As-cast Grain Research Articles

The Influence of As-Cast Grain Size on the Formation of Recrystallized Grains and the Related Mechanical Properties in Al-Zn-Mg-Cu-Based Alloy Sheets.

The influence of as-cast grain size on recrystallization and the related mechanical properties of Al-Zn-Mg-Cu-based alloys was investigated. Grain sizes ranging from 163 to 26 μm were achieved by adding Ti, Cr and Mn, and ZnO nano-particles, which acted as heterogeneous nucleation sites. A decrease in the as-cast grain size led to a corresponding reduction in the recrystallized grain size from 54 to 13 μm. Notably, as-cast grain sizes below 100 μm provided additional nucleation sites at grain boundaries, allowing for a reasonable prediction of recrystallized grain size. Finer grains also contributed to enhanced mechanical properties, with yield strength increasing as recrystallized grain size decreased without significant loss of elongation. Additional strengthening was observed due to η-precipitates at grain boundaries, further improving the properties of fine-grained sheets.

A comprehensive investigation on the effect of SiCp on microstructure and mechanical properties of Mg–5Sb-based hybrid composites

Microstructural development, strengthening mechanisms, and mechanical properties of the newly developed Mg–5Sb-xSiCp (x = 0, 1, 3, and 5) composites were studied in both as-cast and extruded states. The microstructures of composites were composed of α-Mg, in-situ Mg3Sb2, and SiCp phases. The cooling curves display that Mg3Sb2 intermetallics form as the primary phase. During solidification, the SiCp acts as heterogeneous sites for both α-Mg and intermetallics formation. The increase in SiCp content (from 0 % to 5 %) modified the as-cast grain size from 827 μm to 411 μm with the improvement of yield strength (YS) (74–97 MPa). Also, the SiC addition to as-cast facilitates the formation of a randomized texture and a significant reduction in intensity from 13.121 mrd to 6.301 mrd for SiC-Free and 5 wt% added MMCs, respectively. Grain refining and recrystallization are characterized by electron backscatter diffraction (EBSD) analysis. Grain refinement via SiCp and hot extrusion leads to substantial structural refinement, resulting in a decrease in grain size from about 411 μm down to 3.92 μm for MMC with 5 wt% of SiC. Consequently, the best combination of the ultimate tensile strength (UTS) (∼244 MPa) and total elongation (∼8.9 %) was obtained for the hot extruded composite containing 3 wt% SiCp. The prevailing strengthening mechanisms are supposed to be particle strengthening mechanism in the as-cast condition and coefficient of thermal expansion (CTE), Orowan, and Hall-Petch mechanisms in the as-extruded condition. Obviously, adding SiCp and employing hot working lead to significant increase in ultimate compressive strength (from 180 MPa to 321 MPa for 5 wt%).

Effects of addition of Er and Zr on microstructure and mechanical properties of Al–Cu–Mn–Si–Mg alloy

Abstract The effects of addition of Er and Zr on the aging precipitation phase and mechanical properties in cast Al–Cu–Mn–Si–Mg alloy were studied. The addition of Er and Zr can refine the as-cast grains. The average grain size of as-cast alloy containing Er and Zr is 140.60 μm, while the average grain size of as-cast alloy without Er and Zr is 168.54 μm. After T6 heat treatment, the yield strength of the alloy containing Er and Zr reached 334.3 MPa, while the yield strength of the alloy without Er and Zr was only 284.3 MPa. After aging the strengthening precipitates of both alloys contain θ′ phase, Q′ phase and T phase. In the alloys containing Er and Zr the Al3(Er, Zr) phase with L12 structure precipitated during the solution process, which reduced the diameter of the θ′ phase during subsequent aging. After T6 heat treatment, the precipitation strengthening contributed 67.09 % and 61.31 % to the total strength of the alloy with Er, Zr and without Er, Zr, respectively.

