Solution Treatment Aging Research Articles

Ti386/TC4 clad plate manufactured by hot rolling and solution-aging treatment

Clad plate of high strength Ti386 and high plasticity TC4 is manufactured by hot rolling and solution-aging treatment. The interfacial microstructure and tensile properties of Ti386/TC4 clad plate are analyzed under different conditions. Results indicate that the clad plate subjected to 40% rolling reduction achieves a metallurgical bonding as there are no voids at Ti386/TC4 interface and the interfacial bonding strength is superior to the ultimate tensile strength (UTS) of Ti386 base (883 MPa). The microstructure of the clad plate is further refined as the rolling reduction increases to 80%, and the UTS of Ti386 increases to 921 MPa, which is still inferior to that the interface and TC4 base. After solution-aging treatment, the UTS of Ti386 is greatly improved to 1547 MPa, and the clad plate fractures at TC4 side with the UTS of 1010 MPa and elongation (δ) of 14.68%. Finally, the clad plate consisting of Ti386 with 1547 MPa UTS and TC4 with 14.68% δ is obtained with metallurgical interface.

The synergic effects of heat treatment and building direction on the microstructure and anisotropic mechanical properties of laser powder bed fusion Corrax maraging stainless steel

An anisotropic microstructure and mechanical properties are big challenges in the development of various laser powder bed fusion (LPBF) alloys. This study investigated the roles of heat treatment and building direction (BD) on the microstructure and anisotropic mechanical properties of LPBF Corrax maraging stainless steel. The effects of solution treatment (ST) and integrated solution-aging treatment (SAT) were clarified. The results show that the grain size of martensite, amount of austenite, and features of grain boundaries were slightly varied with the building direction due to the thermal history. In the as-built state, the weak <111>α′||BD, <1 1‾ 0>α′||X, and <001>α′||BD textures could be found. After the SAT process, the <1 1‾ 0>α′||X texture was slightly intensified due to the coarsening of large columnar grains. However, the texture of the SAT sample was still weak.Furthermore, the building direction and heat treatment did not lead to obvious anisotropic tensile properties or change the ductile fracture mode. The weak texture and pores in LPBF Corrax did not dominate the tensile properties. Irrespective of sample state, the horizontally-built samples exhibited comparable strengths and slightly higher elongation than the vertically-built ones did. In the as-built condition, this phenomenon can be mainly attributed to the transformation-induced plasticity effect. In the ST and SAT conditions, smaller grain sizes of martensite and higher high-angle grain boundary ratios in the horizontally-built samples provided more resistance to crack propagation. LPBF Corrax maraging stainless steel exhibited superior tensile performances and low anisotropic tensile properties, which are very beneficial to the stability of the material during service.

Effect of heat treatment on the hydrogen embrittlement susceptibility of selective laser melted 18Ni-300 maraging steel

The effects of heat treatment on the hydrogen embrittlement (HE) susceptibility of selective laser melted 18Ni-300 maraging steel were investigated. The results demonstrate that the as-built steel has a microstructure consisting of an Fe–Ni martensite matrix and a cellular structure. Substantial microstructural changes are observed following various heat treatment processes (solution, direct aging, and solution-aging), resulting in varying degrees of increased HE susceptibility. Specifically, after solution treatment, the complete elimination of cellular structure and the growth of grains concurrently increased hydrogen diffusion coefficient of the steel. However, its lower proportion of ∑3 boundaries and higher proportion of ∑11 boundaries played an advantageous role that lead to a marginal increase in the HE susceptibility. In contrast, direct aging and solution-aging treatments enhance the HE susceptibility significantly, which is primarily related to the decomposition of the cellular structure and reversible hydrogen trapping and precipitation strengthening effects of the newly formed Ni3(Ti, Mo) precipitates. Compared with the solution-aging treatment, the direct aging treatment results in the formation of a localized austenite aggregation zone near the molten pool boundaries, which promotes the initiation of hydrogen-assisted cracking and leads to a higher HE susceptibility.

