Microstructure control during twin roll casting of an AZ31 magnesium alloy

The existing twin roll casting technique for magnesium alloys suffers heterogeneity in both microstructure and chemistry and downstream processing is required to improve the strip quality, resulting in cost rise. In the present work, twin roll casting was carried out using an AZ31 magnesium alloy, with the application of intensive shearing melt conditioning prior to casting. The effect of process parameters such as pouring temperature and casting speed on microstructure control during casting and subsequent downstream processing was studied. Experimental results showed that the melt conditioning treatment allowed the production of AZ31 strips with uniform and refined microstructure free of centreline segregations. It was also shown that an optimized combination of pouring temperature and casting speed, in conjunction with a strip thickness control operation, resulted in uniformly distributed stored energies due to enhanced plastic deformation, which promoted recrystallization during casting and subsequent heat treatment. Strips prepared by twin roll casting and homogenization developed similar microstructural features to those prepared by twin roll casting followed by lengthy downstream processing by homogenization, hot rolling and annealing and displayed a weaker basal texture, exhibiting a potentially better formability.The EPSRC (UK

Casting and rolling magnesium alloys

The paper is concerned on the production of magnesium alloy strips by Twin-Roll-Casting and their subsequent hot rolling to a final thickness of ≥ 1 mm. In this connection, specific characteristics of magnesium and of the used alloys are discussed. Subsequently, the deformation behavior and the possibilities to its increase are introduced. Additionally, the production technology of hot strips and the properties obtainable are presented on the example of the alloys AZ31. Mechanical properties and the development of microstructure as well as their change during the way of production clarify the development process. Special attention is paid to the thermal pretreatment of the casting condition with local deformation

Twin roll casting and melt conditioned twin-roll casting of magnesium alloys

Recently, BCAST at Brunel University has developed a MCAST (melt conditioning by advanced shear technology) process for conditioning liquid metal at temperature either above or bellow the alloy liquidus using a high shear twin-screw mechanism. The MCAST process has now been combined with the twin roll casting (TRC) process to form an innovative technology, namely, the melt conditioned twin roll casting (MC-TRC) process for casting Al-alloy and Mg-alloy strips. During the MC-TRC process, liquid alloy with a specified temperature is continuously fed into the MCAST machine. By intensive shearing under the high shear rate and high intensity of turbulence, the liquid is transformed into conditioned melt with uniform temperature and composition throughout the whole volume. The conditioned melt is then fed continuously into the twin-roll caster for strip production. The experimental results show that the AZ91D MC-TRC strips with different thicknesses have fine and uniform microstructure. The strip consists of equiaxed grains with a mean size of 60-70μm. The strip displays extremely uniform grain size and composition throughout the whole cross-section. Investigation also shows that both TRC and MC-TRC processes with reduced deformation are effective to reduce the formation of defects, particularly the formation of the central line segregations

Study of deformation texture in an AZ31 magnesium alloy rolled at wide range of rolling speed and reductions

Having the lowest density among all structural metals, magnesium has opened new horizons for developing commercial alloys with successful use in a wide variety of applications [1-2]. However, the plasticity of Mg is restricted at low temperatures because: (a) only a small number of deformation mechanisms can be activated [3-4], and (b) a preferred crystallographic orientation (texture) develops in wrought alloys, especially in flat-rolled sheets [5-7]. Therefore, manufacturing processes such as rolling and stamping should be performed at elevated temperatures [1, 8]. These barriers to the manufacturing process increase the price of magnesium wrought alloy products and limits the use of Mg to castings [9-10]. As a result, many studies have been conducted to improve formability by investigating the effect of manufacturing process. Therefore the current sheet production techniques, based on DC casting and hot rolling, are basically slow because the demand is easily met [11]. Twin roll casting followed by hot rolling appears to be processing route which can fulfil high volumes and reduced costs. The present authors succeeded in single-pass large draught rolling of various magnesium alloy sheets at low temperature (<473K) by high speed rolling [12]. Based on the data available in those works [13- 17], the sheet obtained by high-speed rolling exhibited a fine-grained microstructure (mean grain size of 2-3 μm), with good mechanical properties. For these advantages, the high speed rolling is a promising process to produce high-quality rolled magnesium alloy sheets at a low cost. For these advantages, the HSR is a promising process to produce high-quality rolled magnesium alloy sheets at a low cost. The goal of this research is thus to investigate the mechanisms responsible for the much higher rollability and the grain refinement after HSR. To do that, in this study, different rolling speeds from 15 to 1000 m/min were employed to twin rolled cast AZ31B magnesium alloy and different reductions

Research on calculation model of rolling force in twin roll inclined strip casting process

