Age Hardening Heat Treatment Research Articles

A Comparative Analysis of a Microstructure and Properties for Monel K500 Hot-Rolled to a Round Bar and Wire Deposited on a Round Surface

Metal manufacturing processes based on deformation (forging, rolling) result in a fine grain structure with a complex dislocation substructure, which positively influence mechanical properties. Casting and additive manufacturing (powder- or wire-based) usually produce a coarse grain structure with a poorly developed dislocation substructure, which negatively affect mechanical properties. Heat treatment may alter phase balance and stimulate precipitation strengthening; however, precipitation kinetics depends on the dislocation substructure. In this paper, a comparative study of the microstructure and strength is presented for Monel K500 alloy containing 63 Ni, 30 Cu, 2.0 Mn, and 2.0 Fe (wt.%), and microalloyed with Al, Ti, and C hot-rolled to a round bar and deposited on a round surface using wire additive manufacturing (WAAM) technology. An increased dislocation density and number density of fine precipitates resulted in 8–25% higher hardness and 1.8–2.6 times higher compression yield stress in the hot-rolled alloy compared to these in the WAAM-produced alloy. However, due to a high work hardening rate, only 3–10% cold deformation was necessary to increase the strength of the WAAM alloy to this of the hot-rolled one. Age hardening heat treatment, through the intensification of the precipitation strengthening mechanism, reduced the value of cold deformation strain required to equalise the properties. Based on the obtained results, a new technology consisting of additive manufacturing, heat treatment, and cold deformation can be proposed. It can produce WAAM components with strength and hardness improved to the level of hot-rolled components, which is a significant development of additive manufacturing.

The effect of Cu–8%P master alloy, SIMA process, thixoforming, and heat treatment on the microstructure and mechanical properties of Al–20%Mg2Si composite

In the present research, the effect of thixoforming and age-hardening heat treatment on the microstructure and mechanical properties of un-modified and modified Al–20%Mg2Si composites produced through the strain-induced melt activation (SIMA) process has been investigated. This method showed promising potential for manufacturing the ideal microstructure, achieving globular grains, and enhancing mechanical properties. Quantitative analysis has revealed that adjusting the semi-solid heat treatment parameters to a temperature of 570 °C and a holding time of 25 min optimizes the globular α-Al grains and Mg2Si particles, achieving the size of 20.62 μm and 66.71 μm and the shape factor of 0.81 and 0.83 for Mg2Si particles and α-Al grains, respectively. The yield strength of the modified Al–20%Mg2Si composite increased by 23.67% and the ultimate tensile strength increased by 21.20%, compared to the un-modified specimen. Both composites underwent the thixoforming process, illustrating the ultimate tensile strength and elongation of 93.68 MPa and 4.32% for the original composite and 138.86 MPa and 7.29% for the modified composite. The modified Al–20%Mg2Si composite was subjected to the effective combination of thixoforming and age-hardening. According to the tensile test results, the yield strength, ultimate tensile strength, elongation, and toughness raised by 138.72%, 140.92%, 267.70%, and 471.12%, respectively, compared to the as-cast specimen. Moreover, its impressive hardness of 125.1HB contributes to its overall performance.

Influence of deep rolling at different temperatures on near-surface and mechanical properties of a Maraging C250 steel

Due to an outstanding combination of high strength and fracture toughness Maraging steels are used in numerous industries, e.g., in the aerospace sector. The high strength can be attributed to precipitation strengthening by conventional age-hardening heat treatments. However, as many of the envisaged applications will suffer from cyclic loadings, the fatigue properties are of significant interest in terms of a reliable use. Generally, Maraging steels are characterized by a relatively low fatigue strength limiting the use in certain applications. In this context, mechanical surface treatment processes are promising candidates to overcome these challenges. In particular, deep rolling represents a suitable process, as it is known for increased depth effects as well as smoother surface profiles compared to other mechanical surface treatment processes. Moreover, aging heat treatments can easily be implemented into the process. Accordingly, the present study focuses on near-surface and mechanical properties of a Maraging C250 steel after deep rolling. Characterization of the near-surface area was conducted by X-ray diffraction and hardness measurements. Mechanical properties were assessed by tensile and fatigue tests. The results presented reveal a great potential of the integration of an aging heat treatment into the deep rolling process eventually leading to significant process time reduction.

