Microstructure and Texture Evolution During the Direct Extrusion and Bending–Shear Deformation of AZ31 Magnesium Alloy

AZ31 alloys were extruded by direct extrusion and bending–shear deformation(DEBS). The microstructure characteristic and texture evolution of DEBSed AZ31 sheets were investigated by electron backscattered diffraction(EBSD). It is found that DEBS technique could effectively refine grains and weaken texture. Besides, we also investigate how twinning affects dynamic recrystallization during hot extrusion. {10–12} extension twins can offer nucleation sites and enough energy to trigger dynamic recrystallization. Moreover, the character of direct extrusion and bending–shear die can lead to the activation of non-basal slip system and further dramatically weaken the basal texture of the microstructure with many preactivated basal slip systems.     

Evolution of Microstructure,Residual Stress,and Tensile Properties of Mg–Zn–Y–La–Zr Magnesium Alloy Processed by Extrusion

The microstructure, texture, residual stress, and tensile properties of Mg–6 Zn–2 Y–1 La–0.5 Zr(wt%) magnesium alloy were investigated before and after extrusion process, which performed at 300 °C and 400 °C. The microstructural characterizations indicated that the as-cast alloy was comprised of α-Mg, Mg–Zn, Mg–Zn–La, and Mg–Zn–Y phases. During homogenization at 400 °C for 24 h, most of the secondary phases exhibited partial dissolution. Extrusion process led to a remarkable grain refi nement due to dynamic recrystallization(DRX). The degree of DRX and the DRXed grain size increased with increasing extrusion temperature. The homogenized alloy did not show a preferential crystallographic orientation, whereas the extruded alloys showed strong basal texture. The extrusion process led to a signifi cant improvement on the compressive residual stress and mechanical properties. The alloy extruded at 300 °C exhibited the highest basal texture intensity, the compressive residual stress and hardness, and yield and tensile strengths among the studied alloys.     

Microstructure and Mechanical Properties of Mg–3Al–Zn Magnesium Alloy Sheet by Hot Shear Spinning

Hot shear spinning experiments with Mg–3.0 Al–1.0 Zn–0.5 Mn(AZ31 B, wt%) magnesium alloy sheets were conducted at various temperatures, spindle speeds and feed ratios to investigate the effects of these processing parameters on the microstructure, crystallographic texture and mechanical properties. The AZ31 B sheet displayed good shear formability at temperatures from 473 to 673 K, spindle speeds from 300 to 600 rev/min and feed ratios from 0.1 to 0.5 mm/rev. During the dynamic recrystallization process, the grain size and texture were affected by the deformation temperature of the hot shear spinning process. Each of the spun sheets presented a strong basal texture, and the c-axis of most of the grains was parallel to the normal direction. The optimal hot shear spinning parameters were determined to be a temperature of 473 K, a spindle speed of 300 rev/min and a feed ratio of 0.1 mm/rev. The yield strength, ultimate tensile strength and elongation in the rolled direction reached 221 MPa, 288 MPa and 14.1%, and those in the transverse direction reached 205 MPa, 280 MPa and 12.4%, respectively. The improved strength and decreased mechanical anisotropy resulted from the fine grain size and strong basal texture.     

同步和异步轧制AZ31镁合金板材的织构及力学性能

采用同步轧制(NR)和异步轧制(AR)工艺对AZ31镁合金挤压板材进行了轧制,研究了轧制过程中组织和织构的演化,以及总压下量和异步比对轧材组织、织构和力学性能的影响。结果表明,在压下量为3%～15%的范围内,同步轧制与异步轧制板材在晶粒尺寸以及均匀性上有相似的变化趋势。轧制过程中,在变形初期,随压下量的增加,孪晶数量不断增加,孪晶使同步轧制与异步轧制板材中晶粒取向都发生偏转,即C轴趋向于垂直于法向(ND),从而使初始挤压板材的丝织构强度减弱;而当压下量达到24%时,孪晶大量减少或消失。在压下量为3%～24%的范围内,同步轧制对板材力学性能的影响并不明显,峰值应变呈交替变化;异步轧制板材在压下量达到24%左右时,表现出了良好的塑性变形能力,抗拉强度达到309MPa,峰值应变达到0.163。     

Microstructure,Texture Evolution,and Mechanical Properties of ECAP-Processed ZAT522 Magnesium Alloy