Microstructural Evolution and Mechanical Behavior of TA15 Titanium Alloy Fabricated by Selective Laser Melting: Influence of Solution Treatment and Aging

In this study, TA15 titanium alloys were successfully prepared using selective laser melting (SLM). The results show that the microstructure of each TA15 specimen is composed of a large number of acicular α’ martensite crystals accompanied by a lot of dislocations and twin structures in the martensite due to non-equilibrium heating and cooling via SLM. After solution treatment and aging treatment, the martensite structure is successfully transformed into a typical duplex structure and an equiaxial structure. When there is an increase in the solution temperature, the size of the equiaxed primary α phase and the elongation of the specimen gradually increases, while the thickness of the layered secondary α phase and the tensile strength of the specimen decreases accordingly. After solution treatment at 1000 °C, the specimens show the best comprehensive mechanical properties, i.e., a high-temperature tensile strength of 715 MPa and a corresponding elongation of 24.5%. Subsequently, an appropriate solution–aging treatment is proposed to improve the high-temperature mechanical properties of SLMed TA15 titanium alloys in aerospace.

Influence of post-treatment on microstructure and mechanical properties of additively manufactured C300 maraging steel

The aim of this work is to explore various homogenization solution-aging post- treatments (HAT) related to maraging steel, manufactured by selective laser melting (SLM), in order to achieve high-level mechanical behaviours in the shortest processing time. Different (HAT) post- treatments experiments, combinate from a common homogenization solution treatment (HT) step performed at 1020 °C for 15 min, using aqueous NaCl solutions for cooling, and aging treatment (HT) step on mechanical properties of as-built maraging steel manufactured by selective laser melting (SLM). Three different aging temperatures (485 °C, 585 °C, and 685 °C) and aging times (120 min, 150 min, and 180 min) were used on the parts. In order to characterize the effects of heat treatment on the microstructure and on the mechanical behaviour, various microscopy techniques, such as confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD), were used. To quantify the mechanical behaviour of SLM maraging steel (C300), hardness measurements and tensile tests were performed after homogenization solution-aging treatments (HAT). Furthermore, a statistical model was developed using analysis of variance (ANOVA) to predict the mechanical behaviour (hardness) and determine the related significant parameter. The model related the mechanical behaviour to the post-treatment properties in the work region. Compared to the as-built parts, the microhardness and ultimate tensile strengths were significantly improved after homogenization solution-aging treatments (HAT). The effects of heat treatment parameters (cooling solutions, aging temperature and aging time) on mechanical properties depend primarily on the microstructure changes that occur. The results showed that the heat-treated parts had a finer and non-continuous microstructure, leading to higher hardness (∼20–50%) and higher ultimate tensile strength (∼25–55%) properties, as compared to the as-built parts. The microhardness and ultimate strength can go up to ∼56 HRC and 2150 MPa, respectively, at the optimal heat treatment regime (solution treatment at 1020 °C for 15 min + aging treatment at 480 °C for ∼175 min).

Novel laser powder bed fusion Corrax maraging stainless steel lattice with superior specific strength and energy absorption

Laser powder bed fusion (LPBF) is a versatile process for producing lattice structures with complex pore features. In this study, a novel LPBF Corrax maraging stainless steel lattice with superior compressive strength and energy absorption was fabricated and investigated. In samples with a cubic lattice structure and 90 vol% porosity, the specific compressive strength and energy absorption of the LPBF Corrax lattices were as high as 53 kN·m/kg and 13.5 kJ/kg, respectively, which were higher than those of LPBF Ti–6Al–4V by 8% and 67%, respectively. Integrated solution-aging treatments further enhanced the specific compressive strength of Corrax lattice to 73 kN·m/kg and maintained the specific energy absorption. Furthermore, the deformation and fracture behaviors of the Corrax lattice were investigated and are discussed. The findings of this study indicate that LPBF Corrax is a potential material for manufacturing cheap, lightweight components with superior mechanical performances.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of 18Ni-300 Maraging Steel Produced by Additive-Subtractive Hybrid Manufacturing.