Effect of Sc on the recrystallization behavior and mechanical properties of Al-Zn-Mg-Cu-Zr alloys under isothermal multidirectional compression

To better achieve grain refinement and further optimize the comprehensive mechanical properties of Al-Zn-Mg-Cu-Zr alloys, this paper investigates the effect of trace Sc on the recrystallization behavior of Al-Zn-Mg-Cu-Zr alloys under isothermal multidirectional compression (IMC) and the mechanical properties in two-stage aging state. It was discovered that the addition of Sc enhanced the tensile and yield strengths of the alloys by 3.8% and 4.3%, respectively, and simultaneously increased the elongation from 13.4% to 15.4%. The OM, EBSD and TEM techniques were used to characterize the microstructure of the alloy. The results showed that the Al3(Sc,Zr) phase produced by the addition of 0.25% Sc not only refines the grains, but also changes the recrystallization behavior of the alloy by pinning the dislocations and (sub) grain boundaries in the combination of IMC deformation. It inhibits the generation of geometric dynamic recrystallization (GDRX) grains and the nucleation of discontinuous dynamic recrystallization (DDRX) grains but promotes the formation of continuous dynamic recrystallization (CDRX) as the predominant mode of dynamic recrystallization. The alloy gains a finer grain structure by simultaneously promoting the formation and inhibiting the growth of recrystallized grains. As a result, the improvement in the overall mechanical properties of Al-Zn-Mg-Cu-Sc-Zr alloys brought about by the addition of Sc can be attributed primarily to the refinement of the initial as-cast grains, as well as fine-grain strengthening due to the inhibition of recrystallized grain growth and the Orovan strengthening of the nanoscale secondary phase Al3(Sc,Zr) itself.

Refined microstructure to improve the mechanical properties of the as-cast NiCoCr multi principal element alloy via mechanical vibration

The NiCoCr multi principal element alloy (MPEA) show excellent ductility at cryogenic temperatures and corrosion-resistance properties under the condition that it prepared by thermal–mechanical processing. However, the coarse as-cast grains negatively impact mechanical properties significantly and grain refinement is necessary for forming complex castings. Most grain refining methods need extra alloying elements, which may result in loss of ductility by brittle second phases. In this work, a significant microstructure refinement of the as-cast NiCoCr MPEA was achieved by pollution-free vacuum mechanical vibration, with the average grain size refined from the initial value of 620 μm to 140 μm. As a result, the room-temperature yield strength was increased by 54 % (from 255 MPa to 392 MPa) without loss of elongation compared to the as-cast condition without vibration.

Microstructure and Mechanical Behavior Comparison between Cast and Additive Friction Stir-Deposited High-Entropy Alloy Al0.35CoCrFeNi.

High-entropy alloys (HEAs) are new alloy systems that leverage solid solution strengthening to develop high-strength structural materials. However, HEAs are typically cast alloys, which may suffer from large as-cast grains and entrapped porosity, allowing for opportunities to further refine the microstructure in a non-melting near-net shape solid-state additive manufacturing process, additive friction stir deposition (AFSD). The present research compares the microstructure and mechanical behavior of the as-deposited AFSD Al0.35CoCrFeNi to the cast heat-treated properties to assess its viability for structural applications for the first time. Scanning electron microscopy (SEM) revealed the development of fine particles along the layer interfaces of the deposit. Quasi-static and intermediate-rate compression testing of the deposited material revealed a significant strain-rate sensitivity with a difference in yield strength of ~400 MPa. Overall, the AFSD process greatly reduced the grain size for the Al0.35CoCrFeNi alloy and approximately doubled the strength at both quasi-static and intermediate strain rates.

Discontinuous dynamic recrystallization behavior and texture evolution of large-size pure titanium flat ingot via electron beam cold hearth melting during short process direct hot rolling

