Search

The influences of Al content on microstructure, mechanical properties, stretch formability and thermal conductivity of Mg-1.5Zn-0.3Ca-xAl-0.2Mn (x: 0.2, 0.5, 1, 1.25, 1.5, 2, wt%) alloys were investigated. With increasing the Al content from 0.2 wt% to 2 wt%, the texture changed from the TD-split texture to the quadrupolar texture at the Al content of 1.25 wt%, and finally became the RD-split texture with an increased texture intensity. The change of texture can be attributed to the formation of Al 2 Ca phase, which weakens the segregation of Ca at grain boundaries due to the decreased amount of Ca solute atoms in the α-Mg matrix. In addition, Al-Mn precipitates changed from a spherical shape to a rod shape accompanied by a largely increased Al/Mn ratio and a decreased amount of precipitates, when the Al content was increased to be larger than 1 wt%. The 0.2–1.5 wt% Al added alloys exhibited excellent stretch formability with the Erichsen values of 8.4–9.1 mm, which were much larger than that (6.8 mm) of the 2 wt% Al added alloy due to texture effect. The 1 wt% Al added alloy had the largest Erichsen value of 9.1 mm, while the 0.2 wt% and 2 wt% Al added alloys exhibited much higher yield strength (165 and 171 vs. 144 MPa). The thermal conductivity continuously decreased with increasing the Al content. Compared to the 2 wt% Al added alloy, the 0.2 wt% Al added alloy exhibited a much higher thermal conductivity (140 vs. 105 W/(m·K)) benefiting from the low concentration of Al solute atoms in the α-Mg matrix. Consequently, a combination of strong mechanical strength, excellent stretch formability and high thermal conductivity was achieved in the low Al-containing alloys with 0.2–0.5 wt% Al. • Mg-1.5Zn-0.3Ca-(0.2–2)Al-0.2Mn alloys with different Al contents were prepared. • High Al content caused texture change from TD-split to RD-split via quadrupole. • 1 wt% Al alloy with TD-split texture has the best formability but low strength. • Thermal conductivity continuously decreased with increasing Al content. • Excellent properties were simultaneously achieved in the low Al-containing alloys. [ABSTRACT FROM AUTHOR]

Static recrystallization behavior of Mg-1.5Zn-0.2Ce (wt%) alloy rolled at 480 °C was investigated at different annealing stages using quasi-in-situ electron backscattered diffraction (EBSD) analyses, which were carried out repeatedly in the same region to trace microstructural evolution. In the as-rolled condition, double twins exhibit the highest fraction compared with tensile and compression twins. Double twins mostly exist in deformed grains with basal orientations, and statically recrystallized grains mainly nucleate at the intersections of double twins and pre-existing grain boundaries. Statically recrystallized grains tend to exhibit TD-tilted orientations and grow along double twins to consume adjacent basal-oriented grains. This is the main reason for inducing the change from a RD-split texture to a well-weakened TD-split texture during annealing. The residual unrecrystallized grains with TD-tilted orientations and the growth advantage of TD-tilted grains also enhance the formation of TD-split texture. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of flame-resistant AZX912 magnesium alloy extruded at different temperatures in the range of 250–400 °C were investigated. With decreasing extrusion temperature from 400 °C to 250 °C, the grain size of dynamically recrystallized grains significantly decreased from 13.6 to 1.8 µm, and the amount of fine Mg 17 Al 12 precipitates, with sizes of 50–200 nm, increased due to dynamic precipitation. The extrusion texture, with the basal plane and < 10 1 ¯ 0 > direction, mostly parallel to the extrusion direction, was remarkably strengthened as the extrusion temperature increased. This may be attributed to the enhanced activity of the prismatic slip. Nanoscale Mg 17 Al 12 precipitates significantly enhanced the mechanical strength, but deteriorated the ductility. The bar extruded at 250 °C exhibited the highest mechanical strength, which was due to the combined effect of the remarkably refined grain structure and the large amount of nanoscale Mg 17 Al 12 precipitates. The extrusion at 400 °C resulted in the lowest tensile elongation, which was attributed to both grain coarsening and basal texture strengthening. The bar extruded at 300 °C exhibited a good balance between mechanical strength and tensile ductility. [ABSTRACT FROM AUTHOR]

