Hot-rolled Alloy Research Articles

Effects of grain size and Al-Mn phase on the corrosion performance of hot-rolled AZ31 magnesium alloy

Effects of grain size and Al-Mn phase on the corrosion performance of hot-rolled AZ31 magnesium alloy

Effect of hot-rolling process on the microstructure, mechanical and corrosion behaviors of dual-phase Co-based entropic alloys

Two compositions from dual-phase Co-based entropic alloys with high corrosion resistance were chosen, and the effect of hot-rolling process on the microstrcture, mechanical property and corrosion resistance was investigated in this work. The processing parameters were designed and optimized by CALPHAD calculations. For the case of hot-rolled alloys, fcc + hcp dual-phase structures were confirmed by different characterization techniques, including XRD, ECCI, and EBSD. After testing various mechanical properties and electrochemical corrosion behaviors at room temperature, the hot-rolled alloys exhibit an outstanding mechanical and corrosion resistance property. The hot-rolling process improves the electrochemical corrosion resistance slightly and promotes hardness as well as strength-ductility greatly. The experimental characterizations provide plentiful information about microstructure, crystallographic orientation, lattice misorientation, grain boundaries, and so on. More details for the strengthening and hardening mechanisms could be obtained from the EBSD analysis. The current work shed lights on the design of new alloy recipe as well as the synthesis of novel grade dual-phase entropic alloys with excellent combination of mechanical properties and corrosion resistance which could be applied in harsh environments.

The microstructure and mechanical properties of the laser-welded joints of as-hot rolled AlCoCrFeNi2.1 high entropy alloy

AlCoCrFeNi2.1 hot-rolled eutectic high entropy alloys were welded by laser welding, yielding a free-defect laser-welded connection. With the use of optical microscopy, EDS, EBSD, and XRD, the microstructure of the base metal (BM), fusion zone (FZ), and heat-affected zone (HAZ) of the joint was examined. The produced joint underwent tensile and micro-hardness testing as well as a fracture morphology examination. A similar tensile strength in the FZ and BM is measured, while a decrease in the elongation. The typical layered lamellar structures, in particular an FCC + BCC dual-phase structure, were all visible in the HAZ, BM, and FZ zones. The α-fiber and γ-fiber as well as other textures are determined by the ODF figure, indicating a potential orientation distribution of the as-hot rolled AlCoCrFeNi2.1 joint. A clear grain refinement characteristics in the fusion zone as a result of the uneven thermal cycling during the welding process. The results of the mechanical test demonstrate the base metal has the highest hardness value, i.e. 500–550 HV0.2, within the welded joint zone. The welded joint has a tensile strength ∼1200 MPa, which is marginally higher than ∼1150 MPa in the base metal, and an elongation that decreases by 20 % from base metal to welded joint, indicating a decrease in the plasticity of the welded joint. A combination of brittle and ductile fracture occurs in welded joints during tensile failure. This study may give possibilities for the engineering application of laser welding of AlCoCrFeNi2.1 eutectic high entropy alloy in the future.

Mechanical properties and stability of hot rolled Zn-0.8Mg alloy

Insufficient mechanical strength and mechanical instability are important factors limiting the application of zinc-based alloys as biodegradable materials. Currently, alloying and plastic deformation are effective methods to improve material properties. Therefore, this paper investigates the effect of hot rolling process on the mechanical properties and stability of Zn-0.8Mg alloys. The results show that after hot rolling, the internal grain of Zn-0.8Mg alloy is refined, the second phase is precipitated, the weaving strength is enhanced, and the overall mechanical properties are significantly improved. The contribution of deformation strengthening can reach about 90 %. The tensile strength, yield strength, and elongation of the alloy were 312.3 MPa, 249.5 MPa, and 15.6 % (141.72 %, 155.96 %, and 189.96 %, respectively) at a rolling volume of 70 %, which meets the clinical criteria for degradable material implants. However, this treatment reduced the stability of the mechanical properties of the Zn-0.8Mg alloy. During natural ageing, a small amount of Mg2Zn11 phase precipitated inside the alloy, reducing the elongation. Compared with cast alloys, hot rolled alloys have higher grain boundary density, which accelerates the precipitation of secondary phases, leading to more pronounced changes in the mechanical properties of the alloys after hot rolling.

