Search

Few studies were reported on the phases’ relationships of AE44 (Mg-4.0Al-4.1RE-0.3Mn, wt.%) and its composites. In this work, AE44 alloy and Saffil (δ-Al2O3)/AE44 Metal matrix composite (MMC) were both prepared by slow shot high pressure die casting (SS-HPDC) technology and their phase constitutions were all studied in detail using experimental techniques combined with CALPHAD (Calculation of Phase Diagram) modeling. The results revealed that the alloy consists of the α-Mg matrix, Al11RE3 intermetallic phase, and one trace phase Al3RE, while the composite contains five major phases: α-Mg, δ-Al2O3, Al3RE, MgO and Mg2Si, and two trace phases of Al2RE and Al11RE3, respectively. Al11RE3 is partly derived from Al2RE, while Al3RE is a product of the peritectoid reaction between the two precipitates. The presence of MgO and Mg2Si is due to the interfacial reaction between the SiO2 binder in the fiber preforms and the molten magnesium during infiltration. The use of SiO2 binder in the preform manufacturing was limited/minimized to reduce the MgO formation in the MMC casting process, which can be detrimental to the fatigue performance of the MMC materials.

The hot-tearing susceptibility of Mg-10Zn-xAl (x = 0, 2, 5, and 7) alloys was studied using constrained rod casting installed with a load cell, thermocouple, and data-management system. Addition of Al content reduced the freezing range and increased the liquid fraction at the end of the primary stage of solidification, during the vulnerable period of alloy solidification. Eutectic healing was observed in alloys containing Al cast at a higher initial mold temperature due to near-equilibrium solidification. Grain refining was confirmed at the microstructural level due to addition of Al. The results also suggested that increasing Al content enabled hot-tearing resistance of Mg-10Zn alloy by facilitating liquid feed for the strain developed during the mid-stage of solidification (0.65Fs to 0.74Fs). Experimental results were compared with Pandat’s simulation results to predict the occurrence of hot tearing in Mg-10Zn-xAl alloys. This indicated that Pandat’s solidification curve could be used to determine the hot-tearing nature of Mg-Zn alloys. The recently proposed hot-tearing criteria of Kou and Clyne–Davie roughly agreed with the experimental results, but did not perfectly predict the influence of different casting conditions.

The effects of different Zn addition (0, 0.2, 0.5, 1.0 wt%) on the microstructure and mechanical properties of cast Mg–1Nd–1Ce–Zr alloy in as-cast, solution-treated and 200 °C peak-aged conditions were studied. Precipitates in cast Mg–1Nd–1Ce–Zr alloy are significantly modified by the Zn addition. In the Zn-free alloy, the disk-shaped prismatic precipitates and the point-like precipitates are the main strengthening phases. When 0.2 Zn is added, the disk-shaped precipitates are refined and very fine basal precipitates form additionally. When 0.5 Zn is added, the basal precipitates become the main strengthening phase. Further increasing the Zn addition to 1.0%, only spare basal precipitates and point-like precipitates exist. The 0.5 Zn addition alloy has the highest strength at room temperature, whose yield strength, ultimate tensile strength and elongation in T6 condition are 136 MPa, 237 MPa and 9%, respectively. Keywords: Mg alloy, Precipitate, Rare earth, Zn addition, Mechanical properties, Mg wheel

A cost-effective α-β titanium casting alloy, Ti-6Al-5Fe-0.05B-0.05C, 1 has been designed using Calculation of Phase Diagrams (CALPHAD) method and the workhorse alloy Ti-6Al-4 V as a baseline. The substitution of iron for vanadium significantly reduces the raw material cost and improves the castability compared to the Ti-6Al-4 V alloy. The very fine α phase in the microstructure of the new alloy, likely due to Fe partitioning, provides exceptionally high strength (1023 MPa yield strength and 1136 MPa ultimate tensile strength) and reasonable ductility (3.71% elongation) for structural applications.

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 ceramic-coated H13 steel mold, has been used to produce near-net-shape permanent metallic mold castings with the new titanium alloy developed. Using this setup, and aided by casting process simulation, a prototype automotive connecting rod was cast successfully. The ZrO2 ceramic coating applied to the H13 steel mold was proven effective in minimizing the metal-mold reactions.

