Texture Selection Mechanisms during Recrystallization and Grain Growth of a Magnesium-Erbium-Zinc Alloy

Binary and ternary Mg-1%Er/Mg-1%Er-1%Zn alloys were rolled and subsequently subjected to various heat treatments to study texture selection during recrystallization and following grain growth. The results revealed favorable texture alterations in both alloys and the formation of a unique ±40° transvers direction (TD) recrystallization texture in the ternary alloy. While the binary alloy underwent a continuous alteration of its texture and grain size throughout recrystallization and grain growth, the ternary alloy showed a rapid rolling (RD) to transvers direction (TD) texture transition occurring during early stages of recrystallization. Targeted electron back scatter diffraction (EBSD) analysis of the recrystallized fraction unraveled a selective growth behavior of recrystallization nuclei with TD tilted orientations that is likely attributed to solute drag effect on the mobility of specific grain boundaries. Mg-1%Er-1%Zn additionally exhibited a stunning microstructural stability during grain growth annealing. This was attributed to a fine dispersion of dense nanosized particles in the matrix that impeded grain growth by Zener drag. The mechanical properties of both alloys were determined by uniaxial tensile tests combined with EBSD assisted slip trace analysis at 5% tensile strain to investigate non-basal slip behavior. Owing to synergic alloying effects on solid solution strengthening and slip activation, as well as precipitation hardening, the ternary Mg-1%Er-1%Zn alloy demonstrated a remarkable enhancement in the yield strength, strain hardening capability, and failure ductility, compared with the Mg-1%Er alloy.

Recrystallization and Grain Growth Phenomena in Stainless Steels for Different Thermo-Mechanical Processes

The mechanical properties of steels are strictly connected to chemical composition as well as to microstructural features obtained after thermo-mechanical processing. As a consequence, recrystallization and grain growth are relevant to the mechanical properties of steels, thus suggesting the necessity of mathematical models able to predict the microstructural evolution after thermo-mechanical cycles. In particular, in stainless steel grades, mechanical characteristics, and a proper microstructure with an adequate grain size distribution, are very important in order to achieve the required formability and deep drawing properties for many applications. This paper deals with the study of microstructural changes, such as grain size variations and recrystallized volume fraction in stainless steels during isothermal treatments through the application of a mathematical model, able in general to describe the primary recrystallization and grain growth in metals. The developed model takes into account the recrystallization phenomenon and Zener drag effect. A general continuity equation is proposed describing in continuous way recrystallization and grain growth phenomena without taking into account textures effect. The influence of input parameters is analyzed.

Physical Modelling of Recrystallization and Grain Growth in Steels: Analysis of Free Parameters

The mechanical properties of steels are strongly affected by grain size and chemical composition variations. Many industrial developments have been carried out both from the point of view of composition variation and grain size in order to exploit the effect of these variables to improve the mechanical proprieties of steels. It is also evident that recrystallization and grain growth are relevant to the mechanical properties of steels, thus suggesting the necessity of mathematical models able to predict the microstructural evolution after thermo-mechanical cycles. It is therefore of primary importance to study microstructural changes, such as grain size variations of steels during isothermal treatments through the application of a mathematical model, able in general to describe the primary recrystallization and grain growth in metals. This paper deals with the recrystallization and grain growth modelling of steels based on the statistical theory of grain growth originally developed by Lücke [1] and here integrated to take into account the effect of recrystallization and Zener drag effect. A general continuity equation is proposed describing in continuous way recrystallization and grain growth phenomena without taking into account textures effect. The effect of input parameters is analyzed.