Fracture behavior of PH15-5 stainless steel manufactured via directed energy deposition

The tensile properties, fracture toughness, and fatigue crack growth (FCG) characteristics of a directed energy deposited precipitation hardened stainless steel (grade: PH15-5; age hardening heat treatment condition: H900) were examined. In the as-fabricated condition, the alloy contains microfissures that are oriented parallel to the build direction, whose appearance was difficult to be detected using optical microscopy. Due to their relative orientation w.r.t. the loading direction, significant anisotropy in tensile and FCG behavior was noted, with the properties being particularly lower when the loading direction is perpendicular to the crack orientation. Despite the presence of microfissures, the alloy’s fracture initiation toughness is comparable to (or in some cases exceeds) those manufactured using either conventionally techniques or laser powder bed fusion. Activation of the extrinsic toughening mechanisms, such as crack deflection when its mode I direction is perpendicular to the microfissures and a combination of crack bridging and deflection when it is parallel, are the micromechanical reasons for the observed high toughness. The efficacy of such mechanisms is observed to depend on the plastic zone size relative to the microfissure spacing. The understanding developed in this study enables the development of strategies for enhancing the damage tolerance of additively manufactured alloys.

Mechanical and damping behavior of artificially aged Al 6061/TiO2 reinforced composites for aerospace applications

In this research, the microstructural and mechanical properties of the as-cast and artificially aged Al6061-TiO2 alloy and its composites developed by the double stir casting process were studied. The reinforcements were added in different weight concentrations and artificial aging was done at 200 °C for 2 h. TiO2 particle reinforcement was adopted because of its better grain refining capacity, high elastic modulus and precipitate pinning effect. Heat treatment was performed for the formation of a high density of fine precipitates which was suitable for stress-bearing applications. The results showed an improvement in the tensile strength and hardness of the heat-treated samples up to 195.2 and 43.68%, respectively, compared to the as-cast samples. After TiO2 addition and age-hardening heat treatment, the SEM fractography showed that the small size dimples were evenly distributed which represented the enhanced ductile nature. The as-cast alloy and its composites had better damping properties compared to the age-hardened specimens. Fracture toughness and elongation showed enhancement in the heat-treated samples than in the as-cast samples. This enhancement is associated with the grain refining effect of TiO2 particles and precipitate formation. Artificially aged Al6061 alloy and its composite showed a better balance of properties.

Age hardening heat treatment behavior of as-cast Mg–Zn–Al alloys

Magnesium alloys have generated renewed interest as a light alloys; replacing some conventional structural materials for weight reduction in applications like aerospace, automotive and electronics industries. In interior components and powertrains, cast alloys are widely used and represent more than 99% of magnesium alloys used today, whereas only a few wrought products are used. Mostly in automotive applications, Mg-engine block can noticeably reduce the weight and consequently its fuel consumption and environmental impact. Due to solid-state precipitates, these alloys are strong in nature and are produced by an age-hardening heat treatment process. In the present work the age hardening behavior of the as cast Mg–Zn–Al alloys (ZA85 alloy) in the composition of 8 wt. %Zn, 5 wt. %Al has been investigated. Through the differential thermal analysis (DTA) studies, it has been found out that dissolution temperature of ternary eutectic precipitates is present in the alloy. Based on the DTA results, the as cast samples have been solutionised at 360 °C temperature for different intervals of time. Solutionising time has been optimized from the enthalpy values of un-dissolved precipitates. The solution treated samples have been then aged at temperature of 180° C for different time intervals. From the peak hardness values, the ageing conditions have been optimized.

