High Strain Rate Rolling Research Articles

Effects of Ga on microstructure and mechanical properties of HSRRed Mg–Zn–Zr alloys

Effects of Ga alloying on microstructure and mechanical properties of Mg–6Zn–0.6Zr alloys and the mechanism have been explored. In addition to being solidly soluble in the α-Mg matrix, Ga also reacts with Zn and Zr to produce GaZr2 and Ga-riched Mg7Zn3 particles. The formation of these intermetallics consumes solute atoms in the α-Mg matrix which weakens its beneficial effect on the dynamic recrystallisation behaviour of the alloys. The Ga addition reduces both strength and ductility of the Mg–6Zn–0.6Zr alloy sheets produced by high strain rate rolling processing due to the bigger grain size and the decreasing degree of dynamic recrystallisation. The decline in ductility can also be ascribed to the existence of the coarse Ga-riched Mg7Zn3 particles.

The twins of α2 phase in β-solidifying TiAl alloy during high strain rate rolling

High strain rate rolling (HSRR) was successfully used to produce TiAl alloy sheets at average strain rate of 7.23 s−1. In present study, β-solidifying Ti-42Al-9V alloys were rolled with a single pass reduction of 80 % within (α + γ) double phase region at 1250 °C. The microstructure of the Ti-42Al-9V alloy sheet was mainly composed of fine needle-like β/γ mixture structure and the block α2 phase which was divided into different contrast by mechanical twins. As investigated, {1 1 2¯ 2}〈1 1 2¯ 3¯〉 contraction twins are the main component. And few {1 0 1¯ 2}〈1 0 1¯ 1¯〉 extension twins are generated in {1 1 2¯ 2}〈1 1 2¯ 3¯〉 primary contraction twins, namely {1 1 2¯ 2}-{1 0 1¯ 2} secondary twinning. Besides, multiple parallel twins and intersectional twins were activated.

Deformation microstructures and texture evolution of the Mg–Zn–Mn alloy with high strain rate rolling

Deformation microstructures and texture evolution of the Mg–Zn–Mn alloy with high strain rate rolling

Achieving Ultra-High-Strength and Good Ductility of the ZK60 Alloy Sheet by High Strain-Rate Rolling

Achieving Ultra-High-Strength and Good Ductility of the ZK60 Alloy Sheet by High Strain-Rate Rolling

High plasticity mechanism of high strain rate rolled Mg-Ga alloy sheets

• The mechanism of high plasticity of Mg-Ga alloy is revealed. • The activation of the non-basal slip leads to the high plasticity of Mg-Ga alloy. • Ga element can promote the activation of the non-basal slip • HSRR is the application of dislocation engineering in wrought magnesium alloys. By observing the microstructure evolution of Mg-Ga alloy during tensile deformation, it is found that the prismatic < a > slip and the pyramidal < c + a > slip occur during the tensile process at room temperature, which finally leads to the plenty of dislocation accumulation. After 8% tensile deformation, the { 10 1 ¯ 2 } extension twin is the main way to coordinate the strain in the c-axis direction for the alloy with the Ga content lower than 2 wt.%, but the pyramidal < c + a > slip is the main way to coordinate the strain along the c-axis direction for the alloy with the Ga content higher than 2 wt.%. The Ga addition can promote the activation of the non-basal slip, which is beneficial to the work-hardening of the alloy to achieve better plasticity. Dynamic precipitation can slightly reduce the increment of dislocations. The preparation method of high strain rate rolling (HSRR) is another important reason for the plasticity of magnesium alloy sheets, and it is an important embodiment of the application of the dislocation engineering concept in magnesium alloy. The non-basal dislocations derived from the HSRR deformation can provide the non-basal dislocation sources when magnesium alloy is deformed at room temperature, resulting in good ductility. This study can be used as a reference for preparing wrought magnesium alloy with high strength and high plasticity by Ga alloying and hot deformation. The initiation of the prismatic <a> slip and pyramidal <c+a> slip is the reason for the high plasticity of Mg-Ga alloy, and the Ga element can promote the activation of the non-basal slip. In addition, high strain rate rolling (HSRR) is another important reason for the high plasticity of magnesium alloy sheet, which is the embodiment of the application of dislocation engineering in wrought magnesium alloys.

