Heat Treatment Process Parameters Research Articles

Two‐stage annealing method for short carbon fiber‐reinforced nylon 6 in fused filament fabrication

AbstractThe mechanical properties of short carbon fiber‐reinforced nylon 6 (CF‐PA6) components formed by fused filament fabrication (FFF) are significantly affected by the process parameters of additive manufacturing and heat treatment. In this study, the effects of printing speed, carbon fiber aspect ratio, and annealing temperature on fiber orientation were investigated by observation of single‐layer‐single‐fiber samples. Furthermore, a two‐stage annealing process was proposed to increase the tensile modulus of CF‐PA6 based on the correlation analysis results between the degree of fiber alignment and the variation of tensile modulus. According to the calculation of the Pearson correlation coefficient, the tensile modulus was highly correlated with the degree of fiber alignment under different printing speeds and fiber aspect ratios. The variation in tensile modulus and fiber orientation was also consistent when the annealing temperature was lower than the crystallization temperature. Conversely, the variation of tensile modulus and fiber orientation were opposite, as the annealing temperature was higher than the crystallization temperature because of the influence of crystallinity. Through increasing the degree of fiber alignment and crystallinity of the parts, the proposed two‐stage annealing method could increase the tensile modulus of the parts to 9.0 GPa, which was 16.81% higher than that of single‐temperature annealing.Highlights The effects of annealing temperature, carbon fiber aspect ratio and printing speed on fiber orientation were illustrated. The relationship between the degree of fiber alignment and the variation of tensile modulus was established. The proposed two‐stage annealing method, considering fiber orientation and crystallinity, significantly increased the tensile modulus of CF270‐PA6 parts from 7.7 to 9.0 GPa. The quantitative analysis of the fiber orientation is realized by the statistical analysis of the plane fiber orientation angle of the single‐layer‐single‐fiber sample.

Optimization Design of Quenching and Tempering Parameters for Crankshaft Based on Response Surface Methodology.

Existing optimization research on the crankshaft heat treatment process is mostly based on one-sided considerations, and less consideration is given to the matching of multiple process parameters, leading to irrational designs of heat treatment. To address this problem, this work investigates the influence mechanisms of cooling speed, tempering temperature, and holding time on the performance evaluation indexes of the straightness, residual stress, and martensite content of a crankshaft based on the response surface method. The results showed that the order of influence of these three different process parameters on the performance evaluation index was cooling speed > holding time > tempering temperature, and the order of influence on the performance evaluation indexes under multifactorial process parameters was cooling speed-holding time > cooling speed-tempering temperature > holding time-tempering temperature. The optimal process parameters were a cooling speed of 1.4 times the cooling oil, a tempering temperature of 555 °C, and a holding time of 6 h, with the straightness of the crankshaft reduced by 9.9%, the surface stress increased by 6.7%, and the martensitic content increased by 7.2% after the process optimization. This work can provide new clues for optimizing the heat treatment process parameters of crankshafts.

Electrical property enhancement of non-heat-treatable wrought aluminum alloys using graphene additives

With growing efforts of electrification, aluminum’s role as a light-weight conductor material has become increasingly prominent. There is a critical need to improve the electrical performance of aluminum at room temperature and high operating temperatures. In this study, the effect of graphene nanoparticle additives on the electrical performance of a non-heat treatable alloy were (AA3003) explored. Graphene’s unusual structure and electronic properties were used to improve AA3003 properties. Here, the effects of graphene on the evolution of electrical properties and microstructural features have been explored on lab scale hot extruded AA3003-graphene composites. Hot pressing schedules and extrusion temperatures were varied to investigate changes in intermetallic dispersion characteristics in the presence of dispersed graphene. We measured a reduction of 10.3 % in the temperature coefficient of resistance in the AA3003 sample with 0.05 wt% graphene extruded at 400 °C, along with a maximum increase of 1.1 % in electrical conductivity at 20 °C. Increasing the hot-pressing times up to 8 hours was also found to consistently increase the electrical conductivity, due to increased precipitation of intermetallic phases. Despite being a non-heat treatable alloy, AA3003 displays interesting precipitation dynamics and grain recrystallization trends that can be modulated with varying levels of heat treatment, graphene concentrations, and hot extrusion process parameters.