The present work investigates the effectiveness of two heat treatment cycles-solution treatment + aging (STA) and direct aging (DA)-on optimizing the microstructure and enhancing the mechanical properties of 18Ni-300 maraging steel (300 MS) produced by additive-subtractive hybrid manufacturing (ASHM). The STA treatment led to a fully martensitic microstructure with minor remnants of the cellular substructures associated with the solidification conditions in ASHM. DA resulted in some reverted austenite and partial dissolution of the cellular morphologies into shorter fragments. Despite the contrasting microstructures, the tensile strength and the macro- and micro-hardness were comparable between STA and DA conditions. By contrast, the potential for improving the ductility was higher with the DA heat treatment. This is attributed to the higher reverted austenite content in the samples treated by DA, i.e., up to a maximum of 13.4% compared to less than 3.0% in the STA samples. For the DA sample with the highest reverted austenite content of 13.4%, the highest local and global fracture strain values of 30.1 and 5.9 ± 0.6% were measured, while the respective values were 23.4 and 4.4 ± 0.1% for the corresponding STA sample. This work suggests that DA of 300 MS produced by ASHM is sufficient to achieve comparable hardness and tensile strength to STA, whilst maintaining reasonable ductility. Avoiding the solution treatment cycle, with its appreciably higher temperatures, could benefit the dimensional stability and surface quality that are important for ASHM of 300 MS parts.

Improved stress relaxation stability of a heat-resistant Al-Cu-Mg-Ag alloy with good mechanical properties by a pre-annealing/solution-aging treatment

Good stress relaxation stability enables heat-resistant aluminum alloys to serve well at high temperatures. From the viewpoint of simultaneous regulation of microstructure and precipitates, a deliberate pre-annealing (200–400 ℃) followed by solution-aging (T6) treatment was proposed to improve the stress relaxation stability of an Al-Cu-Mg-Ag heat-resistant aluminum alloy in this work. A peak effect on the stress relaxation stability was found with a pre-annealing temperature of 325 ℃, which is associated with larger-sized grains and finer-sized precipitates of the alloy. This interesting peak phenomenon is attributed to a good balance of recrystallization and precipitation. Moreover, the regulated microstructure surprisingly assisted the 325 ℃ pre-annealing+T6 treated alloy with good tensile properties. The proposed heat treatment method provides a route for developing high-performance heat-resistant aluminum alloys.

Effects of Solution Aging Treatment on Microstructure and Hardness of Ni30 Superalloy

Using JMatPro numerical simulation to determine the range of process parameters, the solution aging treatment of Ni30 superalloy was carried out, and the influence of different solution treatment temperatures on the microstructure and hardness of the alloy was studied. The results show that with the increase of solution temperature, the grain grows rapidly, the grain growth process conforms to Arrhenius formula, and the activation energy Q of grain growth is about 74.33kJ/mol. The maximum hardness value of the sample is 41.80HRC after solution aging treatment at 980°C.

Research on microstructure and properties of Cu-0.41%Cr-0.20%Zr alloy after solution-aging treatment

The phase analysis of Cu-0.41%Cr-0.20%Zr alloy treated by vacuum melting + solid solution + aging was carried out by means of SEM, TEM, EDXS and XRD. The results show that there are three phases in the alloy, namely the copper matrix phase, the chrome-rich phase and the zirconium-rich phase. The distribution of phase size is bimodal. The coarse phase size is microns scale, and the main components are elemental chromium and Cu5Zr, which are formed during the casting process and are not easy to dissolve in the subsequent aging process. The fine phase size is nanometer scale, and the composition is ordered bcc pure chromium and Cu5Zr. There is no chromium and zirconium intermediate phase. Under this condition, the volume fraction of precipitated phase is about 30 %. The heat treatment process can be further optimized by increasing the aging temperature, lengthening the aging time or adopting the second aging method.