Evolution of Subgrains, Dislocations, and Mechanical Properties in a 2524Al Alloy during High-Strain Rate Rolling

Evolution of Subgrains, Dislocations, and Mechanical Properties in a 2524Al Alloy during High-Strain Rate Rolling

Dynamic recrystallization, texture and mechanical properties of high Mg content Al–Mg alloy deformed by high strain rate rolling

The Al–Mg alloy with high Mg addition (Al–9.2Mg–0.8Mn–0.2Zr-0.15Ti, in wt.%) was subjected to different passes (1, 2 and 4) of high strain rate rolling (HSRR), with the total thickness reduction of 72%, the rolling temperature of 400 °C and strain rate of 8.6 s−1. The microstructure evolution was studied by optical microscope (OM), scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The alloy that undergoes 2 passes of HSRR exhibits an obvious bimodal grain structure, in which the average grain sizes of the fine dynamic recrystallization (DRX) grains and the coarse non-DRX regions are 6.4 and 47.7 μm, respectively. The high strength ((507±9) MPa) and the large ductility ((24.9±1.3)%) are obtained in the alloy containing the bimodal grain distribution. The discontinuous dynamic recrystallization (DDRX) mechanism is the prominent grain refinement mechanism in the alloy subjected to 2 passes of HSRR.

Effect of Heat Treatment on the Microstructure and Properties of High Strain Rate Rolled 7050 Aluminum Alloy

High strain rate rolling (HSRR) is developed to improve the strength, plasticity and stress corrosion resistance of 7050 aluminum alloy simultaneously. The volume fraction of the small-angle grain boundary in the HSRRed alloy sheet is 89.9%. TEM shows that the presence of dislocations and sub-grains promotes the precipitation of the second phase. The alloy in the T6 state has the highest strength (622 MPa) and the biggest elongation to rupture (20.6%), but poor corrosion resistance. The over-aged state shows the best corrosion resistance. The RRA state can achieve the tensile strength equivalent to T6 of 614 MPa, the highest yield strength of 561 MPa and corrosion resistance comparable to the over-aged state. TEM observation shows the existence of sub-grains and dislocations plays an important role in the nucleation of the second phase. The high strength can be attributed to the higher volume fraction of the precipitates, and the high plasticity can be attributed to the higher work hardening rate. The better corrosion resistance can be ascribe to the wider precipitate-free zones at the grain boundary and the presence of the larger size second phase particles.

Achieving high damping and excellent ductility of Al[sbnd]Mg alloy sheet by the coupling effect of Mg content and fine grain structure

Fine-grained Al-xMg (x = 4.5, 6.5 and 9.2, in wt%) alloy sheets with high damping capacity and excellent ductility are prepared by high strain rate rolling (HSRR). Both the damping capacity and the mechanical properties of the alloys are improved compared with the as-homogenized states and increase with the higher Mg content. The three AlMg alloys exhibit similar strain-amplitude-independent damping capacities and the Al-9.2 Mg alloy is a little bit higher. While the strain-amplitude-dependent damping capacity increases with increasing the Mg content in a large strain amplitude range. The as-HSRRed Al-4.5 Mg, Al-6.5 Mg and Al-9.2 Mg alloys exhibit the damping values (Q−1) of 0.0140 ± 0.0005, 0.0167 ± 0.0006 and 0.0178 ± 0.0008 at the strain amplitude of 1 × 10−3. Furthermore, a combination of high ductility (42.8 ± 1.5%), moderate strength (435 ± 2 MPa) are also achieved in the Al-9.2 Mg alloy. The improved damping capacity of the as-HSRRed Al-9.2 Mg alloy are mainly attribute to the low stacking fault energy and the movement of the extended dislocation, the latter of which interaction with Suzuki atmosphere and thus increases energy consumption which plays a dominant role in the damping mechanism of the as-HSRRed alloys. The results of the present study provide new ideas for the development of high damping alloys with high mechanical property.

