戚文军
, 冯晓伟
QI Wenjun, FENG Xiaowei
文献标识码: 分类号 TG146.22 文章编号 1005-3093(2016)07-0531-07
通讯作者:
收稿日期: 2015-12-15
网络出版日期: 2016-07-25
版权声明: 2016 《材料研究学报》编辑部 《材料研究学报》编辑部
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本文联系人: 戚文军
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摘要
利用光学显微镜和扫描电子显微镜分析了热轧态及退火态Mg-3Zn-2Gd合金的组织, 并测试了其室温拉伸力学性能。结果表明: 合金板材经应变为23%~67%的轧制后组织得到细化, 平均晶粒尺寸由10 μ m减至轧制应变为67%时的4 μ m。初始组织中的大量孪晶和剪切带逐渐减少; 随着轧制应变增至67%, 剪切带消失, 组织由动态再结晶晶粒和少量孪晶组成。拉伸力学性能显著提高, 抗拉强度 σ b和屈服强度 σ 0.2分别由未轧制时的255 MPa和215 MPa提高至轧制应变为67%时的305 MPa和300 MPa, 而伸长率 δ 先提高后降低。再经573 K退火处理1 h后, 合金组织发生静态再结晶, 变形不均匀区域消失, 由细小均匀等轴晶组成; σ b和 σ 0.2分别降至265 MPa和235 MPa, δ 提高至19.0%; 拉伸断口呈现大量韧窝, 表现为韧性断裂。
关键词：
Abstract
Microstructure of hot rolled and annealed Mg-3Zn-2Gd alloy was characterized by optical microscopy and scanning electron microscopy. Meanwhile, their tensile mechanical properties at ambient temperature were tested. The results show that the microstructure of the alloy sheet is refined after rolling by the strain range from 23% to 67% and the average grain size decreases from 10 μm to 4 μm by the rolling strain of 67%. Lots of twins and shear bands in the initial microstructure decrease gradually. When the rolling strain increases to 67%, the shear bands disappear, and meanwhile the dynamic recrystallization grains and few twins exist, while the tensile mechanical properties of the alloy are enhanced significantly. Tensile strength σb and yield strength σ0.2 increase from 255 MPa and 215 MPa for the non-rolled alloy to 305 MPa and 300 MPa for the rolled alloy by strain 67% respectively, while the elongation δ first increases, and then decreases. After annealed at 573 K for 1 h, the rolled alloy experienced static recrystallization, in the meanwhile, the non-uniform deformation areas disappeared and finally showed a microstructure of fine and uniform equiaxed grains, and the relevant σ b and σ 0.2 decreased to 265 MPa and 235 MPa, respectively, while δ slightly increases to 19.0%. The tensile fracture consists of a large number of dimples presenting the typical characteristic of ductile fracture.
