Trends in Automotive Lightweighting

Smirnov O., Voron M., Tymoshenko A., Skorobagatko Y., Schwab S., Semenko A.

Semenko A.Y., Parkhomchuk Z.V., Veis V.I., Likhatskyi R.F., Likhatskyi I.F., Tymoshenko А.М., Voron M.M.

Jia Y., He S., Li X.

Abstract The self-piercing riveting (SPR) Forming and tensile tests of hot-rolled steel sheet BR1200HS and aluminum alloy sheet AA 6082-T6 were simulated by Simufact Forming software. The test results show that the diameter of the rivet leg opening, which is the most important parameter affecting the mechanical properties of the joints, shows a first increase and a second decrease with the increase of rivet length, and the Max. tensile loads of the joints have the same variation law. The larger the diameter of the rivet leg opening, the greater the Max. tensile load of the joint, and the greater the effective plastic strain of the rivet of the joint. The rivet length of the joints in the five preferred SPR formation schemes obtained were all 6.5 mm, and only one scheme had a rivet hardness of H4, the rest were H5. The SPR experiment is used to verify the current finite element simulation data can get the final research conclusion. The finite element simulation (FEM) would greatly reduce the test times of the SPR test, save the test consumables and save the test cost.

Zhang Z., Cui Y., Chen Q.

7000 series high strength aluminum alloys are increasingly used in manufacturing automobile body parts to meet the more stringent demands for automobile lightweight. Hot stamping of 7000 series high strength aluminum alloys is a complex thermal-mechanical coupling process and precise simulation is needed to predict material fracture. To obtain damage model of 7075 aluminum alloy in hot stamping, five different stress triaxiality specimens were designed. The fracture strain, critical strain and average stress triaxiality of different specimens were obtained by the hybrid finite element simulation and experiment (FE-EXP) method. GISSMO model of 7075 aluminum alloy at 400 °C was established. Compared with the experimental results of U-shaped part hot stamping under different lubrication conditions, the calibrated GISSMO model was demonstrated to predict the damage behavior of 7075 aluminum alloy during high temperature deformation accurately.

Mapelli C., Villa G., Barella S., Gruttadauria A., Mombelli D., Veys X., Duprez L.

Different lightweight steels alloys have been treated by different isothermal treatments in order to understand the basics of precipitation kinetics of κ-carbide for such class of new steel grades featured by high concentration of Mn and Al. The κ-carbide precipitation plays a significant role to induce the strengthening of these steel grades that maintain a significant ductility up to the fracture as a consequence of their duplex ferrite-austenite structure that exploits the twinning mechanism of austenite during the plastic deformation. In this paper the results about isothermal transformations involving the κ-carbide precipitation have been discussed. In order to deepen the comprehension of the mechanisms involved in precipitation of κ-carbides, the study has been performed by isothermal (Temperature Transformation Treatment) experiments applying different temperatures and holding times. The observed transformations have been measured and it has been possible to apply the JMAK model to fit such results. In addition, it has been observed a relationship between the steel composition and the activation energy for the transformation.

Maculotti G., Bonù S., Bonù L., Cagliero R., Genta G., Marchiandi G., Galetto M.

Abstract Reducing overall vehicle weight is essential to reduce fuel consumption and pollutant emission and to improve noise, vibration, and harshness (NVH) performances. The substitution with lighter alloys can involve the grand majority of vehicle components, depending on the market sector. In several applications, e.g., chassis, pulleys, and viscodampers, metal sheets are formed in several steps, each of whom work-hardens the material reducing the available residual plasticity. Typically, the process is designed via FEM, whose results are affected by the initial conditions, often neglected, and is performed on pre-processed materials from suppliers. In this regard, correctly simulating the first step of the process is critical. However, the related initial conditions, in terms of residual stress and strain induced by former preliminary operations, are often neglected. This work proposes a quick and economical experimental procedure based on a hardness map to estimate initial conditions and to validate FEM results. The procedure allows evaluating the material’s residual plasticity, which is necessary to process engineers to design following manufacturing steps. The approach is demonstrated on an industrially relevant case study, i.e., the blanking of an AA 5754, in use for water pump pulleys.