Interdiffusion coefficients are reported at various compositions in the β (BCC) phase of the Ti-Al-Nb system using solid–solid diffusion couples assembled at three different temperatures of 1060 °C, 1100 °C and 1170 °C. The interdiffusion fluxes were determined after fitting the experimental concentration profiles with MultiDiFlux software and the ternary interdiffusion coefficients were evaluated at various compositions using Kirkaldy’s approach. The interdiffusion of Nb was the slowest, while Ti and Al showed similar interdiffusion kinetics. The main interdiffusion coefficients for the three components are positive. The cross interdiffusion coefficients of Ti and Nb are comparable in magnitude to their respective main terms indicating the presence of strong diffusional interactions in this system. The cross coefficient $$\tilde{D}_{\text{TiNb}}^{\text{Al}}$$ is positive indicating that the interdiffusion flux of Ti is enhanced down the concentration gradient of Nb. The negative value of the cross-term $$\tilde{D}_{\text{TiAl}}^{\text{Nb}}$$ indicates that the interdiffusion flux of Ti is enhanced up the gradient of Al. The tracer diffusion coefficient of Al increases with temperature and decreasing Nb content in binary Ti-Nb alloys. Binary interdiffusivities calculated at Ti-Nb compositions by extrapolation are reasonably consistent with the values reported in the literature.

Forming limits and retained austenite (RA) transformation in Q&P 1180 steel are quantified as a function of plastic strain levels for three different strain paths. In-plane uniaxial tension testing was performed in a standard test frame, while limiting dome height tooling was employed for out-of-plane biaxial and plane strain tension experiments. Sheet specimens were tested incrementally for each strain path, and the RA content at each level of strain was measured using electron backscatter diffraction (EBSD). The biaxial tension strain path resulted in the greatest effective strain prior to necking at 0.355, compared to 0.123 for plane strain and 0.142 for uniaxial tension. EBSD measurements for various levels of plastic strain reveal a clear dependence of RA rate of transformation on strain path for the three linear strain paths that were employed in this work. Thinning strains appear to provide a slightly better correlation to RA transformation than effective strain levels, where biaxial tension achieved the greatest level just prior to necking, followed by plane-strain tension, and then uniaxial tension.

Based on the hot tearing index |∆T/∆(fs)0.5| recently proposed by Kou and the thermodynamic calculations of Pandat software, Al, Cu, and Mn elements were picked up and their influence on hot tearing susceptibility of Mg–xZn (x = 6, 8, 10, wt%) alloys was studied by experiments. The results indicate that Al addition can significantly reduce the hot tearing susceptibility of Mg–Zn alloys. Either 0.5Cu or 0.3Mn addition individually can reduce the HTS of the Mg–6Zn–(1, 4) Al alloys, while adding together increases the susceptibility. The addition of 0.5Cu and 0.3Mn both individually and together increases the HTS of Mg–8/10Zn–1Al alloys. Based on the experimental and calculation results, the index can be modified to |∆T/∆(fs)0.5|(d)2 for more accurate prediction on the hot tearing resistance of Mg–Zn based alloys. Grain refinement significantly improves the hot tearing resistance of Mg–Zn based alloys. Keywords: Hot tearing susceptibility, Mg–Zn, Alloying element, Thermodynamic calculation, Grain size

The microstructural origin of anisotropy in the yield stress and ultimate tensile strength of AlSi10Mg tensile specimens produced by laser powder bed fusion (LPBF) is revealed using a combination of micropillar compression tests and microstructure-based numerical simulations. Uniaxial tensile tests demonstrate that specimens with tensile axis parallel to the build direction (vertical specimen) exhibit a higher yield stress and ultimate tensile strength than those perpendicular to the build direction (horizontal specimen). Micropillar compression experiments and a microstructure-based crystal plasticity model together confirm that the anisotropy has its origin in an elongated Al-Si cellular network (nominally 0.7 µm × 1.4 µm with long axis aligned with the build direction) within individual grains. A multiscale microstructure-based model predicts the mechanical properties of LPBF AlSi10Mg tensile specimens by accounting for the hierarchical microstructural features across length scales, which include the Al-Si network, the crystallographic grain structure, and the differences in microstructure between melt pool interiors and melt pool boundaries. The multiscale model over-estimates the yield stress, but correctly predicts the ultimate tensile strength and the anisotropy in the flow strength of tensile specimens. The model is used to computationally predict new microstructures driven by composition and processing parameters for LPBF AlSi10Mg alloys with improved mechanical properties.