Research on the heat treatment process of Q235A steel

Q235A steel was heat treated by using different heat treatment process parameters. The microstructure after heat treatment was observed microscopically and its hardness was measured. The results indicated that the complete austenitization temperature has not been reached at 850°C and even under water-cooled conditions, only a very small amount of martensite can be obtained. After water cooling at 900°C, 950°C, and 1000°C, lath martensite can be obtained, which made the hardness of water cooling significantly higher than that of oil cooling, air cooling, and furnace cooling. The quenching temperature of 1000°C was too high and the microstructure obtained after water cooling, oil cooling, air cooling, and furnace cooling was relatively coarse, which was not suitable as the heating temperature for heat treatment of Q235A steel.

Local laser heat treatment of AlSi10Mg as-built parts produced by Laser Powder Bed Fusion

Today, complex structural components for lightweight applications are frequently manufactured by laser powder bed fusion (PBF-LB), often using aluminum alloys such as AlSi10Mg. However, the application of cyclic load cases can be challenging as PBF-LB produced AlSi10Mg parts typically have low ductility and corresponding brittle failure behavior in the as-built condition.Therefore, this paper presents investigations on the feasibility of a laser heat treatment of PBF-LB produced AlSi10Mg parts to locally increase the ductility and decrease the hardness in critical areas. Potential heat treatment process parameters were derived theoretically based on the temperature fields in the material calculated assuming three-dimensional heat conduction and a moving heat source. PBF-LB produced specimens were then laser heat treated at varying laser power and scan speed. Hardness measurements on metallographic cross sections showed hardness reductions of over 35 % without inducing hydrogen pore growth.

Design and Optimization of Heat Treatment Process Parameters for High-Molybdenum-Vanadium High-Speed Steel for Rolls.

High-molybdenum-vanadium high-speed steel is a new type of high-hardenability tool steel with excellent wear resistance, castability, and high-temperature red hardness. This paper proposes a composition design of high-molybdenum-vanadium high-speed steel for rolls, and its specific chemical composition is as follows (wt.%): C2%, Mo7.0%, V7.0%, Si0.3%, Mn0.3%, Ni0.4%, Cr3.0%, and the rest of the iron. This design is characterized by the increase in molybdenum and vanadium in high-speed steel to replace traditional high-speed steel rolls with the tungsten element in order to reduce the heavy elements' tungsten-specific gravity segregation caused by centrifugal casting so that the roll performance is uniform and the stability of use is improved. JMatPro (version 7.0) simulation software is used for the composition design of high-molybdenum-vanadium high-speed steel. The phase composition diagram is analyzed under different temperatures. The content of different phases of the organization in different temperatures is also studied. The martensitic transformation temperature and different tempering temperatures with the different types of compounds and grain sizes are calculated. The process parameters of heat treatment of high-molybdenum-vanadium high-speed steel are optimized. The selection of carbon content and the temperature of M50 are calculated and optimized, and the results show that the range of pouring temperatures, quenching temperatures, annealing temperatures, and tempering temperatures are 1360~1410 °C, 1190~1200 °C, 818~838 °C, and 550~600 °C, respectively. Scanning electron microscope (SEM) analysis of the samples obtained by using the above heat treatment parameters is consistent with the simulation results, which indicates that the simulation has important reference significance for guiding the actual production.

A data-driven low-cycle fatigue life prediction model for nickel-based superalloys

A data-driven machine learning method for the low-cycle fatigue (LCF) life prediction of Nickel-based superalloys is proposed to overcome the limitations of empirical formulas. The method integrates three characteristics of the superalloys: chemical composition, heat treatment process and experimental parameters, and constructs a unified fatigue life prediction dataset. The relationship between many different microstructural parameters and LCF life is analyzed using the Pearson Correlation Coefficient (PCC) and Maximal Information Coefficient (MIC). The fatigue life dataset is then used to predict the LCF life with four machine-learning models: Random Forest (RF), Artificial Neural Network (ANN), Support Vector Machine (SVM), and a Genetic Algorithm-based Random Forest (GA-RF). The comparative study results demonstrate that the models accurately predict the LCF life, as evidenced by the respective R2 values of 0.8311, 0.8345, 0.7711, and 0.9272, with GA-RF performing the best and equally better in comparison with the Coffin-Manson model. The proposed method efficiently maps feature-life relationships for the LCF life of Nickel-based superalloys, reducing experimental time and cost and promising applications in the inverse design and manufacture of alloys.