Szybist J.P., Busch S., McCormick R.L., Pihl J.A., Splitter D.A., Ratcliff M.A., Kolodziej C.P., Storey J.M., Moses-DeBusk M., Vuilleumier D., Sjöberg M., Sluder C.S., Rockstroh T., Miles P.

The Co-Optimization of Fuels and Engines (Co-Optima) initiative from the US Department of Energy aims to co-develop fuels and engines in an effort to maximize energy efficiency and the utilization of renewable fuels. Many of these renewable fuel options have fuel chemistries that are different from those of petroleum-derived fuels. Because practical market fuels need to meet specific fuel-property requirements, a chemistry-agnostic approach to assessing the potential benefits of candidate fuels was developed using the Central Fuel Property Hypothesis (CFPH). The CFPH states that fuel properties are predictive of the performance of the fuel, regardless of the fuel's chemical composition. In order to use this hypothesis to assess the potential of fuel candidates to increase efficiency in spark-ignition (SI) engines, the individual contributions towards efficiency potential in an optimized engine must be quantified in a way that allows the individual fuel properties to be traded off for one another. This review article begins by providing an overview of the historical linkages between fuel properties and engine efficiency, including the two dominant pathways currently being used by vehicle manufacturers to reduce fuel consumption. Then, a thermodynamic-based assessment to quantify how six individual fuel properties can affect efficiency in SI engines is performed: research octane number, octane sensitivity, latent heat of vaporization, laminar flame speed, particulate matter index, and catalyst light-off temperature. The relative effects of each of these fuel properties is combined into a unified merit function that is capable of assessing the fuel property-based efficiency potential of fuels with conventional and unconventional compositions.

Li H., Liu X., Wang J.

The influence of preaging (PA) treatments on the bake hardening (BH) response of a AlZnMgCuZr aluminum alloy which served as automotive body structures were studied in this paper. A novel two-step PA treatment was particularly designed and further employed. The mechanical properties of the alloy were tested in detail. The microstructure was characterized by optical microscope (OM), transmission electron microscopy (TEM) and 3D measuring laser microscope (3D–MLM). Meanwhile, the corrosion behavior was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The results indicated that the PA treatment was beneficial for the improvement of BH response after baking at 180 °C immediately after the solution treatment and the micro-hardness reached the peak value (194 HV) after 10 h holding, which had a percentage improvement of 110.87% compared to the hardness under the solution condition. The PA treatments decreased natural aging (NA) adverse effects, while it had the lowest NA effect and optimal BH response under 120 °C/20 min. Such a novel two-step PA treatment was revealed further to decrease the NA effect and increase the BH response compared to the optimal PA treatment, in particular, the BH value could reach 168 MPa and was 21.7% higher than that of optimal PA + NA treatment. The optimal corrosion resistance has been shown up by the combined characterizations of potentiodynamic polarization curves, EIS Nyquist plots, and 3D–MLM images.

Lewis G.M., Buchanan C.A., Jhaveri K.D., Sullivan J.L., Kelly J.C., Das S., Taub A.I., Keoleian G.A.

A large portion of life cycle transportation impacts occur during vehicle operation, and key improvement strategies include increasing powertrain efficiency, vehicle electrification, and lightweighting vehicles by reducing their mass. The potential energy benefits of vehicle lightweighting are large, given that 29.5 EJ was used in all modes of U.S. transportation in 2016, and roughly half of the energy spent in wheeled transportation and the majority of energy spent in aircraft is used to move vehicle mass. We collect and review previous work on lightweighting, identify key parameters affecting vehicle environmental performance (e.g., vehicle mode, fuel type, material type, and recyclability), and propose a set of 10 principles, with examples, to guide environmental improvement of vehicle systems through lightweighting. These principles, based on a life cycle perspective and taken as a set, allow a wide range of stakeholders (designers, policy-makers, and vehicle manufacturers and their material and component suppliers) to evaluate the trade-offs inherent in these complex systems. This set of principles can be used to evaluate trade-offs between impact categories and to help avoid shifting of burdens to other life cycle phases in the process of improving use-phase environmental performance.

