Deformation Behavior of the Percolating Intermetallic Microstructure of High Pressure Die Cast <scp>AZ</scp>91 Alloy

Zhang, Bao; Nagasekhar, A.V.; Sivarupan, Tharmalingam; Cáceres, C. H.

doi:10.1002/adem.201300138

Cited by 18 publications

(21 citation statements)

References 44 publications

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“…Since the major intermetallic phases in AJ52 and the AE alloys tend to have a lamellar structure, it is likely that the morphology of the intermetallic phase also plays a role in influencing the alloy strength, i.e., the strengthening contribution is higher when the intermetallic phase is divorced and continuous rather than being lamellar. This difference can be explained by the additional strengthening effect from the percolating network of the intermetallic phase, which was proposed recently by Zhang et al [51,52] Based on dual-beam focused-ion beam (FIB) tomography and finite element analysis (FEA), Zhang et al [51,52] provided detailed insight into the 3D configuration and deformation behavior of the percolating intermetallic phases in diecast Mg-Al and Mg-RE alloys. They found that the intermetallic phases with profuse spatial interconnection have a higher strengthening effect than what would be expected through dispersion hardening, i.e., isolated particles with the same volume fraction.…”

Section: A Microstructure/tensile Properties Relationshipmentioning

confidence: 96%

Evaluation of Magnesium Die-Casting Alloys for Elevated Temperature Applications: Microstructure, Tensile Properties, and Creep Resistance

Zhu

Easton

Abbott³

et al. 2015

Metall Mater Trans A

127

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Several families of magnesium die-casting alloys have been developed to operate at the elevated temperatures experienced in automotive powertrain applications. Most alloys are based on the Mg-Al system with alloying additions such as silicon, strontium, calcium, and rare earth elements (RE), although alloys with RE as the primary alloying constituent are also considered. This work presents an evaluation of the tensile properties and creep resistance of the most common magnesium die-casting alloys, in conjunction with the analysis of microstructure. The alloys investigated include AS31 (Mg-3Al-1Si), AJ52 (Mg-5Al-2Sr), MRI153A (Mg-9Al-1Ca-0.1Sr), MRI153M (Mg-8Al-1Ca-0.3Sr), MRI230D (Mg-6.5Al-2Ca-1Sn-0.3Sr), AXJ530 (Mg5Al-3Ca-0.2Sr), AE42 (Mg-4Al-2RE), AE44 (Mg-4Al-4RE), and AM-HP2+ (Mg-3.5RE-0.4Zn). It is shown that, among the various alloys evaluated, MRI230D, AXJ530, and AM-HP2+ have higher yield strength than the Al alloy A380, but the ductility is relatively low at room temperature for these alloys. In contrast, AS31 and the AE series alloys have very good room temperature ductility, but their yield strength is lower than that of A380. In terms of creep resistance, MRI230D, AXJ530, AE44, and AM-HP2+ are all comparable to the Al alloy counterpart at 423 K and 448 K (150°C and 175°C). Microstructural factors that are most important to the strength and creep resistance of the Mg die-casting alloys are discussed.

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Section: A Microstructure/tensile Properties Relationshipmentioning

confidence: 96%

Evaluation of Magnesium Die-Casting Alloys for Elevated Temperature Applications: Microstructure, Tensile Properties, and Creep Resistance

Zhu

Easton

Abbott³

et al. 2015

Metall Mater Trans A

127

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“…The spatially interconnected eutectic microstructure that forms in most High Pressure Die Cast (HPDC) Mg-alloys [10,[110][111][112][113] has been shown to introduce hardening effects ranging from a few MPa in AZ91 to ~40 MPa in some Mg-RE alloys. In a Mg-RE alloy, strengthening of the α-Mg matrix in which the eutectic structure was embedded, a ternary addition [112] 4 and 5.…”

Section: Percolating Eutectic Microstructurementioning

confidence: 99%

Thermodynamics-based design of creep resistant Mg solid solutions using the Miedema scheme