Mechanical Properties of 6061 Aluminum Alloy under Cyclic Tensile Loading

During the service process of an aluminum alloy structure, its complex deformation zone experiences repeated loading problems such as repeated tension, compression, bending and reverse bending. At the same time, the cyclic loading and heat treatment process also have a certain impact on the mechanical properties of aluminum alloy extruded tubes. Therefore, the study of heat treatment process parameters has important engineering and practical value for the mechanical properties of aluminum alloy extrusion tubes under cyclic loading conditions. The experiment takes 6061-T6 aluminum alloy extruded tubes as the research objects. In the study, heat treatment and cyclic tensile tests were carried out on 26 aluminum alloy specimens to study the effects of different heat treatment parameters (such as heating temperature, holding time, and cooling method) on the stress–strain hysteresis curves, stress characteristics, hysteretic energy, skeleton curves and failure characteristics of the alloy under the same loading system. In addition, different cyclic tensile tests were carried out on 20 aluminum alloy samples without secondary heat treatment to discuss the effects of different cyclic loading regimes on the mechanical properties of the alloy. The research results indicate that the effect of heating temperature on the cyclic loading performance of the alloy is greater than that of the holding time, and the effect of the cooling method on the cyclic loading performance of the alloy is not obvious. A cyclic tensile loading regime has a significant impact on the strength, elongation and hysteresis energy of the alloy. The hysteretic behavior of the alloy during cyclic tensile loading depends on the applied stress level and loading history. As the number of cycles increases, the shape of the hysteresis curve tends to be stable, but there is no monotonic relationship between the number of cycles loaded and the hysteresis energy.

Effects of additive manufacturing process parameters and heat treatment on texture evolution and variant selection during austenite-martensite transformation in 18%Ni-M350 maraging steel

Variant selection and texture evolution of 18%Ni M350 maraging steel produced by laser-based directed energy deposition (DED) additive manufacturing (AM) technology are investigated in this study. The effects of heat treatment and AM processing parameters, including energy area density (EAD), powder feed rate, and laser power, on variant selection and texture evolution are discussed. Theoretically, 24 martensite variants tend to be formed during a cubic-to-cubic transformation based on the Kurdjumov–Sachs orientation relationship. Identifying the preference of variants in a thermo-mechanical process can pave the way for tailoring the desired product texture. Grain graph and local neighbor voting algorithms using measured electron backscatter diffraction (EBSD) were employed to reconstruct the parent austenite grain structure in this study. Even though no evidence of global variant selection is found, the variant selection tends to take place locally in small parent grains of heat-treated samples. Strong rotated Copper 112110γ and Z 111110γ components are observed in the parent austenite phase of the low EAD sample after heat treatment due to a high degree of recrystallization and second-order twins. A Goss texture 110001α in child martensite transitioned from these strong components is also observed to be strongly derived from packet 3 of this sample. This finding indicates that some low-misorientation variants of packet 3 are more energetically favorable to develop in a heat-treated M350 alloy produced by a low EAD.

Integrated Computing Accelerates Design and Performance Control of New Maraging Steels.

This paper mainly used database technology, machine learning, thermodynamic calculation, experimental verification, etc., on integrated computational materials engineering. The interaction between different alloying elements and the strengthening effect of precipitated phases were investigated mainly for martensitic ageing steels. Modelling and parameter optimization were performed by machine learning, and the highest prediction accuracy was 98.58%. We investigated the influence of composition fluctuation on performance and correlation tests to analyze the influence of elements from multiple perspectives. Furthermore, we screened out the three-component composition process parameters with composition and performance with high contrast. Thermodynamic calculations studied the effect of alloying element content on the nano-precipitation phase, Laves phase, and austenite in the material. The heat treatment process parameters of the new steel grade were also developed based on the phase diagram. A new type of martensitic ageing steel was prepared by selected vacuum arc melting. The sample with the highest overall mechanical properties had a yield strength of 1887 MPa, a tensile strength of 1907 MPa, and a hardness of 58 HRC. The sample with the highest plasticity had an elongation of 7.8%. The machine learning process for the accelerated design of new ultra-high tensile steels was found to be generalizable and reliable.