Investigations on the influence of hot rolling on the creep characteristics of additively manufactured Mg-5Ag alloy

The requirement for lightweight materials that can survive increasingly severe conditions for aerospace components has fueled the research on magnesium alloys. The current work investigates the influence of hot rolling on the creep characteristics of the Mg-5Ag alloy that is fabricated through a selective laser melting process. The creep properties of parent material (PM) and hot-rolled specimens (HRA) are determined by indentation creep tests at 250 °C, 275 °C, and 300 °C. The microstructural evolution, phase transformation kinetics, and texture evolution were deduced using instrumental analysis, including SEM, EBSD, TEM, and XRD. The specimen PM features α-Mg grains with intermetallic Mg-Ag particles along grain boundaries and random grain orientations with low-angle boundaries. However, specimen HRA has a more fraction of Mg-Ag precipitates, a dominant (0001) grain orientation, and higher peak intensity from the (002) plane. The HRA specimen also demonstrates higher apparent activation energies, attributed to microstructural changes from hot rolling. The results show that the creep resistance of the hot rolled Mg-5Ag alloy is superior to as-fabricated Mg-5Ag alloy based on the creep velocity, stress exponent, and apparent activation energy.

Influence of hydrogen ingress and capture on the mechanical properties of spray formed 2195 aluminum alloy

The current research has focused on the hydrogen capturing and its impact on the mechanical properties of spray-formed 2195 (SF2195) aluminum alloy. Microstructure characterization, thermal desorption spectra (TDS) and hydrogen trapping of characteristic microstructure, are used to investigate the generation, migration and trapping of hydrogen. The retention of moisture in the carrier gas is believed to induce high concentration of hydrogen and the amorphous Al2O3 layer within the SF2195 billet, and the local retention of carrier gas brings about pores with the Al2O3 layer on the inner wall. High concentration of hydrogen is captured in the hot-rolled alloy while around 60 % of the hydrogen can be eliminated during the solution-quenching. Particles of T1 phase trap large quantity of hydrogen and the high-density dislocations developed from the pre-stretch promote the migration of hydrogen towards dispersoids and precipitates. The presence of hydrogen and Al2O3 layer contributes to the reduced plasticity of SF2195 alloy. The spreading of flattened pores can induce intensified hydrogen damage effect in local regions and thus contribute to the unusually decreased ductility along the thickness direction in the T8 aged alloy.

Oxidation of additive manufactured 699XA Ni-based alloy under different atmospheres

The oxidation behaviour of an additively manufactured (AM) NiCrAl alloy (VDM® Powder 699XA) was compared with the hot rolled counterpart in different atmospheres (dry air, Ar-10 %H2 and Ar-10 %H2-10 %H2O) for 48 h at 950 and 1100°C. Internal oxidation occurred through the twin boundaries and dislocations in the AM material. Such defects promoted the outward diffusion of Al and the growth of a protective Al2O3 scale at reduced PO2 (Ar-10 %H2 and Ar-10 %H2-H2O), hence restraining the internal oxidation. It is thus demonstrated that this high Cr-containing alloy is a marginal alumina former under controlled conditions like the hot rolled alloy.

Research on Microstructure, Mechanical Properties, and High-Temperature Stability of Hot-Rolled Tungsten Hafnium Alloy.

W-(0, 0.1, 0.3, 0.5) wt.% Hf (mass fraction, wt.%) materials were fabricated by the powder metallurgy method and hot rolling. The microstructure, mechanical properties, and high-temperature stability of alloys with varying compositions were systematically studied. The active element Hf can react with the impurity O segregated at the grain boundary to form fine dispersed HfO2 particles, refining the grains and purifies and strengthening the grain boundary. The average size of the sub-grains in the W-0.3 wt.% Hf alloy is 4.32 μm, and the number density of the in situ-formed second phase is 6.4 × 1017 m-3. The W-0.3 wt.% Hf alloy has excellent mechanical properties in all compositions of alloys. The ultimate tensile strength (UTS) is 1048 ± 17.02 MPa at 100 °C, the ductile fracture occurs at 150 °C, and the total elongation (TE) is 5.91 ± 0.41%. The UTS of the tensile test at 500 °C is 614 ± 7.55 MPa, and the elongation is as high as 43.77 ± 1.54%. However, more Hf addition will increase the size of the second-phase particles and reduce the number density of the second-phase particles, resulting in a decrease in the mechanical properties of the tungsten alloy. The isochronal annealing test shows that the recrystallization temperature of W-Hf alloy is 1400 °C, which is 200 °C higher than rolling pure tungsten.