Biodegradable Zn–0.5Li alloys with supersaturated solid solution—aging treatment for implant applications

To solve the problems of poor mechanical properties and local corrosion caused by the coarse dendrites grain and the second phase of as-cast (AC) Zn–Li alloy, AC Zn-0.5Li alloys were treated by ultra-high pressure (3 GPa) solid solution-aging treatment (UHPS-AT) at 375 °C. The microstructure, mechanical, corrosion behavior, cell compatibility, and antibacterial properties of UHPS-AT Zn-0.5Li alloys were characterized and evaluated. After the UHPS-AT treatment, the TEM images showed the presence of large Zn/β-LiZn4 layered grain inside UHPS-AT alloy, and the dendritic grain and coarse second phase disappeared. The mechanical properties and wear resistance of Zn-0.5Li alloys were improved compared with AC alloys after UHPS-AT treatment. However, the compressive yield strength of UHPS Zn-0.5Li alloy decreased after aging, indicating that the strengthening effect of solid solution is better than that of the second phase precipitation, which was also proved by theoretical calculation. A dense passivation film was formed on the surface of the UHPS-AT sample, hindering further corrosion of the alloy, resulting in the change of the corrosion mechanism from local corrosion in the as-cast state to uniform corrosion in the UHPS-AT state. Cytotoxicity assays with Zn-0.5Li alloys showed that extracts at concentrations below 12.5% were not cytotoxic. Moreover, the Zn-0.5Li alloy exhibited good antibacterial properties against E. coli bacteria.

Revealing the microstructural evolution and its influence on mechanical properties of heterostructured steel fabricated by laser melting deposition

A series of heterostructured materials with variable ratio of 316 powders in 18Ni300 powders were prepared by laser melting deposition (LMD). The microstructural evolution and its influence on tensile features were explored before/after aging treatment or solution-aging treatment. The results indicated that the fraction of γ phase was increased gradually with increasing 316SS, and dislocation caused by the deformation could be migrated and annihilated within the region of γ phase, second phase strengthening could contribute to excellent elongation for 18Ni300 maraging steel. The elongation of the AF4 sample was 235.2% higher than that of the AF0 sample when a 37.5% reduction in the ultimate tensile strength occurred. In addition, thermal stress could exist in the as-cladded sample, an appropriate heat treatment could release the thermal stress and precipitate nanoscale intermetallic compound. Their synergistic effect could contribute to overcoming the strength-elongation trade-off. A relatively ideal sample, a discontinuous γ phase surrounded by α phase, which displayed high strength of 1678.4 MPa with high elongation of 10.9% after solution-aging treatment. Compared with laser cladded 18Ni300 maraging steel, a 41.7% increment in the elongation was obtained at the cost of 11.3% reduction in ultimate tensile strength.

Microstructural evolution and precipitation behavior of Al–7Si–3Cu alloy prepared under 5 GPa

This paper presents a systematic investigation of the microstructural evolution and mechanical properties of Al–7Si–3Cu alloys prepared under high pressure of 5 GPa. It is found that the dendritic structure disappears due to the enhanced stability of the growth interface under high pressure. Meanwhile, a considerable solute-induced modification effect is achieved in the eutectic Si. Besides, unconventional larger eutectic colonies and ultrafine nanocrystalline eutectics are observed within the intragranular area. Combined with detailed microstructural characterization, the crucial role of high pressure on the evolution of these isolated phases is discussed. The study also explores the precipitation behavior and strengthening mechanisms of alloys prepared under direct aging and solution-aging treatments. Upon the direct aging treatment, θ' phases, coarse Al2Cu particles, and Si particles form simultaneously in the matrix owing to the increased solid solubility of alloying elements, which results in the highest mechanical properties with a microhardness of 132.8 HV and compressive stress of 715 MPa. Solution-aging treatment leads to the segregation of Si on θ' phases, which proved to be energetically favorable according to first-principles calculations. This work provides new insights into the microstructural optimization of aluminum–silicon-based alloys through high-pressure manipulation and paves the way for further industrial applications.