Optimisation of hardness profiles in high-speed train axlebox bearings

To produce bearings with more reasonable hardness profiles, a finite element model was established to simulate different heat treatment processes. Based on the simulated hardness profiles, an artificial neural network model was established to fit the relationship between the heat treatment process parameters and the hardness profiles. Genetic algorithm was used to optimise the hardness profiles and the confirmation test was conducted. The results showed that the optimised hardness profile was closer to the optimisation target. The mean absolute error of hardness was reduced by 68.16% and the root mean square error was reduced by 66.72% after optimisation. This method can be used for hardness profile optimisation and provides a reference for the optimisation of the bearing heat treatment process.

Effect of T6 heat treatment on microstructure and mechanical properties of large-weight aluminum alloy flywheel housing parts formed by local-loading squeeze casting

In this research, ZL104 aluminum alloy flywheel housing with large wall-thickness difference and complex shape were formed via local-loading squeeze casting. The effects of T6 heat treatment process parameters (solution time and temperature, aging time and temperature) on mechanical properties and microstructure of ZL104 aluminum flywheel housing were studied. The microstructure of the formed parts with heat treatment was analyzed by scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and optical microscope (OM). The mechanical property test results indicated that the improvement of strength was limited with the increase of solution temperature and solution time, but the elongation improved significantly. For solution treatment, the optimum mechanical properties (ultimate tensile strength, yield strength, and elongation were 243 MPa, 133 MPa, and 14%) were obtained at 550 °C/3 h. The strength increased first and then decreased with the increase of aging time. After 8 h/175 °C aging treatment (following by solid solution), the maximum tensile strength and yield strength reached 312 MPa and 251 MPa, respectively. After T6 heat treatment, the morphology of Si spheroidized and coarsened obviously. The Si particles with fine size were formed. Continuous dynamic recrystallization occurred during heat treatment but was not very sufficient.

Evolution of insulating layers during Heat–Treatment and their effects on magnetic behavior of Fe–Si–Al based soft magnetic composites

As a symbolic ceramic oxide, the reaction of SiO2 as an insulating layer with the Fe–Si–Al/SiO2 soft magnetic composites (SMCs), substrate during heat treatment, as well as the resulting microscopic phase transition of the core–shell structure and its influence on the magnetic properties, are worth investigating. In this study, based on the successful synthesis of Fe–Si–Al based SMCs using fluidised chemical vapour deposition combined with an electric hot–press sintering method, the evolution of the insulating layers was investigated under different heat–treatment temperatures and closely linked to the magnetic performance of the composites. During heat treatment at high temperatures, the formation of high–resistivity oxides (Al2O3) after heat treatment results in a low inter–particle eddy current loss, while excessive temperature causes disintegration of the core–shell heterostructure. This leads to a discernible increase in eddy current and hysteresis losses and a decrease in permeability and resistivity. The SMCs had an Ms of 115.8 emu/g, a resistivity of 6.86 mΩ cm, and a hysteresis loss of 56.3 kW/m3 at 10 mT and 100 kHz when heat-treated at 1373 K for 120 min, which was the best among all samples. This research provides a novel approach to building SMCs with inorganic ceramic insulating layers and a comprehensive understanding of the relationship between the heat–treatment process parameters, microstructure, and magnetic properties which is highly significant for industrial production.

Effect of heat treatment process parameters on the microstructure and properties of GH4720Li superalloy