Keywords：
镁合金具有低密度、高比强度和高比刚度以及良好的阻尼性能、切削加工性、导热性等优点, 在汽车、通讯电子和航空航天等领域正得到日益广泛的应用, 但其仍较差的力学性能和耐腐蚀性能限制了其更广泛的应用 [1-3]。稀土元素溶质原子的加入可减小镁合金的轴比 c / a 和非基面滑移的临界剪切应力, 同时可细化晶粒, 从而提高镁合金轧板的强度、塑形变形能力和降低织构 [4, 5]。研究表明 [6-8], Gd是一种有效改善变形镁合金组织和提高力学性能、且价格较便宜的稀土元素之一。Mg-2.0Zn-0.8Gd合金轧制变形后室温下的高延展性、高应变强化能力和低各向异性(基面织构强度最高值为2.95)甚至可比肩常用铝合金 [6]。Mg-1.11Zn-1.68Gd和Mg-1.06Zn-2.74Gd合金经过合适的热轧退火工艺(热轧前在723 K保温15 min, 热轧后在623 K退火1 h)后在室温下均表现出优异的成形能力: 极限伸长率可达到36%, 平均伸长率亦超过15% [7]。二次成形前的晶粒尺寸在10~30 mm之间和较低的(0002)基面织构可以使Mg-1.06Zn-2.74Gd合金在室温下具有良好的成形能力: 伸长率超过38% [8]。Mg-2Zn-1Gd合金经633 K单道次66%大压下轧制和后续623 K退火1.5 h处理后呈现更优异的机械性能和更弱的各向异性, 其最终伸长率可达28.9%, 初始为退火态的合金板材最终制得的薄板在室温下的成形性更好 [9]。随着Gd含量的增加, 高应变率轧制Mg-Zn-Zr合金的晶粒明显细化, 相组成发生改变, 准晶I相的含量增加, Mg7Zn3含量降低, Gd的添加能降低 α -Mg基体的堆垛层错能, 促进轧制过程中的动态再结晶 [10]。但到目前为此, Mg-Zn-Gd系合金轧制和退火处理过程中组织与性能的演变规律还未完全清楚。为此, 本文将选择Mg-3Zn-2Gd合金挤压板材作为轧制坯料, 依次进行轧制变形和退火处理, 研究其组织与性能的演变规律, 从而为高性能变形镁合金的开发及应用提供技术支撑。
合金锭由工业纯Mg、纯Zn和Mg-30%Gd(质量分数)中间合金在MRL-8型镁合金电阻炉中熔炼而成。待纯Mg熔化后依次将纯Zn和中间合金加入熔体中, 精炼搅拌后升温至1023 K高温静置20 min, 最后待熔体温度冷却至993 K后浇入圆柱型金属模具中得到铸坯。用JY Ultima2型等离子体原子发射光谱仪(ICP)测试该铸坯的具体成分为Mg-2.94Zn-2.06Gd(以下简称Mg-3Zn-2Gd)。整个熔炼过程中, 用CO2+0.2%SF6(体积分数)的混合气体保护熔体。铸坯置于热处理炉中经693 K均匀化处理12 h, 机加工后在638T挤压机上进行挤压实验, 参数为: 挤压板材截面为6 mm×75 mm, 挤压温度(T)为673 K, 挤压速度(V)为1.0 m/min。挤压板材经673 K保温1 h的退火热处理后, 在ZK-RZJ30450W型电脉冲异步轧制机上进行轧制实验, 轧机参数为: 轧辊外径为350 mm, 轧制线速度为30 r/min, 主电动机功率为30 kW。在轧辊上增加轧辊控温装置, 将轧辊温度始终控制在373~423 K范围内。轧制温度为673 K, 每道次间进行673 K退火处理10 min。实验获得三种不同的轧制应变, 分别为23%、33%和67%。最后, 轧制板材经573 K退火处理1 h。
经打磨和抛光后的各试样用苦味酸腐蚀剂(1.5 g苦味酸+25 mL乙醇+5 mL乙酸+10 mL蒸馏水)腐蚀在Leica DM IRM型光学显微镜(OM)上观察组织。在配有能谱仪(EDS)的JXA-8100型电子探针显微分析仪(EPMA)上观察组织和拉伸断口形貌。板状拉伸试样在DNS200型万能材料实验机上进行室温拉伸实验, 拉伸速度为2 mm/min。