Bimodal-Structured Al–Mg Alloy with High Strength and Ductility Processed by High Strain Rate Rolling at Medium Temperature

A bimodal grain distribution is generated in the Al-6.5Mg alloy deformed by high strain rate rolling (HSRR) at 320 °C, in which the fine grains with the average size of 2.1 μm and the coarse grains with the size of hundreds of microns containing ultrafine sub-grains are developed. The deformed microstructures are detected by transmission electron microscopy, X-ray diffraction and electron backscattered diffraction. High strength and considerable ductility are achieved in the HSRRed alloy and the high strength is ascribed to solution strengthening, grain (sub-grain) strengthening and dislocation strengthening. The grain (sub-grain) strengthening is the dominant contributor (~ 146 ± 6 MPa) for yield strength. The generation of new fine grains is primarily observed along the deformation bands related to the high Mg solid content and the high strain rate at 320 °C. The dynamic recrystallization related to the deformation bands is proposed to build the bimodal grain distribution for achieving high strength and considerable ductility. A bimodal grain distribution is generated in the Al–Mg alloy during the high strain rate rolling (HSRR), the formation of fine grains (FGs) is related to the strain-induced deformation bands (DBs). The HSRRed alloy exhibits higher strength and larger ductility than the alloy experienced the traditional rolling (TR).

Development of the fine-grained Mg-0.6Zr sheets with enhanced damping capacity by high strain rate rolling

Fine-grained Mg-0.6Zr sheets are successfully prepared by high strain rate rolling (HSRR) at different strain rates of 10, 20 and 30 s−1. Microstructure, mechanical properties and damping capacity of the as-rolled sheets are carefully investigated. The as-rolled Mg-0.6Zr alloys are featured with average grain size below 10 μm and have only a small amount of dislocation tangles. With the increasing rolling strain rate, the dynamic recrystallization (DRX) grain size increases and the basal plane texture is weakened, resulting in the increase of damping property but little change in mechanical properties. The damping mechanism of the fine-grained Mg-0.6Zr sheets fits with the Granato-Lücke theory.

Microstructures evolution, texture characteristics and mechanical properties of Mg-2.5Nd-0.5Zn-0.5Zr alloy during the high strain rate hot-rolling

The microstructures evolution, texture characteristics and mechanical properties of Mg-2.5Nd-0.5Zn-0.5Zr alloy processed by high strain rate rolling (HSRR) at different temperature were systematically investigated in the current study. The results showed that the initial material was approximately equiaxed grains (23.8 μm) with a large number of divorced eutectic Mg 12 Nd phases precipitated along grain boundaries in a continuous network. After HSRRed, the microstructure was obviously refined, and uniform distributed. The average grain size was refined to 3.63 μm (R673), 2.71 μm (R648) and 2.17 μm (R623), respectively, and corresponding percentage of recrystallization were 46.1%, 49.3% and 63.9%, respectively. R623, R648 presented a strong (0002) basal surface bimodal texture in the RD direction but this texture was in the TD direction in R673, all of which preferential orientation was at 66.3–90° region. An excellent combination of ultimate tensile strength (324 ± 2 MPa), the yield strength (298 ± 3 MPa) and the elongation (6.9 ± 1.5%) were achieved in a fine-grained (2.17 ± 1.17 μm) Mg-2.5Nd-0.5Zn-0.5Zr alloy prepared by HSRR at 623 K. The higher yield strength can be obtained by refinement strengthening, dislocation strengthening, precipitation strengthening and texture strengthening. • Fine-grained alloy sheets with superior properties (298 MPa for tensile yield strength) were achieved by HSRR. • The texture evolution, grain size refining mechanism and strengthening mechanism were analyzed in detail. • Mg-2.5Nd-0.5Zn-0.5Zr alloy sheet was prepared by the high strain rate rolling.

Dynamic Precipitation, Dynamic Recrystallization, and Texture Evolution of Mg-5Zn Alloy Sheets with Trace Ca and Sr Additions.

