抗蠕变镁合金研究进展

综述了国内外高温镁合金的研究进展,讨论了镁合金的抗高温蠕变机理和提高镁合金抗高温蠕变性能的方法,对高温镁合金的研究开发提出了一些建议.     

Intermetallics in Magnesium Alloys

Intermetallic phases can be found in almost every magnesium alloy. These intermetallic compounds play a very important role in optimizing the microstructure and mechanical properties. The present paper reviews the effects of intermetallics in magnesium alloys mainly based on their stabilities: dissolvable intermetallics at low temperatures and thermal stable intermetallics at elevated temperatures. The effects of intermetallics are discussed in the age hardenable and creep resistant magnesium alloys, separately. Finally, the further investigations are remarked on the intermetallics, including their precipitation processes, crystal structures and crystallographic orientation relations with magnesium matrix. The aim is to supply useful information in developing new wrought and creep‐resistant magnesium alloys which will be used in the powertrain at elevated temperatures.     

Fatigue of Magnesium Alloys

Magnesium alloys show a high specific strength and are therefore increasingly used for light‐weight constructions in transportation industry.^[1,2] To predict the behaviour of the material under the influence of cyclic loading it is vital to understand the fatigue behaviour of magnesium alloys. Only when understood properly, it is possible to fully apply the potential weight reduction by using magnesium alloys. A very important aspect in fatigue of magnesium alloys is the influence of a corrosive media and elevated temperatures, of which both are relevant in automotive applications. These two factors tend to have deleterious effects on magnesium alloys and therefore also have to be considered in investigations on the fatigue behaviour of magnesium alloys.     

Progress and Challenge for Magnesium Alloys as Biomaterials

Magnesium alloys are very biocompatiable and show promise for use in orthopaedic implant. Significant progress of research on bioabsorbable magnesium stents and orthopaedic bones has been achieved in recent years. The issues on degradation, hydrogen evolution, and corrosion fatigue and erosion corrosion of magnesium alloys and various influencing factors in simulated body fluid (SBF) are discussed. The research progress on magnesium and its alloys as biomaterials and miscellaneous approaches to enhancement in corrosion resistance is reviewed. Finally the challenges and strategy for their application as orthopaedic biomaterials are also proposed.     

镁合金的生物医用研究

镁是可被人体吸收的常量元素,且具有较高的比强度和比刚度,在医用植入材料领域具有广阔的应用前景.综述了镁及镁合金作为医用植入材料的研究现状,并对医用镁及镁合金的表面改性技术进行了简单叙述.     

轧制AZ91镁合金超塑性研究

研究了轧制态AZ91镁合金在实验温度为350℃－425℃（0．67Tm-0.76Tm）以及应变速率为10^-3s^-1－10^0s^-1下的超塑性变形能力及其特征。实验发现，轧制态AZ91镁合金在350℃（0.67Tm）以及应变速率为10^-3s^－1时获得最大延伸率455．05％，应变速率敏感系数达到0．64。通过分析表明，高应变速率下的超塑性变形过程中主要的变形机制为晶界滑移机制，但其主要的协调机制则是孔洞扩散聚集机制。     

Semi‐Solid Processing of Tailored Aluminium‐Lithium Alloys for Automotive Applications

This paper describes the development and evaluation of thixoformable Al‐Li‐Mg‐based alloys performed at the collaborative research center SFB 289, RWTH Aachen. Scandium and zirconium were added to AlLi2.1Mg5.5 (A1420) with the aid of DoE (Design of Experiments), and precursor billets were manufactured by pressure induction melting (PIM). To evaluate the thixoformability of the synthesized alloys semi‐solid processed connecting rods were manufactured by the rheo container process (RCP). Subsequent heat treatment raised the mechanical properties to maximum values of tensile strength, 430 MPa, yield strength of 250 MPa, and an elongation to fracture of 13 %. The RCP process was designed for the special requirements of highly reactive alloys. The paper presents the remarkable property and process benefits of the semi‐solid processing of Al‐Li alloys.     