Large-size pure titanium ingots melted by single electron beam cold hearth melting (EBCHM)) could be rolled into large-width and heavy-weight titanium strip coils using short process without forging. It is crucial to study the large-span refinement mechanism from highly coarse grains, whose sizes are in the order of ∼cm, to micronmeter. In this study, the recrystallization mechanism and texture evolution of pure titanium with a size of 1570 × 200 × > 8000 mm was investigated by multi-pass simulated rolling and experimental rolling. The results indicated the hot deformation can result in marked reduction in grain size of the as-cast grain, from 3 to 5 cm to 17–23 μm. The discontinuous dynamic recrystallization (DDRX) mechanism of a pure titanium ingot during direct multi-pass hot deformation causes the reconstruction of as-cast microstructure and refinement of hot rolling microstructure. Furthermore, DDRX occurred, during hot deformation, and was accompanied with weakening of deformation texture. Raising the initial hot deformation temperature results in a modification of the texture type of the {0001} crystal plane. The strength of the texture experiences a decrease initially and then eventually an increase. This alteration in strength is inversely related to the degree of dynamic recrystallization. Based on the simulated rolling experiment, the results of experimental rolling also found the coarse as-cast grains was broken and reconstructed. It has strength (average yield strength: 334 MPa, ultimate tensile strength: 371 MPa), ductility (total elongation: 30 %). Such a combination of mechanical properties makes the hot rolling plate a potential choice for sheet practical application.

Grain Refinement in 441 Ferritic Stainless Steel: High Versus Low Ti/Al Ratio after Casting and Hot Rolling

The effect of Ti/Al ratio (mass%) on the evolution of the microstructures after casting and hot rolling of Ca treated 441 dual stabilized ferritic stainless steel (FSS) was investigated in order to understand its effects on grain refinement mechanism. Industrially cast and lab simulated hot rolled samples, were subjected to similar processing conditions but with different Ti/Al ratios of 2.4 and 7.8. The microstructures and inclusions were analysed by the OM, SEM-EDS, SEM-EBSD and AzTecFeature software. The results showed that the steel with higher Ti/Al ratio exhibited finer grains after continuous casting and hot rolling, i.e., the initial finer as-cast structure resulted in finer grains and less substructure after hot rolling. The steel with higher Ti/Al ratio contained more Ti-rich complex inclusions and precipitates (especially TiN), which led to more heterogeneous nucleation of the -ferrite and grain refinement during solidification. On the contrary, the steel with low Ti/Al ratio exhibited coarser as-cast grain structure, less recrystallization and higher volume fraction of substructure after hot rolling. Therefore, it was deduced that the Ti/Al ratio is one of the essential parameters to achieving grain refinement in Ca treated 441 FSS during continuous casting.

As-Cast Grain Refinement of H13 Steel by Cerium Sulfide Formed During Solidification

As-Cast Grain Refinement of H13 Steel by Cerium Sulfide Formed During Solidification

Microstructure-strengthening correlation of 2219 Al alloy subjected to ultrasonic melt treatment, hot rolling and heat treatment

Improving strength while retaining good ductility is crucial for expanding the application of 2219 Al alloy. In this study, refined microstructure, excellent strength and ductility were obtained for the 2219 Al alloy under the combined effects of ultrasonic melt treatment (UMT), hot rolling and T6 heat treatment (HRT6). The mean grain size declined from 664.2 μm to 194.9 μm for the as-cast 2219 Al alloy after 240s UMT, with a refining efficiency of 70.7 %. Meanwhile, the Cu content in Al matrix was increased by 41.7 %, and the area fraction of reticular eutectic structure was accordingly lessened by 64.5 %. The nucleation of θʹʹ/θʹ-Al2Cu phase was actuated owing to the increased Cu content in Al matrix, resulting in more dispersive θʹʹ/θʹ-Al2Cu precipitates in the HRT6 alloy with UMT. Besides, the recrystallization was encouraged because the boundaries of refined as-cast grains provided more favorable nucleation sites, and the increased dispersive θʹʹ/θʹ-Al2Cu precipitates would inhibits the grain boundary merging during HRT6. Thus, the average dimension of the recrystallized grains was decreased to the lowest value of 71.3 μm in the HRT6 alloy with 240s UMT. Meanwhile, the ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) were enhanced to 456.2 MPa, 307.0 MPa and 16.7 %, and precipitation strengthening contributed the most to the YS enhancement. The improved ductility was mainly due to the increased deformation capacity induced by the refined grains and reduced stress concentration caused by the dispersive θʹʹ/θʹ-Al2Cu particles.