图1为Mg-3Zn-2Gd合金挤压板材经轧制前后在轧制面的OM照片。可见, 挤压态组织为细小等轴晶晶粒, 平均晶粒尺寸约10 μ m, 少量第二相颗粒沿挤压方向呈流线分布。当轧制应变为23%时, 组织中等轴晶晶粒明显减少, 塑性变形主要以滑移与孪生为主, 轧制产生的孪晶增多, 第二相分布发生改变, 由于轧制过程中的剪切力作用形成剪切带。剪切带中存在大量再结晶晶粒, 使得晶粒进一步细化, 这是由于异步轧制引起的剪切变形使轧制组织出现变形不均匀现象。孪生和剪切带的出现为再结晶提供形核点。当轧制应变增至33%时, 孪晶减少, 大晶粒不断破碎, 动态再结晶不断进行, 晶粒得到进一步细化。当轧制应变继续增至67%时, 再结晶分数明显增多, 孪晶跟剪切带基本消失, 组织由细小再结晶晶粒及少量孪晶组成, 平均晶粒尺寸约4 μ m。随着轧制应变的增大, 第二相在剪切力作用下分布更分散、均匀, 从挤压态的流线分布转化为均匀分布。图2为Mg-3Zn-2Gd合金挤压板材经应变67%轧制后的EDS分析结果。可见, 细小的第二相由MgZnGd三元相组成, 第二相颗粒的平均尺寸为2~3 μ m。
图1 Mg-3Zn-2Gd合金挤压板材经轧制前后的OM照片
Fig.1 OM graphs of Mg-3Zn-2Gd alloy extrusion sheet before (a) and after rolling (b, c, d)
图2 Mg-3Zn-2Gd合金挤压板材经应变67%轧制后的EDS分析结果
Fig.2 EDS analysis of Mg-3Zn-2Gd alloy extrusion sheet rolled by the strain of 67%
Mg-3Zn-2Gd合金挤压板材分别经轧制后的拉伸力学性能结果列于表1中。可见, 挤压板材的抗拉强度 σ b、屈服强度 σ 0.2和伸长率 δ 分别为255 MPa、215 MPa和11.0%。经轧制后, 随着轧制应变的增大, 合金的综合力学性能逐渐提高, σ b和 σ 0.2分别提高至轧制应变为67%时的305 MPa和300 MPa, 提高幅度分别为20%和39%, 而 δ 先提高至轧制应变为23%时的16.0%, 后降至轧制应变为67%时的7.5%。轧制过程力学性能的变化是由于轧制过程中变形量的增大, 引起晶粒破碎和细化, 晶界和位错增加, 加工硬化现象越来越明显, 合金的屈服强度提高, 塑性降低。轧制态合金的拉伸断口呈现韧性断裂与脆性断裂的复合断裂特征, 主要由解理面和韧窝组成(见图3a和b)。
图3 Mg-3Zn-2Gd合金挤压板材分别经轧制和退火后的拉伸断口SEM像
Fig.3 SEM images of tensile fractures of Mg-3Zn-2Gd alloy extrusion sheets after rolling and annealing, respectively
图4为Mg-3Zn-2Gd合金轧制板材经573 K退火1 h后在轧制面的OM和SEM像。
图4 Mg-3Zn-2Gd合金轧制板材经退火后的OM和SEM像
Fig.4 OM and SEM images of Mg-3Zn-2Gd alloy rolled sheets after annealing
可见, 与轧制态组织相比, 退火态组织中孪晶和剪切带消失, 由大小不等的再结晶晶粒组成, 部分晶粒已开始长大。细小的第二相颗粒部分弥散分布于晶内, 部分沿轧制方向呈流线分布。随着轧制应变提高至67%时, 组织中再结晶过程进行更完全, 因此组织更均匀, 晶粒更细小。经退火处理后, 轧制过程中的加工硬化使合金内部孪晶和晶界处积塞的位错有足够的能量形成静态再结晶核心, 随着时间延长, 组织中的变形区域(孪生和剪切带)消失, 再结晶晶粒长大, 由于退火温度低, 晶粒长大不明显, 组织由均匀的等轴晶组成。
Mg-3Zn-2Gd轧制态合金经退火处理后的拉伸力学性能亦列于表1中。可见, 与轧制态拉伸力学性能相比, 随着轧制应变量的增加, 抗拉强度和屈服强度都不同程度的降低。如轧制应变为67%时, σ b和 σ 0.2分别从轧制态的305 MPa和300 MPa降至265 MPa和235 MPa, 但δ提高至19.0%。由此结果可以看出, 退火状态下加快了变形组织的静态再结晶与回复, 晶粒的回复与长大和变形应力的消除使变形组织更加均匀化, 退火态板材强度降低, 伸长率提高。退火态合金的拉伸断口已转变为完全的韧性断裂, 由大量韧窝组成(见图3c和d)。断口形貌特征的改变说明退火处理将有效改善轧制镁合金的塑性, 可获得强度和塑性适配的镁合金组织。
表1 Mg-3Zn-2Gd合金挤压板材分别经轧制和退火后的力学性能
Table 1 Tensile mechanical properties of Mg-3Zn-2Gd alloy extrusion sheets after rolling and annealing, respectively
| Strain/% | Condition | σ b /MPa | σ 0.2 /MPa | δ /% |
