Difference in extrusion temperature dependences of microstructure and mechanical properties between extruded AZ61 and AZ91 alloys

The effects of extrusion temperature on the microstructure and tensile properties of extruded AZ61 and AZ91 alloys are investigated by subjecting them to hot extrusion at 300 and 400℃.Although the average grain size of the extruded AZ61 alloy slightly increases from 9.5 to 12.6μm with increasing extrusion temperature,its resultant microstructural variation is insignificant.In contrast,the average grain size of the extruded AZ91 alloy significantly increases from 5.7 to 22.5μm with increasing extrusion temperature,and the type of Mg17Al12 precipitates formed in it changes from fine dynamic precipitates with a spherical shape to coarse static precipitates with a lamellar structure.As the extrusion temperature increases,the tensile yield strength of the extruded AZ61 alloy increases from 183 to 197 MPa while that of the extruded AZ91 alloy decreases from 232 to 224 MPa.The tensile elongations of the extruded AZ61 and AZ91 alloys decrease with increasing extrusion temperature,but the degree of decrease is significant in the latter alloy.These different extrusion temperature dependences of the tensile properties of the extruded AZ61 and AZ91 alloys are discussed in terms of their microstructural characteristics,strengthening mechanisms,and crack initiation sites.

Novel Mg-Bi-Mn wrought alloys:The effects of extrusion temperature and Mn addition on their microstructures and mechanical properties

Designing and developing the Mg alloys with low cost and high performance is of the great significance.Novel Mg-1Bi-xMn(x=0,1and 2 wt.%)extruded alloys,in this work,were fabricated at different extrusion temperatures(220,250 and 300℃).The effects of extrusion temperature and Mn addition on the microstructures and mechanical properties of extruded alloys at room temperature were investigated.The results showed that decreasing the extrusion temperature could refine the average grain size,weaken the basal fiber texture intensity and improve the microstructural homogeneity of extruded alloys.When the Mn element was added to the Mg-1Bi alloy,the average grain size further reduced.Simultaneously,the number fraction of low angle grain boundaries(LAGBs)increased,along with the occurrence of regions without dynamic recrystallization(unDRX).The combined effects of grain refinement and coarse unDRXed structure made the textures of the extruded Mg-1Bi-xMn alloys never obviously change.Besides few large size un-dissolved second phases,fine Mg_(3)Bi_(2) and α-Mn phases were precipitated in the extruded Mg-1Bi-xMn alloys and partial nano-scaleα-Mn particles pined at grain boundaries(GBs)to effectively impede the migration of GBs for grain refinement.Microstructural variations determined the extruded Mg-1Bi-2Mn alloy to exhibit the highest yield strength of~319.2 MPa with the appropriate elongation-to-failure of~13%at the extrusion temperature of 220℃,and they enabled the extruded Mg-1Bi-1Mn alloy to show the highest elongation-to-failure of~26%without the obvious loss of yield strength of~252.1 MPa.

Effect of Extrusion Temperature on Free Gossypol and Nutritional Components of Cottonseed Meal

[ Objective] The paper aimed to study effects of extrusion temperature on free gossypol and nutritional components of cottonseed meal. [ Method ] Dif- ferent extrusion temperatures （90, 100, 110, 120 and 130℃ ） were designed, and contents of free gossypol and nutritional components in cottonseed meal were de- termined. [ Result] The optimal temperature for extrusion of cottonseed meal was 120℃, the degradation rate of free gossypol no longer increased with the increas- ing temperature when the temperature exceeded 120℃. The nitrogen solvable index （NSI） in cottonseed meal reduced quickly with the increase of extrusion temper- ature, and the contents of crude fiber, available lysine and total lysine in cottonseed meal decreased significantly, but the contents of total amino acids and essential amino acid reached maximums at the extrusion temperature of 120℃. The content of branched-chain amino acids also reached a maximum at 120℃. [ Conclusion] The extrusion temperature of 120℃ was preferred for lowering free gossypol significantly when maintaining higher nutritional value of cottonseed meal. The paper provided a certain technical basis for extrusion processing of cottonseed meal.

