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By observing the microstructure evolution of Mg-Ga alloy during tensile deformation, it is found that the prismatic slip and the pyramidal 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 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 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.

Effects of Zn addition (0, 0.5, 1.0 and 1.5 wt%) on dynamic recrystallization (DRX) behavior of Al-9.2Mg alloy during high strain rate rolling (with rolling temperature of 400 °C and strain rate of 8.6 s−1) are carefully investigated. The Zn content plays a significant role in the enhanced DRX of Al-9.2Mg alloy. The critical strain (ec) and the peak strain (ep) are reduced from 0.178 ± 0.002 to 0.102 ± 0.001 and 0.211 ± 0.003 to 0.139 ± 0.002 with the Zn content increasing from 0 to 1.5%, respectively. Almost complete DRX grains are obtained in the Al-9.2Mg-0.5Zn alloy. The DRX volume fraction (FDRX), the average DRX grain size (AGS), the volume fraction of high-angle grain boundaries (FHAGBs) and the average grain boundary angle (θAV) are 91.5%, 5.6 μm, 91.1% and 37.6 o, respectively. The Zn addition can enhance the formation of deformation bands (DBs) and promote the DRX process by providing the nucleation sites for new grains, while the increased dynamic precipitates inhibit DRX. Continuous dynamic recrystallization (CDRX) is the dominant DRX mechanism, while discontinuous dynamic recrystallization (DDRX) is also existent. Effects of Zn addition on DRX process of the Al–Mg alloys can be ascribed to the more DBs, the reduced stacking fault energy (SFE) and the dynamic precipitates.

The as-solutionized Mg-4Zn alloys, one candidate material for biological implantation, are featured with the Portevin-Le Chatelier effect during the tensile testing with strain rate of 6.67 × 10−7 s−1, which leads to the higher corrosion rate and the acceleration of stress corrosion cracking. With the increase of the strain, new slip bands are generated and the proliferation of dislocations is very rapid in slip bands. The microgalvanic corrosion occurs between the slip bands (anode) and the low dislocation density region (cathode). The 0.1 wt% Sr addition can reduce the impact of the Portevin-Le Chatelier effect on as-solutionized Mg-4Zn alloy, resulting from the inhibition of twin, the better grain coordination deformation ability, and the lower density of geometrically necessary dislocations.

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.

The effects of Ga addition (1, 2, 3 and 5 wt-%) on the corrosion behaviour of high strain rate rolled Mg–Ga alloys are firstly investigated by weight loss measurement and electrochemical testing. S...

The work uses the optical microscopy (OM), scanning electron microscopy (SEM), tensile testing, immersion testing, and electrochemical measurement to analyze the effects of the Zn addition (0, 0.3, 0.6, 0.9 and 1.2 mass%) on microstructure, mechanical, and corrosion performance of the as-solutionized Mg-5Ga alloy. The addition of Zn can bring about finer grain size, higher tensile strength, and bigger breaking elongation in the Mg-5Ga alloy. The as-solutionized Mg-5Ga-1.2Zn alloy shows optimal comprehensive mechanical performance with the ultimate tensile strength of 260 ± 2.4MPa and ultra-high plasticity (the breaking elongation of 40.3 ± 0.3%). Grain refinement and solution strengthening are mainly conducive to the improvement in strength. Moreover, adding Zn element enhances anticorrosion property of the as-solutionized Mg-5Ga alloy, wherein the as-solutionized Mg-5Ga-0.9Zn alloy has the optimal anticorrosion property in 3.5% NaCl solution, in close relation with finer grain size and more protective corrosion film.

Effects of Zn content (0–1.5, in wt.%) on damping capacities of the as-homogenised and the hot-rolled Al–9.2Mg alloys are investigated. The Zn addition plays a significant role in the strain-amplit...