|---|---|---|---|---|
| 0 | extrusion sheet | 255 | 215 | 11.0 |
| 23.3 | rolling | 270 | 230 | 16.0 |
| annealing | 270 | 230 | 18.5 | |
| 33 | rolling | 300 | 295 | 13.0 |
| annealing | 260 | 220 | 17.5 | |
| 67 | rolling | 305 | 300 | 7.5 |
| annealing | 265 | 235 | 19.0 |
镁合金的热变形机制与铝合金存在诸多相似地方, 热变形过程伴随组织纤维化, 包括内部晶粒、杂质、第二相沿变形方向被拉长、拉细和回复与再结晶。滑移、孪生和晶界迁移为镁合金主要的塑性变形机制 [11, 12]。滑移的实质是位错在切应力作用下沿着滑移面逐步移动, 由于在较高温度(>573 K)下, 柱面滑移的临界分切应力(CRSS)值接近基面滑移{0001}, 柱面滑移系的启动, 增强镁合金塑性变形能力, 位错的滑移和攀移比较容易进行。同时也会伴随着孪晶变形。孪生变形通常发生于难以滑移的晶面处, 使晶体取向发生改变, 使处于不利晶向的滑移系转变为有利晶向, 滑移和孪生的交替作用使镁合金的塑性变形能力得到增强。
本文中Mg-3Zn-2Gd合金在热塑性变形过程中动态再结晶优先发生于变形不均匀的区域(如预先存在的晶界、孪晶和剪切带)。动态再结晶形核机理包括晶界凸出、孪生形核、连续动态再结晶、旋转动态再结晶和非连续动态再结晶 [13]。在高温下轧制变形发生的主要是晶界凸出主导的非连续动态再结晶 [14]。由于Mg-3Zn-2Gd合金在挤压变形后具有较高的动态再结晶分数, 晶界较多, 堆垛层错能较大, 在轧制变形时高密度的位错在晶界处集中, 高密度位错区应力不平衡使晶界发生局部迁移。突出的晶界在基面与非基面的位错交割下, 被分割出去形成亚晶, 亚晶随着应变的增大, 其晶粒取向也会随之增大。由于合金中添加Gd, 造成较多的MgZnGd高温相析出并钉扎于晶界与晶内, 第二相的存在促使在大变形量条件下形成的亚晶粒和亚晶界的取向较大, 晶格畸变增大, 使合金的强化效果明显。随着塑性变形程度的增加, 动态再结晶进行越充分, 组织得到细化效果越显著。其次, 剪切带的形成可旋转动态再结晶晶粒取向, 提高合金塑性变形能力 [15]。Mg-3Zn-2Gd挤压板材具有较强的基面纤维织构和较多再结晶组织, 材料各向异性显著, 这对轧制变形时发生动态再结晶更为有利, 较大的应变量可以形成更多的亚晶粒环绕在原始晶界周围, 与原始晶粒取向不同。而且Gd元素的添加更易形成一些大角度取向的晶粒, 促进亚晶粒的形成, 使原有组织中被拉长的纤维织构大幅减少或消失, 在很大程度上改善Mg-3Zn-2Gd合金的各向异性。
合金在573 K温度下退火处理, 变形组织中发生回复和再结晶过程, 高密度位错向有序的规则排列方向转化, 破碎的晶粒变成完整的晶粒, 拉长的晶粒变成等轴晶粒, 组织趋于均匀化。之前大变形轧制下形成的高密度位错区和晶粒畸变区成为再结晶晶粒的形核区, 亚晶粒在应变能的驱动下也会长大, 多边形化后趋于合并。形成较小的等轴晶粒(如图4c和e所示), 其宏观表现为合金抗拉强度下降, 塑性明显提高。
总之, 大应变加工和Mg-Zn合金中加入Gd会使MgZnGd合金在变形加工中更易形成位错塞积和晶格畸变, 促使亚晶粒形成, 组织得到细化, 提高合金的力学性能。
1. Mg-3Zn-2Gd合金挤压板材经轧制后组织得到细化, 平均晶粒尺寸由未轧制时的10 μ m减至轧制应变为67%时的4 μ m。当轧制应变为23%时, 组织由大量孪晶和剪切带组成; 随着轧制应变增至67%, 剪切带消失, 组织由动态再结晶晶粒和少量孪晶组成。合金的力学性能显著提高, σ b和 σ 0.2分别由未轧制时的255 MPa和215 MPa提高至轧制应变为67%时的305 MPa和300 MPa, 提高幅度分别为20%和39%, δ 先提高后降低。
2. 轧制板材再经退火处理后, 合金组织发生静态再结晶, 变形不均匀区域消失, 由细小均匀等轴晶组成; σ b和 σ 0.2分别降至265 MPa和235 MPa, δ 提高至19.0%。
3. 轧制态拉伸断口呈现韧性断裂与脆性断裂的复合断裂特征, 主要由解理面和韧窝组成, 退火处理后转变为完全的韧性断裂, 由大量韧窝组成。
The authors have declared that no competing interests exist.