Dilute magnesium–aluminum–calcium–manganese alloys have a quick age-hardening response and thus show higher strength after short periods of artificial aging; however, their room temperature formability is rather low. Here, we report that the addition of a small amount of copper (Cu) could substantially increase the Erichsen value of a Mg–0.5Al–0.5Ca–0.3Mn (wt.%) alloy due to the formation of a weakened sheet texture and variation in the distribution of (0002) basal pole figure. Specifically, the 0.03 wt% (300 parts-per-million) Cu-containing alloy showed a large index Erichsen value of 7.4 mm, which was noticeably higher than that of the Cu-free alloy (5.2 mm). Further investigation of the microstructure by transmission electron microscopy revealed that Cu co-segregated with Al and Ca at the grain boundaries, which played a critical role for the formation of the weaker basal texture and finer microstructure in the Cu-containing alloys. Owing to the small amount of the Cu addition, the resultant Mg–0.5Al–0.5Ca–0.3Mn–0.03Cu alloy showed a large thermal conductivity of 131 W/(m·K) in a solution treated condition. Subsequent artificial aging at 170 °C for 8 h (T6) not only improved the thermal conductivity to 141 W/(m·K) but also increased the tensile yield strength from 127 to 181 MPa. The improvement in both thermal conductivity and tensile yield strength by the T6-treatment is associated with the precipitation of densely distributed single-atomic layer Guinier–Preston zones lying parallel to the (0002) basal plane. [ABSTRACT FROM AUTHOR]

AZ61 and AM60 magnesium alloys, with higher mechanical strengths than that of the most commonly used AZ31 alloy, were subjected to high-temperature rolling. Although the basal textures of the as-rolled sheets of both alloys were significantly weakened by annealing, the texture weakening was more significant in the latter than in the former. In addition, splitting of the basal pole was not retained after annealing for the AZ61 alloy, but this type of texture was preserved in the case of the AM60 alloy. The formation of statically recrystallized grains with dispersed orientations resulted in the aforementioned change in texture. The difference in the static recrystallization behavior could be attributed to the solute effect of zinc atoms. The annealed AZ61 and AM60 alloy sheets exhibited excellent stretch formability at room temperature, with Erichsen values of 7.8 and 8.5 mm, respectively, comparable to those of aluminum alloys. The higher Erichsen value for the AM60 alloy compared to that of the AZ61 alloy resulted from the more weakened basal texture and the splitting of the basal pole with an inclination angle of ±20° in the rolling direction, which are favorable for basal slip during sheet forming. [ABSTRACT FROM AUTHOR]

The fabrication of magnesium (Mg) alloy sheets with both high mechanical strength and superior cold formability was sought by optimizing the aluminum (Al) content of the alloy sheets. We investigated the influence of varying Al content from 3 wt% to 8 wt% on the texture, mechanical properties, and stretch formability of AM series Mg alloys, processed by high-temperature rolling. The ultimate tensile strength improved steadily from 247 MPa to 303 MPa with an increase in Al, due to solid solution strengthening. The basal texture intensity decreased with increasing Al content, reached a minimum value at 6 wt% Al, and then increased as more Al was added. The weakest basal texture led to the smallest Lankford value and the largest strain hardening exponent in the AM60 (6 wt% Al) alloy. The alloys with lower Al contents of 3–5 wt% exhibited a high fracture elongation of 27%, which continuously decreased to 23% as the Al content increased to 8 wt%. The AM50 alloy exhibited excellent stretch formability with the largest Erichsen value of 9.1, while the AM30 and AM80 alloys showed much smaller Erichsen values of 5.6 and 6.0, respectively. This can be attributed to a good balance among the decreased r -value, increased n -value, and enhanced tensile ductility in the AM50 alloy, despite its basal texture being slightly stronger than that of the AM60 alloy. [ABSTRACT FROM AUTHOR]

Microstructural evolution and stretch formability of Mg–3Al–1Zn (AZ31) magnesium alloy sheets warm rolled at 225°C by a single differential speed rolling pass with two different initial microstructures were investigated. A cast ingot and that rolled by one pass at a high temperature of 550°C with average grain sizes of ~470μm and ~19μm, respectively, were used as starting materials. Both warm rolled sheets exhibit deformation microstructure in as-rolled condition and the occurrence of texture randomization during subsequent annealing as a result of static recrystallization. New recrystallized grains with a large orientation spread tend to persist in the original orientations of parent deformed grains and twin hosts. Regarding the nucleation sites at pre-existing grain boundaries and double twins, static recrystallization preferentially occurs at the sides of deformed grains and within double twins with their c-axes inclining toward the rolling direction (RD), resulting in a stable end annealing texture with a basal pole tilting toward the RD. For the sheet warm rolled from a cast ingot, incomplete recrystallization originating from less stored energy in the interiors of large deformed grains results in an insufficient texture weakening and an inhomogenous microstructure. Both sheets possess an improved stretch formability compared with conventional AZ31 alloy sheets due to the weakened textures. Benefiting from a weaker basal texture and a more homogenous microstructure, the sheet rolled at 550°C followed by warm rolling at 225°C exhibits a higher Erichsen value of 8.2 compared with that (6.1) of the sheet warm rolled directly from a cast ingot. [ABSTRACT FROM AUTHOR]

