TBF 1180 steel was plastically deformed under different strain paths in order to study both the ductility and RA transformation rates. Specimens were prepared from a 1 mm thick sheet and then tested incrementally under uniaxial tension, plane-strain tension, and biaxial tension. The retained austenite (RA) levels were measured, as a function of the plastic strain, using electron backscatter diffraction (EBSD). The plane-strain tension specimens had the fastest rate of RA transformation as a function of strain, followed by uniaxial tension, and then biaxial tension. The forming limits were measured for each strain path, yielding major limit strains of 0.12 under uniaxial tension, 0.09 under plane-strain tension, and 0.16 under biaxial tension. These results were compared to prior work on a 1.2 mm Q&P 1180 steel sheet, which had a similar yield and ultimate tensile strength, but exhibited slightly greater forming limits than the TBF material. The visual inspection of the micrographs appeared to show an equiaxed RA morphology in the Q&P 1180 steel and a mixture of equiaxed and lamellar RA grains in the TBF 1180 steel. However, the statistics generated by EBSD revealed that both alloys had RA grains with essentially the same aspect ratios. The average RA grain size in the Q&P alloy was found to be about three times larger than that of the TBF alloy. As such, the small but consistent formability advantage exhibited by the Q&P 1180 alloy along all three strain paths can be attributed to its larger average RA grain size, where larger RA grain sizes correlated with a more gradual transformation rate.

Power electronics are crucial for electrified propulsion systems; however, their power density is usually limited by thermal management capability. In this study, a two-phase immersion cooling system with an integrated condenser is designed for a fully functional power module in electric vehicles. Natural air convection cooling, forced air convection cooling, and forced air together with Liquid Cooling Tube (LCT) cooling were implemented for the integrated condenser to evaluate their impacts on vapor condensation and die temperature. Both sealed and non-seal conditions were analyzed to study the influence of vapor pressure. A baseline single-sided watercooling power module is also designed for benchmark evaluation, followed by CFD analysis to investigate the cooling capability limit of both single- and double-sided water-cooling. The results showed the cooling capability on the integrated condenser significantly influenced the evaporation rate and the vapor pressure, which then affected the boiling temperature of the fluid and finally the die temperature. Under high-power conditions, the additional LCT further reduced the die temperature by 10 degrees C compared to pure forced air cooling. Compared to the sealed condition, the non-sealed condition has a constant boiling temperature, and its die temperature is 10 degrees C lower under 1700 W heating power. Leveraging the dielectric property of the Novec fluid, Direct Bond Copper (DBC) layer was removed to further reduce heat resistance in the proposed two-phase immersion cooling system. The upscaling analyses show that at the same chip temperature (160 degrees C) design threshold, the two-phase immersion cooling could enable chips to work up to 12 kW heat generation power, while the single- and doublesided water-cooling could only support 6 kW and 10 kW respectively with large temperature gradient and local hotspots. Benefited from better capability of two-phase immersion cooling, one single chip could be designed with a higher power density, which enables reduced number of dies and cost.

Many low-density metals are also reactive. This article draws inspiration from the passivation oxide layer formed on aluminum to the design of electrochemically stable surface layers on lithium metal electrodes in batteries. First, reactive molecular dynamics simulations are used to compare the oxide layer formation on lithium and aluminum metal surfaces. While a uniform dense aluminum oxide layer forms on aluminum, vertical cracks in the lithium oxide layer lead to a deformed lithium oxide layer. These observations are consistent with the empirical Pilling–Bedworth Ratio (PBR) that uses the molar volume ratio of oxide to metal to determine whether a metal is likely to passivate in dry air by creating a protective oxide layer. A passivation layer needs to form on the lithium metal surface in the presence of electrolytes. The PBR concept is thus extended to the multiple compounds found in the spontaneously formed solid electrolyte interphase (SEI). It is suggested that a mixture of LiF/Li2CO3 or LiF/Li2O or replacing Li2O with Li2S can effectively create a PBR that is in the 1 to 1.3 range for better passivation. While these analyses are consistent with some experimental evidence, a seeding layer concept is proposed to further prevent dendrite growth and simplify the battery manufacturing process. The role of metallic nanoparticles in the metal–carbon nanocomposite seeding layer to control lithium nucleation and growth is investigated by an atomically informed phase field model (AI-PFM). The model predicts the formation of a Li-rich phase with Ag nanoparticles but non-uniform lithium metal nucleation on Au nanoparticles, showing the AI-PFM model to be a desired design tool to evaluate which metallic nanoparticles can be used to control the Li deposition morphology. These results collectively emphasize the need for highly coupled electrochemical–mechanical modeling to solve the challenges of designing a multifunctional passivation layer for metal electrodes in batteries.