Effect of arc oscillation on porosity and mechanical properties of 2319 aluminum alloy fabricated by CMT-wire arc additive manufacturing

In this paper, arc oscillation is applied in the fabrication of 2319 aluminum alloy samples by cold metal transition wire arc additive manufacturing process (CMT-WAAM). The porosity, microstructure and mechanical properties of 2319 aluminum alloy under different arc oscillation patterns were discussed. The results showed that the stirring of arc oscillation can influence the molten pool shape and improve the fluidity, change the thermal distribution and the growth direction of columnar crystal. Arc oscillation has a obvious effect on reducing the grain size and proportion of pores. After using the spiral arc oscillation pattern and asymmetrical trapezoid arc oscillation pattern, the volume fraction of pores reduced from 2.64% to 1.09% and 1.22%, and the size of pores was mainly smaller than 40 μm, respectively. The tensile strength in vertical direction and plasticity were improved with arc oscillation, but its effect on the horizontal tensile strength was not noticeable. After solid solution-aging treatment, the tensile strength of the sample with spiral arc oscillation pattern increased to 277 MPa, with a cross-section reduction of 3.6%.

Abnormal grain growth under solution-aging treatments enables convergence mechanical properties of a Fe-Ni-Cr based austenitic alloy

In this study, systematic heat treatment routes including solution (980 °C to 1130 °C) and aging (675 °C to 775 °C) processes were used to tailor the microstructural evolution and mechanical performance of a Fe-Ni-Cr based austenitic alloy, strengthened by a γ′ phase (Ni3(Ti, Al)). Grain growth was observed with increasing solution treatment temperature from nearly 90 μm (980 °C) to nearly 200 μm (1130 °C). Grain refinement during solution heat processes was found to ascribe to the solute drag effect and the pinning effect of nickel-titanium-enriched segregates and precipitates. During aging, the precipitation behavior of γ′ is found to be almost independent of solution treatment temperatures. Interestingly, abnormal grain growth during aging was observed. The motion of grain boundaries was ascribed to the formation of nickel-titanium-enriched γ′ in the austenitic matrix, thereby contributing to the dissolution of the previously enriched segregates and precipitates from grain boundaries. The studied alloy shows a wide range of mechanical properties, from tensile strength of 1131 MPa with ductility at 36%, to tensile strength of 880 MPa with ductility at 50%. The current study demonstrates that grain refinement of the alloy at solution treatment may not benefit the final mechanical properties.

Influence of build orientation and aging on corrosion behaviour of 18Ni300 maraging steel produced via Powder Bed Fusion using Laser Beam (PBF-LB)

Conventional maraging steel corrodes uniformly but additive manufactured (AM) maraging steel can corrode differently, depending upon the angle of exposure of build layers to the corrosive media. The primary objective of this investigation is to examine the effect of build orientation and solution aging treatment (HT) on the corrosion behaviour of the AM maraging steel and to compare with that produced through the conventional route of casting and hot rolling. In this investigation, corrosion behaviour of maraging steel samples produced by Powder Bed Fusion using Laser Beam (PBF-LB), with different build orientations of 0°, 45°, and 90°, was investigated in a 3.5% NaCl solution. Corrosion resistance of the as-built (AB) samples was found to increase with decrease in the angle of inclination and related to structural heterogeneity and grain boundary density. However, corrosion resistance of the AB samples was decreased following heat treatment (solutioning and aging) and was controlled by precipitation of intermetallic phases and reversed austenite generation. While there was dominance of protective oxide layer of TiO2 in the AB and conventional sample, this oxide layer was not observed on the heat treated (HT) samples. Further, a marked difference was observed in pitting corrosion of the AB and HT samples.

Enhanced mechanical properties of dissimilar MIG welded 7005-T6 and 6063-T6 alloys by PWHT

The welding of high-strength aluminum alloy is critical for liable service of some key parts and components. The solution aging treatment is adopted for 7005-T6 / 6063-T6 dissimilar aluminum alloys. The microstructure, composition distribution and mechanical properties were characterized. The results show that the joint grain is refined after solution aging treatment, and the coarse non-equilibrium phase is dissolved. The diffusion of Zn atoms promoted the precipitation of Mg-Zn (η′) and Mg-Si (β′′). After the solution aging treatment, the main precipitations changed from a small amount of β′′ to the co-existence of η′ and β′′, which improves the tensile strength of the joint. This study mainly reveals the important role of solution aging treatment on dissimilar aluminum alloy joint which provides guidance for dissimilar aluminum alloy welding.