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.

Comparative analysis of the effect of magnesium and zinc on the structure and mechanical properties of hot-rolled and cold-rolled alloy Al–2%Cu–1.5%Mn sheets

Comparative analysis of the effect of magnesium and zinc on the structure and mechanical properties of hot-rolled and cold-rolled alloy Al–2%Cu–1.5%Mn sheets

Microstructural Characterization, Tribological and Corrosion Behavior of H111 Hot-Rolled AA5754 after Homogenization and Aging.

In this study, the microstructural properties, wear resistance, and corrosion behavior of H111 hot-rolled AA5754 alloy before heat treatment, after homogenization, and after aging were examined. The microstructure was mainly composed of the scattered forms of black and gray contrast particles on the matrix and precipitations were observed at the boundaries of the grain. The as-rolled material exhibited a dense pancake-shaped grain structure, which is typical of as-rolled material. Observation along the L-direction did not yield distinct demarcations among the grains and was not uniformly distributed, with precipitates at the grain boundary. When they aged, there was a parallel increase in fine and huge black and gray contrast particles in the zone. Therefore, it could be stated that the amount of fine grains increased due to the rise in the homogenization process. The rolled base metal with the grain orientation was found to be parallel to the rolling direction. On the other hand, the coarse grains were clearly observed in the aging heat-treatment condition. The grains had an elongated morphology consistent with the rolling process of the metal before the heat-treatment process. The aged alloy had the highest hardness with a value of 86.83 HB; the lowest hardness was seen in the alloy before heat treatment with a value of 68.67 HB. The weight loss and wear rate of this material at the end of 10,000 m were, respectively, 1.01 × 10-3 g and 5.07 × 10-9 g/Nm. It was observed that the alloy had the highest weight loss and worst wear resistance before heat treatment. Weight loss and wear rates at the end of 10,000 m were, respectively, 3.42 × 10-3 g and 17.08 × 10-9 g/Nm. According to these results, the friction coefficients during wear were parallel and the material with the lowest friction coefficient after aging was 0.045. While the alloys corroded after aging showed more weight loss, the alloys corroded before heat treatment exhibited better corrosion behavior. Among the alloys, the least weight loss after 24 h was observed in the alloy that was corroded before heat treatment and this value was 0.69 × 10-3 mg/dm2. The highest weight loss was observed in the aged alloy with a value of 1.37 × 10-3 mg/dm2. The alloy before heat treatment, which corroded after casting, showed the lowest corrosion rate with a value of 0.39 × 10-3 mg/(dm2·day) after 72 h. The alloy that was corroded before heat treatment showed the best corrosion behavior by creating a corrosion potential of 1.04 ± 1.5 V at a current density of -586 ± 0.04 μA/cm2. However, after aging, the corroded alloy showed the worst corrosion behavior with a corrosion potential of 5.16 ± 3.3 V at a current density of -880 ± 0.01 μA/cm2.

Investigating the corrosion mechanism of AZ31 alloy bimodal microstructure by the quasi-in-situ EBSD characterization and DFT calculation

The grain characteristic and orientation were analyzed using the electron backscatter diffraction (EBSD) for AZ31 hot-rolled alloys. The corrosion initiation of the bimodal microstructure is revealed for the hot-rolled AZ31 alloys obtained by the quasi-in-situ EBSD, showing the preferential corrosion in the fine grain region. Meanwhile, the non-basal crystal plane grain is easier to corrode than the basal crystal plane grain. The adsorption energies of H2O molecule on the crystal planes of magnesium matrix were calculated by the density functional theory method, and a new insight into the corrosion anisotropy of crystal planes was proposed from the surface adsorption energy.