Squeeze casting is an advanced manufacturing process for aluminum and magnesium alloys, which produces high integrity and heat-treatable cast components. The physics involved in squeeze casting is pressurized solidification and it is important to understand the fundamental knowledge of pressurized solidification and to develop numerical models both at macro- and micro-scales. This review presents the major challenge and novel research dedicated to macro- and micro-modeling on squeeze casting of aluminum and magnesium alloys, including metal displacement and free surface tracking, thermal–mechanical coupled simulation, casting–mold interfacial heat transfer model, shrinkage defect and macrosegregation prediction, pressurized solidification and microstructure modeling, through-process modeling, etc. Finally, the prospects of the macro- and micro-modeling on squeeze casting process are presented.

Automotive applications need low-cost, lightweight, high-temperature alloys to increase vehicle efficiency. The Al–Fe–Si system provides an opportunity to develop such a material, as it consists of three low-cost elements that are all abundant in nature. Specifically, the τ11-Al4Fe1.7Si ternary intermetallic phase is a high-temperature, lightweight phase with high strength and good corrosion resistance. However, this phase exhibits a narrow compositional range of stability, resulting in undesirable microstructures forming during solidification and processing, limiting its use in potential applications. Density functional theory (DFT) calculations and a thermodynamically-driven experimental approach utilizing diffusion couples were employed to study the effect of Mn on the stability and composition range of τ11-Al4Fe1.7Si. The DFT calculations showed a decrease in the energy of the structure when alloying with Mn. Experimental results confirmed the predictions from the DFT calculations, indicating that alloying with Mn increases the compositional range, and thus the processability of this phase. New phase diagrams and equilibria are proposed by exploring and determining phase boundaries for the τ11-Al4Fe1.7Si phase with Mn.

The combination of light metals (aluminum, magnesium and titanium) and innovative casting processes provides cost-effective technologies to produce lightweight components and systems for many industrial applications. This article provides a comprehensive and yet critical review of light alloy development for cast components used in lightweight and high-performance structural and propulsion applications. It also summarized some latest process innovations in gravity casting, high pressure die casting, and low pressure casting, to overcome some fundamental issues related to defect formation in casting processes. Emerging casting processes developed in the last twenty years, such as semisolid processing, squeeze casting, ablation casting, bimetallic overcasting, and diffusion solidification processing, are discussed for further development. Recent advances in casting simulation and the concept of Integrated Computational Materials Engineering (ICME) are summarized for casting applications. Finally, future perspectives in light alloy development (including green alloys, high entropy alloys and metal matric composites), process innovations (such as high integrity casting, multi-material manufacturing and additive manufacturing), and ICME development are presented to stimulate further research and sustainable development in this important field of metals processing technology.