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In-vitro evaluation of Mg-4.0Zn-0.2Ca alloy for biomedical application,
The in-vitro degradation and in-vitro cytotoxicity of the as-extruded Mg-4.0Zn-0.2Ca alloy were investigated. The in-vitro corrosion tests indicate that Zn and Ca elements can dramatically increase the corrosion potential of the as-extruded Mg-4.0Zn-0.2Ca alloy in the simulated body fluid and reduce the degradation rate. The cytotoxicity of the as-extruded Mg-4.0Zn-0.2Ca alloy examined by MTT tests on L929 cells suggest that the alloy has eligible toxicity for implant applications.
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Microstructure, mechanical properties and bio-corrosion properties of Mg-Zn-Mn-Ca alloy for biomedical application,
Microstructure, mechanical properties and bio-corrosion properties of as-cast Mg–Zn–Mn–Ca alloys were investigated for biomedical application in detail by optical microscopy, scanning electronic microscopy (SEM), mechanical properties testing and electrochemical measurement. SEM and optical microscopy observation indicated that the grain size of the as-cast alloys significantly decreased with the increasing of Ca content up to 0.5wt.%. Further increasing of Ca content did not refine the grain more. The phase constitute was mainly controlled by the atomic ratio of Zn to Ca. When the ratio was more than 1.0–1.2, the alloy was mainly composed of primary Mg and lamellar eutectic (α-Mg+Ca 2 Mg 6 Zn 3 ), while the alloy was composed of primary Mg and divorced eutectic (α-Mg+Mg 2 Ca+Ca 2 Mg 6 Zn 3 ) when the atomic ratio was less than 1.0–1.2. The yield strength of the as-cast alloy increased but the elongation and the tensile strength increased first and then decreased with the increasing of Ca content. It was thought that Mg 2 Ca phase deteriorated the tensile strength and ductility. Electrochemical measurements indicated that Mg 2 Ca phase improved the corrosion resistance of the as-cast alloy.
