In this paper, the influence of defects on mechanical properties of high-pressure die-cast aluminum alloy was studied by means of greenhouse stretching, scanning electron microscopy and automatic defect identification and statistics program based on deep learning and threshold segmentation. The results show that the mechanical properties of high-pressure die-cast aluminum alloy castings fluctuate at different positions. The accuracy of the image recognition program was verified by comparing the results of the image recognition program and the manual statistics of the defect area of the fracture. The relationship between the fracture defect area and mechanical properties shows that the porosity and maximum defect size are correlated with the elongation. When the porosity or maximum defect size increases, the elongation of high-pressure cast aluminum alloy shows a downward trend.

In order to study the influence of different hardening and fracture models on the simulation accuracy of automotive materials, the material-level mechanical tests of DP590 sheet under various stress states were designed and carried out. According to the test results, 5 hardening models of Ludwik, Swift, Voce, Hockett-Sherby (H-S), Swift-HockettSherby (S-HS) and 3 fracture models of Modified Mohr-Coulomb (MMC), Damage Initiation and Evolution Model (DIEM) and Johnson-Cook (J-C) were calibrated. The above models were applied to conduct specimen-level simulation and anti-collision beam drop weight test and simulation. The comparison results show that the S-HS hardening model and MMC fracture model have the most accurate prediction results for the deformation behavior and fracture behavior of materials. Combined with other research results, it is recommended to utilize the S-HS hardening model combined with the MMC fracture model to predict the plastic deformation and fracture behavior of high-strength steel plates.

In order to improve the simulation prediction accuracy of failure behavior of AHSS in vehicle crash, this paper studied the principle of 6 typical failure models such as GISSMO in mainstream LS-DYNA solver, it also studied the calibration methods of material fracture limit strain and mesh size regularization, the most crucial parameters affecting the failure behavior prediction accuracy of ultra-high strength steel during vehicle crash simulation. During the calibration process of fracture limit strain, average stress triaxiality should be used in order to describe the non-linearity loading paths. To overcome the limitations of default mesh size regularization method, the paper proposed a customized mesh size regularization method, which can effectively improve the consistency of simulation results for different mesh size models under typical stress states.

In order to meet the energy-saving and emission reduction demand of commercial vehicles, important chassis components such as axles are developing towards high load-bearing, long lifespan and lightweight. A new type of microalloyed structural steel has been developed based on the traditional LZ27Mn2 steel grade for a 13 t trailer axle. A new car axle product has been successfully developed through new material development, structural optimization, heat treatment, and surface shot peening. Compared with the original axle, the new axle has successfully reduced weight by about 13.2%. Yield strength of the new axle matrix is≥800 MPa, tensile strength is≥860 MPa, elongation is ≥ 18%, impact energy at room temperature is≥130 J, and impact energy at -20 ℃ is ≥100 J. The new axle has been tested to meet the requirements for rigidity, strength (safety factor≥6.0) and fatigue life (1.2 million times) and meets the relevant technical requirements of the product.

The safety performance of a newly developed microalloyed 1.8 GPa hot stamped steel brand and the traditional brand was evaluated from material to part level. The results show that microalloyed 1.8 GPa hot stamped steel has more obvious safety advantages than ordinary steel based on 3 key factors: microstructure refinement, second phase precipitation and retained austenite. The dynamic fracture models of the two materials were established. The microalloyed steel has a higher ultimate fracture strain under the same stress state, showing a stronger fracture resistance. Drop weight impact tests were carried out on 2 kinds of 1.8 GPa hot stamped and 1.5 GPa high-strength steel door anti-collision beams. The micro alloy steel 1.8 GPa hot stamped door anti-collision beam has better anti-collision intrusion and collision energy absorption properties.

This paper introduced the hot-rolled zinc-aluminum-magnesium (Zn-Al-Mg) coated steel sheets for automobile chassis from the aspects of coating structure, welding performance, bonding performance, coating performance and corrosion resistance, compared these properties with that of pickling plate and pure zinc coated steel sheets. The results show that the hot-rolled Zn-Al-Mg coated steel sheets have good spot welding, arc welding, bonding and coating properties, which are equivalent to the pure zinc coated steel sheets. The plane corrosion resistance, paint film corrosion resistance and solder joint corrosion resistance of hot-rolled Zn-Al-Mg coated steel sheet are significantly better than those of pickling plate and pure zinc coated steel sheets, which can greatly prolong the service life of chassis parts.