The effects of trace Ca and Sr addition on dynamic precipitates, dynamic recrystallization (DRX) behavior, and texture evolution of Mg–5Zn alloy sheets fabricated by high strain rate rolling (HSRR) were investigated by electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and X-ray diffraction (XRD). The Zn-rich precipitates formed with plate shapes, short-rod shapes, and near-spherical shapes, indicating that the most important function of adding Ca and Sr is to promote the precipitation process. The precipitate density increases, but the precipitate size and DRX volume fraction decrease with the addition of the alloying elements. It is concluded that the effects of combined Ca/Sr addition on promoting precipitation and refining precipitate size are more effective than that of single Ca addition, and the reduction in DRX volume fraction can be attributed to the inhibition of fine precipitation on the nucleation and growth of DRX. Moreover, the macro-texture intensity is mainly related to DRX as the DRX grains are much more randomly oriented than deformed grains. In addition, the texture intensity in DRX regions is primarily associated with the precipitates, which can inhibit DRX grain rotation due to their pinning effect on the grain boundaries.

Microstructure Characterization and Mechanical Properties of an AM60B Magnesium Alloy Sheet Prepared by the Double‐Pass High Strain Rate Rolling with Gradient Cooling

AM60B magnesium alloy sheets with excellent mechanical properties are prepared by a double‐pass high strain rate rolling (HSRR) with gradient cooling from 370 to 340 °C. A bimodal lamellar structure, consisting of fine dynamically recrystallized grains, shear bands and fine precipitates, is obtained after the second‐pass HSRR. Formation mechanisms of shear bands are studied in depth. The results show that the formation of shear bands are closely related to the high‐density intersected twin lamellae, boundaries of initial coarse grains and the extensive dynamic recrystallization (DRX), respectively. It is also clarified that the HSRR process of the coarse grained AM60B alloy is dominated in succession by the twinning deformation stage and the following shear bands flow stage. Dynamic precipitation behavior is induced in the double‐pass HSRR process. The DRX is promoted by fine precipitates, resulting in local refinement of the HSRR'ed microstructure. Moreover, the weak basal texture is obtained with peak intensity less than 10. The high‐density twins, DRX and shear bands are suggested as main causes for the basal texture weakening. An outstanding matching between tensile strength and ductility at room temperature are obtained owing to the bimodal lamellar structure and the weakened basal texture.

Effect of the Strain Rate on the Damping and Mechanical Properties of a ZK60 Magnesium Alloy.

High strain rate rolling (HRSS) of a ZK60 magnesium alloy at 300 °C with a strain rate from 5 s−1 to 25 s−1 was used to research the effect of the rate on the mechanical properties and damping capacity of the ZK60 alloy. The results show that as the strain rate increases, the tensile strength decreases from 355 MPa at 25 s−1 to 310 MPa at 5 s−1. Two damping peaks (P1 and P2) are detected in the high strain rate rolled ZK60 alloys at different strain rates. The P1 peak appears at low temperatures and is caused by grain boundaries sliding. The P2 peak appears at high temperatures and is caused by recrystallization. As the strain rate increases from 5 to 20 s−1, the dynamic recrystallization (DRX) volume percent rises and the dislocation density decreases, both of which cause the P1 peak to become more and more obvious, and activation energy rises. At the same time, the dislocation density decreases and leads to a decrease in the storage energy, which reduces the recrystallization driving force and shifts the P2 peak to high temperatures. When the strain rate reaches 20 and 25 s−1, DRX occurs fully in the sheet, so the activation energy of the P1 peak and the temperature where the P2 peak appears are basically equal.