Effect of Extrusion Temperature on the Mechanical Properties and Corrosion Behavior of LZ91 Alloys

Microstructural observations,tensile tests,potentiodynamic polarization measurements,and corrosion morphology examinations are conducted to investigate the effect of extrusion temperature on the mechanical properties and corrosion behavior of LZ91 alloys.The results show that the tensile strength of the LZ91 alloy is increased by 86 MPa after extrusion at 25℃.Meanwhile,the corrosion resistance is improved by about 2.7 times,and the maximum corrosion depth is decreased by 60μm.The increase in the tensile strength can be mainly attributed to theα-Mg precipitate strengthening inβ-Li.The improvement of the corrosion resistance is due to the fact that the nano-sized MgLiZn and refinedα-Mg precipitates inβ-Li weaken the effect of the cathodic phase on micro-galvanic corrosion,thereby decreasing the cathodic current density and local corrosion susceptibility.However,when the extrusion temperature is increased to 300°C,the corrosion rate is significantly accelerated due to the increase of the micro-galvanic corrosion caused byα-Mg precipitate coarsening at high temperatures.

Effect of Initial Microstructure Prior to Extrusion on the Microstructure and Mechanical Properties of Extruded AZ80 Alloy with a Low Temperature and a Low Ratio

Magnesium(Mg)alloys are the lightest metal structural material for engineering applications and therefore have a wide market of applications.However,compared to steel and aluminum alloys,Mg alloys have lower mechanical properties,which greatly limits their application.Extrusion is one of the most important processing methods for Mg and its alloys.However,the effect of such a heterogeneous microstructure achieved at low temperatures on the mechanical properties is lacking investigation.In this work,commercial AZ80 alloys with different initial microstructures(as-cast and as-homogenized)were selected and extruded at a low extrusion temperature of 220℃and a low extrusion ratio of 4.The microstructure and mechanical properties of the two extruded AZ80 alloys were investigated.The results show that homogenized-extruded(HE)sample exhibits higher strength than the cast-extruded(CE)sample,which is mainly attributed to the high number density of fine dynamic precipitates and the high fraction of recrystallized ultrafine grains.Compared to the coarse compounds existing in CE sample,the fine dynamical precipitates of Mg17(Al,Zn)12form in the HE sample can effectively promote the dynamical recrystallization during extrusion,while they exhibit a similar effect on the size and orientation of the recrystallized grains.These results can facilitate the designing of high-strength wrought magnesium alloys by rational microstructure construction.

Microstructural characteristics and low-cycle fatigue properties of AZ91 and AZ91-Ca-Y alloys extruded at different temperatures

The commercial AZ91 alloy and nonflammable SEN9(AZ91-0.3Ca-0.2Y,wt%)alloy are extruded at 300°C and 400°C.Their microstructure,tensile and compressive properties,and low-cycle fatigue(LCF)properties are investigated,with particular focus on the influence of the extrusion temperature.In the AZ91 and SEN9 materials extruded at 300°C(300-materials),numerous fine Mg_(17)Al_(12)particles are inhomogeneously distributed owing to localized dynamic precipitation during extrusion,unlike those extruded at 400°C(400-materials).These fine particles suppress the coarsening of recrystallized grains,decreasing the average grain size of 300-materials.Although the four extruded materials have considerably different microstructures,the difference in their tensile yield strengths is insignificant because strong grain-boundary hardening and precipitation hardening effects in 300-materials are offset almost completely by a strong texture hardening effect in 400-materials.However,owing to their finer grains and weaker texture,300-materials have higher compressive yield strengths than400-materials.During the LCF tests,{10-12}twinning is activated at lower stresses in 400-materials than in 300-materials.Because the fatigue damage accumulated per cycle is smaller in 400-materials,they have longer fatigue lives than those of 300-materials.A fatigue life prediction model for the investigated materials is established on the basis of the relationship between the total strain energy density(ΔW_(t))and the number of cycles to fatigue failure(N_(f)),and it is expressed through a simple equation(ΔW_(t)=10·N_(f)-0.59).This model enables fatigue life prediction of both the investigated alloys regardless of the extrusion temperature and strain amplitude.