The dynamic recrystallization (DRX), precipitation and texture evolution of the ZK60 alloy sheets rolled at 300 °C with different strain rates were studied, and the effects of texture on the plasticity were also clarified. The DRX grain sizes at five strain rates (5–25 s−1) are 1.4 μm, 1.2 μm, 1.8 μm, 2.4 μm and 2.8 μm, respectively, while the DRX volume fractions are 35.8%, 75.0%, 82.0%, 88.0% and 93.0%, respectively. The maximum intensity values of the (0002) texture are 7.91, 8.22, 7.64, 5.76 and 5.34 at five strain rates, respectively. The strongest (0002) texture is observed at the strain rate of 10 s−1, which is related to the relatively low DRX volume fraction and the precipitation density. The tensile strength (UTS) and yield strength (YS) increases firstly and then decreases, while the elongation (EL) gradually increases with increasing the strain rate, suggesting that the plasticity of the alloy sheet can be improved by decreasing the basal texture intensity and increasing the dispersion degree of the basal texture. The optimal comprehensive mechanical properties are obtained at the strain rate of 10 s−1, with UTS of 358 MPa, YS of 291 MPa and EL of 21.5%. The DRX grain sizes at five strain rates (5–25 s−1) are 1.4 μm, 1.2 μm, 1.8 μm, 2.4 μm and 2.8 μm, respectively, while the DRX volume fractions are 35.8%, 75.0%, 82.0%, 88.0% and 93.0%, respectively. The maximum intensity values of the (0002) texture are 7.91, 8.22, 7.64, 5.76 and 5.34, respectively. The tensile strength (UTS) and yield strength (YS) increases firstly and then decreases, while the elongation (EL) gradually increases with increasing the strain rate, and the optimal comprehensive mechanical properties are obtained at 10 s−1, with UTS of 358 MPa, YS of 291 MPa and EL of 21.5%

Hot-rolled high-Mg-alloyed Al–Mg alloy (Al–9.2Mg–0.8Mn–0.2Zr–0.15Ti, labeled as 5A12) plates were successfully friction stir welded at rotating rates ranging from 750 to 1500 r·min−1 at a constant welding speed of 50 mm·min−1. The joints were characterized by optical microscopy (OM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron-dispersive spectroscopy (EDS), and tensile testing. All the joints are volume defect-free and exhibit fine, equiaxed dynamic recrystallization (DRX) grains with high-angle grain boundaries (HAGBs) fractions of 88.6%–93.3% in the nugget zones (NZs). The DRX grain size and the second-phase particle size in the NZs have a parabolic relation with the rotating rate. Furthermore, among the joints tested, the joint prepared at 1000 r·min−1, which has the highest ultimate tensile strength ((478 ± 3) MPa) and the largest elongation to rupture (22.5% ± 1.4%)—approximately 87.5% and 145.2% those of the base metal, respectively, exhibits the smallest grain size of 2.93 μm, as well as the smallest particle size in the NZs. These excellent mechanical properties can be ascribed to the combined effects of the fine DRX grains with high fraction of HAGBs and the fine second-phase particles with a uniform distribution.

The microstructure evolution, dynamic recrystallization (DRX) and precipitation of the ZM61 alloy sheets prepared with different rolling conditions were studied. The DRX grain sizes (dDRX) at four high strain rate rolling (HSRR) temperatures (275–350 °C) are 1.9, 2.3, 2.6 and 3.1 μm, respectively, while the DRX volume fractions (fVDRX) are 69, 73, 76 and 82%, respectively. 300 °C is selected as the optimal HSRR temperature. The dDRX and fVDRX of the alloys prepared by pre-rolling (PR) at 300 °C + HSRR are 1.0 μm and 91%, respectively. The PR treatment does not change the types of the precipitates but promotes the precipitation. The tensile strength (UTS) of 369 MPa and yield strength (YS) of 261 MPa can be achieved by HSRR at 300 °C, while a further increase in both UTS and YS can be obtained by PR treatment.

Microstructure, texture modification and mechanical anisotropy of the high strain rate rolled Mg–xGa alloys (x = 1, 2, 3 and 5, in wt%) were carefully investigated by EBSD, XRD, tensile testing, etc. The Ga addition can promote the transformation from the substructure to the recrystallized grains in the process of dynamic crystallization (DRX) so as to obtain the uniform microstructure and enhance the formation of twinning during deformation, which weakens the texture of the sheet and eventually forms the higher scatter texture. Moreover, the Mg–2Ga alloy shows the lowest texture intensity and thus exhibits the best combination of strength and plasticity and excellent plasticity, with the elongation-to-failure from 31.1 to 34.5% in three testing directions. The higher Ga content brings about the bigger work hardening index (n value) of the alloy sheet. The n value in the RD direction rises from 0.18 to 0.27 with the increasing Ga addition from 1 to 5%. The Mg–Ga alloys have very low plastic anisotropy and their plastic strain ratios are about 1. The Mg–2Ga alloy shows the lowest r value (1.07) and its ∆r value is 0.02. The wrought Mg–Ga alloys can achieve both high plasticity and low plastic anisotropy, which are promising for the industrial applications.

