5Zr alloy after solution. These undissolved phases can strengthen the grain boundaries at temperatures higher than 573 K. But the room temperature mechanical properties of Mg–4Y–8Sm–0.5Zr alloy during the thermo-mechanical treatments were greatly weakened for the brittleness of these undissolved intermetallic phases.

A comparative study of different leaching processes for the extraction of Cu, Ni and Co from a complex matte

The extraction behaviors of Cu, Ni and Co from a complex matte under different leaching conditions have been discussed. The synthetic Cu-Ni-Co-Fe-S matte was prepared by melting the pure metals. The matte contained 24.95% Cu, 35.05% Ni, 4.05% Co, 11.45% Fe, 24.5% S, similar composition as is expected to be obtained by reduction smelting of the Pacific Ocean nodules followed by sulphidisation of the alloy. The different phases identified are CuFeS2, CuS2, (FeNi)9S8, (FeNi)S2, Ni9S8, Ni3S2, (CoFeNi)9S8 and Co metal. The merits and demerits of each process of dissolution i.e., H2SO4/oxygen pressure leaching, atmospheric FeCl3 leaching, NH4OH/(NH4)2SO4 pressure leaching are discussed in detail. Out of the three, the H2SO4/oxygen pressure leaching process is found to be the most suitable with more than 99% metal extraction efficiency within 1 h of leaching time. From the X-ray diffraction analysis, the different undissolved phases corresponding to different leaching processes have been identified. The metal extraction efficiency decreased in case of atmospheric FeCl3 leaching and NH4OH/(NH4)2SO4 pressure leaching processes due to the formation of product layer such as elemental sulfur and goethite, respectively.