Effect of Annealing and Double Aging on the Microstructure and Mechanical Properties of Hot-Rolled Al17Cr10Fe36Ni36Mo1 Alloy

Effect of Annealing and Double Aging on the Microstructure and Mechanical Properties of Hot-Rolled Al17Cr10Fe36Ni36Mo1 Alloy

Strength-ductility synergy and anisotropy evolution of Cu-Be sheets with different Be contents

This study examines the evolution of mechanical properties and texture of hot rolled Cu-Be alloy sheets with varying Be content. The Cu-3.0Be alloy exhibits superior performance attributed to its fine grain structure, weaker texture, and lower dislocation density.

Effect of annealing treatment of hot-rolled AZ31 magnesium alloy on properties and stress corrosion resistance of MAO coatings

PurposeThis study aims to study the formation mechanism of micro-arc oxidation (MAO) coating on AZ31 magnesium alloy and how the annealing process affects its corrosion resistance.Design/methodology/approachThis study involved immersion experiments, electrochemical experiments and slow strain rate tensile experiments, along with scanning electron microscopy, optical microscopy observation and X-ray diffraction analysis.FindingsThe findings suggest that annealing treatment can refine the grain size of AZ31 magnesium alloy to an average of 6.9 µm at 300°C. The change in grain size leads to a change in conductivity, which affects the performance of MAO coatings. The MAO coating obtained by annealing the substrate at 300°C has smaller pores and porosity, resulting in better adhesion and wear resistance.Originality/valueThe coating acts as a barrier to prevent corrosive substances from entering the substrate. However, the smaller pores and porosity reduce the channels for the corrosive solution to pass through the coating. When the coating cracks or falls off, the corrosive medium and substrate come into direct contact. Smaller and uniform grains have better corrosion resistance.

Influence of gradual stress relieving on the microstructure, texture development, grain structure and orientation of the hot-rolled Ti6Al4V–5Cu alloy

In order to investigate the influence of gradual stress relieving treatment on the microstructure, texture evolution, grain structure, and misorientation distribution of the hot-rolled Ti6Al4V–5Cu (α+β) alloy deformed in various thickness reduction ratios (TRR's) of 15%, 58%, and 73% to maintain the burger orientation relationship (BOR), different stress reliving treatment was specially designed for relieving the residual stresses occurred due to the hot deformation process. Using IPF maps, the majority of the α grains, specifically the elongated ones were found nearly at 45 ° with respect to the rolling and transverse direction. The study also show that the heat treatment schedule on the 58% deformed alloy significantly promote the transformation of β to α phase and a special microstructure with an equiaxed grains is produced. The local misorientation angle distribution due to stress reliving treatment has also discussed. Using EBSD analysis, the alloy processed under highest TRR's (i.e., 73%) and subsequent stress relieving treatment could result a serious internal crystalline instability with various degree of element diffusion rate, which promote a severe and ease of alloy coarsening. Thus, coarsening encourage the formation of grains with the highest softening potential, comparatively. It is obvious that the stress-relived treatment does not result a change in microstructure. However the internal residual stresses on the hot deformation were relieved, the texture intensity had increased quietly. A significant textural behavior could be achieved on the 73% hot-rolled alloys by the stress-relieving process to align the α/β fiber texture interface in parallel coincidence to maintain the BOR.

Study on anisotropic mechanical behavior of AZ31 magnesium alloys under free-end torsion

In this study, the mechanical behavior and microstructure of a hot-rolled AZ31 magnesium alloy sheet under free-end torsion with torsional axis along rolling direction (RD), normal direction (ND) and 45° in ND-RD plane, have been investigated both experimentally and numerically. The mechanical behavior under torsion, including stress-strain response, Swift effect and strain hardening rate, present obvious anisotropy. The Swift effect is sensitive to the direction of torsion axis and exhibits remarkable anisotropy with axial elongation in ND sample and axial shortening in RD and 45° samples. The axial elongation or shortening is determined by both slips and extension twin, with extension twin exerting a greater influence on the extent of the axial deformation. During shear straining, the dominant deformation mode transforms basal slip to prismatic slip with the axial direction deviating from ND to RD, while the second-order pyramidal ⟨c+a⟩ slip is nearly not activated during whole deformation attributed to its high critical resolved shear stress. Based on the effective Schmid factor (ESF) of deformation modes, the grains with favored orientation would get activation of {101‾2} extension twin due to the high ESF, resulting in the different twin volume fractions. Additionally, the activation of twin relative to basal slip has a connection with the increasing trend of normalized strain hardening rate.

