FSP对AZ31合金型材加工硬化率及力学性能的影响

对AZ31镁合金挤压型材实施了搅拌摩擦加工(Friction Stir Processing·FSP),利用光学显微镜和拉伸试验机研究了搅拌摩擦加工对试样加工硬化率及力学性能的影响。结果表明,AZ31镁合金经搅拌摩擦加工后,晶粒得到细化,均匀伸长率和总伸长率相近,室温伸长率达22%;拉伸应变超过0.03时,搅拌区材料的加工硬化率超过母材,此时搅拌区和母材的显微组织中均出现变形孪晶,不同的是搅拌区材料的变形孪晶整体呈带状分布,且加工硬化率也较高。     

搅拌摩擦加工AZ31细晶镁合金超塑性行为研究

借助搅拌摩擦加工工艺制备了AZ31细晶镁合金,研究对比了原始母材和各种晶粒尺寸细晶镁合金的超塑性行为。结果表明：AZ31板材平均晶粒尺寸由7.67μm细化到0.94μm~3.21μm。在450℃,应变速率5×10-4/s-1时原始母材最大延伸率为630%,搅拌摩擦加工后的材料最大延伸率为405%,说明晶粒尺寸与超塑性性能没有线性关系。超塑性变形机制主要是晶界滑移,孪生对变形也有一定影响。断裂机制是晶间微小空洞的形成、长大和连接。     

搅拌摩擦加工AZ31细晶镁合金超塑性行为

借助搅拌摩擦加工工艺制备了AZ31细晶镁合金,研究对比了原始母材和各种晶粒尺寸细晶镁合金的超塑性行为。结果表明:AZ31板材平均晶粒尺寸由7.67μm细化到0.94~3.21μm。在450℃,应变速率5×10~(-4) s~(-1)时原始母材最大延伸率为630%,搅拌摩擦加工后的材料最大延伸率为405%,说明晶粒尺寸与超塑性性能没有线性关系。超塑性变形机制主要是晶界滑移,孪生对变形也有一定影响。断裂机制是晶间微小空洞的形成、长大和连接。     

FSP法制备细晶镁合金微观组织及其耐腐蚀性能

采用搅拌摩擦加工(Friction stir processing,FSP)技术对AZ31镁合金进行加工处理,通过金相显微镜(OM)、显微硬度计、电子万能拉伸试验机、扫描电镜(SEM)与浸泡腐蚀等手段,研究了经过FSP加工后镁合金的微观组织、硬度及耐蚀性能。结果表明,改变FSP加工参数可得到不同程度的AZ31镁合金细晶组织,力学性能较母材均有所提升;当旋转速度为750 r/min、加工速度为47. 5 mm·min~(-1)时,镁合金微观组织细化最显著,力学性能最优。FSP加工产生动态再结晶,致使晶界增多,Mg17Al12相发生固溶,使750 r/min-47. 5 mm·min~(-1)参数下的试样在3. 5wt%Na Cl溶液中的耐蚀性能有较大提升。     

搅拌摩擦加工细晶AZ91镁合金的加工特性（英文）

搅拌摩擦加工细化AZ91镁合金,研究钻孔过程中不同切割速度和进料速率下晶粒尺寸和二次相对加工特性的影响。经搅拌摩擦加工得到了过饱和AZ91镁合金,晶粒尺寸由(166.5±8.7)μm细化到(21.7±13.5)μm。相比未加工的AZ91镁合金(HV(108.2±15.6)),经搅拌摩擦加工的合金硬度为HV(88.95±6.1),这归因于二次相的减少。然而,搅拌摩擦加工AZ91合金的平均切割力略微减小。相比未加工的AZ91镁合金,搅拌摩擦加工AZ91合金的钻孔边缘损伤较低。因此,虽然在钻孔过程中晶粒细化可以略微增大切割力,但在AZ91镁合金加工过程中边缘处理较好。     

搅拌摩擦加工工艺对AZ31镁合金显微组织与拉伸性能的影响

利用搅拌摩擦加工技术,研究了不同工艺对AZ31镁合金显微组织和拉伸性能的影响。结果表明:当进给速度为200、400 mm/min、搅拌针转速低于1000r/min时,AZ31镁合金的显微组织由于发生动态再结晶,获得了均匀细小的等轴晶,平均晶粒尺寸小于7μm。随着搅拌针转速提高,该合金显微组织不断粗化。与母材相比,经搅拌摩擦加工后,AZ31镁合金的应变强化效应明显增强,塑性明显提高,但屈服强度有所降低。采用搅拌速度600 r/min、进给速度400mm/min,工艺FSP处理后,该合金获得了最佳的综合力学性能。     