Superplasticity and mechanical properties of Al–Mg–Si alloy doped with eutectic-forming Ni and Fe, and dispersoid-forming Sc and Zr elements

The development of Al–Mg–Si-based alloys with advanced superplasticity and improved mechanical properties is an important task for further applications of superplastic blow-forming technology in the production of complex-shape parts. The current study focuses on the influence of eutectic forming Ni and Fe and dispersoid forming Sc and Zr alloying elements on the microstructural evolution, superplastic behavior, and tensile properties at room temperature for the Al-1.2%Mg-0.7%Si-1.0%Cu (AA6013-type) alloy. The X-Ray diffraction, scanning, and transmission electron microscopy were used for microstructural characterization. The bimodal particle size distribution was observed after the thermomechanical treatment of the alloy studied. The high density of the L12 coherent dispersoids with a mean size of 10 ± 1 nm providing a significant Zener pinning effect was formed during homogenization annealing. The near-equiaxed coarse particles with a size in a range of 0.5–5.0 μm belonged pre-dominantly to the Mg2Si and Al9FeNi phases, which led to an important particle-stimulated nucleation (PSN) effect. The alloys studied exhibited a superplastic behavior in temperature and strain rate limits of 440–520 °C and 1 × 10−3 s−1 - 1 × 10−2 s−1, respectively, with an elongation-to-failure range of 350–480%. The age-hardening heat treatment provided a yield strength of 370 ± 4 MPa, an ultimate tensile strength of 415 ± 2 MPa, and elongation of 6 ± 1%.

Effect of Ta/W Ratio on Microstructural Features and Segregation Patterns of the Single Crystal PWA1483 Ni-Based Superalloy

Microstructure and microsegregation pattern of four Ni-based single crystal (SX) PWA1483 superalloys with different Ta/W ratios of 0.75, 1.0, 1.32, and 1.5 (in wt.%) were investigated. The alloys were directionally solidified by the Bridgman method with a withdrawal rate of 3 mm/min and thermal gradient of about 7 K/mm, followed by an age hardening heat treatment. The experimental observations showed that the Ta/W ratio influenced microstructures and elemental microsegregation patterns of the SX superalloys. Based on the EDS results, W, Mo, Cr, and Co segregated to the dendrite core regions, while Ta, Ti, and Al to the γ/γ′ eutectic and interdendritic zones. The microsegregation degree of Ta and Ti was increased with increasing Ta/W ratio. In addition, Ta and Ti tended to partition to γ′ phase while Mo, W, Co, and Cr to γ matrix phase. By increasing the Ta/W ratio, microporosity was decreased, while the volume fraction of TCP phase and γ/γ′ eutectic structure increased. The superalloy with the Ta/W ratio of 1 showed the best homogeneous distribution of alloying elements in both γ and γ′ phases with no sign of secondary grain defect.

Influence of Ageing Time on Mechanical Properties and Weibull Probability Distribution of Tensile Strength of Ternary Al–Zn–Mg Alloy Produced from Aluminium and Zinc Scrap

In this work, a cast alloy of Al–Zn–Mg was developed from aluminium from recycled beverage cans and zinc scraps from battery and the influence of age-hardening heat treatment of the alloy on mechanical properties and reliability analysis on the tensile strength was investigated. The cast Al–Zn–Mg alloy was subjected to age-hardening heat treatment at different times. The aluminium, cast alloy and age-hardened alloy were characterized using XRF, XRD and TEM. The mechanical properties were investigated using a hardness test, impact strength test and percentage elongation. Also, the tensile strength data were subjected to a reliability analysis using Weibull probability distribution. From the results, it shows that 24 h ageing time is enough to have optimum mechanical properties due to an increase in size of the stable MgZn2s phase particles. The reliability analysis shows that the alloy aged at 24 h has tensile strength value (229.72 MPa) in the range reported for Al–Zn–Mg alloy’s temper designations.

Development of Precipitation Hardening Parameters for High Strength Alloy AA 7068.

