Sheet metal forming operations in the automotive industry, including stamping, flanging, bending,... more Sheet metal forming operations in the automotive industry, including stamping, flanging, bending, hemming and trimming, are dominantly done at room temperature (RT). Unfortunately, the poor RT formability of magnesium due to its hexagonal close-packed structure and generally strong texture has limited the use of these processes in high-volume automotive production. However, the formability of magnesium can be improved via fine grain structure and random texture to enable some RT forming operations. This paper presents the latest magnesium alloy development and evaluation by the United States Automotive Materials Partnership (USAMP) in collaboration with its university partners. A new sheet alloy developed in a recent USAMP project, ZAXME11100 (USAMP Alloy 2 Plus), offers excellent ductility (31% tensile elongation) and RT formability (7.8 mm Erichsen index) in a solutiontreated condition (T4), and a high yield strength (270 MPa) upon post-forming aging treatment (T6), promising RT forming for automotive applications.
Metallurgical and Materials Transactions, Nov 8, 2008
Fig. 8-Hysteresis loops (a) at first cycle and (b) at half-life cycle for different total strain ... more Fig. 8-Hysteresis loops (a) at first cycle and (b) at half-life cycle for different total strain amplitudes.
This paper investigates the intergranular deformation behavior and its effect on the overall duct... more This paper investigates the intergranular deformation behavior and its effect on the overall ductility of a Mg-Gd-Y alloy, using in-situ tension in scanning electron microscopy (SEM) combined with electron backscattered diffraction (EBSD) and digital image correlation (DIC) techniques. At regions surrounding grain boundaries, the majority of activated dislocation slip traces were found to form in pairs across grain boundary, and the basal-to-basal (B-B) slip pair is the dominant type. Strain
In this study, the room temperature thermal conductivity and microstructure of MgÀCe, MgÀSm and M... more In this study, the room temperature thermal conductivity and microstructure of MgÀCe, MgÀSm and MgÀY binary alloys in as-cast and solution treated conditions were investigated. Quantitative study was conducted on the effect of rare earth elements (in solid solution and intermetallic compounds) on the thermal conductivity of MgÀRE alloys. The reduction in thermal conductivity was determined to be about 123.0 W/(m$K) and 6.5e16.4 W/(m$K), respectively, per 1 at.% RE addition in the form of solid solution or intermetallic compounds with Mg. The thermal conductivities of MgÀRE alloys were fitted using modified Maxwell and EMT models based on the distribution, volume fractions and shape of intermetallic compounds. The modified structural models provide a good fit to the experimental thermal conductivity data.
In this work, Mg-(5, 6, 7) Al-3Ca-0.3Mn (wt.%) alloys were fabricated by permanent mould direct c... more In this work, Mg-(5, 6, 7) Al-3Ca-0.3Mn (wt.%) alloys were fabricated by permanent mould direct chill casting followed by indirect extrusion, to achieve ultrahigh strength. The microstructure and mechanical properties of these alloys were systematically investigated. While C36-(Mg, Al)2Ca was identified to be the major eutectic phase in the as-cast alloys, and a bimodal microstructure composed of fine dynamically recrystallized (DRXed) grains and coarse unDRXed grains was observed in the as-extruded alloys. The as-extruded Mg-5Al-3Ca-0.3Mn (wt.%) alloy exhibits a yield strength of 420 MPa and ultimate tensile strength of 451 MPa with an elongation to failure of 4.1%. The ultrahigh strength is mainly due to dense homogeneously dispersed Mg 2 Ca nano-precipitates, grain refinement and strong basal texture. Further Al addition substantially decreases the number density of Mg 2 Ca
This paper presents an overview on the application of CALPHAD (CALculation of Phase Diagrams) met... more This paper presents an overview on the application of CALPHAD (CALculation of Phase Diagrams) methodology in the design and development of advanced lightweight metallic materials including magnesium, aluminum, titanium, aluminum-based metal matrix composites, and high entropy alloys. In this work, CALPHAD methodology has been established and summarized from the construction of databases describing thermodynamics, atomic mobility, kinetics, thermo-physical properties (such as viscosity) to the application of computational design of lightweight materials. The examples in this paper have demonstrated the effectiveness and capability of CALPHAD methodology in accelerating the design of advanced lightweight materials by optimizing the compositions and various heat-treatment conditions, modifying the evolution of microstructures during processing, and finally predicting the mechanical properties (e.g., yield strength and hardness) of the lightweight components. Although the examples are given in lightweight alloys for structural applications, the fundamental methodology and modeling principles are applicable to all materials and engineering applications. Thus, the future of the advanced material design will be strongly based on development of CALPHAD methodology such as the construction of reliable databases coupled with CALPHAD-based models for various applications.