搅拌摩擦加工制备镁合金表面复合层的显微组织和力学性能

选用轧态AZ31镁合金为基体、C60颗粒为增强相,采用搅拌摩擦加工技术(FSP)制备镁合金表面复合材料,搅拌针头旋转速度为600 r·min~(-1),加工速度为118 mm·min~(-1),分别进行1～3道次FSP加工后,通过金相、透射、硬度和拉伸等测试,对搅拌加工区复合显微组织和力学性能进行表征分析。研究表明:FSP可使镁合金晶粒显著细化; C60加入后,在1～3道次FSP内,随着加工道次升高,C60分散程度上升,复合材料平均晶粒尺寸降低,材料硬度上升,抗拉强度上升,但弥散于晶间的团聚颗粒使其拉伸性能低于母材;添加C60后的试样中,2道次硬度有明显上升,最高硬度可达母材的1. 73倍,3道次试样硬度平均值最高。结果表明,可通过FSP制备镁基表面复合层强化材料。     

退火工艺对搅拌摩擦加工镁合金微观组织和显微硬度的影响

采用搅拌摩擦加工(Friction stir processing,FSP)技术对AZ31镁合金进行加工,通过采取不同温度及保温时间的退火工艺,研究了FSP镁合金在退火过程中的微观组织演变过程及硬度变化规律。结果表明,FSP成功制备了细晶AZ31镁合金,其平均晶粒尺寸细化程度达54.9%。当退火温度在200～300 ℃时,加工区(SZ)晶粒尺寸较为稳定,且组织发生不同程度的均匀化和细化;当温度超过300 ℃时,加工区晶粒互相吞噬而快速长大。在退火温度较低、短时间保温时热影响区(HAZ)组织变化不明显,而延长保温时间或者升高温度,HAZ区组织会迅速细化、均匀化;当退火温度超过300 ℃时,再结晶会在短时间内完成,随后晶粒继续长大。在300 ℃下保温60 min为最优退火工艺,可使SZ、HAZ组织分别细化10.9%、35.6%。     

搅拌摩擦加工处理对AZ31镁合金高应变率变形行为的影响

对15 mm厚热轧态AZ31镁合金板进行搅拌摩擦加工处理,进给速度V=400 mm/min,搅拌针旋转速度U=600 r/min~1 400 r/min。利用Hopkinson压杆测试装置对不同状态的AZ31镁合金进行了高应变率冲击试验,分析了搅拌摩擦加工工艺对该合金动态应力-应变行为及其应变率效应的影响。结果表明,在高应变率冲击条件下,搅拌摩擦加工后的AZ31镁合金的动态屈服强度提高。V=400 mm/min、U=600 r/min搅拌摩擦加工工艺处理的AZ31镁合金获得了最好的冲击变形抗力,且搅拌摩擦加工处理后AZ31镁合金的动态应力-应变行为对应变率不敏感。晶粒细化是提高合金抗冲击变形能力的主导因素。     

搅拌摩擦焊焊接速度对AZ31镁合金焊接接头性能的影响

选用单板搅拌摩擦焊方法对AZ31镁合金进行焊接试验,利用光学显微分析、微观硬度分析、拉伸性能测试等方法,对焊接接头的微观组织和力学性能进行研究。结果表明,搅拌摩擦焊对AZ31镁合金焊接接头有明显的细化晶粒效果,且焊缝区硬度分布也随晶粒尺寸的降低而呈逐渐升高的趋势。经搅拌摩擦焊后,AZ31镁合金抗拉强度明显提高。     

Evaluation of corrosion resistance of multipass friction stir processed AZ31 magnesium alloy

Multipass friction stir processing (FSP) is an effective method to produce a homogeneous microstructure and enhance the mechanical properties of magnesium (Mg) alloys. However, few studies have concentrated on the variation of corrosion resistance of Mg alloys during multipass FSP. Electrochemical alternating current (AC) impedance, polarization behavior, hydrogen evolution, and corrosion morphology were used to investigate the effects of subsequent passes on the corrosion resistance of FSP AZ31 plates. A quasi‐in‐situ observation of the growth of corrosion products was carried out to further study the corrosion behaviors of FSP AZ31 alloy. It is found that subsequent passes could further reduce the grain size of FSP AZ31 alloy and result in an increase in the hardness compared with the first pass. Moreover, subsequent passes are beneficial to the improvement in the corrosion resistance of AZ31 alloy. Pitting corrosion occurs in FSP AZ31 plates, which has not changed after subsequent passes.     