The mechanical properties after age hardening heat treatment and the kinetics of related phase transformations of high strength AlZnMgCu alloy AA 7068 were investigated. The experimental work includes differential scanning calorimetry (DSC), differential fast scanning calorimetry (DFSC), sophisticated differential dilatometry (DIL), scanning electron microscopy (SEM), as well as hardness and tensile tests. For the kinetic analysis of quench induced precipitation by dilatometry new metrological methods and evaluation procedures were established. Using DSC, dissolution behaviour during heating to solution annealing temperature was investigated. These experiments allowed for identification of the appropriate temperature and duration for the solution heat treatment. Continuous cooling experiments in DSC, DFSC, and DIL determined the kinetics of quench induced precipitation. DSC and DIL revealed several overlapping precipitation reactions. The critical cooling rate for a complete supersaturation of the solid solution has been identified to be 600 to 800 K/s. At slightly subcritical cooling rates quench induced precipitation results in a direct hardening effect resulting in a technological critical cooling rate of about 100 K/s, i.e., the hardness after ageing reaches a saturation level for cooling rates faster than 100 K/s. Maximum yield strength of above 600 MPa and tensile strength of up to 650 MPa were attained.

Review of the Quench Sensitivity of Aluminium Alloys: Analysis of the Kinetics and Nature of Quench-Induced Precipitation.

For aluminium alloys, precipitation strengthening is controlled by age-hardening heat treatments, including solution treatment, quenching, and ageing. In terms of technological applications, quenching is considered a critical step, because detrimental quench-induced precipitation must be avoided to exploit the full age-hardening potential of the alloy. The alloy therefore needs to be quenched faster than a critical cooling rate, but slow enough to avoid undesired distortion and residual stresses. These contrary requirements for quenching can only be aligned based on detailed knowledge of the kinetics of quench-induced precipitation. Until the beginning of the 21st century, the kinetics of relevant solid-solid phase transformations in aluminium alloys could only be estimated by ex-situ testing of different properties. Over the past ten years, significant progress has been achieved in this field of materials science, enabled by the development of highly sensitive differential scanning calorimetry (DSC) techniques. This review presents a comprehensive report on the solid-solid phase transformation kinetics in Al alloys covering precipitation and dissolution reactions during heating from different initial states, dissolution during solution annealing and to a vast extent quench-induced precipitation during continuous cooling over a dynamic cooling rate range of ten orders of magnitude. The kinetic analyses are complemented by sophisticated micro- and nano-structural analyses and continuous cooling precipitation (CCP) diagrams are derived. The measurement of enthalpies released by quench-induced precipitation as a function of the cooling rate also enables predictions of the quench sensitivities of Al alloys using physically-based models. Various alloys are compared, and general aspects of quench-induced precipitation in Al alloys are derived.

Comparative effect of Mn/Ti solute atoms and TiC/Ni3(Al,Ti) nano-particles on work hardening behaviour in Ni[sbnd]Cu alloys fabricated by wire arc additive manufacturing

Two NiCu alloys with various contents of Mn, Ti, Al and C were deposited in a shape of single-bead multi layered walls using wire arc additive manufacturing technology. To modify solute atom concentrations and particle number density values, the as-welded alloys were subjected to annealing at 1100 °C and age-hardening heat treatment in the 610-480 °C temperature range. Microstructure characterisation was carried out using optical, scanning, conventional transmission and atomic resolution transmission electron microscopy. Work hardening behaviour was studied using tensile testing. For similar deposition and heat treatment conditions, an alloy with higher C and Al, and lower Mn contents exhibited a higher number density of >20 nm TiC particles, higher number density of <20 nm γ′-Ni3(Al, Ti) particles, and, associated with these, superior hardness, tensile strength, strain hardening rate and toughness. The comparative effect of solid solution and precipitation strengthening on work hardening behaviour and fracture mode is discussed.

Experimental Investigation on Silicon Carbide Reinforced Duralumin based MMC Produced by Cold Compacting

In the present investigation, an attempt is made to fabricate the Duralumin(DA) based Silicon Carbide (SiCp-6 and 12% wt.) reinforced composite by cold compacting the ball milled powders. The mechanically mixed powders taken into the die cavity are applied with a steady axial load in the range 22-30 T to produce the cylindrical compacts. The compacts are further subjected to sintering by holding it at a constant temperature of 5800C in Muffle furnace for 5 h and allowed to cool in the same for 18 h. The hardness of sintered composite is found to have improved as compared to the sintered duralumin compact prepared under similar process conditions. The SEM images showed the uniform distribution of the reinforcements in the matrix and the elemental composition is confirmed by the EDAX spectrum. The sintered specimens were further subjected to age hardening heat treatment. Specimens were soaked at 5500C for 2 h followed by water quenching at room temperature. The quenched specimens were artificially aged in the furnace at temperatures of 100, 150, and 2000C for various durations of time. The peak hardness obtained because of aging heat treatment is found to be much better than the corresponding sintered compacts. Compacts peak aged at 1000C exhibited better tensile strength than the other category of specimens. The composites developed in the present study would be most suitable in the applications requiring high strength and resistance to heat and wear.

