Hot Rolling Treatment Research Articles

Facile Preparation of High-Performance Reduced Graphene Oxide (RGO)/Copper (Cu) Composites Based on Pyrolysis of Copper Formate.

Graphene has attracted much interest in many scientific fields because of its high specific surface area, Young's modulus, fracture strength, carrier mobility and thermal conductivity. In particular, the graphene oxide (GO) prepared by chemical exfoliation of graphite has achieved low-cost and large-scale production and is one of the most promising for Cu matrix composites. Here, we prepared a high strength, high electrical conductivity and high thermal conductivity reduced graphene oxide (RGO)/Cu composite by directly heating the GO/copper formate. The oxygen-containing functional groups and defects of RGO are significantly reduced compared with those of GO. The tensile yield strength and thermal conductivity of RGO/Cu composite with RGO volume fraction of 0.49 vol.% are as high as 553 MPa and 364 W/(m·K) at room temperature, respectively. The theoretical value of the tensile yield strength of the composite is calculated according to the strengthening mechanism, and the result shows that it agrees with the experimental value. After hot-rolling treatment, the ductility and conductivity of the composite materials have been greatly improved, and the ductility of the RGO/Cu composite with RGO volume fraction of 0.49 vol.% has been increased to four times the original. This work provides a highly efficient way to fabricate a high-performance RGO-reinforced Cu composite for commercial application.

Evolutions of the microstructures and mechanical properties of TC18 titanium alloy processed by hot-rolling in β single-phase region

In this study, hot rolling treatment followed by water quenching was conducted on a TC18 titanium alloy in β single-phase region with varying reductions. Experimental evidences from X-ray diffraction and transmission electron microscopy indicate the formation of α phase, induced by sufficient stress and assisted by ω phase. In addition, the existence of α" phase and diffuse streaks were also observed during the hot working processing. Furthermore, dynamic recrystallization (DRX) including continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) was proved to exist in the hot rolling process. During the whole DRX process, with increasing the deformation degree, recrystallized grains nucleated preferentially at high-energy areas such as grain boundaries and shear bands, then accumulated and grew until achieving a complete recrystallization state. It should be noted that DDRX mainly occurred at the grain boundaries, while CDRX grains nucleated within the shear bands. The elongation gradually decreased and tensile strength gradually increased with the increment of the deformation degree.

An effective approach to improve microstructure and tribological properties of cold sprayed Al alloys

Abstract Cold spray is considered as an emerging technique for preparing wear-resistant metal matrix composite coatings on the surface of various kinds of metallic materials. In this work, a viable strategy of “cold spraying + hot rolling post-treatment” was successfully applied to prepare wear-resistant B4C/6061 Al composite coating on commercially available 6061 Al plates. The results revealed that hot rolling post-treatment results in uniform distribution of B4C particles in the alloy matrix, good inter-splat bonding, and sufficient plasticity in the splats through effective healing of the defects and splat boundaries in the as-sprayed deposit. As a result, the coating/substrate bonding strength in the hot rolled sample increased two-fold when compared with that of the as-sprayed sample. Moreover, hot rolling process resulted in much improved tribological properties of the coating with the wear rate ∼40% of that of the substrate. The obtained results indicated that the idea of combining cold spraying and hot rolling treatment is quite effective for improving the tribological properties of Al alloy plates. Further, this approach seems equally good for repairing/remanufacturing of unserviceable 6061 Al alloy components.