Effect of Zr Addition on Recrystallization Behavior of Extruded Al-Mg-Si Alloys Containing Mn

Effects of Zr addition on recrystallized structure and texture in extruded Al-Mg-Si alloy containing Mn have been investigated. Materials were homogenized at temperatures in the range 550 °C to 590 °C and extruded at 500 °C at the speed of 10m/min. In extruded Al-Mg-Mn-Si-Zr alloy, the fraction of Cube oriented grains reached 40% as homogenization temperature raised to 590 °C. On the other hand, the fraction of Cube oriented grains in extruded Al-Mg-Mn-Si alloy was limited to 20-30 %. In addition, to clear the formation process of recrystallized grains in these alloys, observation of hot-compression deformed and recrystallized grain structures were carried out. It was suggested that moderate Zener drag promoted the preferential recrystallization of cube oriented grains

Microstructural Evolution during Isothermal Annealing of a Cold-Rolled Al-Mn-Fe-Si Alloy with Different Microchemistry States

In this paper, investigations of the softening behaviour of a supersaturated Al-Mn-Fe-Si alloy during annealing after cold rolling have been carried out. Two different homogenization conditions were considered, of which one gives a condition of a large amount of small pre-existing dispersoids, i.e. providing a significant static Zener drag, while the other gives a condition where both concurrent precipitation and dispersoid drag effects are limited. The homogenized samples with different microchemistry states were then cold-rolled to different strains before subsequent annealing at 300°C. The softening and concurrent precipitation behaviours have been monitored by hardness and electrical conductivity measurements respectively, and the microstructural evolution has been characterized by EBSD. It is clearly demonstrated that the actual microchemistry state, i.e. amount of solutes and second-phase particle structures as determined by the homogenization procedure strongly influence the softening behaviour where a fine dispersion of pre-existing dispersoids together with concurrent precipitation slow down the recrystallization kinetics considerably and give a very coarse and elongated grain structure.

Effects of Driving Force and Boundary Migration Velocity on Formation of Recrystallization Texture in Cold Rolled Pure Aluminum Sheets

The effects of net driving force for migration of high angle grain boundaries were emphasized beside many other factors which could influence the process of texture formation during recrystallization annealing of 95% cold rolled pure aluminum sheets. The net driving force consists basically of stored energy. However, it could be reduced by recovery, boundary drag, solute drag and Zener drag in different extents, in which only boundary drag is mis-orientation dependent. It was indicated that both oriented nucleation and oriented growth have obvious influence on recrystallization texture, and how far they influence the texture depends also on the level of net driving force when the grain growth starts during annealing. Oriented growth, which is induced by the differences in boundary drag of differently oriented grains, and the corresponding texture formation, could be observed easily when the recrystallization proceeds under relative higher solute drag and Zener drag in commercial purity aluminum. The oriented nucleation process prevails during recrystallization of sufficiently recovered high purity aluminum with very low solute drag and Zener drag, after which strong cube texture forms. In this case the oriented growth indicates limited effect. Both the oriented growth and oriented nucleation will fail if high purity deformation matrix without clear solute drag and Zener drag has not experienced an obvious recovery before recrystallization grain growth, since extremely high net driving force leads to very small critical nucleus size and multiplicity of growing grains, which results in randomization of recrystallization texture.

Characterization the Softening Behavior of Cold Rolled AlMnFeSi-Alloys during Conditions of Concurrent Precipitation

In the present work an Al-Mn-(Fe-Si) model alloy has been subjected to different homogenization treatments, to achieve materials with different microchemistry states in terms of constituents, levels of Mn in solid solution (potential for concurrent precipitation) and dispersoid densities, followed by cold rolling and back-annealing. Characterization of the microchemistry state after homogenization and the evolution in dispersoid precipitation and its effects on the softening behavior after deformation has been performed. It is demonstrated that variations in microchemistry may have dramatic effects on the softening kinetics and the final grain structures, where both pre-existing fine and dense dispersoids before back annealing as well as precipitation concurrent with recovery and recrystallization strongly retard kinetics and generally lead to a coarse grain structure, while conditions with no or limited concurrent precipitation softens much faster and generally results in an even, fine and equi-axed grain structure. The different softening behaviors have been discussed in terms of Zener drag effects derived from the dispersoid evolutions.