Single pass large strain electroplastic rolling (LSER) was conducted on AZ31 alloy, using pulsed ... more Single pass large strain electroplastic rolling (LSER) was conducted on AZ31 alloy, using pulsed electric current of different current densities, to improve the rollability of magnesium alloy sheet. It was found that TD (transverse direction)-split texture developed in the alloy once the current density exceeded a critical value (in the present case 90 A/mm 2 ). Microstructure and texture analysis reveal that deformed grains, rather than the dynamically recrystallized grains, are the major contributor to the overall TD-split texture. Intragranular misorientation axis (IGMA) and viscoplastic self-consistent (VPSC) modeling were employed to analyze the influence of the pulsed electric current on the deformation mechanisms. Prismatic <a> type geometrically necessary dislocations (GNDs) were found to be dominant in the deformed grains of the specimens with TD-split texture. VPSC modeling indicates that the TD-split texture is likely due to the enhanced prismatic <a> activity caused by the electric current. The special athermal effect of the pulsed electric current on the deformation mechanisms makes LSER a promising technique for texture modification in magnesium alloys for improved formability.
Experiments were designed to compare the rollability of magnesium alloy AZ31 sheet in two rolling... more Experiments were designed to compare the rollability of magnesium alloy AZ31 sheet in two rolling schedules at the same rolling temperatures: multi-pass electroplastic rolling (ER) and warm rolling (WR). While cracks occur in WR sheet at an accumulative true strain of -0.24, the sheet can be rolled by ER up to an accumulative true strain of -1.09 without edge-cracking. This rollability enhancement in ER sheet was found to be related to the improved homogeneity of plastic deformation and dynamic recrystallization (DRX), which postpones the crack initiation. A 'twinning -shear banding -DRX' microstructure evolution model was proposed to explain the effect of pulsed electric current on the homogeneity of deformation and subsequent DRX. The use of ER sheet could pave the way for low-cost applications of lightweight magnesium components.
Abstract The relationships between fatigue strength and ultimate tensile strength as well as hard... more Abstract The relationships between fatigue strength and ultimate tensile strength as well as hardness have been studied in high-strength NZK alloys (Mg– y Nd– z Zn– x Zr) and other magnesium alloys. In the absence of casting defects, clear linear relationships have been found between the fatigue strength and the ultimate tensile strength and the hardness values in these magnesium alloys in both T4 (solutionized) and T6 (solutionized and aged) conditions. The fatigue strength models developed in this work alloys can be directly applied to other defect-free magnesium alloys.