Microstructural evolution, high temperature tensile deformation behavior, and deformation mechanism in an Mg–Zn–Y–Ca–Zr alloy processed by multidirectional forging and hot rolling

To explore high temperature ductility, a new Mg-2.70Zn-1.34Y-0.37Ca-0.02Zr (wt.%) alloy has been fabricated by novel multidirectional forging (MDF) and hot rolling. The microstructure and mechanical properties were investigated. The average grain size of MDF + hot rolled alloy is 10.89 ± 0.90 μm refined from the as-cast average grain size of 60.03 ± 0.72 μm. The ultimate tensile strength of 260.51 ± 1.03 MPa, yield strength of 192.29 ± 1.21 MPa, and elongation of 17.83 ± 0.72 % were obtained at room temperature. For high temperature tensile behavior, microstructural examination revealed that continuous dynamic recrystallization and discontinuous dynamic recrystallization are the main softening mechanism in the temperature range of 573–673 K, while dynamic grain growth with bimodal grains and twins is discovered at 723 K in this alloy. X-ray diffraction and scanning electron microscopy –energy dispersive spectroscopy examinations revealed that the constituent phases are composed of α-Mg solid solution and intermetallic compounds of Ca2Mg6Zn3, Mg3YZn6 (I-phase), and Mg3Zn3Y2 (W-phase). The microstructural evolution, such as dynamic recrystallization and dynamic grain growth at desired tensile temperatures, is related to the thermal stability of constituent phases. The elongation to failure of 215.4 % was demonstrated at 673 K and 1.67 × 10−2 s−1, exhibiting high strain rate quasi-superplasticity. A power-law constitutive equation was established. The deformation activation energy of 177.948 kJ/mol and stress exponent of 4.494 revealed that the dominant deformation mechanism of this alloy at elevated temperatures of 573–723 K is dislocation climb controlled by lattice diffusion.

The effect of trace rare earth on grain size and properties of copper coating

Copper coating was fabricated by the forging process. The quasi-static properties of the coating were simulated by low power microscope, metallographic microscope, scanning electron microscope, bench Brinell hardness, and thermal simulation tester. The effects of rare earth on the as-cast grains, recrystallized grains, mechanical properties, and dynamic properties of the copper dome were studied. The experimental results show that the as-cast grains and recrystallized grains can be refined obviously by adding rare earth, and the mechanical properties can be improved in different amplitude. The samples with rare earth addition are more sensitive to strain rate and have higher yield strength at higher strain rate.

Optimizing microstructure and enhancing mechanical properties of Al–Si–Mg–Mn–based alloy by novel C-doped TiB2 particles

Grain size, grain orientation, the size and distribution of the precipitated phases are very important for the mechanical properties of particle reinforced aluminum matrix alloys. In this work, the effects of C-doped (C–TiB2) particles on the microstructure and properties of the Al–Si–Mg–Mn alloys were systematically studied. The results show that the as-cast grain size of (C–TiB2)/Al–Si–Mg–Mn alloy is refined to 29.7 μm by 0.5 wt% C–TiB2 particles, and the grain size instability due to static recrystallization can be effectively inhibited in the heat treatment progress after hot deformation, stabilizing the fine grain structure. Furthermore, 0.5 wt% C–TiB2 particles tend to distribute with the AlFeMnSi and Mg2Si phases, refining the size of precipitates. The C–TiB2 particles can also improve the geometrically necessary dislocation density and change the grain orientation of the T6 treated (C–TiB2)/Al–Si–Mg–Mn alloy, thus reducing the average value of the Schmidt factor and increasing the deformation difficulty. The above effects of 0.5 wt% C–TiB2 on the microstructure of the (C–TiB2)/Al–Si–Mg–Mn alloy cause the yield strength and the uniform elongation to synergistically improve by 13.8% and 18.7%, respectively, compared to the matrix alloy.

