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For both notchback-type and fastback-type models, it has been found that critical geometries which increase the aerodynamic drag exist, and the time-averaged wake patterns basically consist of an arch vortex behind the rear window and trailing vortices in the wake. The unsteady characteristics of the wake seem to be directly related to aerodynamic drag. However, the unsteady characteristics of these wake patterns for notchback and fastback cars were not clear. The purpose of present paper is to clarify these phenomena. We try to analyze experimentally the unsteady characteristics by measuring the velocity fluctuations in the wake, the pressure fluctuations on the trunk deck and the drag-force fluctuations acting on the model. At the same time, the analysis of the numerical simulation was made by using the same numerical model as the experimental model. The computed flow visualization behind the rear window showed a fluctuating arch vortex.

In order to investigate the corrosion resistance of organic composite-coated steel sheets ( OCS ) in a real automotive environment, many kinds of corrosion tests were performed on test pieces and real automotive doors. Tests with a corrosive solution including iron rust were introduced to simulate the real corrosive environment of automotive doors. The relationship between the components of OCS and the corrosion resistance in the rust-including tests was examined. In addition, electrochemical studies were performed. Results indicate OCS has much better corrosion resistance than plated steel sheets with heavier coating weight in all tests. OCS shows excellent corrosion resistance in rust-free corrosive solution, however, some types of OCS do have corrosion concerns in rust-including tests. It became clear that these OCS types have an organic coating with lower cross-linking.

Spot friction welding (SFW) is a cost-effective spot joining technology for aluminum sheets compared with resistance spot welding (RSW) [1]. In this study, coated mild steel was spot friction welded to 6000 series aluminum using a tool with shoulder diameter of 10 mm and welding conditions of 1500-2000 rpm and time of 5 s. Testing showed that tensile shear strength increased as the solidus temperature of the coating on the steel decreased. Microstructure characterizations of steel/Al joint interfaces showed that zinc from the coatings was incorporated into the stir nuggets and that intermetallic phases may have formed but not in continuous layers. Some Al-Zn oxides that appeared to be amorphous were also found in the joint interfaces.

The residual stresses produced by static and progressive induction hardening processes were investigated using different diameter bars and different heating conditions. The x-ray diffraction method of stress measurement was used. Compressive stresses were observed at and slightly below the surface in the hardened zone, while lower compressive stresses or tensile stresses were seen at the ends of this zone. These stresses depended on the shapes and sizes of the heated zone and the cooling patterns. Shot peening was seen to convert the tensile stress to a compressive value.

Recently, it has become more important to improve the corrosion resistance of automotive body panels, and the amount of coated steel sheets has been increasing for this application. Several types of coated steel sheet, such as Zincrometal, hot-dip galvanized steel sheets, galvannealed steel sheets and electrogalvanized steel sheets are widely available. Sumitomo Metal Industries have studied new coated steel sheets for automotive body panels, and have succeeded in the development of the new NiZn alloy plated product “SZ”, the deposit of which includes about 13% nickel. This paper discusses the plating conditions, production process, properties and performance of SZ.

Two types of TS 450 to 600 MPa grade hot rolled high strength steels have been developed whose strength increases by a post-deformation heat treatment. One is a nitrogen added steel, produced by a low temperature coiling method. This steel shows an increase in tensile strength by about 60 to 90 MPa after a conventional baking treatment. The other is a Cu-bearing steel, produced also by a low temperature coiling method. This steel shows much larger increase in tensile strength by about 200 MPa due to the precipitation hardening of copper, but it requires an additional heat treatment at a relatively high temperature such as 600° C.

Galvannealed steel sheet (GA) is very extensively used for vehicle panels. However ζ-phase (FeZn13) in GA coat causes poor stamping formability. Previously, there were no easy methods to evaluate the influence of ζ-phase on the frictional characteristics other than the X-ray diffraction method. This study will discuss the development of a new testing method: Dr. STAMP Method that is both efficient and convenient with pin-on-disc tester.

This paper describes the lap welding of Zinc-coated steel sheet using a high power continuous wave YAG laser. The well-known problem of welding the Zinc-coated sheet is related to the low boiling point of zinc compared with the melting point of steel. During lap welding, zinc coating at the interface vaporize rapidly and causes defects1)2). In this study, therefore, lap welding was performed by YAG laser. The effects of type of coating layer, welding conditions, tensile strength and corrosion resistance after electro-deposition was examined. It was found that the weldability of coated steel is different by type of coating. Zn-Ni coated steel showed good weldability, but galvanealed steel inevitably pore pits with no gap set up. These defects not only lower the strength of joint, but also produce irregular bead where easily corroded after electro-deposition.

The substantial part of the drag of an automobile is the pressure drag. Therefore, the car must be designed as it produces minimum pressure drag. The present paper describes effects of geometrical configuration of the rear part of a car on the aerodynamic drag. Experiments were made on 1/5 scale models of fastback and notchback design. For the fastback car the drag depends heavily on the angle of a rear window. At a certain critical angle the drag shows a sharp peak. This peak drag can be reduced drastically by the tapering of plan form of the rear geometry. For the notch-back design some combination of the angle of rear window and height of trunk deck shows similar maximum in the drag. Methods of avoiding the large drag were also found. Our experiment was extended to the measurement of structure of wake by hot wire anemometers and total pressure tubes. The correlation between the wake structure and drag was clarified by the consideration of vorticity and circulation.

