Plastic anisotropy and the role of non-basal slip in magnesium alloy AZ31B

The activity of non-basal slip systems and dynamic recovery at room temperature in fine-grained AZ31B magnesium alloys

Magnesium alloys have received an increasing interest in the past 12 years for potential applications in the automotive, aircraft, aerospace, and electronic industries. Many of these alloys are strong because of solid-state precipitates that are produced by an age-hardening process. Although some strength improvements of existing magnesium alloys have been made and some novel alloys with improved strength have been developed, the strength level that has been achieved so far is still substantially lower than that obtained in counterpart aluminum alloys. Further improvements in the alloy strength require a better understanding of the structure, morphology, orientation of precipitates, effects of precipitate morphology, and orientation on the strengthening and microstructural factors that are important in controlling the nucleation and growth of these precipitates. In this review, precipitation in most precipitation-hardenable magnesium alloys is reviewed, and its relationship with strengthening is examined. It is demonstrated that the precipitation phenomena in these alloys, especially in the very early stage of the precipitation process, are still far from being well understood, and many fundamental issues remain unsolved even after some extensive and concerted efforts made in the past 12 years. The challenges associated with precipitation hardening and age hardening are identified and discussed, and guidelines are outlined for the rational design and development of higher strength, and ultimately ultrahigh strength, magnesium alloys via precipitation hardening.

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Precipitation and Hardening in Magnesium Alloys

Magnesium and its alloys do not in general undergo the same extended range of plasticity as their competitor structural metals. The present work is part I of a study that examines some of the roles deformation twinning might play in the phenomenon. A series of tensile test results are reported for the common wrought alloy AZ31. These data are employed in conjunction with a simple constitutive model to argue that View the MathML source twinning (which gives extension along the c-axis) can increase the uniform elongation in tensile tests. This effect appears to be similar to that seen in Ti, Zr and Cu–Si and in the so called TWIP phenomenon in steel.

Twinning and the ductility of magnesium alloys Part I: “Tension” twins

Friction stir processing (FSP), developed based on the basic principles of friction stir welding (FSW), a solid-state joining process originally developed for aluminum alloys, is an emerging metalworking technique that can provide localized modification and control of microstructures in near-surface layers of processed metallic components. The FSP causes intense plastic deformation, material mixing, and thermal exposure, resulting in significant microstructural refinement, densification, and homogeneity of the processed zone. The FSP technique has been successfully used for producing the fine-grained structure and surface composite, modifying the microstructure of materials, and synthesizing the composite and intermetallic compound in situ. In this review article, the current state of the understanding and development of FSP is addressed.

Friction stir processing technology: A review

Microstructural and Morphological Changes During Thermal Cycling of Cu Thin Films

Creep of type 316 stainless steel, strengthened by thermally unstable precipitates, was analyzed by two different creep concepts; One assumes creep to be a steady state process characterized by minimum creep rate, and the other supposes that two relaxation processes, strain hardening and weakening due to microstructural degradation, take place simultaneously during creep. In the former the minimum creep rate cannot provide correct information on creep process, but in the latter a rate constant for the relaxation processes gives a rational conclusion that creep is a diffusion-controlled process. When microstructural degradation severely occurs like engineering materials, creep deformation should be analyzed as a relaxation type phenomenon rather than a steady state process.

An Examination of Constitutive Laws by High Temperature Creep of Engineering Materials

Compression creep tests of a Ti-48%Al (mole fraction) alloy were carried out at 1150K with soft-orientated PST crystal Parallel twinning took placed uring the creep Changes in lamellar microstructure caused by the parallel twinning were investigated, and their effects on creep deformation behavior were disc ussed The results show that the parallel twinning occurs in an early stage of creep, and makes significant contribution to creep strain in the domains favorably oriented for the twinning The nucleation of parallel twins finishes at a strain of about 3% There is a critical resolved shear stress for parallel twinning, and it is about 50 Mpa in the Ti-48%Al PST crystals at 1150K The activity of parallel twinning increases with increasing applied stress or in a coarse lamellar mater ial The addition of parallel twins reduces the average value of lamellar spacin g In general, the refinement of lamellar structure should improve creep resistance However the strengthening by parallel twinning is not evident in creep of the soft PST crystals because the soft deformation modes are the dominant deformation mode in the crystals

Changes in lamellar microstructure by parallel twinning during creep in soft PST crystal of TiAl alloy

Une equation de fluage est proposee, elle est basee sur le fait qu'un processus de durcissement par deformation et qu'un processus d'adoucissement mecanique, chacun suivant une fonction exponentielle en fonction du temps, travaillent independamment lors du fluage. Analyse par cette equation des donnees de fluage pour trois aciers avec differentes teneurs en chrome (0,38-0,94-11,90). Comparaison des parametres de l'equation entre les trois aciers

Kouichi Maruyama

Papers

Microstructural and Morphological Changes During Thermal Cycling of Cu Thin Films

An Examination of Constitutive Laws by High Temperature Creep of Engineering Materials

Changes in lamellar microstructure by parallel twinning during creep in soft PST crystal of TiAl alloy

An Analysis of High Temperature Creep as Relaxation Processes with Special Reference to CrMoV Steels

Reduction in steady-state creep rates by aluminum-doping in zinc single crystals