The controlling plastic deformation mechanisms (i.e. slip or twinning) and the structural crash p... more The controlling plastic deformation mechanisms (i.e. slip or twinning) and the structural crash performance of Mg alloys are strongly influenced by loading mode, texture and microstructure. This paper summarizes the main results from an experimental program to assess these effects for commercial Mg alloy extrusions (AM30 and AZ31), sheet (AZ31), and high pressure die castings (HPDC, AM50 and AM60). Uniaxial tensile and compressive tests were performed over a wide range of strain rate and temperature (i.e. 0.00075e2800 s À1 and 100 C to À150 C) using conventional servo-hydraulic and high-strain-rate universal test machines and a split-Hopkinson-bar (SHB) apparatus. In primarily-slip-dominant deformation, the true stressestrain curves showed approximate power-law behavior, and the effects of strain rate and temperature on yield strength could be approximately described by constitutive equations linearly dependent on the rate parameter, Tlnð5:3 Â 10 7 =_ 3Þ where T is test temperature in Kelvin and _ 3 is strain rate in s À1 . In primarily-twin-dominant deformation, the effects of strain rate and temperature on yield and initial flow stress were negligible or small from quasi-static to 2800 s À1 owing to the athermal characteristics of mechanical twinning; the effects may become more pronounced with exhaustion of twinning and increasing proportion of slip.
ABSTRACT This paper reports the significantly improved high cycle fatigue performance of a new ma... more ABSTRACT This paper reports the significantly improved high cycle fatigue performance of a new magnesium alloy NZ30K-T6 (Mg-3Nd-0.2Zn-0.45Zr) compared with commercial AZ91-T6 alloy (Mg-9Al-1Zn). The test samples were taken from the bulkhead areas of automotive V6 engine blocks made of low pressure sand casting process, and tested at room and elevated (150 degrees C) temperatures. The room-temperature fatigue strength of the NZ30K-T6 alloy at 10(7) cycles is approximately 90 MPa, about 38% increase compared to that of AZ91-T6 alloy. Increasing test temperature (from 25 degrees C to 150 degrees C) reduces the fatigue strength of NZ30K-T6 alloy by as much as 23%. Oxide films are found to be the main cause of the fatigue crack initiation in all failed samples examined. Fatigue lives of the samples containing oxide films can be quantitatively predicted by a model using the sizes of the casting defects (i.e., oxide films in this study). The fatigue fracture behavior of the magnesium alloy castings is also well described by Weibull modulus and the characteristic fatigue life.
Twinning of a polycrystalline Mg-3Al-0Mn alloy at a uniaxial tensile strain rate of 0.001 s À1 to... more Twinning of a polycrystalline Mg-3Al-0Mn alloy at a uniaxial tensile strain rate of 0.001 s À1 to a total strain of 0.02 was studied by transmission electron microscope. The deformation of twins, necking and cracking, was observed. Meanwhile the interception of twins resulted in double twinning and slip along the double twin boundaries. Their effects are discussed in view of work hardening/softening of magnesium alloys.
The application of titanium components is generally limited by their high raw material and manufa... more The application of titanium components is generally limited by their high raw material and manufacturing costs. In this paper, a lower cost cast titanium alloy based on the Ti-Al-Fe system has been designed using an ICME approach. The new alloy Ti-6Al-5Fe-0.05B-0.05C (all wt.%) significantly reduces raw material cost and demonstrates improved castability compared with the baseline Ti-6Al-4V alloy. The fine primary and secondary α phase microstructure in the new alloy, due to Fe partitioning, provides exceptionally high strength (1023 MPa yield strength and 1136 MPa ultimate tensile strength) and reasonable ductility (3.7% elongation) for structural applications. On the manufacturing front, the high cost multi-step investment casting process currently used can now be replaced with a low-cost permanent mold casting process using steel molds and a novel ceramic coating. An experimental casting setup, including an induction skull melting (ISM) system, a gravity tilt-pour system and a ce...