Abstract: Mg–3Al–1Zn magnesium alloy sheets rolled at 350°C, 450°C and 525°C, which exhibit approximately the same grain size but a significant decrease in basal texture intensity with increasing rolling temperature, were used for investigating the influence of initial texture on deep drawing behaviour at room temperature. The sheets rolled at 350°C and 450°C fracture at drawing ratios of 1.5 and 1.7, respectively, while the sheet rolled at 525°C can be successfully drawn at a large drawing ratio of 1.8. The fracture site changes from the shoulder of drawn cup to the edge of the flange with the weakening of initial basal texture. At the flange, the basal texture dramatically changes to the TD-texture with basal planes perpendicular to the sheet plane accompanied with sheet thickening. Both tensile twinning and basal slip contribute to this texture change due to compressive stress along the circumferential direction. In the case of weak initial texture, relatively restricted tensile twinning and more activated basal slip delay the development of the TD-texture, which is favoured for maintaining deformation capability at the flange and in turn enhances deep drawability. The deformation behaviour is discussed in terms of the change in Schmid factor for basal slip during deep drawing. [Copyright &y& Elsevier]

Abstract: The annealing behaviours of Mg–3Al–1Zn magnesium alloy sheets warm rolled at 225°C and 150°C using differential speed rolling, which are mainly characterized by dynamic recrystallized microstructure and deformation microstructure, respectively, were investigated at different annealing stages. Static recrystallization occurs for the sheet rolled at 150°C while only grain growth proceeds for the sheet rolled at 225°C. For the sheet rolled at 225°C, the grain growth of dynamic recrystallized grains eliminates the basal pole inclination in the rolling direction. In contrast, for the sheet rolled at 150°C, the grain growth after static recrystallization retains the basal pole inclination, which is favoured for sheet forming. This difference in texture evolution may be attributed to the dynamic or static recrystallization prior to grain growth, which results in residual dislocation densities for the former and thus leads to the preferential growth of harder oriented basal grains at the centre of (0001) pole figure with lower dislocation densities during annealing. [Copyright &y& Elsevier]

Abstract: The Mg–3Al–1Zn magnesium alloy sheets rolled at 573 and 798K characterized by strong and weak basal textures, respectively, were further subjected by a single high temperature rolling pass at 798K. The sheet rolled only at 798K throughout rolling exhibits a double peak texture in both of as-rolled and annealed conditions. By contrast, for the sheet rolled at 573 and 798K, the reduction rate of basal texture intensity is larger and the single peak of the rolling texture changes to the double peak with basal poles largely tilting in the RD at ∼20° after annealing, which is rarely observed in wrought magnesium alloys. This phenomenon is resulted from static recrystallization and may be related to enhanced pyramidal 〈c+a〉 slip during high temperature rolling due to the initial strong basal texture. [Copyright &y& Elsevier]

Abstract: The microstructural and textural evolution during post-annealing as well as mechanical properties of a Mg–4Y–3RE magnesium alloy sheet processed by differential speed rolling at 823K were investigated. The as-rolled sheet exhibits deformation microstructure regardless of the high rolling temperature. Static recrystallization occurs around second-phase particles as a result of particle-stimulated nucleation and also at pre-existing grain boundaries due to solute effects of rare-earth elements, resulting in randomization of basal texture. Despite a large amount of second-phase particles, the weakened texture leads to a moderate stretch formability with an Erichsen value of 4.4. [Copyright &y& Elsevier]

Abstract: The effects of increasing rolling temperature from 723K to 828K at the last rolling pass on microstructure, texture, mechanical properties and stretch formability of a Mg–3Al–1Zn magnesium alloy previously rolled at 723K were investigated. In the as-rolled condition, the basal texture strengthens slightly with increasing the rolling temperature whereas it weakens more remarkably after static recrystallization during annealing for the sheets rolled at higher temperatures. Only by increasing the rolling temperature from 723K to 798K, the Erichsen value is significantly increased from 4.5 to 8.6 due to the weakened texture for the annealed sheets. Further increasing the last rolling temperature does not appear to further improve the stretch formability. [Copyright &y& Elsevier]