For the twin roll inclined strip casting process, the tilt angle function is introduced to describe the casting process, and the mathematical model of the calculation of the rolling force coupled with the tilt angle function is proposed, and the relationship between the influence of the tilt angle on the rolling force is derived, thus enriching the casting and rolling theory

공정변수에 따른 쌍롤박판주조 Mg-2Y-1Zn 마그네슘 합금의 기계적 및 부식 특성 평가

학위논문(석사)--서울대학교 대학원 :공과대학 재료공학부,2019. 8. 신광선.Magnesium and its alloys have gained utmost attention as potential lightweight structural materials owing to their low density. However, the application of magnesium alloys is still limited by their low strength and poor corrosion resistance compared to aluminum alloys. Recently, Mg-RE-Zn alloys have shown good mechanical and corrosion resistance by forming long period stacking ordered (LPSO) phase. In the present study, Mg-2Y-1Zn (at. %) alloy was cast by horizontal twin-roll casting (TRC) process. The cast strips were processed through hot-rolling and analyzed for their mechanical properties and degradation behavior. The tensile behavior of the alloy showed improved mechanical property with higher preheating temperatures. Electrochemical and immersion tests indicated that the corrosion resistance was enhanced by higher preheating and annealing temperatures. The SKPM measurement revealed that the LPSO phase acts as a micro cathode to form galvanic couple with the alpha Mg which dominated the corrosion mechanism. The alloy showed its unique microstructure when solution heat-treated and the corrosion resistance was greatly improved by forming dense surface film.1 Introduction 1 2 Background and Objective 4 2.1 Twin-roll casting 4 2.2 Hot-rolling of Mg alloys 6 2.3 Degradation of Mg 7 3 Experimental Procedure 12 3.1 Twin-roll casting 12 3.2 Hot-rolling of TRC strips 14 3.3 Characterization of hot-rolled sheets 16 4 Results and Discussion 18 4.1 Twin-roll casting 18 4.1.1 Casting of Mg-2Y-1Zn strips 18 4.1.2 Microstructure of cast strips 20 4.1.3 Mechanical properties of cast strips 29 4.1.4 Corrosion properties of cast strips 32 4.2 Hot-rolling of TRC strips 43 4.2.1 Microstructure 43 4.2.2 Mechanical properties 51 4.2.3 Corrosion properties 59 4.3 Hot-rolling of solution heat-treated strips 81 4.3.1 Microstructure 84 4.3.2 Mechanical properties 88 4.3.3 Corrosion properties 88 5 Data Analysis 102 5.1 Comparison with gravity cast alloy 102 5.2 Comparison with the literature 113 6 Conclusion 116 References 119Maste

Analysis of the flow imbalance on the profile shape during the extrusion of thin magnesium sheets

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in AIP Conference Proceedings 1567, 1098 (2013) and may be found at https://doi.org/10.1063/1.4850162.The extrusion process facilitates the production of magnesium sheets featuring a very thin thickness as well as excellent surface properties by using a single process step only. However, the extrusion of the magnesium sheets applying not optimized process parameters, e.g. low billet temperature or/ and poorly deformable magnesium alloy, produce pronounced buckling and waving of the extruded sheets as well as a variation of accuracy in profile shape along the cross section. The present investigation focuses on the FEM-simulation of the extrusion of magnesium sheets in order to clarify the origin of the mentioned effects. The simulations identify the flow imbalance during extrusion as the main critical factor. Due to the flow imbalance after passing the die a large compression stress zone is formed causing the buckling and waving of the thin sheets. Furthermore, the simulations of the magnesium sheet extrusion reveal that the interaction of the material flow gradients along the width and along the thickness direction near the die orifice lead to the variation of the accuracy in profile shape

The Effect of Misch Metal Additions on the Structure and Workability of Al-Mg (7-100/.) Alloys

ON the alloying elements used in aluminium alloys, copper was one of' the earliest employed commercially and for many years it has been the principal one. Aluminium-copper alloys to which manganese, magnesium or silicon has been added, belong to the important group generally known as "Duralumin". The binary alloys of aluminium with magnesium attra- cted the interest of investigators as early as 1900. There have been numerous attempts to utilise for general purposes alloys containing as Much as 10% magnesium ; alloys containing up to 30% magnesium have been used for special purposes

Magnesium Alloys Structure and Properties

Magnesium Alloys Structure and Properties is a comprehensive overview of the latest knowledge in the field of magnesium alloys engineering. Modern magnesium alloys are promising for a variety of applications in many branches of the industry due to their excellent mechanical properties, high vibration, damping capacity, and high dimensional stability. This book discusses the production, processing, and application of magnesium alloys. It includes detailed information on the impact of alloying additives and selected casting technologies, as well as modern manufacturing technologies based on powder metallurgy, the production of composites and nano-composites with metal matrixes, and methods for improving alloy properties