镁合金疲劳性能的研究现状及展望

总结了近些年镁合金疲劳性能的研究,阐述了镁合金疲劳裂纹萌生和扩展理论,介绍了显微组织、冶金因素、环境介质、平均应力、温度等方面对镁合金疲劳性能的影响情况,归纳了提高镁合金疲劳强度和疲劳寿命的主要手段：表面形变强化、表面涂层处理、原料质量的改善以及晶粒细化等。展望了镁合金疲劳性能的研究前景。     

铸造镁合金疲劳研究现状

归纳了典型铸造镁合金的疲劳强度和疲劳寿命研究现状,介绍了铸造镁合金疲劳裂纹的萌生及扩展机制,以及基体组织、晶粒尺寸、第二相、铸造缺陷和工作环境等多种因素对镁合金疲劳性能的影响规律,总结了提高镁合金疲劳性能的方法,最后对铸造镁合金疲劳方面的研究进行了展望。     

镁合金焊接接头疲劳性能研究现状和发展趋势

对近年来镁合金及其焊接接头疲劳性能的研究现状和最新成果与进展进行了总结,指出了目前在镁合金焊接接头疲劳研究领域存在的问题与不足,最后分析了镁合金焊接接头疲劳性能和疲劳寿命的研究方向和工作重点.     

AM50镁合金孔挤压强化对其疲劳性能的影响

目的研究孔挤压处理对AM50镁合金疲劳性能的影响。方法对AM50镁合金进行孔挤压强化处理,使试样表面产生有益的残余压应力分布,并对残余应力的分布进行测定。对未处理镁合金及孔挤压镁合金进行疲劳性能测试,对比疲劳寿命及疲劳裂纹扩展速率,对疲劳断口进行扫描,分析孔挤压对AM50镁合金疲劳性能的影响。结果孔挤压处理后,孔周围残余压应力深度达到5.5 mm,且最大压应力值达-563 MPa,试样的疲劳寿命较未处理时增加了9倍,疲劳裂纹扩展速率大大降低,疲劳裂纹源由未处理时的孔表面转移到了挤压强化层内部。结论孔挤压可以明显抑制疲劳裂纹的萌生,延长疲劳寿命。     

AZ31镁合金激光-MIG复合焊接接头组织和疲劳性能研究

为了提高AZ31镁合金激光-MIG复合焊接接头的可靠性,本文开展了10mm厚AZ31镁合金组织和疲劳性能研究,分析了复合焊接接头的组织、硬度及疲劳性能。结果表明:镁合金激光-MIG复合焊缝形貌呈V型,焊缝热影响区较小,焊缝区为细小的等轴晶组织,且电弧区晶粒大小大于激光区,焊接接头软化区小。镁合金激光-MIG复合焊接接头沿焊接方向疲劳性能呈现出"先减后增,而后再减"的变化规律。     

深冷处理对AZ31B镁合金焊接接头疲劳性能的影响

研究了深冷处理对镁合金焊接接头疲劳性能影响。采用TIG焊接AZ31B镁合金,在-160℃、保温12 h深冷工艺下对镁合金焊接接头进行深冷处理。测试未深冷组和深冷组镁合金焊接接头疲劳性能,用最小二乘法拟合实验数据得到S-N曲线,计算2×106循环次数下,未深冷接头疲劳性能为36.42 MPa,深冷接头疲劳性能为41.26 MPa,深冷处理后接头疲劳强度提高13.29%。用盲孔法分别测试未深冷和深冷后垂直焊缝不同位置的残余应力。结果表明:深冷处理后焊接残余应力下降;深冷处理后焊缝晶粒比未深冷焊缝晶粒明显细化。未深冷接头疲劳断口为解理断裂,深冷后接头疲劳断口为韧性断裂,说明深冷处理可提高焊接接头韧性。深冷处理可以提高镁合金焊接接头疲劳性能。     

ZK60高强度镁合金喷丸强化疲劳性能实验研究

为了研究喷丸强化处理对ZK60镁合金疲劳性能的影响,采用气动式喷丸机对ZK60高强度镁合金试样进行喷丸强化,利用X射线衍射技术对喷丸处理试样表面进行残余应力测试分析,并利用扫描电镜分析了镁合金试样表面晶粒尺寸变化,对所有试样进行疲劳性能测试,分析喷丸强化对ZK60镁合金疲劳性能的影响,同时对疲劳断口进行扫描分析。实验结果表明:喷丸强化在ZK60镁合金试样表面产生了一定的残余压应力分布,且残余压应力最大值可达-198 MPa,同时,喷丸强化可使ZK60镁合金试样表面粗糙度减小,喷丸区域晶粒得到明显细化,喷丸强化使得试样表面完整性得到极大改善,从而提高了ZK60镁合金材料的疲劳性能,喷丸试样疲劳寿命相对于未处理试样最大提高了36%,疲劳裂纹源由试样表面转移到喷丸强化层以内,从而抑制了疲劳裂纹的萌生。     