This article investigated the effect of Mg content (4.5, 6.5 and 9.2, in wt%) on the damping capacities of Al–Mg alloys. The results indicate that the damping behavior can be divided into three regions. Region I refers to the low strain amplitude region (e

Micro-alloying is thought to improve the performance of Al–Mg alloys commonly used in transport applications. The effect of Ce addition (not higher than 0.9 wt-%) on the microstructure, corrosion b...

Microstructure, biocorrosion, and stress corrosion cracking (SCC) behavior of as-cast Mg-4Zn-xSr alloys (x ≤ 0.4, in mass%) are studied by scanning electron microscopy, immersion testing, slow strain rate tensile testing, etc. A minor Sr addition (≤0.2%) in Mg-4Zn alloy can reduce the average corrosion rate and the corrosion current density in Hank’s solution, resulting from grain refinement, dispersion of the smaller secondary phase particles, and the more-protective corrosion product film. Thus, a minor Sr addition (≤0.2%) can improve both strength and plasticity of the Mg-4Zn alloy without increasing the SCC susceptibility, and the Mg-4Zn-0.1Sr alloy exhibits the best comprehensive properties.

Effects of the sole and the combined addition of Ca and Sr on microstructure and mechanical properties of as-cast and as-rolled Mg–5Zn alloys were carefully investigated by OM, SEM, hot-compression testing and tensile testing. Ca is more effective than Sr in the microstructural refinement of as-cast alloys. High-strain-rate rolling (HSRR) produces more deformed twins and thus provides more nucleation sites for dynamic recrystallization (DRX). The addition of Ca and Sr can promote dynamic precipitation during HSRR, the precipitation process would consume the storage energy and thus increases the critical strain value of DRX, resulting in the retarded DRX effect by the addition of Ca and/or Sr. The as-rolled Mg–5Zn–0.4Ca–0.2Sr alloy exhibits a good combination of strength and ductility, with the ultimate tensile strength of 317 MPa, the yield strength of 235 MPa and the elongation to rupture of 24%.

The Mg–xGa (x = 1, 2, 3 and 5 in mass%) alloys are subjected to high strain rate rolling (HSRR) at 275 °C with the rolling strain rate of 9.1 s−1 to develop high performance Mg alloy sheets with high plasticity. Effects of Ga content on microstructure and mechanical properties of the Mg–Ga alloys are investigated by SEM, XRD, tensile testing and etc. The Ga addition can reduce the critical strain of DRX in Mg alloys, which is associated with the reduced stacking fault energy, the increased twinning density during deformation and the more DRX nucleation sites during HSRR. With the Ga content increasing from 2 to 3%, the reduced DRX degree is attributable to the hindrance of dynamic precipitates. With the Ga content increasing from 3 to 5%, the slightly increased DRX degree can be ascribed to the relatively coarse precipitates. The Mg–2 Ga alloy sheet, featured with complete DRX, exhibits an ultra-high plasticity (with the elongation to rupture of 36.6%) and a relatively low anisotropy of yield strength and plasticity. The Mg–5 Ga alloy sheet has the best comprehensive mechanical properties, with the ultimate tensile strength of 292 MPa, yield strength of 230 MPa and elongation to rupture of 30.3%, which can be ascribed to the combination of grain refinement strengthening and precipitation strengthening. Effects of Ga content on microstructure, dynamic recrystallization (DRX) and mechanical properties of the Mg-Ga alloys prepared by high strain rate rolling (HSRR) are systematically studied. Among all the alloys, the HSRRed Mg-2Ga alloy exhibits the smallest DRX critical strain, an ultrahigh plasticity (δ up to 36.6%) and a low anisotropy of yield strength and plasticity, due to the complete DRX. The HSRRed Mg-5Ga alloy shows the optimal mechanical properties, with σb of 292 MPa, σ0.2 of 230 MPa and δ of 30.3%. The high strength is mainly attributed to precipitation strengthening and grain refinement strengthening.