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Microstructures, aging behaviour and mechanical properties in hydrogen and chloride media of backward extruded Mg-Y based biomaterials,
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{112-2}<1123> slip system in magnesium, |
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| [6] |
Room-temperature ductility and anisotropy of two rolled Mg-Zn-Gd alloys,
To develop new magnesium alloy sheets with high formability at room temperature, the microstructure, texture, ductility and anisotropy of rolled EMg-1%Zn-1%Gd and Mg-2%Zn-1%Gd sheets were investigated. The microstructures were characterized as fully recrystallized grains with a large amount of homogeneously distributed fine particles in the matrix. The sheets exhibit an excellent ultimate elongation of nearly 36% and an uniform elongation greater than 15%. The Mg-1%Zn-1%Gd sheet has a random basal texture and the basal pole is tilted by about 30 from the normal direction towards the transverse direction. The planar anisotropy is shown to be as low as 0. The flow curves of the two Mg-Zn-Gd alloys display an abrupt yielding with a remarkable linear hardening at high strain rate after a plastic strain of roughly 3%. The majority of grains in the tilted texture have an orientation favorable for both basal slip and tensile twining because of a high Schmid factor. The low planar anisotropy, the large uniform elongations and the high strain-hardening rate observed in the Mg-Zn-Gd sheets imply excellent room temperature formability. (C) 2010 Elsevier B.V. All rights reserved.
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| [7] |
Excellent room-temperature ductility and formability of rolled Mg-Zn-Gd alloy sheets,
In order to develop new magnesium alloy sheets with high formability at room temperature, the microstructure, texture, ductility, and stretch formability of rolled Mg-2%Gd-1%Zn and Mg-3%Gd-1%Zn sheets were investigated. The microstructures of these rolled sheets consist of fine recrystallized grains with a large amount of homogeneously distributed tiny particles in the matrix. The basal plane texture intensity is quite low and the basal pole is tilted by about 30 from the normal direction toward both the rolling direction and the transverse direction. The sheets exhibit an excellent ultimate elongation of similar to 50% and a uniform elongation greater than 30%, and the Erichsen values reach similar to 8 at room temperature. The flow curves of the two Mg-Gd-Zn alloys sheets display a remarkable linear hardening after an obvious yield point. The majority of the grains in the tilted texture have an orientation favorable for both basal slip and tensile twinning because of a high Schmid factor. The excellent stretch formability at room temperature can be attributed to the non-basal texture and low texture intensity, which led to the following characteristics: a lower 0.2% proof stress, a larger uniform elongation, a smaller Lankford value and a larger strain hardening exponent. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.
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| [8] |
Influence of texture and grain size on the room-temperature ductility and tensile behavior in a Mg-Zn-Gd alloy processed by rolling and forging,
It was found that the rolled Mg-2.74Gd-1.06Zn (wt.%) alloy sheets could exhibit excellent room-temperature ductility and formability by our previous studies. In this work, the Mg-2.74Gd-1.06Zn alloy was processed using hot rolling, forging and annealing treatments in order to control the texture and the grain size. Emphasis was laid upon the influence of these factors on the room-temperature ductility and the tensile behavior. The results showed that the excellent tensile ductility of the Mg-2.74Gd-1.06Zn alloy sheets should be mainly attributed to its low intensity of (0002) pole figure, instead of the non-basal texture type. The Mg-2.74Gd-1.06Zn alloy sheets with a grain size of 10-30 mu m all exhibited a large elongation-to-failure (>38%); comparing with the weak texture, the grain size had a negligible effect on their room-temperature ductility. As grain size increased further (>50 mu m), the twining activity increased substantially during the post-uniform deformation, leading to its premature failure and low post-uniform elongation. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.
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| [9] |
Microstructure and mechanical property evolution of Mg-Zn-Gd alloy with different initial states during processing, 不同初始态Mg-Zn-Gd加工过程中组织和性能的演变,
主要研究了初始状态分别为轧态和退火态的Mg-2%Zn-1%Gd合金在360℃进行单道次66%大压下轧制和其后的退火加工过程中组织和性能的演变规律.通过金相观察、拉伸实验和杯突实验分析表明：不同初始状态Mg-Zn-Gd合金随着加工过程的进行其力学性能及演化规律也明显不同.这是由对应组织中的剪切带、孪生密度和晶粒尺寸共同决定的.初始退火态Mg-Zn-Gd合金经大压下轧制和热处理加工之后表现出了更优秀的机械性能和更小的各向异性,其最终伸长率可达28.9%.初始为退火态的MgZn-Gd合金板材最终制得的薄板在室温下的成形性更好.