Interactive study on phase morphology and mechanical characteristics of diffusion annealed and age hardened Al7075–steel powder reinforced metal matrix composites

This paper expounds the effects of diffusion annealing and age hardening heat treatments on the phase morphology and mechanical properties of Al7075–eutectoid steel powder (0.8 wt% carbon steel) reinforced composites. Eutectoid steel powder ranging from 55–70 μm is selected due to its ability to improve the bulk hardness of the composite. In the present study three different weight fractions of eutectoid steel powder composites are prepared by conventional stir casting process. The material is cast in the form of rods inside the permanent stainless steel mould from where some samples are cooled in still air to room temperature. From these samples some are diffusion annealed from isothermal holding of 6 h i.e., above recrystallization temperature (600 °C) followed by boiling water quench and few are subjected to age hardening for a fixed time duration of five hours. Age hardening is carried out at solutionising temperature 560 °C tailed by aging at two temperatures 100 °C and 180 °C independently. All the samples in each category are subjected to critical property characterization and the phase arrangement information are characterized by scanning electron microscopy. From the analysis of microstructure and destructive tests, it is clear that the as-cast (stir-cast) samples display dendritic segregations with wider grain boundary area, is responsible for the inferior mechanical properties. It is also found out that diffusion annealing and age hardening heat treatments eliminates micro-segregation and improve mechanical properties of Al7075–eutectoid steel powder reinforced composites. It is concluded that chemical inhomogeneity in dendrites can be eliminated by selecting the suitable heat treatment with proper heat treatment parameters.

Microstructure and Mechanical Properties of Spray Formed and Hot Pressed/Heat Treated Al-(20-30 wt%) Mg2Si-2% Cu Alloy

In the present investigation, Al-(20-30%wt) Mg2Si-2Cu alloys were synthesized by spray forming process and further processed by hot pressing for densification. The alloys were further subjected to age hardening heat treatment. The spray formed, age hardened and as-cast alloys were characterized by microstructure and mechanical properties. The microstructure of spray formed alloys exhibited finer and evenly distributed primary β-Mg2Si particles and θ-Al2Cu phase and clusters of discrete and high volume fraction of Q-phase. As-cast alloys mainly consist of large sized polygonal primary β-Mg2Si, coarse Chinese script of Al2Cu and needle shaped eutectic Q-phase. Hot pressing of the spray formed alloy promotes the microstructural refinement, reduction in porosity, fragmentation and redistribution of secondary phases. Artificial age hardened alloys exhibits the large quantity of θ-Al2Cu precipitates less than 2 μm size uniformly distributed in the matrix. The β phase re-precipitates in a very fine spherical form results in an increase in the area fraction of β-Mg2Si phase during aging. The significant enhancement in ultimate strength in heat treated and sprays formed alloys as compared to the as-cast alloy. The SEM of fracture surfaces of tensile specimens was taken on spray formed age hardened and as cast alloys. The fractographs revealed the transformation from brittle mode to ductile dimples.

Effect of Homogenizing and Age Hardening on Mechanical Property Enhancement of TIG Welded Al6061 SiC&lt;sub&gt;p&lt;/sub&gt; Composites

This paper explains the type of heat treatments used to improve the bulk hardness and tensile properties of Tungsten Inert Gas (TIG) welded Al6061-SiC reinforced composites. Composites with 8, 10 and 12 wt% of SiC (25 μm) are TIG welded using ER5356 filler material and the hardness, tensile property and microstructural analysis in as weld condition is carried out. Age hardening heat treatment is performed and peak hardness values are noted at different aging temperatures and subjected to characterization. Al6061-12 wt% SiC shows reduction in tensile strength in comparison with the other two in spite of improvement in hardness. Since hardness is more, there arise ambiguity in knowing the actual cause of decrease in the tensile strength. Optical micrographs of the samples are taken and identified the presence of dendritic segregation as the actual cause for the (UTS) reduction. To remove dendritic segregation, all the as weld samples are subjected to 5h homogenizing at 500°C, age hardened and characterized. The result showed substantial hike in UTS with substantial improvement in hardness, homogeneous distribution of hardness over the cross-section in the weld bead. The depth and distribution of hardness and bulk property improvement are observed by the combined effect of homogenizing and low temperature age hardening.