Secondary-phase Transformation of Duplex Stainless Steels during Industrial Manufacturing

A new type of lean S32205 duplex stainless steel was studied on its secondary phase formation during industrial manufacturing. Different from the common S32205 duplex stainless steels, such lean S32205 duplex stainless steels contain more carbon and nitrogen elements, which promotes the formation of Cr2N and Cr23C6 secondary precipitations. The secondary-phase transformation is preferred at boundaries, either in the ferrite phase or at interphase interfaces after rolling, and even a few secondary precipitates can be found at the as-cast ferrite grain interiors as well. The influence of the secondary phase transformations on pitting resistance and hot ductility was investigated.

Changes in microstructure and mechanical properties of 2219 Al alloy during hot extrusion and post-extrusion aging

2219 Al alloy is widely used in the aerospace industry owing to its outstanding properties. In this study, we evaluated the effects of the extrusion temperature and extrusion ratio on the microstructure and mechanical properties of extruded 2219 Al alloy specimens, including the changes during post-extrusion aging. In the extrusion temperature range of 380–500 °C, the mechanical properties of the bar after extrusion at 470 °C were the best. Furthermore, extrusion ratios up to 25:1 produced extruded rods with excellent mechanical properties and microstructure. Increasing the extrusion temperature increased the dissolution of the eutectic θ phase in the solid solution and accelerated the breakage of the inclusions contained Mn/Fe. Some larger and coarse as-cast grains were mechanically fractured during hot extrusion, with the fragments then rotated towards directions with high Schmid factors, thus forming banded dynamic recrystallization regions. The grain boundaries of the recrystallized grains were predominantly low-angle boundaries. The 2219 Al alloy aged at 170 °C for 16 h produced the densest and most uniform distribution of needle-like nanoscale θ′ phase inside the grains, resulting in an average hardness of 149 HV. Further increasing the aging time and temperature resulted in the aggregation and growth of θ′ phase precipitates.

Superplasticity in a coarse-grained as-cast magnesium alloy

Superplasticity of a coarse-grained cast Mg–2.5Gd–0.5Zr alloy was investigated by assessing the strain rate sensitivity index (m-value) through the shear punch testing (SPT) method in the temperature range of 623–748 K and shear strain rate range of 2.8 × 10−3–2.2 × 10−2 s−1. The initial as-cast grain size of about 150 μm was reduced to about 3.5 μm at the end of the test. This severe grain refinement caused by dynamic recrystallization (DRX) facilitated superplasticity in the studied cast alloy. According to the respective m-values of 0.51 and 0.53 obtained at 698 and 723 K, and the activation energy of 80 kJ mol−1, the prevailing mechanism of deformation was suggested as grain boundary sliding (GBS) controlled by grain boundary diffusion.

Microstructure Evolution and Localized Corrosion Susceptibility of an Al-Zn-Mg-Cu-Zr 7xxx Alloy with Minor Cr Addition.

Microstructure optimization of Al-Zn-Mg-Cu-Zr aluminum alloys, particularly through recrystallization inhibition, for improved strength and corrosion resistance properties has been an important consideration in alloy development for aerospace applications. Addition of rare earth elements, sometimes combined with Cr, has been found to be beneficial in this regard. In this study, the role of a single addition of 0.1 wt.% Cr on microstructure evolution of an Al-Zn-Mg-Cu-Zr (7449) alloy during processing was systematically investigated by optical light microscopy, scanning electron microscopy, electron backscatter diffraction and scanning transmission electron microscopy. Susceptibility to localized corrosion after aging to T4, T6 and T76 conditions was evaluated by potentiodynamic polarization (PDP) measurements and an intergranular corrosion (IGC) test. A decrease in recrystallized fraction with 0.1 wt.% Cr addition was observed, which is attributed to the formation of Cu- and Zn-containing E (Al18Mg3Cr2) dispersoids and the larger as-cast grain size. Moreover, the depletion of alloying elements from solid solution due to the formation of the Cu- and Zn-containing E (Al18Mg3Cr2) dispersoids and η Mg(Zn,Cu,Al)2 phase at its interface affects grain-boundary precipitation. The observed decrease in localized corrosion susceptibility with minor Cr addition is correlated with the microstructure and equally discussed.