医用镁合金的腐蚀行为与表面改性

对镁及镁合金作为生物材料的可能性和研究进展进行了评述。介绍了镁及镁合金的腐蚀行为与影响其耐蚀性能的主要因素。同时对医用镁及镁合金的几种表面改性技术进行了讨论。     

镍基耐蚀合金研究进展

镍基耐蚀合金被广泛应用于苛刻环境下的工业领域.介绍了镍基耐蚀合金的成分及分类,综述了国内外各种耐蚀合金的发展历程及研究现状,主要论述了Ni-Cu系、Ni-Cr系、Ni-Fe-Cr系、Hastelloy系等.我国有丰富的镍资源,但相关研究还不够系统,笔者认为应加强镍基耐蚀合金的开发,并展望了镍基耐蚀合金未来的发展前景.     

镁合金及其成形工艺与应用状况

综述了镁合金的种类、特点及性能，全面介绍了包括塑性成形、半固态成形、RSP等在内的镁合金成形方法，并对镁合金在航空航天、汽车、3C等工业的应用历史及现状进行了概述，分析了镁合金目前存在的问题，指出了下一步研究的重点，并展望了镁合金的发展前景。     

High Temperature Creep and Superplasticity in a Mg-Zn-Zr Alloy

Creep and superplasticity were investigated by testing a fine-grained extruded Mg-Zn-Zr magnesium alloy under a wide range of applied stress in the temperature range between 100 and 300 ℃. Grain boundary sliding became the dominating mechanism at 200 ℃, leading to a true superplastic behaviour at 300 ℃, where superplasticity was attained even under relatively high strain rates (5×10-3 s-1 ). By contrast, for lower temperatures, the straining process was controlled by dislocation climb. A comprehensive model, taking into account the simultaneous operation of the different mechanisms, was developed to describe the strain rate dependence on applied stress.     

镁合金无铬化学转化膜的耐蚀性研究

在非高锰酸钾的锰盐和磷酸盐组成的体系中，加入镁缓蚀剂，在AZ31D镁合金上获得了化学转化膜，用阳极极化曲线和中性盐溶液浸泡测试了转化膜的耐蚀性，转化膜经5％NaCl侵蚀后具有自愈合能力。XRD分析表明，转化膜主要为Mn3(PO4)2;SEM观察表明，转化膜为规则的结晶状形貌。     

Microstructural Evolution during Partial Remelting of Al-Si Alloys Containing Different Amounts of Magnesium

The effect of magnesium on the microstructures of A356 aluminum alloy in as-cast and semi-solid conditions was investigated. The result showed that magnesium refined the size of primary α（Al） phase and eutectic silicon. Magnesium also modified considerably the eutectic silicon and decreased the size of globular α（Al） solid phase in the semi-solid processed alloy. Coarsening rate of the solid α（Al） phase during partial remelting at semi-solid temperature decreased by adding magnesium, probably due to the decrease of both the solid- liquid interfacial energy and inter-diffusion coefficient of solute atoms.     

Constitutive equations in creep of Mg–Al alloys

The creep response of commercial Mg–Al alloys for die-casting was described by taking into account the distinctive microstructure consisting of α-Mg primary grains and a divorced eutectic formed by supersaturated α-Mg and β-Mg₁₇Al₁₂ typical of these materials. The α-Mg grains were assimilated to soft zones in a composite reinforced by hard zones rich in precipitates, the latter being the grain boundary regions of supersaturated α-Mg and β-Mg₁₇Al₁₂. Constitutive equations correlating minimum creep rate, applied stress and temperature were derived for dilute Mg–Al solid solutions and used to calculate the forward stress acting in soft and hard regions, respectively, on the assumption that both creep with a similar strain rate. The role of the particles was then expressed by a threshold stress; as a consequence, Si addition resulted in a substantial increase in the threshold stress in the hard zones, a mechanism that explains the reduction in minimum creep rate observed in the high-temperature low-stress regime in Mg–Al–Si compared with Mg–Al–Zn alloys.