Microstructure evolution and mechanical properties of the ZM61 alloy sheets under different pre-rolling and high strain rate rolling temperatures

Abstract

Ultrafine lamellar structure AM60B magnesium alloy sheet prepared by high strain rate rolling

The rolled sheet was successfully prepared for the as-cast AM60B magnesium alloy by using the high strain rate rolling (HSRR) in the temperature range of 310 °C – 370 °C. An ultrafine lamellar structure consisting of small angle grain boundaries was developed in the HSRRed sheet by the detwinning of high-density twins. The ultrafine lamellar structure was characterized by means of the high-resolution transmission electron microscopy technique, and the effect of temperature on the detwinning was analyzed. Furthermore, the morphological difference of the ultrafine lamellar structure and its effect on the mechanical properties of the rolled sheet were investigated. The results show that the dislocation motion, cross twinning, dynamic recovery and dynamic recrystallization have multiple interactions with the detwinning behavior in different modes. And the degree of detwinning and the post-rolling microstructure are greatly affected by the interaction. Dynamic precipitation of the second phase is induced by the HSRR process at 370 °C. Nano particles precipitate along twin grain boundaries and form the ‘precipitation band’. However, the detwinning is not affected by the ‘precipitation band’. In addition, it is also revealed from the results that a uniform and fine fully-lamellar structure is developed as the HSRR process is conducted at a medium temperature of 340 °C. Meanwhile, the alloy rolled at 340 °C has relatively optimal mechanical properties, and the strength and ductility are well balanced.

Microstructure, Texture Characteristics, Mechanical and Bio-Corrosion Properties of High Strain Rate Rolled Mg–Zn–Sr Alloys

Microstructure, texture characteristics, mechanical and bio-corrosion properties of the Mg–5Zn–xSr alloys (x = 0, 0.2, 0.6, 1.0) prepared by high strain rate rolling are carefully studied. A low level of Sr addition enhances dynamic precipitation of nano-scale MgZn2 particles in the as-rolled Mg–5Zn alloy, with 0.6%Sr showing the maximum efficiency. These high-density MgZn2 particles can pin grain boundaries of dynamic recrystallization grains and inhibit their growth. A low level of Sr addition (≤ 0.6%) enhances the (0002) basal texture, but 1.0%Sr is just the reverse. The as-rolled Mg–5Zn–0.6Sr alloy exhibits the best combination of ultimate tensile strength (359 MPa) and elongation to rupture (20%). The high strength can be attributable to a reduced grain size, precipitation and basal texture strengthening. The Mg–5Zn–xSr alloys exhibit excellent bio-corrosion resistance, but a minor Sr addition cannot bring about further bio-corrosion resistance improvement due to the multiple actions of grain size, DRX degree, dynamic precipitates and texture characteristics. The 0.6%Sr addition can greatly improve the strength of the as-rolled alloy at no expense of bio-corrosion resistance.

Degradation, stress corrosion cracking behavior and cytocompatibility of high strain rate rolled Mg-Zn-Sr alloys

The major obstacle of Mg alloys to the clinical applications is their rapid degradation behavior. In the present study, high strain rate rolling (HSRR) and Sr micro-alloying are conducted to improve bio-corrosion & stress corrosion cracking (SCC) resistance, reduce SCC susceptibility and enhance cytocompatibility of Mg-4Zn alloy. The effects on bio-corrosion & SCC resistance improvement are more pronounced with the higher Sr content (≤0.2%), attributable to grain refinement, the enhanced microstructural homogeneity and the more compact corrosion film. Sr addition can promote the cell growth at the early stage and improve the cell adhesion ability.

Effect of microstructures and textures on the anisotropy of mechanical properties of AZ31 magnesium alloy sheets subjected to high strain rate rolling

The AZ31 magnesium alloy sheets with different microstructures and textures were produced by high strain rate rolling (HSRR) at various temperatures and strain rates. Tensile tests were carried out on AZ31 magnesium alloy sheets along rolling direction (RD), transverse direction (TD) and 45° along the rolling direction (45° RD) at room temperature. The microstructures and textures were determined. The Schmid factors (SFs) contour lines were also calculated. The tilt angle of the c-axis towards the RD affects the anisotropy of tensile strength. For the AZ31 magnesium alloy sheets subjected to relatively low strain rate rolling, the anisotropy of yield strength is comparatively obvious, due to the elongated grains. When the loading direction is close to basal plane, prismatic slip is not favored during tension deformation at room temperature. The anisotropy of yield strength mainly depends on the critical resolved shear stress/Schmid factor (CRSS/m) ratios of second-order (2nd-order) pyramidal slip.