A Study of {10-12} Twinning Activity Associated with Stress State in Mg-3Al-1Zn Alloy during Compression

An eight-sided prism sample, obtained from a hot-rolled AZ31 magnesium alloy sheet, was compressed at room temperature along the transverse direction to investigate the influence of local strain on twinning behavior using electron backscatter diffraction (EBSD) measurements, hardness distribution, and metallographic observations. The octagonal surface of the sample was divided into distinct regions based on hardness distribution and metallographic observations. Combined analysis of the Schmid factor (SF) and the strain compatibility factor (m’) was employed to study twin variant selection. Basal on SF ratio distribution, the Schmid factor criterion, can predict over 75% of observed twin variants in regions A and D (normal stress samples). In contrast, 64% of twin variant selection behavior in region C (shear stress sample) can be effectively explained using a pure shear model. Twin variants with high strain compatibility factors may prefer activation to reduce stress concentration. The strain compatibility factor is more appropriate than the Schmid factor for analyzing the effect of local strain on the selection behavior of twin variants.

3D characterization of splits in tested fracture mechanics specimens using X-ray computed tomography

Splits are delaminations that may appear perpendicular to the crack plane during fracture toughness tests of certain materials, such as hot-rolled metal alloys. X-ray computed tomography (CT) was used to conduct a 3D analysis of the geometrical and morphological characteristics of the splits in SE(B) specimens machined from a DH36 steel. Tomograms and 3D reconstructions of the CT results were compared with high-resolution images obtained through optical microscopy (OM) and scanning electron microscopy (SEM). Quantitative and qualitative comparisons revealed a good agreement between the results, validating the split characterization by CT. It was discussed whether characterizing the splits just by the routinary fracture surface observation conducted in fracture mechanics specimens can hide important phenomena such as plane changes, branching, and interactions between delaminations. On the other hand, CT enables an accurate and comprehensive characterization of the morphological and geometrical attributes of splits. Contrasts between the analysis and characteristics of deformed and undeformed splits were made. Finally, the limitations and challenges of the 3D split characterization by CT were also discussed, exploring experimental and image processing issues. These findings emphasize that a more thorough understanding of the internal structure of splits can be achieved by applying CT analysis, contrasting with traditional fracture surface examination. This study highlights the relevance of CT in revealing hidden complexities within the internal structure of specimens with splits.

Enhancing mechanical strength, tribological properties, cytocompatibility, osteogenic differentiation, and antibacterial capacity of biodegradable Zn-5RE (RE = Nd, Y, and Ho) alloys for potential bone-implant application

Degradable zinc (Zn) based metals exhibit great promise as potential load-bearing bone-implant materials due to their suitable biodegradability, good fabricate-friendliness, biocompatibility, and favorable osteogenesis-promoting capacity. Nevertheless, most as-cast Zn-based metals display poor mechanical properties due to their coarse grain size and few slip systems, which is challenging to meet bone-implant application requirements. Herein, the alloying using rare earth (RE) elements of neodymium (Nd), yttrium (Y), and holmium (Ho) combined with hot-rolling was used to prepare the hot-rolled (HR) Zn-5RE binary alloys for load-bearing bone fixation or bone repair applications. HR Zn–5Y sample demonstrated the best mechanical properties matching with an ultimate tensile strength of ∼260 MPa, yield strength of ∼200 MPa, elongation of ∼43.5%, strength-elongation product of ∼11.3 GPa%, and macro-hardness of ∼104.7 HB among the HR samples, close to the requirements of mechanical properties for degradable bone-implant materials. HR Zn–5Y sample exhibited the lowest corrosion rate of ∼178 μm/y measured by electrochemical polarization testing, the degradation rate of ∼29 μm/y measured by static immersion testing, and high tribological properties in Hanks’ solution. The diluted Zn–5Y extract showed an appropriate cytocompatibility to 3T3 and MG-63 cells and moderate osteogenic differentiation ability to 3T3 cells among HR Zn-5RE and pure Zn extracts. Meanwhile, the HR Zn–5Y sample showed a suitable and effective antibacterial capacity against S. aureus and E. coli. Overall, the HR Zn–5Y sample is a promising moderate load-bearing bone-implant material for bone pins, plates, and guiding bone regeneration membrane application.