Abstract: The recrystallization and grain growth behaviour of Mg–3Al–1Zn alloy sheets with a deformation microstructure, obtained by a combination of high-temperature rolling and subsequent warm rolling, was investigated at different stages of annealing. The basal texture was significantly weakened as a result of the formation of new grains with a largely altered c-axis orientation relative to the initial basal orientation owing to discontinuous static recrystallization during primary recrystallization. The new grains nucleated mostly at the pre-existing grain boundaries rather than at the intersections of twins or within the twins. Subsequent grain growth led to further progression of the texture weakening accompanied by an enhancement in the basal pole inclination. [Copyright &y& Elsevier]

The Mg–3Al–1Zn magnesium alloy sheets with initial extrusion and casting microstructures were symmetrically rolled at a high temperature of 823K, followed by a warm rolling at 498K. The initial texture plays a vital role in texture development and results in inclination angle of split basal pole varying from ±15° to ±40°. The sheet rolled perpendicular to extrusion direction exhibits a homogeneous microstructure with an inclination angle of ±25° and the highest Erichsen value of 9.7. [Copyright &y& Elsevier]

Mg–3Al–1Zn alloy sheets were rolled at high temperatures up to 823K and subsequently rolled at 498K using differential speed rolling. The basal texture intensity dramatically weakens with a largely tilted basal pole after annealing. The Erichsen value significantly increases from 3.7 to 9.5 with an increase in the rolling temperature from 498 to 823K prior to warm rolling due to texture effects. This high Erichsen value is comparable to those of aluminum alloys. [Copyright &y& Elsevier]

Abstract: The microstructural and textural evolution of the hot-extruded AZ31 alloy plate during differential speed rolling (DSR) has been investigated. For the hot-extruded plate, a large texture gradient exists in the thickness direction while the grain size distribution is nearly homogenous. The textural evolutions at near-surface and mid-layer regions are different between the DSR processed and the normal symmetric rolled sheets. The inclination of basal pole at the mid-layer increases at an accelerating rate with progress of the DSR processing due to the enhancement of the unidirectional shear bands. The deformation tends to concentrate on the previously formed shear bands, which exhibit a favored crystalline orientation for further shear localization. [Copyright &y& Elsevier]

The influence of reduction per pass over the range of 9–63% on the microstructure and texture of Mg–3Al–1Zn magnesium alloy sheets processed by differential speed rolling at the same total reduction of 63% have been investigated. With increasing reduction per pass, the number of unidirectional shear bands increases, resulting in a more homogeneous microstructure and a weaker basal texture at mid-layer. The inclination direction of the basal pole with respect to the rolling direction depends on the reduction per pass. [Copyright &y& Elsevier]

Mg–6Al–1Zn magnesium alloy sheets were rolled at high temperatures of 723–793K using differential speed rolling. The Erichsen value remarkably increases about 1.5 times due to the weakened basal texture regardless of the coarser grains with increasing the rolling temperature from 723 to 793K. The sheet rolled at 793K exhibits a combination of a superior stretch formability with an Erichsen value of 7.0 and a high tensile strength of 300MPa at room temperature. [Copyright &y& Elsevier]

Abstract: The microstructure and the texture of the Mg–3.10Al–1.06Zn–0.35Mn (in wt.%) alloy processed by differential speed rolling (DSR) were investigated by optical microscopy, X-ray texture analysis and electron backscattered diffraction (EBSD) analysis. The DSR processed sheet exhibited the unidirectional shear bands with an inclination to the rolling direction. The macro-texture analysis results showed a large inclination of c-axis toward the opposite direction of the rolling direction at about 15°. On the other hand, the micro-texture analysis revealed that the inclination directions of c-axis were reverse between the shear bands and the remaining coarse grain regions, and the latter dominated the macro-texture. This anomalous texture can be attributed to the formation of the unidirectional shear bands. [Copyright &y& Elsevier]

Abstract: Though Mg alloys are promising candidates for biodegradable stents, it is very difficult to fabricate stent tubes with high dimensional accuracy using Mg alloys because of their low deformability. This study aimed to develop thin-walled, high-quality Mg alloy tubes with good performance in stent applications. Cold drawing with a fixed mandrel was carried out for extruded Mg-0.8%Ca and AZ61 alloy tubes using optimized drawing parameters and lubrication, and stent tubes with 1.5–1.8mm outer diameter and 150μm thickness were fabricated. A dimensional evaluation showed that the tube dimensional errors were within 0.02–2.5%. Also, an immersion test of pure Mg with different crystal orientations showed that the crystal orientation affected the corrosion properties, results that are the same with other Mg alloys. The crystal orientation of the stent tube could be controlled by changing the deformation amount and direction in the drawing, showing that it is possible to further improve the biodegradability of stents by approaching their fabrication from a processing aspect. [Copyright &y& Elsevier]