搅拌摩擦加工AZ31镁合金的超塑性

对搅拌摩擦加工AZ31镁合金的微观组织和拉伸力学行为进行了研究。结果表明,通过搅拌摩擦加工,热轧AZ31板材的平均晶粒尺寸由92.0μm细化到11.4μm。搅拌摩擦加工板材在高温下具有优异的塑性,伸长率在温度为723K和应变速率为5×10-4s-1的条件下达到1050%。该材料还具有高应变速率超塑性,在723K和1×10-2s-1的条件下伸长率达到268%。在相同实验条件下,母材由于晶粒尺寸粗大,没有显示出超塑性。     

Cover Picture: Materials and Corrosion. 1/2020

Cover: Friction stir processing (FSP) and subsequent aging heat treatment were used to modify the microstructure of AZ80 magnesium alloy. EBSD images (left) and pole figures (right) of (a, b) base material (BM), (c, d) FSP, (e, f) FSP-with aging treatment (5 h at 180°C) and (g, h) FSP-with aging treatment (24 h at 180°C) samples. The average grain size of FSP sample was refined from (a) to (c) due to dynamic recrystallization through FSP. After aging heat treatment, the average grain size of FSP-5 and FSP-24 samples was slightly larger (e, g) than that of the FSP sample. The pole figures clearly demonstrate that BM sample possessed an obvious preferred grain orientation. More detailed information can be found in: Liying Huang, Kuaishe Wang, Wen Wang, Pai Peng, Ke Qiao, Qiang Liu, Microstructural evolution and corrosion behavior of friction stir processed fine-grained AZ80 Mg Alloy, Materials and Corrosion 2020, 71, 93.     

Enhanced corrosion behavior and mechanical properties of AZ91 magnesium alloy developed by ultrasonic-assisted friction stir processing

In this study, ultrasonic-assisted friction stir processing (UaFSP) and friction stir processing (FSP) were conducted on AZ91 magnesium alloy sheets, and their microstructure, corrosion behavior, and mechanical properties were comparatively investigated. Scanning electron microscopy, open-circuit potential, and potentiodynamic polarization were used to study the corrosion behavior of the material. Electrochemical measurements reveal that employing UaFSP, the corrosion rate of the AZ91 magnesium alloy was significantly reduced where lower corrosion current density for UaFSP specimens was obtained (2.09 µA/cm²) compared with 3.42 µA/cm² for the FSP and 6.82 µA/cm² for the base metal. This is mainly attributed to the alteration of morphology and better distribution of the β-Mg₁₇Al₁₂ phase during UaFSP. By using ultrasonic vibration in FSP, a finer grain structure was obtained, which improved the tensile strength and hardness of the AZ91 Mg alloy.     

AZ31镁合金搅拌摩擦焊焊缝电化学性能的分析

试验的样品为3 mm厚挤压态AZ31镁合金,采用搅拌摩擦焊接工艺对焊而成.通过静态失重法、动电位极化曲线以及交流阻抗谱(electrochemical impedance spectroscopy,EIS)测试,研究了室温下浓度5%(质量分数)NaCl溶液中AZ31镁合金搅拌摩擦焊焊缝和母材的电化学行为.结果表明,在室温腐蚀介质中通过静态失重法测得AZ31镁合金母材和焊缝在168 h后的平均腐蚀速率分别为0.154和0.135 g/(m2·h),通过动电位极化曲线及交流阻抗谱(EIS)测得AZ31镁合金母材和焊缝的腐蚀电流分别为0.001 63和0.000 45 A/cm2,极化电阻分别为9.553和12.61Ω/cm2.AZ31镁合金搅拌摩擦焊焊缝的抗腐蚀性能优于其母材的表现.     