Precipitation evolution and its correspondence to mechanical properties in Mg-4Sm-xZn-0.4Zr (x=0,... more Precipitation evolution and its correspondence to mechanical properties in Mg-4Sm-xZn-0.4Zr (x=0, 0.3, 0.6, 1.3) (wt.%) alloys are systematically investigated in this work. Precipitation sequences at 200 o C are identified using transmission electron microscopy (TEM), highresolution TEM (HRTEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). A new precipitate β' Z is found to present with the increase of Zn addition. With higher Zn content (> ~1 wt.%), basal γ-series precipitates dominate. The transitionin precipitation sequence agrees wellwith the change of mechanical properties. The microstructure and property evolution in the optimum Mg-4Sm-0.3Zn-0.4Zr alloy is modeled based on obtained experimental data through a combination of classical nucleation and growth model and the CALPHAD (CALculation of PhAse Diagram) simulation. The obtained
The solidification microstructures of AE42 (Mg-4Al-2RE, wt%) alloys with three different cooling ... more The solidification microstructures of AE42 (Mg-4Al-2RE, wt%) alloys with three different cooling rates are investigated using CALculation of PHase Diagrams (CALPHAD) simulation and experimental validation. The results show that high cooling rates can refine the microstructure and decrease the formation of particulate Al 2 RE intermetallics. Particularly, the Mg 17 Al 12 phase, predicted by CALPHAD simulation using the Scheil model, is not observed in the highpressure die casting (HPDC) sample. The suppression of Mg 17 Al 12 in HPDC AE42 alloy at high cooling rates and high pressure is likely due to the supersaturation of Al in (Mg), in addition to the preferential formation of Al 11 RE 3 and Al 2 RE phases.
The effects of thermal history on precipitation behavior and precipitation kinetics in Mg-3Nd-0.2... more The effects of thermal history on precipitation behavior and precipitation kinetics in Mg-3Nd-0.2Zn (wt. %) alloy were studied. The microstructure analysis of the aged alloys revealed the presence of new phases in the microstructure in addition to the old description: Super saturated solid solution (SSSS) → G. P. zones → β" → β'/β 1 → β, reported for Mg-Nd system. In this regard, the sequence of precipitation for the studied alloy was identified as: Super saturated solid solution (SSSS) → Clusters of atoms → G. P. zones (I, II, III) → β' → β 2 → β 1 / γ' → β. The formation of clusters of solute atoms in this system was confirmed by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and atom probe tomography analysis. In addition, new metastable phases designated as G. P. zones (I, II, III) and β 2 were
Sheet metal forming operations in the automotive industry, including stamping, flanging, bending,... more Sheet metal forming operations in the automotive industry, including stamping, flanging, bending, hemming and trimming, are dominantly done at room temperature (RT). Unfortunately, the poor RT formability of magnesium due to its hexagonal close-packed structure and generally strong texture has limited the use of these processes in high-volume automotive production. However, the formability of magnesium can be improved via fine grain structure and random texture to enable some RT forming operations. This paper presents the latest magnesium alloy development and evaluation by the United States Automotive Materials Partnership (USAMP) in collaboration with its university partners. A new sheet alloy developed in a recent USAMP project, ZAXME11100 (USAMP Alloy 2 Plus), offers excellent ductility (31% tensile elongation) and RT formability (7.8 mm Erichsen index) in a solutiontreated condition (T4), and a high yield strength (270 MPa) upon post-forming aging treatment (T6), promising RT forming for automotive applications.
Metallurgical and Materials Transactions, Nov 8, 2008
Fig. 8-Hysteresis loops (a) at first cycle and (b) at half-life cycle for different total strain ... more Fig. 8-Hysteresis loops (a) at first cycle and (b) at half-life cycle for different total strain amplitudes.
This paper investigates the intergranular deformation behavior and its effect on the overall duct... more This paper investigates the intergranular deformation behavior and its effect on the overall ductility of a Mg-Gd-Y alloy, using in-situ tension in scanning electron microscopy (SEM) combined with electron backscattered diffraction (EBSD) and digital image correlation (DIC) techniques. At regions surrounding grain boundaries, the majority of activated dislocation slip traces were found to form in pairs across grain boundary, and the basal-to-basal (B-B) slip pair is the dominant type. Strain
In this study, the room temperature thermal conductivity and microstructure of MgÀCe, MgÀSm and M... more In this study, the room temperature thermal conductivity and microstructure of MgÀCe, MgÀSm and MgÀY binary alloys in as-cast and solution treated conditions were investigated. Quantitative study was conducted on the effect of rare earth elements (in solid solution and intermetallic compounds) on the thermal conductivity of MgÀRE alloys. The reduction in thermal conductivity was determined to be about 123.0 W/(m$K) and 6.5e16.4 W/(m$K), respectively, per 1 at.% RE addition in the form of solid solution or intermetallic compounds with Mg. The thermal conductivities of MgÀRE alloys were fitted using modified Maxwell and EMT models based on the distribution, volume fractions and shape of intermetallic compounds. The modified structural models provide a good fit to the experimental thermal conductivity data.