The solution temperature and aging temperature of GH4720Li superalloy are the critical factors in determining its microstructure stability and mechanical properties. However, the matching of solution temperature, primary aging temperature, and second aging temperature greatly influences the final microstructure and mechanical properties, and the mechanism was rarely studied. In this paper, the effects of solution temperature, aging temperature, and other process parameters on the grain size, precipitated phase, and mechanical properties of GH4720Li superalloy were systematically studied by orthogonal experiment, and a set of optimal heat treatment process parameters were found. The results show that the sample was solution treated in the temperature range of 1060 °C ∼ 1120 °C. When the solution temperature was 1160 °C ∼ 1100 °C, although the primary γ ′ phase gradually dissolved, the secondary γ ′ phase gradually increased, and the primary γ ′ phase was pinned at the grain boundary to hinder the grain growth, and the hardness of the alloy gradually increases. When the solution temperature exceeded 1100 °C, the primary γ ′ phase dissolved in large quantities, the grains grew up rapidly, and the hardness of the alloy decreased. The sample was subjected to two-stage aging treatment in the temperature range of 650 °C ∼ 770 °C and 760 °C ∼ 880 °C. As the aging temperature increased, the primary γ ′ phase of the sample gradually grew, and the ability to pin the grain boundary weakened. The volume fraction of the secondary γ ′ phase of the sample gradually decreased and coarsened, resulting in grain growth and a gradual decrease in the hardness of the sample. When the samples were treated by 1100 °C/OC × 4 h + 650°C /AC × 8 h + 760 °C/AC × 8 h, the grain size of the sample was the smallest, the average grain size was 4.5 μm, the distribution of γ ′ phase was the most uniform, and the mechanical properties are the best, reaching 47 HRC.

Investigation on heat treatment of large-sized and complex AlSi9Mg aluminum alloy components formed by squeeze casting

AlSi9Mg aluminum alloy flywheel housing components were formed via squeeze casting and T6 heat treatment was applied to the formed components. The influence of solid solution temperature, solid solution time, aging temperature and aging time on the microstructure and mechanical properties of AlSi9Mg aluminum alloy components formed by squeeze casting were investigated. The results showed that T6 heat treatment changed the morphology of the eutectic silicon in the microstructure from long fibrous to short rods and round spheres. The spheroidization of eutectic Si phase was more obvious with an increase of solution temperature, and the eutectic Si phase not dissolved in the matrix became coarse and grew with an extension of solution time. In terms of mechanical properties, the tensile strength and elongation of AlSi9Mg specimens after heat treatment showed an increasing trend with a rise of solution temperature, but the yield strength decreased, while the three mechanical properties of specimens all improved first and then decreased with an increase of solution time, aging temperature and aging time. Comprehensive consideration of three mechanical properties showed that the optimal heat treatment process parameters in this experiment were solution temperature of 540 ℃, solution time of 180 min, aging temperature of 175 ℃ and aging time of 300 min. In addition, β''−Mg2Si strengthening phases and disc-shaped strengthening phases were precipitated during T6 heat treatment, which were also one of the reasons for the improvement of the casting properties.

Effect of direct aging and annealing on the microstructure and mechanical properties of AlSi10Mg fabricated by selective laser melting

PurposeThis paper aims to systematically investigate the effect of the heat treatment process parameters on the microstructure and mechanical properties of the selective laser melting (SLM) AlSi10Mg alloy.Design/methodology/approachThe samples with very low porosity were fabricated with optimized processing parameters on a self-developed SLM system. The heat treatment of using the temperature of 170°C∼400°C and the holding time of 0.5∼12 h was studied, and the evolution of the microstructure and mechanical properties of AlSi10Mg alloy under direct aging and annealing was investigated and obtained.FindingsAfter annealing above 300°C for 1 h, the dendrite Si in the sample occurs spheroidization, and the molten pool contour becomes blurred or even disappeared completely, but low-temperature heat treatment does not change the morphology and size of grains significantly. Except for holding at 200°C for 1 h, all other heat treatment processes cause the tensile and yield strengths of SLM AlSi10Mg alloys to decrease and the elongation to increase. When the annealing temperature is higher than 200°C, the higher the temperature and the longer the holding time, the more obvious this effect is.Originality/valueThe correlation between the mechanical properties and microstructure of SLM AlSi10Mg alloy under different conditions was obtained. According to the characteristics of SLM forming, the direct aging and annealing process are mainly studied, which provided new information for the heat treatment of SLM AlSi10Mg alloy and promoted the engineering application of SLM AlSi10Mg alloy.