Integrated printed BDNF/collagen/chitosan scaffolds with low temperature extrusion 3D printer accelerated neural regeneration after spinal cord injury

Recent studies have shown that 3D printed scaffolds integrated with growth factors can guide the growth of neurites and promote axon regeneration at the injury site.However,heat,organic solvents or cross-linking agents used in conventional 3D printing reduce the biological activity of growth factors.Low temperature 3D printing can incorporate growth factors into the scaffold and maintain their biological activity.In this study,we developed a collagen/chitosan scaffold integrated with brain-derived neurotrophic factor(3D-CC-BDNF)by low temperature extrusion 3D printing as a new type of artificial controlled release system,which could prolong the release of BDNF for the treatment of spinal cord injury(SCI).Eight weeks after the implantation of scaffolds in the transected lesion of T10 of the spinal cord,3D-CC-BDNF significantly ameliorate locomotor function of the rats.Consistent with the recovery of locomotor function,3D-CC-BDNF treatment could fill the gap,facilitate nerve fiber regeneration,accelerate the establishment of synaptic connections and enhance remyelination at the injury site.

Influence of size and distribution of W phase on strength and ductility of high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca alloy processed by indirect extrusion

A high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca （wt%） alloy containing W phase （Mg3Y2Zn3） prepared by permanent mold direct-chill casting is indirectly extruded at 350 ℃ and 400 ℃, respectively. The extruded alloys show bimodal grain structure consisting of fine dynamic recrystallized （DRXed） grains and unre- crystallized coarse regions containing fine W phase and β2′ precipitates. The fragmented W phase particles induced by extrusion stimulate nucleation of DRXed grains, leading to the formation of fine DRXed grains, which are mainly distributed near the W particle bands along the extrusion direction. The alloy extruded at 350 ℃ exhibits yield strength of 373 MPa, ultimate tensile strength of 403 MPa and elongation to failure of 5.1%. While the alloy extruded at 400 ℃ shows lower yield strength of 332 MPa, ultimate tensile strength of 352 MPa and higher elongation to failure of 12%. The mechanical properties of the as-extruded alloys vary with the distribution and size of W phase. A higher fraction of DRXed grains is obtained due to the homogeneous distribution of micron-scale broken W phase particles in the alloy extruded at 400 ℃, which can lead to higher ductility. In addition, the nano-scale dynamic W phase precipitates distributed in the unDRXed regions are refined at lower extrusion temperature. The smaller size of nano-scale W phase precipitates leads to a higher fraction of unDRXed regions which contributes to higher strength of the alloy extruded at 350 ℃.

Three-dimensional-printed collagen/chitosan/secretome derived from HUCMSCs scaffolds for efficient neural network reconstruction in canines with traumatic brain injury

The secretome secreted by stem cells and bioactive material has emerged as a promising therapeutic choice for traumatic brain injury(TBI).We aimed to determine the effect of 3D-printed collagen/chitosan/secretome derived from human umbilical cord blood mesenchymal stem cells scaffolds(3D-CC-ST)on the injured tissue regeneration process.3D-CC-ST was performed using 3D printing technology at a low temperature(20C),and the physical properties and degeneration rate were measured.The utilization of low temperature contributed to a higher cytocompatibility of fabricating porous 3D architectures that provide a homogeneous distribution of cells.Immediately after the establishment of the canine TBI model,3D-CC-ST and 3D-CC(3D-printed collagen/chitosan scaffolds)were implanted into the cavity of TBI.Following implantation of scaffolds,neurological examination and motor evoked potential detection were performed to analyze locomotor function recovery.Histological and immunofluorescence staining were performed to evaluate neuro-regeneration.The group treated with 3D-CC-ST had good performance of behavior functions.Implanting 3D-CC-ST significantly reduced the cavity area,facilitated the regeneration of nerve fibers and vessel reconstruction,and promoted endogenous neuronal differentiation and synapse formation after TBI.The implantation of 3D-CC-ST also markedly reduced cell apoptosis and regulated the level of systemic inflammatory factors after TBI.