The dynamic precipitation behavior before dynamic recrystallization (DRX) in a ZM51 alloy during hot compression at strain rate from 1 s−1 to 20 s−1 was investigated by transmission electron microscope (TEM) and small-angle X-ray scattering (SAXS) technique. The DRX critical strain decreases with increasing the strain rate. With the same deformation temperature and the identical strain, (0001)α plates (β′2) are dominant in the matrix at the strain rate of 1 s−1, while [0001]α rods (β′1) and spherical precipitates (β′2) occur at the higher strain rate (έ ≥ 10 s−1). At the higher strain rate, the total volume fraction of precipitates decreases initially and then increases, with the maximum value of 3.41%. The average length of β′1 rods decreases from (27 ± 11) nm to (20 ± 5) nm, and the mean rod diameter decreases from (16 ± 5) nm to (10 ± 3) nm. While the average thickness and mean diameter of β′2 plates decrease to (10 ± 2) nm and (15 ± 5) nm, respectively, and the spherical β′2 radius decreases from (15 ± 2) nm to (12 ± 3) nm. When deformed at 300 °C with a strain rate of 10 s−1, the alloy is featured with three types of precipitates with the strain of 0.05, indicating that the evolution regularities of dynamic precipitates during the high strain rate deformation is different from that in the static aging process.

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.

High strain rate rolling (HSRR) and artificial aging are conducted to improve mechanical properties and bio-corrosion resistance of Mg-4Zn alloy by modifying grain size and precipitates. The under-aged state is the most corrosion resistant among four states in single and double aging. Bio-corrosion resistance of the as-rolled alloy can be improved by double aging of 70 °C × 10 h + 160 °C × 2 h, resulting from stress relief and uniformly distributed nano-scale G.P. zones and β1′ precipitates.

Effects of Sn addition (0–1.5 mass%) on dynamic recrystallization (DRX) of Mg-5Zn-1Mn alloy during high strain rate ( e =9.1 s−1) deformation are investigated by hot compression testing. With a higher Sn addition, the strain corresponding to the maximum softening rate and the critical strain corresponding to the onset of DRX decrease at first and then increase, while the DRX fraction is just the reverse. The Mg-5Zn-1Mn-0.9Sn alloy shows the biggest DRX extent. Continuous DRX with twin nucleation is the dominant DRX mechanism for all the alloys. The high density dislocations inside twins gradually evolve into the cellular structures and sub-grains by dynamic recovery, and sub-grains turn into the DRX nuclei. The Sn addition can adjust the nucleation rate and the nucleus growth rate of DRX by regulating the inclination for twinning, adjusting stacking fault energy (SFE) and changing the amount of precipitates. Solute Sn atoms not only promote DRX nucleation by increasing twin density but also stimulate the DRX nucleus growth by reducing SFE. With the higher amount of MgZn2 and Mg2Sn dislocation-induced precipitates, the negative effect on DRX derived from the precipitates becomes effective, including hindering the formation of cellular structures and preventing the rotation and the growth of sub-grains by the pinning effect.

Effects of Sn on microstructure and mechanical properties of Mg–5Zn–1Mn alloy subjected to high strain rate rolling (9.1 s-1), 300°C and 80% pass reduction are investigated. With higher Sn content, the dynamic recrystallisation (DRX) grain size gradually decreases due to the stronger pinning of nano-scale precipitates at grain boundaries and the DRX fraction first increases due to the enhanced effect on DRX by decreasing stacking fault energy and then decreases due to more precipitates at grain boundaries. Ultimate tensile strength (UTS) and elongation to rupture (Er) of as-rolled alloys increase and then decrease. Alloy with 0.9 mass% Sn exhibits the highest DRX fraction (95 vol.-%), the finer DRX grain size (1.22 µm), UTS of 358 MPa and Er of 20.4%.