In this work,the high-strength Mg-5Zn-2Al-2Sn(ZAT522,in wt%) Mg alloys was obtained at 220℃ and 130℃ by a two-step equal channel angular pressing(ECAP).For each stage,two passes were used.The results showed a remarkable grain refinement after the first stage of ECAP(A2 samples),leading to a fine-grained structure with average size of 1.40 μm.The additional stage(A4 samples) caused further grain refinement to 1.18 μm,and an ultra-fine grain structure(700 nm)appeared in the precipitate-rich region.The grain refinement mechanism for both samples was discussed in detail.To this end,the original extrusion fiber texture evolved into a new strong texture characterized by the base planes tilted toward the ECAP shear plane,with a higher Schmid factor value of 0.34.Compared with the as-extruded alloy,the yield strength of the A2 samples increased from 180 to 245 MPa,which was mainly attributed to the combined effects of grain boundary strengthening and precipitation strengthening.In the case of A4 samples,the dislocation strengthening resulted in a net increase in yield strength to 335 MPa,while the ductility was significantly reduced.     

热挤压对7055铝合金力学性能及组织的影响

采用挤压铸造成形工艺制备7055高强铝合金,研究了热挤压参数对合金力学性能及微观组织的影响,并与铸态下的力学性能及微观组织进行了对比.结果表明,热挤压态下的7055铝合金的微观组织和力学性能均优于铸态,并且晶粒随着比压的增加趋于细化,抗拉强度随着比压的增加趋于提高.当比压为75 MPa时,在730 ℃温度下进行挤压浇注,经过双级固溶处理和时效后,合金的晶粒明显细化,抗拉强度达到681.4 MPa,伸长率达到7.14%.     

Effect of Extrusion Strain Path on Microstructure and Properties of AZ31 Magnesium Alloy Sheet

The mechanical properties of AZ31 magnesium alloy sheets processed by different extrusion strain paths were examined in correlation with concurrent microstructure and texture evolution. The conventional extrusion(CE) and asymmetric extrusion(ASE) paths were performed on Mg alloy sheets. The textures at near surface and mid-layer of ASE sheets were various throughout sheet thickness direction as a result of extra asymmetric shear strain. This can stimulate the orientation of(0002) basal planes to incline approximately 12° toward the shear direction. Moreover, the basal texture of ASE sheet was weakened compared with CE one. Enhancing the ambient formability of extruded Mg alloy sheet fabricated by ASE path was accomplished by the tilted weak basal texture.     

Improvement of Mechanical Properties of Magnesium Alloy ZK60 by Asymmetric Reduction Rolling

The improvement of mechanical properties of ZK60 processed by asymmetric reduction rolling(ARR) was investigated in this paper. The grain refinement and basal texture intensity decrease were attributed to the introduction of shear stress produced by ARR process. Compared to conventional symmetrical rolled(SR) ZK60 alloys, ARRed ZK60 exhibited finer, more homogeneous grains and higher mechanical properties. The intensity of basal texture of ARRed ZK60 after annealing was lower than that of SRed ZK60 after annealing. ZK60 sheet with good combination of strength and ductility could be obtained by ARR process. The yield strength(YS) and ultimate tensile strength(UTS) of the ARRed ZK60 sheet were increased 150% and 91.3%, compared to those of SRed ZK60 sheet, from 80 to 200 MPa and from 140 to264 MPa, respectively. Simultaneously, the elongation to failure increased by 68.75% in the ARR sheet(27%) when compared to that of the SR sheet(16%).     

挤压比对热挤压AZ80镁合金管材组织和性能的影响

选用不同的挤压比对变形镁合金AZ80进行管材热挤压工艺试验研究,对挤压前后材料组织与力学性能的变化进行分析。结果表明,热挤压可以显著细化AZ80镁合金的晶粒,而且随着挤压比的增加,晶粒变得更加细小;增大挤压比也可以提高AZ80镁合金的抗拉强度和屈服强度。结果表明,挤压比为18.2,坯料温度为390℃,模具预热温度为360℃,凹模的半模角为60°～70°,可得到均匀的合金组织和良好的力学性能。     