In this paper, Thermo-Calc software was used for composition design, and the temperature control rolling control cooling process was formulated in combination with the Continuous Cooling Transformation (CCT) curve measured by thermal simulation. By reducing the oxygen content of electric furnace tapping, optimizing the soft blowing process of external refining and adopting protective casting measures, type A inclusion level of hot rolled wire rod ≤1.0, type B inclusion level≤0.5, type C inclusion level=0, and type D inclusion level≤1.0, type Ds inclusion level=0. Ferrite-pearlite microstructure can be obtained by controlled rolling, temperature and cooling process, with tensile strength ≥ 740 MPa, elongation ≥ 22%, surface shrinkage ≥52%, total decarburization depth≤0.10 mm, grain size level ≥ 9 and cold forging meeting 1/3 of the requirements without cracking. The results indicate that the non-quenched and tempered cold heading steel developed in this research can be simultaneously used to make automotive chassis components such as steering ball pins, Grade 10.9 bolts, and brake system guide rods.

In order to avoid the patent limitation of hot stamping steel with traditional Al-Si coating, a new hot stamped steel with thin coating was developed. The mechanical properties of this steel sheet were ensured by strictly limiting the upper and lower limit of coating thickness. Tensile testing machine was used to verify the mechanical properties before and after heating, metalloscope was carried out to verify the microstructure and coating evolution before and after heating, the salt spray test was used to test the anti-corrosion property of steel sheet after hot stamping, welding glue applied on the existing production line was utilized to verify the glue matching properties of steel sheet, the existing production coating process was conducted to verify pre-treatment compatibility and electrophoretic coating performance of steel sheet. Result of all the verification indicates that the hot stamped steel with the new thin Al-Si coating meets the requirement of mechanical properties, anti-oxidation and anti-corrosion, in addition, it is compatible with the conventional welding and coating process.

From the perspective of the design, process and quality of the automobile brake pedal module and by the application of new materials such as long glass fiber and magnesium-aluminum alloy, the thick plate pedal arm has been optimized into a double U-shaped double buckle hollow pedal arm, the solid central shaft has been modified to hollow design and aluminum alloy integrated die-casting technology and other technological innovations have been applied to 5~6 stamped and welded parts of pedal support. By combining design verification methods such as CAE analysis and experimental verification, lightweight pedal has been developed. The manufacturing cost of the pedal is reduced by 5% while ensuring the performance requirements of the pedal and weight of the brake pedal is reduced by 20%.

A diesel engine failed during running, its mileage was only more than 2 743 kilometers. After disassembling, it was found that the needle valve body of high pressure common rail injector of cylinder 6 cracked in axial direction, failure analysis was performed. By means of macroscopic trace analysis, scanning electron microscope fracture analysis, energy spectrum analysis, metallographic analysis and microhardness test, it is pointed out that the main cause for the cracking of needle valve body is the existence of fusiform defect in the matrix of needle valve body head, which is the raw material slag containing Zr, O and other elements. The material of needle valve body is ASP steel, in its production process, when the liquid steel flows through the atomizing nozzle (high density zirconia material), a small part of the nozzle material falls into the liquid steel, forming the slag inclusion. The crack initiates and spreads from the slag inclusion, leading to early fatigue fracture of needle valve body.

This paper discussed the determination of hexavalent chromium content in automobile materials and its uncertainty evaluation process based on colorimetric method. Hexavalent chromium in automobile materials was determined by UV spectrophotometry with a pretreatment method of lye digestion, and the uncertainty of measurement results was evaluated. A mathematical model is established to analyze and discuss the source of uncertainty measurement, calculation and result representation. The results show that the preparation process of standard solutions, measurement repeatability and calibration curve fitting quantification are the main contributors to the uncertainty of measurement results, which should be paid attention to in the testing process.