In this work, Mg-(5, 6, 7) Al-3Ca-0.3Mn (wt.%) alloys were fabricated by permanent mould direct c... more In this work, Mg-(5, 6, 7) Al-3Ca-0.3Mn (wt.%) alloys were fabricated by permanent mould direct chill casting followed by indirect extrusion, to achieve ultrahigh strength. The microstructure and mechanical properties of these alloys were systematically investigated. While C36-(Mg, Al)2Ca was identified to be the major eutectic phase in the as-cast alloys, and a bimodal microstructure composed of fine dynamically recrystallized (DRXed) grains and coarse unDRXed grains was observed in the as-extruded alloys. The as-extruded Mg-5Al-3Ca-0.3Mn (wt.%) alloy exhibits a yield strength of 420 MPa and ultimate tensile strength of 451 MPa with an elongation to failure of 4.1%. The ultrahigh strength is mainly due to dense homogeneously dispersed Mg 2 Ca nano-precipitates, grain refinement and strong basal texture. Further Al addition substantially decreases the number density of Mg 2 Ca
This paper presents an overview on the application of CALPHAD (CALculation of Phase Diagrams) met... more This paper presents an overview on the application of CALPHAD (CALculation of Phase Diagrams) methodology in the design and development of advanced lightweight metallic materials including magnesium, aluminum, titanium, aluminum-based metal matrix composites, and high entropy alloys. In this work, CALPHAD methodology has been established and summarized from the construction of databases describing thermodynamics, atomic mobility, kinetics, thermo-physical properties (such as viscosity) to the application of computational design of lightweight materials. The examples in this paper have demonstrated the effectiveness and capability of CALPHAD methodology in accelerating the design of advanced lightweight materials by optimizing the compositions and various heat-treatment conditions, modifying the evolution of microstructures during processing, and finally predicting the mechanical properties (e.g., yield strength and hardness) of the lightweight components. Although the examples are given in lightweight alloys for structural applications, the fundamental methodology and modeling principles are applicable to all materials and engineering applications. Thus, the future of the advanced material design will be strongly based on development of CALPHAD methodology such as the construction of reliable databases coupled with CALPHAD-based models for various applications.
Single pass large strain electroplastic rolling (LSER) was conducted on AZ31 alloy, using pulsed ... more Single pass large strain electroplastic rolling (LSER) was conducted on AZ31 alloy, using pulsed electric current of different current densities, to improve the rollability of magnesium alloy sheet. It was found that TD (transverse direction)-split texture developed in the alloy once the current density exceeded a critical value (in the present case 90 A/mm 2 ). Microstructure and texture analysis reveal that deformed grains, rather than the dynamically recrystallized grains, are the major contributor to the overall TD-split texture. Intragranular misorientation axis (IGMA) and viscoplastic self-consistent (VPSC) modeling were employed to analyze the influence of the pulsed electric current on the deformation mechanisms. Prismatic <a> type geometrically necessary dislocations (GNDs) were found to be dominant in the deformed grains of the specimens with TD-split texture. VPSC modeling indicates that the TD-split texture is likely due to the enhanced prismatic <a> activity caused by the electric current. The special athermal effect of the pulsed electric current on the deformation mechanisms makes LSER a promising technique for texture modification in magnesium alloys for improved formability.