AZ31镁合金轧制变形后组织性能研究

本文研究了不同轧制变形量和轧制速度对AZ31镁合金板材微观组织和力学性能的影响。轧制变形可显著细化AZ31镁合金板材的晶粒尺寸并提高其综合力学性能。当轧制速度为5m/min,轧制变形量为50%时,板材平均晶粒尺寸最细可达到9μm,其抗拉强度、屈服强度和延伸率分别提高到280MPa、180MPa和30%以上,同时探讨了AZ31镁合金屈服强度与晶粒大小之间的关系。在大量AZ31镁合金轧制相关文献和本文一系列实验研究的基础上,对比分析了不同轧制工艺对AZ31镁合金综合力学性能的影响。研究表明,本文所采用轧制工艺可显著提高AZ31镁合金板材的综合力学性能,同时降低板材轧向和横向的各向异性。     

热挤压及固溶处理对AZ61镁合金组织和性能的影响

研究了不同温度下的热挤压工艺以及后续的固溶热处理对AZ61镁合金显微组织和力学性能的影响.利用扫描电子显微镜观察分析了AZ61镁合金拉伸断口形貌,探讨了其拉伸断裂机制.结果表明,热挤压可以细化晶粒、产生高密度位错从而有效提高合金的力学性能,试验发现在385℃下挤压AZ61镁合金组织均匀,塑性最好.经过热处理之后,370℃下挤压AZ61镁合金的强度有很大提高;385℃下挤压AZ61镁合金强度和塑性下降;400℃下挤压AZ61镁合金的塑性显著提高.     

径向挤压对Zn-15Al合金线材组织和性能的影响

为了改善锌铝合金线材加工使用性能,依据90°转角挤压原理,采用径向挤压出线工艺制取线材,研究了线材拉拔后的微观组织和力学性能,并与轴向挤压出线工艺进行对比.结果表明,径向挤压出线工艺可明显细化合金组织,且有纤维化倾向.线材抗拉强度降低15%,而伸长率提高30%.该工艺有利于线坯的拉拔加工,减少喷枪送丝途中的阻力.     

Effect of Extrusion Temperature on the Microstructure and Mechanical Properties of Mg–5Al–2Ca Alloy

In this work, the Mg–5Al–2Ca alloy was extruded at 573, 623 and 673 K, with a ratio of 16:1 and a constant speed of 3 mm/s. Results demonstrate that the Al2Ca particle is formed in Mg–5Al–2Ca alloy. The size, amount and distribution of Al2Ca particles are influenced evidently by extrusion temperature. Unlike previous reports, the intensity of basal texture increases with increasing extrusion temperature, and the reasons are analyzed and given. Even though the average grain size increases as the extrusion temperature increased from 573 to 623 K, the YS, UTS and elongation of asextruded Mg–5Al–2Ca alloy are almost kept the same at 573 and 623 K. The reason is speculated as the balance of grain size, Al2Ca phase and texture at the two temperatures. The work hardening rate depends on extrusion temperature, and the largest θ value of Mg–5Al–2Ca alloy is obtained when the extrusion was performed at 623 K.     

Effects of Welding Speed and Post-weld Hot Rolling on Microstructure and Mechanical Properties of Friction Stir-Welded AZ31 Magnesium Alloy

The as-rolled AZ31 Mg alloy sheets are welded by friction stir welding(FSW) in this study, followed by annealing and hot rolling with different reductions. The effects of welding speed and the rolling reduction on the microstructure, tensile properties, microhardness and fracture surfaces of the specimens are investigated. The results show that the microstructures of the FSW joint in different regions become more and more consistent as the hot rolling reduction increases. The mechanical properties of the FSW joints and the joint coefficient are improved with increasing rolling reduction; however,the hardness value in the stirred zone decreases firstly and then increases. When the rolling reduction is 50%, the tensile strength of FSW joint is close to that of base metal. The sample L_3 achieves the best comprehensive properties, with the yield strength, ultimate tensile strength and elongation of 162, 287.9 MPa, and 17.9%, respectively.     