Zhang X., Yao F., Ren Z., Yu H.

During resistance spot welding, the welding current is the most important process parameter, which determines the welding heat input and then has a great influence on the welding quality. In present study, the CR590T/340YDP galvanized dual phase steel widely used as automobile material was carried out using resistance spot welding. The effect of welding current on the weld formation, microstructure, and mechanical properties was studied in detail. It was found that the quality of weld appearance decreased with the increase of welding current, and there was a Zn island on the weld surface. The microstructure of the whole resistance spot welded joint was inhomogeneity. The nugget zone consisted of coarse lath martensite and a little of ferrite with the columnar crystal morphology, and the microstructure of weld nugget became coarser when the welding current was higher. There was an optimum welding current value and the tensile strength reached the maximum. This investigation will provide the process guidance for automobile body production.

Shaha S.K., Czerwinski F., Kasprzak W., Friedman J., Chen D.L.

Tensile and low cyclic fatigue tests were used to assess the influence of micro-additions of Ti/V/Zr on the performance of Al–7Si–1Cu–0.5Mg (wt.%) alloys in the as-cast and T6 heat-treated conditions and their improvement was compared to the base alloy. The microstructure of the as-cast Al–7Si–1Cu–0.5Mg (wt.%) base and modified alloys consisted of α-Al, eutectic Si, and Cu, the Mg- and Fe-based phases Al 2.1 Cu, Al 8.5 Si 2.4 Cu, Al 7.2 Si 8.3 Cu 2 Mg 6.9 and Al 14 Si 7.1 FeMg 3.3 . In addition, the micro-sized Ti/V/Zr-rich phases Al 6.8 Si 1.4 Ti, Al 21.4 Si 4.1 Ti 3.5 VZr 3.9 , Al 6.7 Si 1.2 TiZr 1.8 , Al 2.8 Si 3.8 V 1.6 Zr and Al 5.1 Si 35.4 Ti 1.6 Zr 5.7 Fe were identified in the modified alloys. It was also noticed that increasing the content of Ti–V–Zr changed the morphology of Ti/V/Zr-rich phase. The tensile test results showed that the T6 heat-treated alloy modified with the addition of a higher content of Ti–V–Zr achieved the highest tensile strength of 343 MPa over the base alloy and alloys modified with additions of Ti, Ti–Zr and lower contents of Ti–V–Zr. The plastic strain energy density coefficient of the alloy modified with the addition of a higher content of Ti–V–Zr in the T6 temper condition was higher than the other studied alloys and reached 162 MJ m −3 . The fatigue life of the same alloy was considerably longer than that of the other studied alloys, including the base alloy. The fractography revealed that all the studied alloys showed similar fracture behavior. The tensile cracks propagated through the eutectic Si and primary phases, exhibiting intergranular fracture along with some cleavage-like features of the plate-shaped Zr–Ti–V-rich intermetallics with the presence of fatigue striations on the latter, indicating their ductile nature. It is believed that the morphological changes of intermetallic precipitates containing Zr, Ti and V enhance the fatigue life of the alloy modified with additions of larger amounts of Ti–V–Zr in the T6 condition.

Henriksson F., Johansen K.

In the automotive industry, mass reduction and lightweight design is a continuing trend that does not show signs of declining. When looking at where to reduce weight in a vehicle, the body is a pre ...

Shaha S.K., Czerwinski F., Kasprzak W., Friedman J., Chen D.L.