The isothermal aging response at 170 °C of three extruded Al–Mg–Si alloys that had been solution-treated and quenched was experimentally tracked to understand the influence of Mg + Si content and the Mg/Si ratio on microstructure and mechanical behavior. Transmission electron microscopy (TEM) was employed to quantitatively characterize the needle-shaped β'' precipitates in the underaged, peak-aged and overaged conditions; while the alloy with a high Mg + Si content raised the number density of β'' precipitates, a higher Mg/Si ratio increased the number density but decreased the size of β'' precipitates in the peak-aged condition. In the overaged condition, coarsening of β'' precipitates occurred primarily along its length. Single crystal micropillar compression tests were conducted in the naturally-aged, under-aged, peak-aged and over-aged conditions to correlate the microstructure to the critical resolved shear stress (CRSS). In the peak-aged condition, the alloy with the high Mg + Si content and a Mg/Si ratio corresponding to the β'' stoichiometry (Mg5Si6) exhibited the highest CRSS. A precipitation kinetics model that assumed a cylindrical morphology for the β'' phase with a fixed aspect ratio was developed to describe β'' phase microstructure evolution as a function of alloy chemistry, solution treatment temperature and artificial aging parameters. The results from this model served as input to a dislocation-precipitate interaction model to calculate single crystal yield strength. The predictions from these analytical models were validated with experimental results from this study and from the literature and fundamental insights were obtained on the role of microstructural parameters in affecting yield strength for non-spherical precipitates.

The properties of TRIP-assisted steels are influenced by the transformation of retained austenite into martensite during deformation via the mechanically-induced martensite transformation. In the present work the effect of strain path on isothermal stress-assisted martensite nucleation and variant selection are studied by the coupling of the kinetic Monte Carlo method with the finite element method. This coupled model centers on a thermomechanical model of the martensitic transformation, and the model is tuned and validated against transformation data gathered experimentally for a TRIP-assisted dual phase steel (Ennis et al. (2017)). The effect of the proximity of adjacently transforming regions (kinematic coupling) is also studied as a function of strain path. The model results demonstrate how the rate of martensite nucleation is affected by the strain path (uniaxial tension, biaxial tension, and plane strain) and how the kinematic coupling between adjacent transforming regions is unique to each path. These phenomena are discussed in the context of the Magee effect, which is the relationship between stress state and the suppression/assistance of the nucleation of specific variants of martensite. The implications of martensite nucleation’s sensitivity to strain path and kinematic coupling are discussed for TRIP-assisted steels that transform by isothermal stress-assisted nucleation.

Crystalline low agglomerated tungsten diselenide (WSe2) nanoparticles were successfully produced by the aerosol synthesis method. The particle size and morphology were changed by process parameters. The products were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The WSe2 nanoparticle morphology varies from a spherical shape to flake-like, layered structures. Usually, as-prepared particles consist of 5–7 single layers of WSe2. These as-synthesized WSe2 nanoparticles were used as anodes to assemble lithium-ion batteries. A high reversible capacity and very stable cycle performance can be obtained, implying that these WSe2 nanostructures could provide new types of electrode materials for rechargeable Li-ion batteries.

Squeeze casting technology for magnesium alloys has a great application potential in automobile manufacturing and has received increasing attention from both academic and industrial communities. In this study, the pressurized solidification behavior of magnesium alloy AZ91D in squeeze casting process was investigated using computer-aided cooling curve analysis (CA-CCA). It was found that the applied pressure increased both the start and end temperatures of primary α-Mg formation but had little effect on the sizes of temperature ranges. Moreover, the applied pressure increased the start temperature and decreased the end temperature of eutectic reaction during the solidification, resulting in a larger temperature range of eutectic reaction compared with solidification under atmospheric pressure. The grains were remarkably refined, and the eutectic fraction increased with increasing applied pressure. The dendritic microstructure with a larger secondary dendrite arm spacing (SDAS) was observed under a higher applied pressure at the central part of the experimental casting. By correlating the CA-CCA and SDAS data, it was found that SDAS and the cooling rate at the maximum α-Mg growth could be fit into the power law equation in classic solidification theories.