Hot-rolled Al-added medium Mn steel (Fe-8Mn-2.85Al-1Si-0.2C): Microstructural evolution and tensile behavior

In this study, a low Al (<3%) added medium manganese steel has been developed through melting casting route in an open-air induction furnace. The cast steel ingot has been intercritical annealed at 720 °C after hot deformation, that includes hot forging and hot rolling treatment, respectively. Microstructure characterization coupled with X-ray diffraction (XRD) has been performed after each processing step to understand the extent of austenite formation and its subsequent transformation to ferrite/martensite. The processed steel possesses the ultimate tensile strength, yield strength and ductility of 1000±20 MPa,700±10 MPa and 18.5 ± 0.5, respectively. To understand the possible cause of enhanced strength and deformation mode rietveld analysis has been carried out. It reveals that developed (final processed) steel possesses ∼18% (volume%) of austenite that subsequently reduced to ∼6.139% after tensile testing, indicating significant transformation of austenite to martensite (continuous and enhanced TRIP effect). The morphological characteristic of martensite in developed steel has been investigated using transmission electron microscopy (TEM). It reveals lath morphology of martensite due to low carbon content. The TEM and 3D atom probe analysis reveals the precipitation of intergranular type kappa (k) carbide in intercritically annealed specimens due to probable segregation of C and Al. However, volume fraction of the same is low. The SFE of the steel has been found to be ∼16 mJ m− 2, calculated by the modified Olson and Cohen method that also concludes TRIP is the preferred deformation mechanism in the developed steel.

Microstructure and corrosion behavior of Al-TiB2/TiC composites processed by hot rolling

The microstructure and corrosion behavior of Al-5 wt.% TiB2/TiC composites after hot rolling treatment were investigated by scanning electron microscope, immersion tests, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. The results show that corrosion of α-Al phase initiates at the interfaces between the matrix and the agglomeration clusters of TiB2 and TiC particles. After hot rolling deformation, the dispersive distribution of reinforcement particles and the grain refinement of the Al matrix suppressed the rapid expansion of corrosion pits, which become smaller and shallower, indicating that the corrosion resistance of Al-TiB2/TiC composites has been enhanced by hot rolling treatment.

Achieving strength-ductility synergy in cold spray additively manufactured Al/B4C composites through a hybrid post-deposition treatment

Cold spray additive manufacturing (CSAM) provides a potential solid state manufacturing route to fabricate variety of aluminum matrix composites (AMCs) with reduced possibility of undesired chemical reactions and residual thermal stresses. This study presents a hybrid (i.e. hot compression + hot rolling) post-deposition treatment to reinvigorate the mechanical properties of cold spray additively manufactured Al/B4C composites. The as-deposited samples were initially subjected to 30% thickness reduction via hot compression treatment at ∼500 °C followed by a hot rolling treatment with 40% thickness reduction in 2 passes. Electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM) results revealed that after hybrid post-deposition treatment (involving 70% accumulative thickness reduction), the aluminum grains in the matrix were extensively refined due to simultaneous operation of continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX). Furthermore, interfacial defects were remarkably reduced while the nature of Al/Al and Al/B4C interfacial bonding was changed from sheer mechanical interlocking to metallurgical bonding which facilitated efficient transference of applied load to uniformly dispersed bimodal B4C particles. As a result, ultimate tensile strength (UTS) and elongation (EL) of the as-deposited sample were simultaneously improved from ∼37 to 185 MPa and ∼0.3% to 6.2%, respectively.

In-situ Sip/A380 alloy nano/micro composite formation through cold spray additive manufacturing and subsequent hot rolling treatment: Microstructure and mechanical properties