医用可降解镁合金腐蚀疲劳行为研究进展

镁合金由于良好的生物安全性和力学承载性,同时兼具可控的体内外降解速率,被誉为新一代的"革命性医用金属材料"。然而,在湿润气氛条件下镁合金的耐蚀性能较差,尤其是在复杂载荷和腐蚀疲劳作用下(经历动态交变载荷及腐蚀介质协同作用)镁合金的力学固定/支撑功能急剧骤减,导致植入物过早/提前失效。因此,本文从医用镁合金疲劳失效的施加载荷、频率与腐蚀因素的耦合机理出发,针对医用镁合金体内外腐蚀疲劳寿命、断口微区特征和腐蚀速率间定量关系,阐述交变载荷下腐蚀疲劳失效微观机制。同时,深入解析了疲劳微裂纹萌生/扩展机理,全面总结了提升镁合金腐蚀疲劳性能的举措,以及展望了生物医用可降解镁合金的应用前景和发展方向。     

合金元素对体育器材用镁合金疲劳性能的影响

在Mg-Zn-Zr镁合金中添加不同含量的合金元素Sr或V,对其微观组织、室温疲劳性能和热疲劳性能进行研究。结果表明,添加合金元素Sr或V,尤其是复合添加Sr和V,可以有效改善Mg-Zn-Zr镁合金的室温疲劳性能和热疲劳性能。与未添加合金元素相比,复合添加Sr和V可使其室温疲劳寿命增加248.2%,在300~0℃循环1 000次后的单位面积质量增重减少79.2%。     

镁合金在汽车车身上的应用研究

为了克服汽车车身钢结构的总重偏重、工艺复杂等缺点,从汽车轻量化的角度出发,采用镁合金来替代某汽车前车体的钢结构来进行研究。介绍了镁合金材料在总重上的优势,以及镁合金的制造工艺,提出其在工艺上的优势。最后通过有限元分析软件进行结构疲劳耐久性能分析。结果表明,采用镁合金材料在保证车身疲劳耐久性能的基础上,实现了汽车车身的轻量化。通过此次研究也为汽车车身轻量化设计在关注疲劳耐久性上提供了参考。     

挤压变形Mg-x%Al-3%Ni合金的低周疲劳行为

通过对挤压变形Mg--x%Al--3%Ni(x=4, 5, 6, 7, 质量分数)合金进行总应变控制模式的室温疲劳实验, 研究了不同Al含量的挤压变形Mg--x%Al--3%Ni合金的循环应力响应、疲劳寿命和循环应力--应变行为. 结果表明: 不同Al含量的挤压变形Mg--x%Al--3%Ni合金均表现为循环应变硬化; 挤压变形Mg--x%Al--3%Ni合金的应变疲劳寿命与塑性应变幅、弹性应变幅间的关系分别服从Coffin--Manson和Basquin关系式.     

热处理对AE42压铸镁合金低周疲劳行为的影响

研究了固溶+时效处理(T6)对AE42压铸镁合金在疲劳加载条件下的循环应力响应行为、疲劳寿命以及断裂行为的影响。结果表明,压铸态和固溶+时效态的AE42镁合金均表现为循环应变硬化,固溶+时效处理可导致AE42压铸镁合金的循环应力幅有所提高,并可有效提高AE42压铸镁合金的疲劳寿命。疲劳断口形貌观察结果表明,疲劳裂纹萌生于疲劳试样的表面,并以穿晶方式扩展。     

压铸稀土镁合金高周疲劳试验研究

采用升降法对AZ91D、AZ91D 1?和AZ91D 2?压铸镁合金室温高周疲劳行为进行了试验研究。结果表明:适量稀土Ce的添加能够使压铸镁合金AZ91D的室温拉伸性能和疲劳强度得到提高;利用升降法计算出3种成分合金在应力比R=0.1、循环基数为107下的条件疲劳极限分别为96.7 MPa1、16.3 MPa和105.5 MPa,相当于其抗拉强度的46%左右;合金的疲劳断口呈现出准解理与韧窝断裂的混合特征。     