An experimental investigation of the spatio-temporal characteristics of propagative plastic instabilities in quasi-static, room-temperature tensile tests of fully annealed Mg ZEK100, a rare earth containing Mg alloy (0.2 wt.% Nd), is presented with the aid of stereo digital image correlation. Results from specimens aligned with the sheet transverse direction revealed the nucleation of a Luders band at the fixed specimen end, followed by continuous propagation to, and ultimate termination at, the moving end during yield point elongation (YPE). Serrations in tensile flow curves, observed both during and after YPE, were attributed to propagating deformation bands, similar to the Type A Portevin-Le Châtelier (PLC) bands. Both strain and strain-rate contours enabled exploration of band nucleation and quantification of band kinematics. We also used TEM, EBSD, and electron diffraction to examine microstructural evolution during tensile deformation. Results were used to determine which, if any of the commonly cited microstructural mechanisms, such as diffusing solute pinning of mobile dislocations, precipitate shearing of dislocations, or solute locking of dislocations by a rare earth addition, is responsible for the observed Ludering and PLC behavior. We found evidence that Ludering is due to twinning. Although we could not definitively demonstrate a microstructural mechanism that is responsible for PLC effect, pinning and depinning of dislocations via diffusing Zn solute clouds could not be ruled out as the underlying cause. Implications of the experimental results for theoretical model development are discussed.

The nucleation and propagation of 〈011] superdislocations in intermetallic TiAl were investigated using molecular dynamics simulations and static energetics calculation, as part of our systematic effort to understand the twining and dislocation behavior of alloys based on γ-TiAl. It was found that compared to ordinary dislocations in disordered crystals, superdislocations in ordered TiAl lattice behave differently when sheared in the two opposite senses along [ $$ 0 {\bar{\text{1}}\text{1}} $$ ] direction. This difference is due to the lower L10 lattice symmetry compared with the face-centered cubic (fcc) lattice that it based on, with different yield stress and strain, and dislocation core dissociation and motion. Superdislocations nucleated in the form of loops dissociated in a planar manner into four Shockley partials separated by three kinds of faults: superlattice intrinsic stacking fault (SISF), anti-phase domain boundary (APB) and complex stacking fault (CSF), with partial separations depending on the sense of shearing and dislocation character. During loop expansion, the dislocation core changes both in width and dissociation manner depending on the character of the segment in the loop. The core contains four partials close to edge orientation, gradually changing to three fold near 60°, and finally into twofold dissociation around 30° character. Superdislocations may have multiple critical resolved shear stresses (CRSS) for motion depending on dissociation and shearing sense even for the same slip system, with lower critical stress for the motion when SISF is in leading position.

The effects of extrusion parameters on the microstructure and tensile properties of the Mg–2Zn–0.5Ce, Mg–1Zn–1Mn–0.5Ce, and Mg–2Zn–1.5Gd alloys were investigated by conducting indirect extrusion at different temperatures, ram speeds, and extrusion ratios. All of the extruded alloys exhibited a bimodal grain structure composed of equiaxed fine recrystallized (DRXed) grains and elongated coarse unDRXed grains, except for some alloys extruded at a high temperature and a fast speed. With an increase in the temperature, speed, and ratio of extrusion, the average size and area fraction of the DRXed grains increased as a result of the temperature rise at the deformation zone caused by deformation heating. The yield strength increased with a decrease in the size of the DRXed grains according to the Hall–Petch relation, while the elongation increased with an increase in the fraction of the DRXed grains due to the suppression of {10−11}–{10−12} double twinning, irrespective of alloy composition. Due to these relationships between the microstructural characteristics and tensile properties, the yield strength decreased but the elongation increased when the temperature, speed, and ratio were increased.

The current study shows the dramatic effect of an electric field (EF) and use of nanosized cryomilled grains on accelerating sintering kinetics during spark plasma sintering of blended elemental powder compacts of Ti53Al47 targeted to produce γ-TiAl intermetallic compounds. The EF had the dominating effect since it reduced the activation barrier for diffusion through Al3Ti leading to faster growth of Al3Ti; the precursor to γ-TiAl. The Avrami exponent (n) determined for the micrograin compact lies between 1.0 and 1.5, which indicates that reaction sintering is controlled by bulk diffusion in these compacts, while for cryomilled compacts this is between 0.7 and 1.0 suggesting the important role of dislocations and grain boundaries on the transformation during reaction sintering. The activation energies were found to be in increasing order as: cryomilled compacts with EF (182 kJ/mol); micrograin compacts with EF (290 kJ/mol); cryomilled compacts without EF (331 kJ/mol); and micrograin compacts without EF (379 kJ/mol). The cryomilled microstructure also enhanced the sintering kinetics because of the availability of faster diffusing paths in Al and Ti including larger grain boundary area and dislocation density.