Microstructure and properties of spinning deformed A356 alloy subject to the solution-DCT-aging multiplex heat treatment

The effect of DCT time (1 h,12 h, 24 h, 36 h and 48 h) on the microstructure and mechanical properties of spinning deformed A356 alloy subject to solution-DCT-aging multiplex heat treatment (hereinafter referred to as “DCT multiplex heat treatment”) was studied. The results demonstrate that the best DCT time of multiplex heat treatment is 36 h, which is the critical time for the recrystallization process. Then the recrystallization texture will appear in the 48 h DCT sample. The equal-area-circle diameter of α-Al matrix and Si phase are 24.8 μm and 1.5 μm respectively after 36 h DCT, which are 53.3% and 53.1% smaller than those after sole solution-aging treatment. After 36 h DCT, the tensile strength, yield strength, elongation and microhardness of A356 alloy arrive at the maximum simultaneously as 302.21 MPa, 272.93 MPa, 20.37% and 98.8HV separately, which are increased by 6.8%, 4.1%, 24.0% and 3.9% in comparison to the sole solution-aged sample. Short-term DCT (<36 h) can increase the residual stress and prompt the dislocation density, while long-term DCT (>36 h) is diametrically opposite. The crystal plane of DCT-ed α-Al matrix rotates towards the (200) crystal plane, and accelerates the formation of nanometer Mg2Si precipitates in the matrix, and twin structure can be observed in the Si crystal. The main strengthening and toughening mechanisms of DCT alloy concerns with fine grain strengthening, precipitation strengthening, dislocation strengthening and twin strengthening.

A rapid and effective method for alloy materials design via sample data transfer machine learning

One of the challenges in material design is to rapidly develop new materials or improve the performance of materials by utilizing the data and knowledge of existing materials. Here, a rapid and effective method of alloy material design via data transfer learning is proposed to efficiently design new alloys using existing data. A new type of aluminum alloy (E2 alloy) with ultra strength and high toughness previously developed by the authors is used as an example. An optimal three-stage solution-aging treatment process (T66R) was efficiently designed transferring 1053 pieces of process-property relationship data of existing AA7xxx commercial aluminum alloys. It realizes the substantial improvement of strength and plasticity of E2 alloy simultaneously, which is of great significance for lightweight of high-end equipment. Meanwhile, the microstructure analysis clarifies the mechanism of alloy performance improvement. This study shows that transferring the existing alloy data is an effective method to design new alloys.

Microstructure and Fatigue Performance of Ti6Al4V Produced by Laser Powder Bed Fusion after Post-Heat Treatment

With the development of additive manufacturing (AM), the Ti-6Al-4V alloy manufactured by laser powder bed fusion (LPBF) is becoming more widely studied. Fatigue fracture is the main failure mode of such components. During LPBF processing, porosity defects are unavoidable, which hinders the exploration of the relationship between fatigue performance and microstructure. In this study, a laser remelting method was used to reduce porosity defects inside the Ti-6Al-4V alloy. Three annealing treatments (AT) and three solution-aging treatments (SAT) were used to study the effect of the two-phase zone (α + β) microstructure on fatigue life and fatigue crack growth behavior. Fatigue life and crack growth rate (CGR) curves were obtained, and fatigue fracture surface and crack growth fracture surface were analyzed. The results show that microstructure influences fatigue life but has little effect on CGR. Compared with the as-built specimen, the fatigue life of the AT and SAT specimens increased significantly at 850℃ by 101 and 63.7 times, respectively. The thickness of the α lath and the location of crack nucleation together affect the fatigue life. In the stable growth stage, the layered microstructure of α colonies is the most resistant to crack growth.