钕对二元高铝镁合金组织及性能的影响

研究了稀土元素钕对Mg-15Al合金显微组织和力学性能的影响。试验结果表明:加入钕后,Mg-15Al合金的α-Mg晶粒明显细化,α+β共晶组织由粗大网状变得分散、细小,钕与铝结合形成稳定的Al11Nd3,合金的抗拉强度和伸长率均得到显著提高。钕加入量为1.0%时,组织细化效果最好,Mg-15Al合金的综合力学性能达到最佳。当钕加入量为1.5%时,α-Mg晶粒又变大、抗拉强度略有下降。     

超细晶Mg-2.5Zn-1Ca合金制备及其组织性能研究

通过挤压+等通道转角挤压(ECAP)复合加工工艺制备了超细晶Mg-2.5Zn-1Ca合金,采用OM、SEM、XRD、EBSD等手段分析变形过程中微观结构演变特征,结合力学性能变化,研究变形过程中合金强化机制。结果表明,经挤压+ECAP变形后,晶粒与第二相颗粒明显细化,其中挤压+2道次ECAP后获得了均匀的细晶组织,平均晶粒尺寸约1.1μm;同时,细小的Ca₂Mg₆Zn₃颗粒弥散分布于基体中。晶粒细化是剧烈塑性变形、动态再结晶和细小弥散的Ca₂Mg₆Zn₃相共同作用的结果。ECAP变形使合金的力学性能显著提高,2道次有最高的抗拉强度和延伸率,分别为275 MPa和17%。随着ECAP变形道次的增加,织构强度逐渐减弱,基面织构逐渐转变为一种新的织构,并且ECAP变形合金有较高的非基面施密特因子,组织均匀细化,使得材料有更好的延伸率。     

Al-Ti、Al-Ti-C中间合金对AZ91D镁合金组织和性能的影响

研究了Al-5Ti、Al-5Ti-0．25C和Al-8Ti-2C中间合金对AZ91D镁合金的组织、力学性能和耐腐蚀性能的影响。结果表明,添加Al-5Ti中间合金使晶粒粗化,而添加Al-5Ti-0．25C和Al-8Ti-2C中间合金使晶粒细化,Al-8Ti-2C中间舍金的细化效果明显且细化后组织细小均匀;添加Al-5Ti中间合金使合金的力学性能降低,而添加Al-5Ti-0．25C和Al-8Ti-2C中间合金均使合金的拉伸强度和伸长率得到了提高;添加Al-5Ti、Al-5Ti-0．25C和Al-8Ti-2C中间合金均使合金的耐腐蚀性能得到了改善。对于AZ91D合金而言,Al-8Ti-2C中间合金是一种良好的晶粒细化剂。     

挤压比对Mg—Zn—Zr—RE合金组织和性能的影响

研究了不同挤压比对铸态Mg-5．4Zn-0．3Zr-0．98RE镁合金微观组织和力学性能的影响。研究表明,当挤压比较小时,微观组织呈现出粗晶和细晶组成的混晶组织;随着挤压比增加到16,微观组织发生完全再结晶,获得均匀、细小的再结晶组织。动态再结晶是铸态镁合金Mg-5．4Zn-0．3Zr-0．98RE晶粒细化的机制。在挤压温度为250℃,挤压比为16时,合金获得的力学性能最好,抗拉强度为345MPa,屈服强度为223MPa,断后伸长率为21．4％。     

热挤压工艺对AZ31镁合金组织与力学性能的影响

在不同挤压条件下对AZ31镁合金进行了热挤压试验,并对挤压前后材料组织与力学性能的变化进行了分析.研究结果表明,AZ31镁合金热挤压时发生了动态再结晶,材料组织比铸态时细化,力学性能大幅度提高;AZ31镁合金挤压后的组织及力学性能受挤压温度及冷却方式影响,在本试验范围内,AZ31镁合金在623 K挤压后空冷得到的组织均匀细小,力学性能良好.     

Microstructure, Texture and Mechanical Properties of Extruded Mg-Zn-Zr Mg Alloy Profiles

通过X射线衍射分析、金相分析和力学性能测试对大尺寸ZK60镁合金挤压型材的微观组织、织构取向和室温力学性能进行系统研究。结果显示,挤压态ZK60镁合金中主要由α-Mg和Mg Zn2相组成,此外还有少量的Mg2Zn11和Zn2Zr3相。挤压变形后初始的粗大铸态组织沿着挤压方向被极大地细化和破碎,同时伴有部分动态再结晶发生。大部分晶粒的基面沿着挤压方向和横向排列而不是常规的挤压纤维状取向分布。沿着45o方向取样展现出最好的断裂伸长率,其中间和边部分别为28%和23%,而最大抗力强度则体现在沿着挤压方向拉伸样品在中间和边部分别为325和312 MPa。