Effect of friction stir processed microstructure on tensile properties of an Al-Zn-Mg-Sc alloy upon subsequent aging heat treatment

An as-cast Al-Zn-Mg-Sc alloy was friction stir processed varying tool related parameters, yielding microstructures with different grain sizes (0.68, 1.8 and 5.5μm). Significant increases in room temperature ductility were obtained in these materials with reasonable enhancement in strength. It is demonstrated that the type of microstructure produced by friction stir processing (FSP) has a significant influence on the choice of post-FSP heat treatment design for achieving improved tensile properties. It is also found that the ultrafine grained FSP material could not achieve the desired high strength during the post-FSP heat treatment without grain coarsening, whereas the micro-grained FSP materials could reach such strength levels (>560MPa) under conventional age hardening heat treatment conditions.

Brittle fracture behavior of a laser additive manufactured near-β titanium alloy after low temperature aging

The near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) fabricated by laser additive manufacturing was further annealed by multiple low temperature aging heat treatments. Microstructures and fracture surfaces were observed by optical and electron microscopes. Brittle tensile fracture behaviors were analyzed and cleavage fracture and quasi-cleavage fracture were distinguished. Results show that athermal ω phases in Ti-55511 have negligible strengthening effect because of their very small sizes and low content. With the aid of age hardening heat treatment, nano-scaled α phases precipitate, leading to higher microhardness. But the tensile properties of Ti-55511 did not effectively improve because brittle fracture happens due to the precipitation of nano-scaled α phases, which have similar sizes with brittle ω phases. The brittle fracture behavior is more relevant to α phase sizes instead of their volume fractions. With aging temperature increasing, the sizes of nano-scaled α phases increase and the alloy brittleness slightly decreases.

Influence of build orientation on static and axial fatigue properties of maraging steel specimens produced by additive manufacturing

Additive manufacturing involves a layer-by-layer build-up of mechanical parts and it is a manufacturing technology that can be adopted with different engineering metal materials like steels, aluminium and titanium alloys. Aim of the present investigation is to analyse the influence of the build orientation on static and axial fatigue properties of maraging steel specimens manufactured by Direct Metal Laser Sintering (DMLS) of EOS metal powders. After manufacturing, some of the specimens were subjected to age hardening heat treatment (490 °C for 6 hours, followed by air cooling). Both heat treated and as-manufactured specimens have been built at 0° as well as at 90° orientation with respect to the specimen’s axis. Analyses of the crack initiation point are performed in order to investigate the fatigue failure mechanisms. Finally, the fatigue strength of the additively manufactured specimens was compared with that exhibited by vacuum melted specimens of the same steel reported in literature.

Evolution of microstructure and mechanical properties of coated Co-base superalloys during heat treatment and thermal exposure

New γ′-strengthened Co-base superalloys show an interesting potential for high temperature applications. However, protective coatings are needed as for Ni-base superalloys to ensure sufficient oxidation and corrosion resistance. Therefore the properties of a commercial coating on a multinary new γ′-strengthened Co-base superalloy have been studied. Especially the influence of the coating process on the substrate also after long term annealing is discussed. It was found that the highly deformed areas at the coating–substrate interface indicated by a high local misorientation and caused by the sandblasting process led to a recrystallization of the interdiffusion zone during the age hardening heat treatment. A chemical gradient of γ and γ′ promoting elements was found in the interdiffusion zone causing a change in hardness as measured by nanoindentation. Depending on the composition two separate recrystallized regions formed in the interdiffusion zone, one with single phase γ-(Co,Ni) and the other with a cellular two phase microstructure of discontinuously grown γ and γ′.