Temperature-dependent crack induced by microstructure evolution in 20Mn2SiMoCuV bainite wheel steel

Several severe cracks were found in novel 20Mn2SiMoCuV bainite wheel tread after 100,000 km test running, which will significantly affect bainite wheel’s service safety. The reason for cracks generation was investigated through microstructure observation and wheel/shoe contact analysis. Results showed that cracks were caused by microstructure evolutions resulting from temperature variations during quickly heating and cooling repeatedly in braking at contact interface of wheel tread and brake shoe. Temperature increased to above 500 °C at contact area will reduce the bainite wheel microstructure stability, leading to retained austenite decomposition to brittle martensite and cementite precipitation along grain boundary and lath boundary. Both above brittle martensite and cementite provided location for crack initiation and propagation. Therefore, some measures can be suggested to prevent initiation and propagation of cracks such as optimizing heat treatment process parameters to improve microstructure stability and adjusting matching of wheel tread/brake shoe to coordinate thermal conductivity.

Evolution of Microstructure and Mechanical Properties of Al-Zn-Mg-Cu Alloy by Extrusion and Heat Treatment

Herein, composite extrusion deformation and heat treatment process at various temperatures were studied on a new type of Al-Zn-Mg-Cu alloy billet. The influence of pre-deformation and the final forming of extrusion and heat treatment of annular channel corner extrusion on the microstructure evolution and mechanical properties were explored. The results show that the extrusion process could further refine the structure and break the coarse θ phase. The grains can be refined again after the deformed sample was treated by solution-aging treatment. At the same time, a fine, dispersed second phase is precipitated around the fine recrystallized grains. This is the main reason for the increase in alloy elongation and tensile strength. The best heat treatment process parameters for the formed cup-shaped structure are 480 °C × 1 h solid solution and 120 °C × 24 h aging. The strengthening of the alloy mainly includes three mechanisms: fine grain strengthening, precipitation strengthening, and dispersion strengthening.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Al–9Si–0.4Mg–0.1Cu Alloy

Herein, effect of heat treatment on the microstructure and mechanical properties of a newly developed Al–9Si–0.4Mg–0.1Cu alloy treated by Al–6Sr–7La is investigated, and optimal T6 heat treatment process parameters are determined through optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis, and quantitative statistics. The results show that the distribution of α‐Al is more uniform after T6 heat treatment (solution treated at 540 °C for 5 h and aged at 170 °C for 6 h) with eutectic silicon possessing fine grain and high roundness. Meanwhile, Al–6Sr–7La increases peak aging hardness and reduces peak aging time. During the under‐aging process, a large amount of Guinier Preston zone and a small amount of Mg5Si6 phase precipitate, which have strengthening effect on the alloy. At peak aging state, the coherent precipitated Mg5Si6 phase in α‐Al leads to the highest microhardness. Continuing to prolong aging time, the coherent relationship between metastable phase Mg5Si6 and the matrix is weakened, resulting in the decrease in microhardness. In addition, after T6 heat treatment, both tensile strength and elongation of the alloy are significantly improved and the reasons are discussed.

Preparation and Consolidation Mechanism of Nickel Laterite Carbon Composite Hot Briquette

Blast furnace smelting process has advantages in producing ferronickel products because of its low comprehensive energy consumption and high production efficiency. However, laterite nickel ore has poor performance of pellets and lump ore due to its own characteristics. At present, the main lumping method is low basicity sinter, which is difficult to optimize the charge structure. This paper mainly studies the preparation process of laterite nickel carbon composite hot briquette (LN-CCHB) and the influence of process parameters on the basic compressive strength properties, so as to explore a new charge for smelting laterite nickel in blast furnace process. Results showed that the influence of pressure and temperature of hot briquette on the compressive strength of NL-CCHB is obvious. The compressive strength of NL-CCHB increases with the increase of briquetting pressure increases first and then decreases with the increase of hot briquetting temperature. The FC/O ratio (the ratio of the fixed carbon mol (C) in coal to the reducible oxygen mol (O) in iron oxides) has little effect on the compressive strength of NL-CCHB. In the experimental range, the mixture of laterite nickel ore and pulverized coal can obtain NL-CCHB with compressive strength of more than 1300N after hot briquetting. After heat treatment, NL-CCHB with compressive strength of more than 1800N can be obtained. The optimum hot briquetting process parameters are: FC/O ratio 1.25, hot briquetting temperature 450°C, hot briquetting pressure 80MPa. The optimum heat treatment process parameters are: FC/O ratio 1.50, heat treatment temperature 550°C.