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

Life Assessment of Elevated Temperature Components by Reference to Creep Damage.

A modified stress distribution for a subsonic moving dislocation

SYNOPSIS A theoretical equation to evaluate the steady-state creep-rates, ɛ˙s, based on a recovery creep model is derived: ɛ˙sαrσα2λ2, where r is the recovery rate, which can be determined from results of stress-reduction tests, σα the applied stress, and X the dislocation link-length. Two cases of recovery are considered, i. e., recovery of dislocation networks at sub-boundaries and that of three-dimensional networks within subgrains. The high-temperature steady-state creep of Fe-Mo solid solutions, creep characteristics of which have been reported to be well rationalized as viscous glide creep, is analyzed using this equation. It is shown that stress dependence of λs is well explained from the viewpoint of recovery, in which the activation and the annihilation of dislocations at sub-boundaries are considered to take place.

Analysis of Steady-state Creep of Fe-Mo Alloys from the Viewpoint of Recovery

Thermal cycling was performed in Al-lmo%Si thin films deposited on Si wafers. After a given number of cycling between room temperature and 723 K, residual stress was measured at room temperure. Residual stress was found to increase with increasing the cycling number up to the 4th cycle, followed by further a continuous decrease by further cycling. The intial increase was found to be related to the increase of lattice dislcocations and their tangling. The following decrease was caused by crack formation along grain boundaties or by film delamination in some cases.

Thermal Cycling Fatigue in Aluminum-Alloy thin Films on Silicon Substrate

Lamellar microstructures of a Ti-48 mol.% Al alloy were varied by changing heating rate in the α + γ dual phase field, and their creep properties were investigated at 1150 K and 316 MPa. The minimum creep rate of the alloy first decreases and then increases with increasing the heating rate. Average spacing of α2 lamellae decreases and density of γ/α2-lamellar boundaries increases with increasing the heating rate. The high density of γ/α2 boundaries stabilizes the lamellar microstructure during creep, resulting in the decrease in the minimum creep rate. With increasing the heating rate, α2 lamellae are discontinuous and γ/α2 boundaries become less efficient in retarding recovery. This microstructural degradation results in the increase in creep rate at high heating rate. A reduction of creep rate by one order of magnitude from as-grown lamellar microstructure is achieved at the optimal heating rate.

Kouichi Maruyama

Papers

Life Assessment of Elevated Temperature Components by Reference to Creep Damage.

A modified stress distribution for a subsonic moving dislocation

Analysis of Steady-state Creep of Fe-Mo Alloys from the Viewpoint of Recovery

Thermal Cycling Fatigue in Aluminum-Alloy thin Films on Silicon Substrate

Effect of heating rate in α + γ dual-phase field on lamellar microstructure and creep resistance of a TiAl alloy