Experiments were designed to compare the rollability of magnesium alloy AZ31 sheet in two rolling... more Experiments were designed to compare the rollability of magnesium alloy AZ31 sheet in two rolling schedules at the same rolling temperatures: multi-pass electroplastic rolling (ER) and warm rolling (WR). While cracks occur in WR sheet at an accumulative true strain of -0.24, the sheet can be rolled by ER up to an accumulative true strain of -1.09 without edge-cracking. This rollability enhancement in ER sheet was found to be related to the improved homogeneity of plastic deformation and dynamic recrystallization (DRX), which postpones the crack initiation. A 'twinning -shear banding -DRX' microstructure evolution model was proposed to explain the effect of pulsed electric current on the homogeneity of deformation and subsequent DRX. The use of ER sheet could pave the way for low-cost applications of lightweight magnesium components.
Abstract The relationships between fatigue strength and ultimate tensile strength as well as hard... more Abstract The relationships between fatigue strength and ultimate tensile strength as well as hardness have been studied in high-strength NZK alloys (Mg– y Nd– z Zn– x Zr) and other magnesium alloys. In the absence of casting defects, clear linear relationships have been found between the fatigue strength and the ultimate tensile strength and the hardness values in these magnesium alloys in both T4 (solutionized) and T6 (solutionized and aged) conditions. The fatigue strength models developed in this work alloys can be directly applied to other defect-free magnesium alloys.
The controlling plastic deformation mechanisms (i.e. slip or twinning) and the structural crash p... more The controlling plastic deformation mechanisms (i.e. slip or twinning) and the structural crash performance of Mg alloys are strongly influenced by loading mode, texture and microstructure. This paper summarizes the main results from an experimental program to assess these effects for commercial Mg alloy extrusions (AM30 and AZ31), sheet (AZ31), and high pressure die castings (HPDC, AM50 and AM60). Uniaxial tensile and compressive tests were performed over a wide range of strain rate and temperature (i.e. 0.00075e2800 s À1 and 100 C to À150 C) using conventional servo-hydraulic and high-strain-rate universal test machines and a split-Hopkinson-bar (SHB) apparatus. In primarily-slip-dominant deformation, the true stressestrain curves showed approximate power-law behavior, and the effects of strain rate and temperature on yield strength could be approximately described by constitutive equations linearly dependent on the rate parameter, Tlnð5:3 Â 10 7 =_ 3Þ where T is test temperature in Kelvin and _ 3 is strain rate in s À1 . In primarily-twin-dominant deformation, the effects of strain rate and temperature on yield and initial flow stress were negligible or small from quasi-static to 2800 s À1 owing to the athermal characteristics of mechanical twinning; the effects may become more pronounced with exhaustion of twinning and increasing proportion of slip.
ABSTRACT This paper reports the significantly improved high cycle fatigue performance of a new ma... more ABSTRACT This paper reports the significantly improved high cycle fatigue performance of a new magnesium alloy NZ30K-T6 (Mg-3Nd-0.2Zn-0.45Zr) compared with commercial AZ91-T6 alloy (Mg-9Al-1Zn). The test samples were taken from the bulkhead areas of automotive V6 engine blocks made of low pressure sand casting process, and tested at room and elevated (150 degrees C) temperatures. The room-temperature fatigue strength of the NZ30K-T6 alloy at 10(7) cycles is approximately 90 MPa, about 38% increase compared to that of AZ91-T6 alloy. Increasing test temperature (from 25 degrees C to 150 degrees C) reduces the fatigue strength of NZ30K-T6 alloy by as much as 23%. Oxide films are found to be the main cause of the fatigue crack initiation in all failed samples examined. Fatigue lives of the samples containing oxide films can be quantitatively predicted by a model using the sizes of the casting defects (i.e., oxide films in this study). The fatigue fracture behavior of the magnesium alloy castings is also well described by Weibull modulus and the characteristic fatigue life.