Cost and weight reduction considerations make it very important to evaluate and reduce aerodynamic noise in the early stage of vehicle develpment. For these reasons, a method to evaluate aerodynamic noise quantitatively is needed. As an initial step, our first paper investigated airflow around the A-pillar of a full-scale vehicle. As a result, vortical flow structure and the influence of the vortical flow on the pressure fluctuations were clarified. As the second step, this paper presents an estimation method for the aerodynamic noise from a vehicle. Based on Lighthill's equation, we propose an evaluation equation to estimate aerodynamic noise. The aerodynamic noise radiated externally from a vehicle is estimated as ∑(Pfi,fi,Sfi)2 Where Pfi is the fluctuating pressure on the surface of the vehicle, fi the frequency and Sfi the correlation area. The method is applied to the aerodynamic noise problem associated with the A-pillar of a vehicle.

A method was studied for simultaneous zinc phosphating on aluminum and steel surfaces to obtain high corrosion resistance on aluminum surfaces, which conventional phosphatic processing could not provide with sufficient corrosion resistance. Since aluminum is protected by an oxide film on its surface, it has poor processability with zinc phosphating solutions applied to steel. An appropriate quantity of fluoride was therefore added to improve processing, and the coating film, aluminum composition and surface conditions were optimized to suppress filiform corrosion, which is characterized by string-like blisters of paint film starting from a paint defect. In addition, in view of the actual production environment, the corrosion resistance of the ground area made for readjustment after stamping was studied for the optimization of the processing solution.

Magnesium has the lowest specific gravity of all metals used for structural members. The application of magnesium for a road wheel leads to improved vehicle handling and drivability because of the reduction of an unsprung weight. The authors have developed new magnesium alloy which shows excellent mechanical properties and attained a magnesium forged road wheel that is 30% lighter than aluminum wheels.

Gas shielded metal arc welding is generally applied to automobile chassis parts. However, the weld parts with the E-coat show poor corrosion resistance. Therefore, the corrosion mechanism of the weld parts was investigated. The results found two reasons why the weld parts corroded faster than the non weld parts:(1)inadequate phosphating (2)defects in the E-coat. After detailed investigation, it was clarified that the major cause of poor corrosion resistance was the defects in the E-coat caused by slags formed on the surface of the weld bead. Therefore the amount of slag has to be decreased to improve the corrosion resistance. The effect of shielding gas composition on the amount of slag was then investigated. In the case of Ar and oxidizing gas mixture, the corrosion resistance improved as the oxidizing gas content decreased. This was due to the reduction of slags.

A new process for manufacturing high-strength gears has been developed to meet the requirement of automobile transmission miniaturization. The points of the process are to increase the shot peening intensity and to perform optimal control of the initial (before shot peening) microstructure by heat treatment corresponding with the peening intensity in order to obtain higher residual compressive stress. The new process, named Carbonitriding and Hard Shot Peening in Mazda, brings a much higher fatigue strength than the one obtained by the conventional carburizing and shot peening process.

As a demand for vehicles of higher functionality grows, automakers and material suppliers are devoting increasing efforts to develop technologies for greater safety, lighter weight, higher corrosion resistance, and enhanced quietness. The resin-sandwiched vibration damping steel sheet (VDSS), developed as a highly functional material for reducing vehicle vibration and noise, has been used for oil pans1) and compartment partitions2). First applied for a structural dash panel of the new Mazda 929, a Zn-Ni electroplated VDSS which allows direct electric welding has contributed to greater weight reduction as well as improved quietness.

Effects of split injection, with a relatively short time interval between the two sprays, on the spray development process, and the air entrainment into the spray, were investigated by using laser induced fluorescence and particle image velocimetry (LIF-PIV) techniques. The velocities of the spray and the ambient air were measured. The cumulative mass of the ambient air entrained into the spray was calculated by using the entrainment velocity normal to the spray boundary. The vortex structure of the spray, formed around the leading edge of the spray, showed a true rotating flow motion at low ambient pressures of 0.1 MPa, whereas at 0.4 MPa, it was not a true rotating flow, but a phenomenon of the small droplets separating from the leading edge of the spray and falling behind, due to air resistance. The development processes of the 2nd spray were considerably different from that of the 1st spray because the 2nd spray was injected into the flow fields formed by the 1st spray.

In search for thinner auto-body panels, investigation has been made on the level of yield strength of high strength steel sheets in view of the fact that the dent resistance must be at least equal to that of today's mild steel panels. Dent resistance should be evaluated for slight dent, and loss of the dent resistance caused by thinning is most remarkably seen in this case. Rephosphorized aluminum killed steel with bake-hardenability is most favourable, taking the necessary resistance to slight dent and the formability into consideration.