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

In creep of alpha-iron, IS effects (interstitial-substitutional interaction) were reported. Similar effects are expected in ternary substitutional solid solutions. In the present report, effects of the second substitute (the third element), whose size misfit is small, on creep behavior and the transition stress from Alloy-type to Metal-type have been investigated experimentally. Three alloy systems are employed, i.e. aluminum-magnesium-zinc, aluminum-magnesium-lithium and alpha iron-beryllium-manganese solid solutions. Although no change in equivalent magnesium concentration by the addition of zinc nor lithium is expected, creep rates and the transition stress in Al-Mg alloys are affected by these third elements. Similar changes are observed in alpha iron-beryllium-manganese system. Substitutional elements are not always independent with each other, so that the apparent interaction between the first substitute, i.e. magnesium or beryllium, and a dislocation can be affected by the third elements.

Effects of the third element on creep behavior of Al-Mg and αFe-Be solid solution alloys

The present invention relates to an alloy that is mainly composed of Mo, Si, B, Ti, at least one of Zr and Hf, and at least one of C and N. The present invention also relates to a method for producing an alloy that is mainly composed of Mo, Si, B, Ti, at least one of Zr and Hf, and at least one of C and N by a casting process.

Alloy and method for producing same

Prediction of long-term creep curves

Effects of Alloying Elements of the Creep Resistance of Thixomolded Mg‐Al‐Ca‐X (X=Si, Zn, Mm, Ba, Sr) Alloys

During thixomolding ® of Mg alloys, fine grains (size of ∼ 10 μm) and continuous eutectic compounds are formed along grain boundaries. These compounds are partly responsible for the superior creep strength of Mg alloys. In this study, we investigate the effects of eutectic compounds formed along grain boundaries in thixomolded ® Mg 96 Zn 2 Y 2 on creep deformation at 573 K. By performing microstructure analyses, we find that two types of continuous eutectic compounds―Mg 3 Y 2 Zn 3 and Mg 12 YZn―are formed in the alloy. The strain rate of Mg 96 Zn 2 Y 2 is about two orders of magnitude lower than that of a heat-resistant alloy Mg 93 Al 5 Ca 2 (Mg-6 mass%Al-3 mass%Ca) at 573 K. The stress exponent n at 573 K is approximately 7, and it is considered that creep deformation is controlled by dislocation motion. All scribe lines produced on a specimen of Mg 96 Zn 2 Y 2 are curved. Furthermore, in the case of a specimen with a creep strain of 7%, no abrupt steps are observed at grain boundaries and interfaces between the α-Mg matrix and eutectic compounds. Our results indicate that eutectic compounds formed along grain boundaries are effective in suppressing grain boundary sliding.

Kouichi Maruyama

Papers

Effects of the third element on creep behavior of Al-Mg and αFe-Be solid solution alloys

Alloy and method for producing same

Prediction of long-term creep curves

Effects of Alloying Elements of the Creep Resistance of Thixomolded Mg‐Al‐Ca‐X (X=Si, Zn, Mm, Ba, Sr) Alloys

Effects of Eutectic Compounds Formed along Grain Boundaries in Thixomolded® Alloy Mg96Zn2Y2 on Creep Deformation