Mechanical Characteristics of Superplastic Deformation of AZ31Magnesium Alloy

As the lightest constructional metal on earth, magnesium (and its alloys) offers a great potential for weight reduction in the transportation industry. Many automotive components have been already produced from different magnesium alloys, but they are mainly cast components. Production of magnesium outer body components is still hindered by the material’s inferior ductility at room temperature. Magnesium alloys are usually warm-formed to overcome this problem; however, it was observed that some magnesium alloys exhibits superior ductility and superplastic behavior at higher temperatures. More comprehensive investigation of magnesium’s high temperature behavior is needed for broader utilization of the metal and its alloys. In this work, the high temperature deformation aspects of the AZ31B-H24 commercial magnesium alloy are investigated through a set of uniaxial tensile tests that cover forming temperatures ranging between 23 and 500 °C, and constant true strain rates between 2 × 10⁻⁵ and 2.5 × 10⁻² s⁻¹. The study targets mainly the superplastic behavior of the alloy, by characterizing flow stress, elongation-to-fracture, and strain rate sensitivity under various conditions. In addition, the initial anisotropy is also investigated at different forming temperatures. The results of these and other mechanical and microstructural tests will be used to develop a microstructure-based constitutive model that can capture the superplastic behavior of the material. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6–9, 2005.     

析出相对镁合金变形机理影响的研究进展

阐述了具有析出沉淀相镁合金变形行为的研究现状;概括了析出沉淀相对镁合金微观变形机制和再结晶行为的影响;总结了析出沉淀相的硬化机理以及不同形态析出物的硬化模型;提出了此研究领域亟待解决的科学问题。目前,针对析出沉淀相的形态、分布以及惯习面对镁合金不同滑移系和孪生行为的影响尚缺乏系统的研究;关于析出相与再结晶机制的交互作用并没有得到重视;此外,适用于析出沉淀强化镁合金更为普遍的硬化模型有待进一步研究。     

Corrosion behavior of magnesium and magnesium alloys

The automotive industry has crossed the threshold from using magnesium alloys in interior applications such as instrument panels and steering wheels to unprotected environment such as oil pan, cylinder head and wheels. The expanding territory of magnesium leads to new challenges.mainly environmental degradation of the alloys used and how they can be protected. The present critical review is aimed at understanding the corrosion behavior of magnesium and magnesium alloys in industrial and marine environments, and the effect of microstructure, additive elements and inhibitors on the corrosion mechanism.     

Influence of Twinning Texture on the Corrosion Fatigue Behavior of Extruded Magnesium Alloys

Bio-magnesium alloys have received great attention due to their degradability and biocompatibility.Corrosion fatigue failure is a huge challenge in vivo for bio-magnesium alloy implants.Understanding the eff ects of twinning textures on the corrosion fatigue of magnesium alloys is meaningful for the applications.In the current study,pre-compression strains of 2% and 4% were carried out on extruded rods.The effects of twinning texture on the corrosion performance and corrosion fatigue resistance were investigated.The hydrogen evolution tests indicated that twinning texture enhanced the corrosion resistance of longitudinal cross section by improving uniformity of surface energy.The results of corrosion fatigue tests indicated that the differences in mechanical damage caused by twinning texture dominated the corrosion fatigue behavior under high stress amplitude.The secondary cracks of surface deteriorated the corrosion fatigue resistance of the original specimens under low stress amplitude.The compact corrosion film and the re-passivation of matrix suppressed the hydrogen induced cracking,thereby improving the corrosion fatigue resistance of the pre-compression specimens.     

压铸镁合金高温蠕变研究现状及进展

综述了压铸镁合金高温蠕变的失效形式及机理 ,结合汽车用镁合金部件的实际制备 ,分析和讨论了提高压铸镁合金抗高温蠕变性能的方法 ,提出了在开发耐高温蠕变镁合金时应注意的问题。     

Improving the properties of magnesium alloys by equal channel angular pressing

Some aspects of grain refinement in the process of equal channel angular pressing (ECAP) are considered. Characteristics of strength, fatigue, and superplasticity of magnesium alloys AZ31, ZK60, and AS21X are studied. The possibilities of increasing the rate of hydrogen absorption by alloy ZK60 after ECAP treatment are discussed.