Ultrasonic melt processing upon direct-chill casting of aluminium alloys

Ultrasonic melt processing (USP) has been known for decades for beneficial effects in as-cast aluminium alloys, including degassing, grain and structure refinement. In the last 10 years the authors performed a series of research projects dedicated to understanding the nature of these effects, by dedicated advanced experiments and by developing numerical models that adequately reflect the complicated physics involved, aiming at further optimising the technology so that it becomes feasible for scale-up applications and attractive for industrial use. Based on the main USP mechanisms previously studied by in-situ observations coupled with acoustic pressure measurements, i.e. fragmentation, deagglomeration and dispersion of the solid phases and inclusions, technological approaches are suggested and tested for grain refinement upon direct-chill casting of Al alloys. Results showed that USP in the melt flow in the launder significantly improves the as-cast structure of a billet, opening the way for upscaling.

High Strain Rate Quasi-Superplasticity Behavior in an Ultralight Mg-9.55Li-2.92Al-0.027Y-0.026Mn Alloy Fabricated by Multidirectional Forging and Asymmetrical Rolling.

To explore new approaches to severe plastic deformation and the ductility of a multicomponent magnesium-lithium alloy, an ultralight microduplex Mg-9.55Li-2.92Al-0.027Y-0.026Mn alloy was made by novel multidirectional forging and asymmetrical rolling, and the superplasticity behavior was investigated by optical microscope, hot tensile test, and modeling. The average grain size is 1.9 μm in this alloy after multidirectional forging and asymmetrical rolling. Remarkable grain refinement caused by such a forming, which turns the as-cast grain size of 144.68 μm into the as-rolled grain size of 1.9 μm, is achieved. The elongation to failure of 228.05% is obtained at 523 K and 1 × 10-2 s-1, which demonstrates the high strain rate quasi-superplasticity. The maximum elongation to failure of 287.12% was achieved in this alloy at 573 K and 5 × 10-4 s-1. It was found that strain-induced grain coarsening at 523 K is much weaker than the strain-induced grain coarsening at 573 K. Thus, the ductility of 228.05% is suitable for application in high strain rate superplastic forming. The stress exponent of 3 and the average activation energy for deformation of 50.06 kJ/mol indicate that the rate-controlling deformation mechanism is dislocation-glide controlled by pipe diffusion.

Hot deformation behavior of Sc/Nb modified AA2195 Al–Li–Cu alloys

The hot workability of third generation AA2195 (Al–Li–Cu–Ag–Mg–Zr) alloy with different Sc (0.15–0.25 wt%) and Nb (0.15–0.25 wt%) additions in the homogenized condition was investigated using processing maps approach. The additions of Sc and Nb were found to be beneficial in refining the as-cast grain size of AA2195 and changing the morphology from less dendritic grain structure to a globular or equiaxed form. Hot compression tests carried out in the temperature, T, range of 300–450 °C and strain rate, ε˙, of 10−3 – 10 s−1 were utilized to generate processing maps at a true strain, ε = 0.5. The flow curves of the alloys exhibit a typical dynamic recovery (DRV) characteristics and Arrhenius type constitutive equations successfully predicted flow stress of the alloys. The results obtained from the processing maps and complementary microstructural analysis of the deformed specimens revealed that 0.15 wt% additions of Sc and Nb (separately or in combination) are optimum to improve its workability. However, increasing Sc and Nb contents to 0.25 wt% relatively expanded flow instability regions. With the aid of the processing maps, deformed specimens microstructural analysis, activation energy and Zener-Hollomon parameter, Domain D-3 occurring at higher temperatures and strain rates were identified as the “safe” regimes for hot working of AA2195 with optimum Sc and Nb contents (0.15 wt% added separately or in combination). Limited pancake type grain morphology with higher fractions of dynamically recrystallized (DRX) grains was observed in Domain D-3. The microstructural manifestation in the flow instability regions was flow localization (at higher strain rates), cavities formation at the grain boundaries & precipitates, particles breakage and wedge cracking at the triple junctions at lower strain rates.