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| [10] |
Effects of minor Gd addition on microstructures and mechanical properties of the high strain-rate rolled Mg-Zn-Zr alloys,
Effects of minor Gd addition (0, 0.2, 0.5 and 0.8mass%) on microstructure and mechanical properties of the high strain-rate rolled (HSRR) Mg–5.5Zn–0.6Zr-based alloys are investigated by OM, XRD, SEM, TEM and mechanical testing. The Mg–5.5Zn–0.6Zr alloy consists of the α-Mg matrix and the Mg 7 Zn 3 phase. Minor Gd addition can effectively refine grains and change phase compositions. The quasicrystal I-phases (Mg–Zn–Gd ternary phase) are formed and mainly aggregated along the grain boundaries in the Mg–5.5Zn–0.6Zr-based alloys with minor Gd addition. The amount of the I-phase increases with the increase of Gd addition, but the amount of the Mg 7 Zn 3 phase decreases. With the Gd addition up to 0.8mass%, the main phases of the alloy are the α-Mg matrix and I-phases. The Gd addition can reduce the stacking fault energy of the α-Mg matrix and thus promote the dynamic recrystallization (DRX) during the HSRR process. The broken quasicrystal I-phase particles resulted from the HSRR process play a role in promoting the nucleation of DRX, inhibiting the growth of the DRX grains and refining grains. Meanwhile, the dispersion strengthening and precipitation strengthening of the I-phase particles contribute to the enhanced strength. The as-rolled Mg–5.5Zn–0.6Zr–0.8Gd alloy exhibits an optimal strength-ductility balance, with the ultimate tensile strength of 327MPa, the yield strength of 242MPa and the elongation to rupture of 22%, respectively. The addition of Gd can effectively weaken the recrystallization texture and modify the tensile fracture mechanism from quasi-cleavage to ductile.
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| [11] |
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| [12] |
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| [13] |
Research progress on plastic deformation mechanism of Mg alloys, 镁合金塑性变形机理研究进展,
简述了具有密排六方(hcp)结构镁合金材料各种可能的滑移和孪生系统及其临界切变应力; 以镁合金塑性变形机理为主线, 分别对单晶和多晶镁合金材料塑性变形行为及微观机理的影响规律, 轧制、挤压及不同严重塑性变形模式下镁合金织构的形成机理, 形变镁合金材料退火过程中回复与再结晶及镁合金材料在热变形过程中的动态再结晶机理, 以及沉淀硬化镁合金塑性变形机理、特别是沉淀相与位错滑移及孪生的交互作用机理等进行了总结与评述. 同时, 对高成形性镁合金及提高镁合金塑性成形能力的塑性变形机理进行了讨论.
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| [14] |
Dynamic recrystallization in pure magnesium, |
| [15] |
Dynamic recrystallisation and the development of microstructure during the high temperature deformation of magnesium,
Polykristalline Proben aus Mg-0,8Al lurden im Druckversuch bei h02heren Temperaturen verformt. Danach lurden Mikrostruktur und Textur untersucht. Oberhalb von ~425 K folgt dynamische Rekristallisation auf die Bildung von Verformungsllillingen. Nach den optischen und elektronenmikroskopischen Beobachtungen treten Gitterrotationen in den Korngrenlbereichen auf, in denen dann die Rekristallisation einsetlt. Die dynamische Rekristallisation llischen 425 und 600 K enth01lt nur einen unbedeutenden Beitrag durch landerung von Groβlinkelkorngrenlen, 01hnelt jedoch einem Mechanismus, der bei einigen Mineralen gefunden lorden ist. Unterhalb von ~600 K lird die Verformung bei gr02βeren Dehnungen inhomogen. Sie ist beschr01nkt auf Scherlonen, die aus feink02rnigen, durch Rekristallisation gebildeten Gebieten bestehen. Diese Gebiete sind geometrisch leicher als der Rest der Proben.
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