The Ga addition contributes to the enhanced microstructure uniformity of magnesium alloy sheets. The fine equiaxed recrystallized grains are found on the surface and in the interior of Mg-Ga alloy sheets. The cross-sectional grain orientation of pure Mg tends to be random due to a large amount of the deformed microstructure, while that of Mg-Ga alloy is mainly parallel to 10 1 - 1 . The fine equiaxed uniform microstructure with the low dislocation density brings about excellent mechanical properties for the Mg-Ga sheet and contributes to the greatly improved work hardening ability, with its plasticity about 485% higher than that of pure Mg.

The effect of pre-rolling prior to the high strain rate rolling (HSRR) on the dynamic recrystallization (DRX), dynamic precipitation and mechanical properties of Mg–6Zn–1Mn (ZM61) was investigated. Aiming this, a set of pre-rolling tests were carried out at the temperature of 300 °C with pre-rolling strain of 20 and 40%. The results show that pre-rolling treatment greatly homogenize the microstructure and refine DRX grains. The original twins induced by pre-rolling accelerate the DRX process and provide more nucleation sites for DRX grains. The precipitates induced by pre-rolling increase the precipitation density and lead to a strong interaction between DRX grains and precipitates. The ZM61 alloy sheet prepared with 20% pre-rolling strain at 300 °C followed by HSRR at 300 °C exhibits the UTS of 392 MPa and elongation of 16.8%. The advanced mechanical properties can be ascribed to the combined effect of grain refinement hardening and nano-precipitation strengthening.

Fine-grained Mg-5Zn-1Mn-0.6Sn alloy sheets of 2 mm in thickness were welded by fiber laser welding. The appearance and microstructures of the welding joints and liquation behaviors in the partially melted zone (PMZ) were investigated. The results show that, with the lower welding power and higher welding speed, the width and depth of the joints decrease. Moreover, some pores are detected at a very high welding speed. There are two kinds of liquation phenomena in the PMZ. One is the liquation network along grain boundaries associated with the liquation of substrate and segregation-induced liquation, the other is the molten pool involved with the liquation of the residual second phases at the boundaries. However, the liquation of substrate and the segregation-induced liquation are the main liquation mechanism in the PMZ.

Effects of minor Sr addition (0, 0.2, 0.6 and 1.0 mass%) on microstructure, mechanical and corrosion properties of the as-cast Mg-5Zn-based alloy system are investigated by SEM, XRD, mechanical testing and etc. The Sr-free alloy is composed of three phases i.e. α-Mg, Mg 7 Zn 3 and MgZn, while the alloys with the Sr addition of 0.6% or higher consist of α-Mg, Mg 7 Zn 3 , MgZn and Mg 11 Zn 4 Sr 3 . Minor Sr addition can effectively refine grains of the as-cast Mg-5Zn alloy and bring about more grain-boundary compounds. The as-cast alloy with 0.2%Sr addition exhibits the best combined mechanical properties with the ultimate tensile strength and elongation of 233 MPa and 15%. Corrosion tests in 0.9%NaCl solution and Hank's solution show that the degradation rate decreases significantly in the following order of Mg-5Zn, Mg-5Zn-0.6Sr, Mg-5Zn-1Sr and Mg-5Zn-0.2Sr. The as-cast Mg-5Zn-0.2Sr alloy also shows the optimal corrosion resistance both in 0.9%NaCl solution and in Hank's solution.

The aging precipitation behaviors and mechanical properties of Mg-5Ga-xZn (x = 0, 0.3, 0.6, 0.9 and 1.2, in wt%) alloys are studied by SEM, TEM, STEM and tensile testing. The peak-aged alloys are composed of α-Mg and Mg5Ga2. It is firstly proposed that the rod-like Mg5Ga2 precipitate has an orientation relationship (OR) of 002 Mg 5 Ga 2 ‖ 11 2 - 0 Mg and its length direction is parallel to 01 1 - 0 Mg . The Zn addition can refine Mg5Ga2 rods and increase the number, causing the accelerated aging kinetics and the slightly enhanced age hardening response. This effect can be ascribed to the Zn segregation at the interface. Moreover, the Zn addition can improve the strength of the peak-aged Mg-5Ga alloy but reduce the ductility.