To provide insight into the influence of an electric field on the kinetics of diffusion, fully lamellar γ-TiAl was processed by a rapid, two-stage, solid-state reactive sintering via spark plasma sintering (SPS) of a cryomilled Ti, Al powder blend. Cryomilling was implemented in the current study to attain a nanostructured grain size in the Ti and Al powder blend, and thereby provide insight into the influence of grain size on the underlying diffusion kinetics. Following a two-step process involving SPS at 873 K (600 °C) for 15 minutes and 1523 K (1250 °C) for 30 minutes, a fully lamellar TiAl alloy, with submicron lamellar spacing, was successfully obtained. Microstructural refinement in the Ti and Al powders during cryomilling led to an increase in solid-state diffusion, and the underlying mechanisms are discussed in detail.

This paper summarizes the bi-metallic experiments using a high-vacuum test apparatus to understand the interfacial phenomena between Mg (AM60) and Al (A390) samples. The test results show significantly improved wetting and metallurgical bonding between the molten magnesium and aluminum substrate when a “zincate+galvanizing” surface treatment was applied. This surface treatment removes the intrinsic Al2O3 layer on the aluminum substrate and, in turn, forms a very thin metallic zinc film on the substrate. Interfacial reactions between the aluminum substrate and the molten magnesium led to the improved metallurgical bonding and significantly improved shear strength in the bi-metallic samples with “zincate+galvanizing” surface treatment. However, long reaction times led to the formation of excessive intermetallic compounds at the interface, which reduced bond strength.

An in situ synchrotron X-ray imaging technique was used to examine laser powder bed fusion (LPBF) of a chrome-molybedum, AISI 4140, ferrite–bainite steel, from a moving laser source. Since 4140 has received only minimal attention in the AM literature, focus here was on the effects of melt pool dynamics, vapor cavity depths, build layer height, and the origin of porosity on the 4140 as-built microstructure. Four build parameter sets, which enabled variation of laser power, scan speed, laser spot size, and specific energy density (SED), were applied. Vapor cavity and melt pool depths were measured for each single-track laser scan. Direct imaging of the LPBF process demonstrated that the primary source of porosity in the build originates from incorporation of entrapped gas within the powder irrespective of build parameter set. High resolution SEM and EBSD demonstrated that the as-built microstructure did not vary significantly with build parameter set over a broad range of SED. The fast solidification rates observed (0.06–0.08 m/s) lead to fine martensite packet/block size distributions (1–3 µm) with the potential for increased material strength.

Various powder compacts with targeted compositions of TiAl and Ti3Al were consolidated by field-activated sintering, specifically spark plasma sintering (SPS) at various temperatures, to examine phase growth under a superimposed electric field. While compacts with a composition of TiAl showed significant porosity after sintering, Ti3Al compacts showed no porosity. The porosity is attributed principally to volume changes associated with the formation of Al3Ti and the Kirkendall effect. The kinetics underlying Al3Ti growth during SPS are also explained.

A phase field model for simulating the precipitation of multi-variant β-Mg17Al12 phase during the aging process of Mg–Al-based alloys was developed in which the interface anisotropy and the elastic strain energy were taken into account. A special numerical technique based on a hexagonal and an orthogonal mesh was employed to deal with the precipitate orientation and calculate the elastic strain energy. The model reveals the contribution of the interface anisotropy and the elastic strain energy in the evolution of the precipitates.

The application of lightweight aluminum sheets to fabricate automotive components for vehicle weight reduction continues to be limited due to their low formability and high cost. This report summarizes a metallurgical investigation of the influence of various microstructural attributes on the forming and failure characteristics of aluminum sheets produced by lower cost continuous casting processes. The study has identified the combination of microstructural attributes, such as grain size, texture, and second phase particle distribution, in the sheets which make some sheets more formable than others and has traced the origin of these features to the processing history. The results show that the microstructural features present in the sheets have their origin in the casting, rolling, and recrystallization processes involved in their fabrication.

Magnesium alloys are increasingly being used in automotive industry for weight reduction and fuel economy improvement. Extruded tubular sections provide further opportunities in mass-efficient designs of automotive structural and interior applications. In this paper, microstructural evaluation indicates that twinning is the predominant deformation mechanism for magnesium alloys at room and moderate temperatures. Dynamic recrystallization is observed at temperatures as low as 150°C, leading to the formation of fine grains as a “necklace” at prior grain boundaries. These new grains cause strain localization and instability due to a loss in strain hardening, and result in failure by cavitation.