Cold gas dynamic spray (cold spraying, CS) has emerged as a promising solid state manufacturing technique to fabricate thick metallic deposits with limited risk of oxidation, phase transformations and residual thermal stresses. As-sprayed deposits usually exhibit poor mechanical properties and often require post-spray heat treatments to reduce inter-splat defects. In most of the cases, traditional heat treatments offer limited benefits to rejuvenate the mechanical properties of the deposit. This preliminary work presents an effective way to modify the microstructure and improve the mechanical properties of cold sprayed A380 aluminum alloy. As-sprayed alloy deposits were subjected to hot rolling treatments with different thickness reductions. Results suggest that the hot rolled samples show better strength and ductility compared with their as-sprayed state. Microstructural evolution and resulting mechanical properties, at different processing conditions, were analyzed through optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), high resolution transmission electron microscopy (HRTEM) and tensile tests. Sample with thickness reduction of 40% displayed highest values of ultimate strength (UTS, 420 ± 2.1 MPa) and elongation (Elf, 5 ± 2.3%) compared with the corresponding values of as-sprayed (100 ± 13.4 MPa, 0%) and conventionally heat treated (186 ± 17 MPa, 0.93 ± 0.05%) samples. The improvement in mechanical properties of the rolled samples were mainly attributed to the progressive elimination/reduction of inter-splat defects together with in-situ composite microstructure formation. EBSD and HRTEM revealed that in-situ composite structure was formed through progressive refinement and uniform distribution of Si particles in α-Al matrix containing coherent θ′ precipitates.

Microstructure, texture and mechanical properties of a Mg– Gd–Nd alloy under different thermo-mechanical treatments

In current work, the influences of hot extrusion and rolling treatments on the microstructure and texture developments, as well as mechanical properties of Mg–1.5Gd– 1.5Nd (wt.%) alloy were investigated. It was shown that the alloy underwent completely dynamic recrystallization during thermal-mechanical processing, resulting in fine equiaxial grain structure. Especially for the hot rolling treatment that heavy deformation led to even smaller grain size of the alloy. Unlike the strong basal textures obtained in conventional Mg alloy sheets, the extruded and rolled alloy sheets both revealed modified basal texture with tilt of basal poles towards extrusion/rolling direction. Through orientation distribution function (ODF) analysis, the textures were deeply analyzed and two types of rare earth textures were obtained in the extruded and rolled alloy sheets. The variations in microstructure and texture played an important role in the mechanical properties, and also planar anisotropies of the alloy sheets.

Dynamic mechanical analyze of superelastic CuMnAl shape memory alloy

A new shape memory alloy was obtain from high purity Cu, Mn and Al elements using a induce furnace. The intelligent material present negative transformation temperatures and an austenite like state at room temperature. The austenite state of CuMnAl shape memory alloy present superelasticity property. Five kilograms ingot was obtain of Cu10Mn10Al alloy. From the base material (melted state) were cut samples with 6 mm thickness using a mechanical saw. After an homogenization heat treatment the samples were hot rolled through four passes with a reduction coefficient of 20%. Experimental lamellas were obtained with 1.5 mm thickness and 90x10 mm length and width. After the hot rolled treatment the materials were heat treated at 800°C for 20 minutes and chilled in water. Four samples, one just laminated and three heat treated by aging, were analyzed with a Netzsch DMA equipment to establish the elastic modulus and the internal friction values of the materials. Metallic materials microstructure was analyzed using a scanning electron microscope Vega Tescan LMH II type. After the aging heat treatment a decrease of internal friction is observed on the entire analyze range which is assigned to formation of Al-based precipitates that block the internal movement of the alloy characteristic phases.

Effect of deformation temperature on the ductile–brittle transition behavior of a modified 9Cr–1Mo steel

A modified 9Cr–1Mo steel received in normalized and tempered condition has been subjected to four different hot-rolling treatments at different rolling temperatures (1050°C, 1000°C, 950°C and 875°C) applying a constant true strain of ~0.7. The rolled plates were tempered and tested for tensile and Charpy impact properties following standard procedures. Hot-rolling increased the strength by more than 100MPa, but reduced the ductility of the steel by more than 10%. The ductile-to-brittle transition temperature (DBTT) was found to increase by more than 25°C after hot-rolling as compared to As-received steel. Among the rolled samples, the plates rolled at 950°C and 1050°C showed higher upper shelf energy (comparable to As-received steel), whilst the plate rolled at 1050°C showed the lowest DBTT. In terms of superior strength–toughness combination rolling at 1050°C can be considered to be optimum. The results have been analyzed considering the effect of rolling on parameters related to the microstructure and crystallographic texture of the steel, such as, effective grain size, ferrite fraction, fraction of low-angle boundaries, fraction of cleavage planes on the main fracture plane and the fraction of slip planes along the 45° to the main fracture plane.

