Heat treatment of 7xxx series aluminium alloys—Some recent developments

The 7xxx series alloys are heat treatable wrought aluminium alloys based on the Al-Zn-Mg（-Cu） system. They are widely used in high-performance structural aerospace and transportation applications. Apart from compositional, casting and thermo-mechanical processing effects, the balance of properties is also significantly influenced by the way in which the materials are heat-treated. This paper describes the effects of homogenisation, solution treatment, quenching and ageing treatments on the evolution of the microstructure and properties of some important medium to high-strength 7xxx alloys. With a focus on recent work at Monash University, where the whole processing route from homogenisation to final ageing has been studied for thick plate products, it is reported how microstructural features such as dispersoids, coarse constituent particles, fine-scale precipitates, grain structure and grain boundary characteristics can be controlled by heat treatment to achieve improved microstructure-property combinations. In particular, the paper presents methods for dissolving unwanted coarse constituent particles by controlled high- temperature treatments, quench sensitivity evaluations based on a systematic study of continuous cooling precipitation behaviour, and ageing investigations of one-, two- and three-step ageing treatments using experimental and modelling approaches, in each case, the effects on both the microstructure and the resulting properties are discussed.

可持续与“假道伐虢”的设计战略研究

人类有改造自然的能力,但这种力量在自然界面前却又显得微不足道。为了弥补自身所犯过失,人类集思广益,以可持续发展为核心的可持续设计战略便顺应而生。假道伐虢设计几乎是与可持续设计背道而驰的一种设计模式。文章从宏观的设计角度出发,通过案例研究,以有形和无形、变与不变为研究关键要素分析两者的本质与特征。通过理论研究,试图寻觅出更适合人类社会发展的设计模式和适宜人类生存的设计战略。

Failure behavior and criteria of metallic glasses

Metallic glasses(MGs)constitute an emerging class of advanced structural materials due to their excellent mechanical properties.However,brittle failure at room temperature and the resultant complicated fracture behavior greatly limit their wide engineering applications.Over the past decades,the deformation and fracture in ductile or brittle mode referring to material compositions,load conditions,sample size,etc.,have been widely studied,and significant progress has been made in understanding the failure behavior of MGs.Micromechanisms of fracture have been revealed involving shear banding,cavitation and the nature of the crack tip field.The ductile-to-brittle transition and inherent governing parameters have been found.To well describe and predict the failure behavior of MGs,failure criteria for ductile and brittle MGs have been established empirically or based on atomic interactions.In this paper,we provide a detailed review of the above advances and identify outstanding issues in the failure of MGs that need to be further clarified.

Structure and coalbed methane occurrence in tectonically deformed coals

Research on structure of tectonically deformed coals(TDC) is a key issue in coal and gas outburst prevention and coalbed methane(CBM) exploitation.This paper presents a summary on the research progress in TDC's structural-genetic classification,tectonic strain influence on coal microstructure,coal porosity system,coal chemical structure and constituents,and their relationship with the excess coalbed methane.Previous studies suggested that tectonic deformation had significant influence on coal microstructure,coal super microstructure,and even chemical macromolecular structure.The main mechanisms of coal deformation are the tectonic stress degradation and polycondensation metamorphism(dynamical metamorphism).Besides,under different deformation mechanisms,the ultra-and micro-structure and chemical constituents of TDC presented distinct characteristics.Based on these achievements,we propose one possible evolutionary trend of TDC with different deformation mechanisms,and suggest that the coal and gas outburst in the TDC,especially in the mylonitic coals,may be not only controlled by geological structure,but also influenced by the tectonic stress degradation of ductile deformation.Therefore,further study on TDC should be focused on the controlling mechanism of deformation on structure and composition of coal,generation conditions and occurrence state of excess coalbed methane from deformation mechanism of coal.

Influence of Pre-deformation on Phase Transformations and Microstructures in NearβTi Alloy During Aging

The influence of pre-deformation on phase transformations,microstructures and hardening response in nearβTi alloy Ti5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe(wt%)during aging treatment was studied.The results show that obviousαphase refinement and stronger age hardening effect can be achieved when the alloy is slightly deformed before aging treatment.Because the formation of intermediate phases(O′,ωand O′′)suppresses long-range stress induced martensitic transformation and mechanical twinning,the alloy is mainly deformed via dislocation slipping during loading.Large numbers of crystal defects are generated during predeformation.With increasing the predeformation,the number density of dislocations increases gradually.These crystal defects generated by pre-deformation may partly annihilate upon early aging,but the precipitation ofαcan also be promoted,resulting in refinedαprecipitates.In the sample with 5%pre-strain,the average thickness ofαprecipitates decreases by 57%after aging at 600℃ compared with the sample without pre-strain,and the number density increases from 7.0±1 laths/μm^(2)to 22.0±3 laths/μm^(2).Some platelet-shapedαphases form when the samples experience comparably large pre-strains such as 12%and 20%.It proves that the refinedαprecipitates and better hardening effect can be achieved by pre-deformation plus aging treatment for titanium alloy.