The Al–7Si–1Cu–0.5Mg (wt%) alloy with micro-additions of Ti, V and Zr after varied solidification rates in as-cast and T6 heat treated states was subjected to monotonic tension, compression and cyclic deformation. The solidification rate affected the secondary dendrite arm spacing (SDAS), precipitate size which eventually control the flow stress during compression/tension and cyclic deformation. For the as-cast state, a reduction in the SDAS from 30 μm to 18 μm caused an increase of the ultimate strength from 354 MPa to 367 MPa and was accompanied by a slight reduction in the alloy deformability from 42.5% to 41.6%. For the T6 state, the strength increased from 413 MPa to 419 MPa and deformability reduced from 52.4% to 51.0%. The reduction of SDAS in the above range also caused a substantial increase in fatigue life. According to fractography, the tensile cracks propagated mainly through the eutectic Si and primary phases, exhibiting intergranular fracture along with some cleavage-like features through the plate-shaped Zr–Ti–V–rich intermetallics. The presence of fatigue striations on the plate-shaped intermetallics proved their ductile nature and had a positive effect on fatigue life. The EBSD analysis revealed differences in crystallographic texture and the contribution of dynamic recovery during deformation. The benefits of Zr–V–Ti additions in improving the alloy overall performance in automotive applications are discussed.

Shaha S.K., Czerwinski F., Kasprzak W., Friedman J., Chen D.L.

High-temperature tensile and low-cycle fatigue tests were performed to assess the influence of micro-additions of Ti, V, and Zr on the improvement of the Al-7Si-1Cu-0.5Mg (wt pct) alloy in the as-cast condition. Addition of transition metals led to modification of microstructure where in addition to conventional phases present in the Al-7Si-1Cu-0.5Mg base, new thermally stable micro-sized Zr-Ti-V-rich phases Al21.4Si4.1Ti3.5VZr3.9, Al6.7Si1.2TiZr1.8, Al2.8Si3.8V1.6Zr, and Al5.1Si35.4Ti1.6Zr5.7Fe were formed. The tensile tests showed that with increasing test temperature from 298 K to 673 K (25 °C to 400 °C), the yield stress and tensile strength of the present studied alloy decreased from 161 to 84 MPa and from 261 to 102 MPa, respectively. Also, the studied alloy exhibited 18, 12, and 5 pct higher tensile strength than the alloy A356, 354 and existing Al-Si-Cu-Mg alloy modified with additions of Zr, Ti, and Ni, respectively. The fatigue life of the studied alloy was substantially longer than those of the reference alloys A356 and the same Al-7Si-1Cu-0.5Mg base with minor additions of V, Zr, and Ti in the T6 condition. Fractographic analysis after tensile tests revealed that at the lower temperature up to 473 K (200 °C), the cleavage-type brittle fracture for the precipitates and ductile fracture for the matrix were dominant while at higher temperature fully ductile-type fracture with debonding and pull-out of cracked particles was identified. It is believed that the intermetallic precipitates containing Zr, Ti, and V improve the alloy performance at increased temperatures.

Peinado V., García L., Fernández Á., Castell P.

The manufacturing of medium-sized hollow parts using a foamed high density polyethylene was studied using a conventional accumulator blow extrusion machine and a systematic capture of pictures during the parison formation. To fully monitor the parison formation, several experiments were carried out varying the chemical foaming agent content from 0 wt.% to 2 wt.% and increasing the push extrusion speed. Results pointed out greater wall thickness, diameter, and length of parisons with higher weight percentage of blowing agent and extrusion speed. A full experimental characterisation of parison dimensions was essential to assure a proper prediction of the blowing step. Information was used as input for modelling and simulations of the blowing phase of an industrial container. To validate the proposed methodology, a blow moulding process of a generic container was simulated using Ansys Polyflow v13 software and its finite element analysis which provided an accurate approximation of the wall thickness expected. Further real tests on the simulated container also demonstrated that, in those parisons with a 1 wt.% CFA concentration and higher blowing pressure, there was remarkable improvement on their packaging properties such as decreasing of the total weight of the container and an enhancement of its surface quality.