Both silicon and tin have a high specific capacity (3600 mAh g −1 for Li 15 Si 4 and 992 mAh g −1 for Li 22 Sn 5 respectively) and are among the most attractive materials for potential negative electrodes in lithium ion batteries. However, mechanical degradation induced by the large volume expansion during the cycling has limited their practical application. In this work, we developed a new class of Si–Sn nanocomposites with unique phase-separated nanostructure, where the amorphous Si nanoparticles are thermodynamically precipitated out from Si–Sn alloy and embedded within the Sn matrix. The phase separation-induced nanostructure provides the capability to mitigate the mechanical degradation, by preventing the nucleation and propagation of microcracks during lithiation. The nanocomposite electrode exhibits relative high capacity (1400 mAh g −1 ) and excellent cycling stability with the optimum composition and nanostructure.

In this work, the tin oxide/carbon nanotubes (SnO 2 /CNT) nanocomposite, where SnO 2 nanoparticles were deposited on the functionalized single wall CNTs, has been shown to exhibit desirable electrochemical performances as the negative electrodes for the lithium ion batteries. CNTs not only suppressed the mechanical degradation of SnO 2 and therefore provided the composite electrode with excellent capacity retention (>650 mAh g −1 with less than 10% capacity loss after 100 cycles), but also enhanced the electronic conductivity of the electrodes leading to excellent rate capability. The nanostructure of the nanocomposite has been shown to be critical for mitigating the mechanical degradation of electrodes.

In an effort to reduce material cost, experimental steel alloys were developed that incorporated Cu precipitation in lieu of costly Co alloying additions in secondary hardening carburizing gear steels. This work utilizes three-dimensional atom probe tomography to study one of these prototype alloys and quantify the nanoscale dispersions of body-centered cubic (bcc) Cu and M2C alloy carbides used to strengthen these steels. The temporal evolution of precipitate, size, morphology, and interprecipitate interactions were studied for various tempering times. Findings suggest that Cu precipitation does act as a catalyst for heterogeneous nucleation of M2C carbides at relatively high hardness levels; however, the resultant volume fraction of strengthening carbides was noticeably less than that predicted by thermodynamic equilibrium calculations, indicating a reduced potency compared with Co-assisted precipitation. Microstructural information such as precipitate size and volume fraction was measured at the peak hardness condition and successfully used to recalibrate alloy design models for subsequent alloy design iterations.

Ultrahigh hardness levels greater than 700 VHN can be obtained in secondary hardening carburizing steels but depend on costly Co alloying additions to maximize hardness achieved through M2C-type carbide precipitation strengthening. This study aims to incorporate nanometer-scale bcc Cu precipitates to both provide strength as well as catalyze M2C nucleation in the absence of or with reduced Co. Cu additions of 1.0 and 3.7 wt pct were investigated, using a series of mechanistic models coupled with thermodynamic computational tools to derive final compositions. Thirty-pound experimental heats were cast of each designed alloy, samples of which were carburized and tempered to determine their hardness response. Characterization revealed the successful incorporation of Cu alloying additions into this family of steels, demonstrating a secondary hardening response even in the absence of Co. Matrix strength levels were close to those predicted by design models; however, all four alloys demonstrated a hardness deficit of approximately 200 VHN at the carburized surface, suggesting recalibration of the M2C precipitation strengthening model may be required in these alloys.

Mg–Al–Ca alloys provide excellent creep resistance and castability for elevated temperature applications. Computational thermodynamics calculations and experimental investigation of the Mg–Al–Ca ternary system have validated the earlier development of creep-resistant AX52 (Mg–5Al–2Ca1) and AX53 (Mg–5Al–3Ca) alloys. The Scheil simulation of alloy solidification has suggested key guidelines of alloy composition design in promoting the thermally stable (Mg,Al)2Ca phase, while replacing the less stable Mg17Al12 in the microstructure. The suppression of the Mg17Al12 phase can increase the solidus temperature, reduce the freezing range, and increase the latent heat during solidification, all of which contribute to improved castability in the AX53 and AX52 alloys compared with the AX51 (Mg–5Al–1Ca) alloy. The quantitative phase equilibrium data, microstructure characterization, as well as the thermal physical properties of the Mg–Al–Ca alloy system generated from this study are important basis for further optimization of alloy composition and microstructure for elevated temperature applications.