The overarching objective of this USAMP project was to develop and demonstrate door panels made from magnesium (Mg) sheet with a cost penalty over conventional steel stampings of no more than $\$5.50$/kg saved. The technical approach integrated experiments with advanced computational tools based on Integrated Computational Materials Engineering (ICME) methods to develop new alloy chemistries and their thermomechanical processing that promise improved formability and lower forming temperatures. A penultimate task before finally forming the stampings was to incorporate actual microstructure into models that would enable formability simulations. This approach would, for the first time, account for individual magnesium grains moving in an anisotropic fashion unlike that for aluminum or steel that have isotropic properties upon which the current simulation tools are based. In separate activities, new coatings and lubricants to facilitate forming and improved corrosion protection and joining strategies, were developed to ensure that the door could be produced with stated product requirements. A technical cost model, which included parts production, assembly, and paint for a door specifically designed for Mg sheet, showed the cost penalty to be between $\$4.26$ to $\$6.60$/kg saved, which enveloped the project’s cost targets. The cost of the coated Mg sheet was identified as the key driver for the cost penalty. The mass of the Mg-intensive door was 7.9 kg, which was 54% less than the baseline steel door.

Most of the applications of magnesium in lightweighting commercial cars and trucks are die castings rather than sheet metal, and automotive applications of magnesium sheet have typically been experimental or low-volume serial production. The overarching objective of this collaborative research project organized by the United States Automotive Materials Partnership (USAMP) was to develop new low-cost magnesium alloys, and demonstrate warm-stamping of magnesium sheet inner and outer door panels for a 2013 MY Ford Fusion at a fully accounted integrated component cost increase over conventional steel stamped components of no more than $2.50/lb. saved ($5.50/kg saved). The project demonstrated the computational design of new magnesium (Mg) alloys from atomistic levels, cast new experimental alloy ingots and explored thermomechanical rolling processes to produce thin Mg sheet of desired textures. A new commercial Mg alloy sheet material was sourced and pretreated with protective coil coatings, and its properties fully characterized. The Mg sheet was successfully warm-formed using novel lubricants into intermediate size benchmark parts and full-size automotive door inner and outer panels. The project also explored conventional welding processes for joining of Mg sheet, developed novel corrosion treatments for multi-metal assembly coatings, performed computer simulations of door panel forming using two new material cards based on crystal plasticity theory, and concluded with a door static and dynamic performance analysis. An overall cost driver and sensitivity assessment task compared the final cost penalty depending on the cost of the primary magnesium sheet.

The hot-tearing susceptibility of Mg-10Zn- x Al ( 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 (0.65 F s to 0.74 F s ). Experimental results were compared with Pandat’s simulation results to predict the occurrence of hot tearing in Mg-10Zn- x Al 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.

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 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.

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 degrees 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. (C) 2019 Published by Elsevier B.V. on behalf of Chongqing University.

Based on the hot tearing index vertical bar Delta T/Delta(f(s))(0.5)vertical bar 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 vertical bar Delta T/Delta(f(s))(0.5)vertical bar(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. (C) 2018 Published by Elsevier B.V. on behalf of Chongqing University.

A cost-effective alpha-beta 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 alpha 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. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Using in situ, high-speed imaging of a hard wedge sliding against pure aluminum, and image analysis by particle image velocimetry, the deformation field in sliding is mapped at high resolution. This model system is representative of asperity contacts on engineered surfaces and die–workpiece contacts in deformation and machining processes. It is shown that large, uniform plastic strains of 1–5 can be imposed at the Al surface, up to depths of 500 μm, under suitable sliding conditions. The spatial strain and strain rate distributions are significantly influenced by the initial deformation state of the Al, e.g., extent of work hardening, and sliding incidence angle. Uniform straining occurs only under conditions of steady laminar flow in the metal. Large pre-strains and higher sliding angles promote breakdown in laminar flow due to surface fold formation or flow localization in the form of shear bands, thus imposing limits on uniform straining by sliding. Avoidance of unsteady sliding conditions, and selection of parameters like sliding angle, thus provides a way to control the deformation field. Key characteristics of the sliding deformation such as strain and strain rate, laminar flow, folding and prow formation are well predicted by finite element simulation. The deformation field provides a quantitative basis for interpreting wear particle formation. Implications for engineering functionally graded surfaces, sliding wear and ductile failure in metals are discussed.