Microstructure,Mechanical Properties,and Corrosion Behavior of Mg-Al-Ca Alloy Prepared by Friction Stir Processing

Friction stir processing (FSP) was used to modify the microstructure and improve the mechanical properties and corrosion resistance of an Mg-Al-Ca alloy. The results demonstrated that, after FSP, the grain size of the Mg-Al-Ca alloy was decreased from 13.3 to 6.7 μm. Meanwhile, the Al₈Mn₅ phase was broken and dispersed, and its amount was increased. The yield strength and ultimate tensile strength of the Mg-Al-Ca alloy were increased by 17.0% and 10.1%, respectively, due to the combination of fine grain, second phase, and orientation strengthening, while the elongation was slightly decreased. The immersion and electrochemical corrosion rates in 3.5 wt% NaCl solution decreased by 18.4% and 37.5%, respectively, which contributed to grain refinement. However, the stress corrosion cracking (SCC) resistance of the modified Mg-Al-Ca alloy decreased significantly, which was mainly due to the filiform corrosion induced by the Al₈Mn₅ phase. SCC was mainly controlled by anodic dissolution, while the cathodic hydrogen evolution accelerated the SCC process.     

Microstructural evolution and corrosion behavior of friction stir processed fine-grained AZ80 Mg alloy

Friction stir processing (FSP) and subsequent aging heat treatment were used to modify the microstructure of AZ80 magnesium alloy. The influence of FSP and aging heat treatment on the corrosion behavior was systematically studied by using potentiodynamic polarization, immersion, and slow strain rate tensile tests. The results revealed that FSP led to grain refinement, rapid dissolution of β-phase, and the deflection of c-axis from transverse direction (TD) and processing direction (PD) by approximately 55° and 25°, respectively, improving the static corrosion and stress corrosion cracking (SCC) resistance. The aging heat treatment rendered a little influence on the grain size and slightly affected the grain orientation. The content of β-phase in FSP-5 and FSP-24 samples was 8.1 and 21.8 wt.%, respectively. Static corrosion and SCC resistance of FSP-5 and FSP-24 samples were lower than those of the FSP samples. Compared with FSP-5 sample, the amount of β-phase and the proportion of Al₂O₃ increased in FSP-24 sample, leading to enhanced static corrosion and SCC resistance. SCC behavior was controlled by anodic dissolution, whereas the presence of hydrogen accelerated the SCC.     

Machining characteristics of fine grained AZ91 Mg alloy processed by friction stir processing

AZ91 Mg alloy was considered and friction stir processing (FSP) was adopted to achieve grain refinement to investigate the effect of grain size and secondary phase on machining characteristics during drilling at various speeds and feeds. Super saturated AZ91 Mg alloy was obtained after FSP and the grain refinement was achieved from (166.5±8.7) µm to (21.7±13.5) µm. Surprisingly, hardness reduced for FSP AZ91 Mg alloy (88.95±6.1) compared with AZ91 alloy (108.2±15.6), which was attributed to the reduced secondary phase. However, the mean cutting force for FSP-treated (FSPed) AZ91 Mg alloy was marginally increased. The edge damage of the drilled holes was lower for FSPed AZ91 Mg alloy compared with unprocessed AZ91 Mg alloy. Hence, it can be understood that the grain refinement may slightly increase the cutting forces during drilling but better edge finishing can be achieved in machining of AZ91 Mg alloy.     

碳酸钠对搅拌摩擦加工AZ31镁合金缓蚀性能的影响

通过搅拌摩擦加工(FSP)手段,对3 mm厚的AZ31镁合金板材作表面加工处理.然后在质量分数为5%的NaCl腐蚀溶液中添加不同浓度的碳酸钠作为缓蚀剂,通过动电位极化曲线以及交流阻抗(EIS)测试,研究了室温下该缓蚀剂对镁合金母材及搅拌摩擦加工处理镁合金电化学行为的影响.结果表明,添加缓蚀剂后,FSP镁合金及母材的腐蚀电流密度均减小,极化电阻及电荷转移电阻均增大,而且FSP镁合金的缓蚀效率要优于母材的缓蚀效率,且随浓度的增加而增加,碳酸钠是一种有效的无机缓蚀剂,并且其缓蚀作用效果与金属表面状态密切相关.     

Microstructures and properties of aluminum film and its effect on corrosion resistance of AZ31B substrate

Aluminum films with thickness of 8.78-20.82μm were deposited on the AZ31B magnesium alloys by DC magnetron sputtering.The influences of aluminum film on the micro-mechanical properties and corrosion behavior of the magnesium alloys were investigated.The morphology of aluminum film was examined by scanning electron microscopy and the microstructure of aluminum film was analyzed by X-ray diffiactometry.Nanoindentation and nanoscratch tests were conducted to investigate their micromechanical properties.More...