This study examines the response of pure Mg and its alloys, both binary Mg–Ce and ternary Mg–Al–Ce, during compression testing over a wide range of (true) strain rates and temperatures. Process maps were generated by plotting the instability parameter and efficiency of energy dissipation for microstructural evolution as a function of test temperature and strain rate. Microstructural features of each of the deformed samples were examined to generate a microstructure/micromechanism map as a matrix that was overlaid on the process map drawn in the temperature–strain-rate space. The combination of both maps delineated the desirable “safe” process window for each of the materials. Addition of 0.5% Ce to pure Mg reduced the extent of the “safe” process window despite increasing the flow stress, while alloying with both Ce and Al widened this window as determined by the extent of the desirable DRX domain. The process maps in general suggest a much wider range of temperature and strain rate for “safe” deformation compared to the microstructure maps.

This paper presents the results of a transmission electron microscopy study of the microstructure of extruded Mg–Nd–Zn alloys that exhibit improvement in strength, making them potential candidates for bumper beam applications. Three sets of extruded rods with 0%, 0.2% and 0.5% Zn addition are prepared to examine the effect of Zn on the precipitates in the as-extruded and aged condition. At least five different precipitate phases with different structures, morphologies and distributions were identified and correlated with the mechanical properties. Zn is seen to have no effect on the precipitation sequence of Nd-rich phases but seems to control the growth of those phases. It is found that small amount of Zn can lead to drastic changes in the nature of the precipitate phase due to the strong affinity between Zn and Nd in the alloy to form Mg–Nd–Zn intermetallics, affecting the strength and ductility. Control of both the Nd and Zn content are necessary to take advantage of the “rare earth texture” induced by Nd to improve ductility and precipitation strengthening by the Mg–Nd–Zn intermetallics when Zn is present.

Titanium offers performance as well as mass saving benefits in automotive components subjected to reciprocating and suspension loads and in components subjected to extreme temperatures and gradients. However, the extensive use of titanium is hampered by the high cost of the raw material and the special handling that is needed. This article outlines the technological and economic challenges faced and highlights some example materials and process developments that attempt to address these hurdles.

The limited extrudability of AZ31 (Mg–3Al–1Zn) alloy is reported to be caused by incipient melting of the Mg17Al12 binary phase with a eutectic temperature of 438 °C. Computational phase equilibria and microstructural examination, however, show that Mg–Al–Zn ternary phases with eutectic temperatures as low as 338 °C are actually present in the AZ31 alloy, which is indeed the real limitation to its extrudability. The significantly improved extrudability of AM30 alloy (Mg–3Al–0.3Mn) is due to the absence of these zinc-containing eutectic phases.

A model describing the thermal and mechanical effects on heterogeneous nucleation during squeeze casting of metal alloys has been developed based on classical nucleation theory. Squeeze casting experiments were carried out using an aluminum alloy, where the temperature change inside the casting during pressurized solidification was measured and the grain density at the locations where the temperature was measured was determined. By correlating the grain density and local thermal history, a quantitative function of nucleation rate with pressure and temperature was obtained.

This paper investigates the effects of different surface pretreatments on the adhesion and performance of CVD diamond coated WC–Co turning inserts for the dry machining of high silicon aluminum alloys. Different interfacial characteristics between the diamond coatings and the modified WC–Co substrate were obtained by the use of two different chemical etchings and a CrN/Cr interlayer, with the aim to produce an adherent diamond coating by increasing the interlocking effect of the diamond film, and halting the catalytic effect of the cobalt present on the cemented carbide tool. A systematic study is analyzed in terms of the initial cutting tool surface modifications, the deposition and characterization of microcrystalline diamond coatings deposited by HFCVD synthesis, the estimation of the resulting diamond adhesion by Rockwell indentations and Raman spectroscopy, and finally, the evaluation of the dry machining performance of the diamond coated tools on A390 aluminum alloys. The experiments show that chemical etching methods exceed the effect of the CrN/Cr interlayer in increasing the diamond coating adhesion under dry cutting operations. This work provided new insights about optimizing the surface characteristics of cemented carbides to produce adherent diamond coatings in the dry cutting manufacturing chain of high silicon aluminum alloys.