Microstructure and mechanical properties of hot-rolled ZrB alloys

The microstructure, mechanical property behavior, and fracture characteristics of Zr–χB alloys (χ=0, 0.05, 0.3, 0.8wt%) obtained by casting and hot-rolling were investigated. Microstructural observation indicated that the dendritic equiaxed prior-β grain morphology was slightly elongated after hot-rolling treatment. The widths of the α lath of all the hot-rolled Zr–χB alloys were similar, and the length of the α lath decreased with increasing boron concentration. Tensile test results showed that the improved strength of the Zr–χB alloys can be primarily attributed to grain refinement. Strengthening the Zr–χB alloys could also be achieved by a shear-lag model mechanism because of the high strength and modulus of the ZrB2 whiskers. The refinement of the α lath and the presence of the ZrB2 whiskers were responsible for the reduced elongation-to-failure. Fractography indicated that fracture behavior strongly depends on the orientation of the ZrB2 whiskers. The effect of this orientation on the fracture mechanisms of the ZrB2 whiskers and the Zr–χB alloys was also discussed.

Triggering rare earth texture modification in magnesium alloys by addition of zinc and zirconium

Two Mg alloys, Mg–1Zn–1Ce–0.6Zr and Mg–1Zn–1Gd–0.6Zr (wt.%), were subjected to large strain hot rolling treatment, followed by annealing at different temperatures. Nucleation of recrystallization initiated inside shear bands and in the vicinity of particles, resulting in a panorama of orientations with varying stored energies. Recrystallization resulted in the evolution of new, softer orientations, in terms of slip, accompanied by significant texture weakening. On comparison with their respective binary counterparts, the quaternaries established the significant role played by the additional presence of non-rare earth (non-RE) elements (Zn, Zr) in augmenting the RE texture modification effect. Contrary to Mg–1Ce, deformation/recrystallization texture modification in Mg–1Zn–0.6Zr–1Ce was governed by a complex interplay between precipitate redissolution and segregation events. Moreover, compared to Mg–1Gd, the Mg–1Zn–0.6Zr–1Gd alloy revealed deformation/recrystallization texture transition at lower annealing temperature. Such a behavior was attributed to an increased tendency of RE–non-RE solute-pairing/clustering in the latter, thereby amplifying solute drag and magnifying selective growth events. Tensile tests conducted post-annealing revealed remarkable ductility improvement in the quaternary alloys over their binary equivalents.

Microstructure and porosity in thixomolded Mg alloys and minimizing adverse effects on formability

The purpose of this research is to investigate possible changes in warm formability of thixomolded Mg alloys by applying severe deformation processing. The microstructure of as-thixomolded magnesium alloys can be complex, as it can contain a variety of constituents such as Mg 17Al 12 intermetallic particles, shrinkage and gas porosity, as well as internal oxide films and entrapped residues. These inherent heterogeneities affect their fracture properties when these alloys are hot rolled to sheet or formed. It has been found in this research that dissolved gases and heterogeneities can adversely influence warm formability of the molded sheet, and contribute to variability in strength and ductility. Using thixomolded AM60 Mg (Mg–6%Al) plate from a commercial supplier, various heat treatments, hot rolling treatment and friction stir processing treatment were performed to introduce severe plastic deformation processing to alter microstructure. Macrostructure and microstructure resulting after these treatments demonstrated that for a given lot of thixomolded Mg plate, considerable changes in the microstructure, porosity and warm formability can be caused by stirring and severe deformation processing approach. The knowledge gained from this study could benefit thixomolding community, as well as Mg wrought materials applications in regard factors that affect formability of these materials.