Twinning of a polycrystalline Mg-3Al-0Mn alloy at a uniaxial tensile strain rate of 0.001 s À1 to... more Twinning of a polycrystalline Mg-3Al-0Mn alloy at a uniaxial tensile strain rate of 0.001 s À1 to a total strain of 0.02 was studied by transmission electron microscope. The deformation of twins, necking and cracking, was observed. Meanwhile the interception of twins resulted in double twinning and slip along the double twin boundaries. Their effects are discussed in view of work hardening/softening of magnesium alloys.
The application of titanium components is generally limited by their high raw material and manufa... more The application of titanium components is generally limited by their high raw material and manufacturing costs. In this paper, a lower cost cast titanium alloy based on the Ti-Al-Fe system has been designed using an ICME approach. The new alloy Ti-6Al-5Fe-0.05B-0.05C (all wt.%) significantly reduces raw material cost and demonstrates improved castability compared with the baseline Ti-6Al-4V alloy. The fine primary and secondary α phase microstructure in the new alloy, due to Fe partitioning, provides exceptionally high strength (1023 MPa yield strength and 1136 MPa ultimate tensile strength) and reasonable ductility (3.7% elongation) for structural applications. On the manufacturing front, the high cost multi-step investment casting process currently used can now be replaced with a low-cost permanent mold casting process using steel molds and a novel ceramic coating. An experimental casting setup, including an induction skull melting (ISM) system, a gravity tilt-pour system and a ce...
Precipitation evolution and its correspondence to mechanical properties in Mg-4Sm-xZn-0.4Zr (x=0,... more Precipitation evolution and its correspondence to mechanical properties in Mg-4Sm-xZn-0.4Zr (x=0, 0.3, 0.6, 1.3) (wt.%) alloys are systematically investigated in this work. Precipitation sequences at 200 o C are identified using transmission electron microscopy (TEM), highresolution TEM (HRTEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). A new precipitate β' Z is found to present with the increase of Zn addition. With higher Zn content (> ~1 wt.%), basal γ-series precipitates dominate. The transitionin precipitation sequence agrees wellwith the change of mechanical properties. The microstructure and property evolution in the optimum Mg-4Sm-0.3Zn-0.4Zr alloy is modeled based on obtained experimental data through a combination of classical nucleation and growth model and the CALPHAD (CALculation of PhAse Diagram) simulation. The obtained
The solidification microstructures of AE42 (Mg-4Al-2RE, wt%) alloys with three different cooling ... more The solidification microstructures of AE42 (Mg-4Al-2RE, wt%) alloys with three different cooling rates are investigated using CALculation of PHase Diagrams (CALPHAD) simulation and experimental validation. The results show that high cooling rates can refine the microstructure and decrease the formation of particulate Al 2 RE intermetallics. Particularly, the Mg 17 Al 12 phase, predicted by CALPHAD simulation using the Scheil model, is not observed in the highpressure die casting (HPDC) sample. The suppression of Mg 17 Al 12 in HPDC AE42 alloy at high cooling rates and high pressure is likely due to the supersaturation of Al in (Mg), in addition to the preferential formation of Al 11 RE 3 and Al 2 RE phases.
The effects of thermal history on precipitation behavior and precipitation kinetics in Mg-3Nd-0.2... more The effects of thermal history on precipitation behavior and precipitation kinetics in Mg-3Nd-0.2Zn (wt. %) alloy were studied. The microstructure analysis of the aged alloys revealed the presence of new phases in the microstructure in addition to the old description: Super saturated solid solution (SSSS) → G. P. zones → β" → β'/β 1 → β, reported for Mg-Nd system. In this regard, the sequence of precipitation for the studied alloy was identified as: Super saturated solid solution (SSSS) → Clusters of atoms → G. P. zones (I, II, III) → β' → β 2 → β 1 / γ' → β. The formation of clusters of solute atoms in this system was confirmed by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and atom probe tomography analysis. In addition, new metastable phases designated as G. P. zones (I, II, III) and β 2 were
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