Abaspour¹

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Most current creep resistant alloy design methods for Mg alloys aim at incremental strengthening of existing alloys such as AZ91 thorough addition of ternary and quaternary elements, or alternatively through RE's additions. The most remarkable improvements has been through either Mg-Y or recently developed Mg-Gd-Y-Zr and Mg-Y-Nd-Zr alloys, although still below the strength of MgTh alloys, which are being phase out due to Th's radioactivity.Many micromechanisms proposed to account for the observed improvements in either hardness or creep strength of Mg alloys including solid solution and/or precipitation hardening, dynamic precipitation, solute dragging/solute clustering and more importantly atomic size controlled diffusivity more often than not are little more than ad-hoc, after-the-fact explanations, valid at best for the particular system under consideration. Hence, extrapolation to other alloy-systems is either not possible or contradictory. In practice, a feasible path for systematic, either precipitationhardened or creep-resistant Mg alloys, selection and design is still lacking.The aim of the present work was to use atomic level thermodynamical arguments that suggest that extending the athermal regime through short range order (SRO) is a most feasible path to increasing the creep strength of Mg alloys. Potential solutes were sorted out and ranked based on their tendency to developing SRO using the Miedema's phenomenological scheme. The predictions were corroborated by experiments involving dilute binary alloys as well as through a collection of data from the literature.Monotonic compression and stress relaxation tests were carried out on specimens of 6 cast binary alloys with (at.%) 2.5 Al, 0.6 Sn, 2.2 Zn, 0.8 Gd, 1.3 Y and 0.9 Nd, and of a similarly cast AZ91D alloy for reference. The solute concentration in the binary alloys was kept deliberately low to limit precipitation hardening effects during the testing. Compression testing was carried out at 298K (25°C), 373K (100°C) and 453K (180°C) The relative tendency or lack of it, of most solutes to develop SRO rationalizes a number of observations in current multicomponent Mg alloys while it disputes the viability of several other micromechanisms often considered.The feasibility of strengthening HPDC Mg alloys through a combination of percolating eutectics and residual solute in solution, or, more generally, age hardenable alloys through either homogeneously nucleated, coherent with the Mg matrix, precipitates, or via internally ordered precipitates mimicking Mg-Th alloy system, is also considered by making parallels with either the Al-Zn or the Al-Cu alloy systems. Examples of these approaches were discussed using data from the literature, such as experiments on alloys combining Mn and Sc to introduce order in the soft Mn precipitates, or the use of Na to provide finely dispersed, homogeneously nucleated clusters with the aim of refining the subsequent precipitation in alloys such as Mg-Sn. III Declaration by authorThis thesis is composed of my or...

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“…[1][2][3][4][5] An example is given in Figure 1, where lighter color represents the network of eutectic (a-Mg)-Mg 12 Ce in a HPDC Mg-0.51 at% Ce alloy, locating at the grain boundary between adjacent grains of a-Mg matrix. [1][2][3][4][5] An example is given in Figure 1, where lighter color represents the network of eutectic (a-Mg)-Mg 12 Ce in a HPDC Mg-0.51 at% Ce alloy, locating at the grain boundary between adjacent grains of a-Mg matrix.…”

Section: Experimental Observationmentioning

confidence: 99%

“…The establishment of a micromechanical model is based on microstructural observations that intermetallic/eutectics are interconnected in a series of HPDC and sand squeeze-cast Mg alloys, cf. [1][2][3][4][5] An example is given in Figure 1, where lighter color represents the network of eutectic (a-Mg)-Mg 12 Ce in a HPDC Mg-0.51 at% Ce alloy, locating at the grain boundary between adjacent grains of a-Mg matrix.…”

Section: Experimental Observationmentioning

confidence: 99%

“…Nagasekhar et al [1] employed focused dual ion beam tomography to reveal the 3D morphology of percolating intermetallic in Mg-Al alloys and qualitatively analyzed its contribution to material strength. Subsequently, Zhang et al [2] utilized these actual morphologies and established a finite element model (FEM) to quantitatively determine the strength of the intermetallic network and its influence on overall mechanical behavior of Mg alloys. They found that presence of network led to a noticeable increase in alloy strength without compromising material ductility.…”

Section: Introductionmentioning

confidence: 99%

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A Micromechanical Approach Investigating the Effects of Percolating Eutectic Network on Mechanical Behavior of Magnesium Alloys

Bao

2017

Adv Eng Mater

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A novel two-dimensional (2D) micromechanical model presented is capable of predicting eutectic network strength and structural efficiency consistent with computed results on the basis of three-dimensional (3D) actual morphology of eutectic network, and shows considerable advantages in terms of efficiency, practicability and computation cost. Another critical advantage lies in the capability of evaluating network-matrix interaction and the incorporation of interaction strength leads to an improved agreement between numerical and experimental flow behavior of the Mg alloy. The analysis also suggests that network-matrix interaction is comparable with dispersion and network strengthening with respect to the contribution to alloy yield strength.

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Deformation Behavior of the Percolating Intermetallic Microstructure of High Pressure Die Cast AZ91 Alloy

Cited by 18 publications

References 44 publications

Evaluation of Magnesium Die-Casting Alloys for Elevated Temperature Applications: Microstructure, Tensile Properties, and Creep Resistance

Evaluation of Magnesium Die-Casting Alloys for Elevated Temperature Applications: Microstructure, Tensile Properties, and Creep Resistance

Thermodynamics-based design of creep resistant Mg solid solutions using the Miedema scheme

A Micromechanical Approach Investigating the Effects of Percolating Eutectic Network on Mechanical Behavior of Magnesium Alloys

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