Thermodynamic calculation software Thermo-Calc was used to calculate the influence of the change of Nb and Ti content on the precipitation behavior of carbon nitride, the composition of 1 800 MPa hot-formed steel was determined. The equilibrium phase diagram, the precipitation temperature of the main precipitated phase, the change of element content with temperature and the growth behavior of the precipitated phase were calculated, the basic data of the main phase composition and phase transformation characteristics were obtained. The mechanical properties and 3 point bending properties of microalloy 1 800 MPa hot stamping steel have been tested. The test results show that the steel has good toughness. The microstructure of the hot formed steel after quenching was characterized by Electron Back Scattering Diffraction (EBSD). The characterized results show that the small austenitic grains and small martensitic blocks are the main causes for the high toughness of the 1 800 MPa hot formed steel. Finally, the delayed fracture sensitivity of the hot-formed steel was measured by hydrogen filling and slow drawing method. The measured results show that the hot stamping steel has excellent delayed fracture sensitivity when the hydrogen filling time is less than 2 h.

This paper introduced various kinds of conveying equipments of automobile welding lines, including high-speed rolling beds, servo sliding tables, reciprocating conveyor chain, stacked conveyor chain, air reciprocating conveyor and automatic guiding cart convey, introduced the application forms of various kinds of conveying equipment in welding line and the common application scenarios in the welding workshop. By explaining the principle and technical parameters of different conveying equipments, the paper expounded the basic usage concept of conveying form of welding line to ensure the rationality of equipment selection and improve factory efficiency.

This paper summarized the research status and existing problems of automobile lightweight technologies at home and abroad from 3 aspects of structure lightweight, lightweight materials and manufacturing processes lightweight, mainly including the basic principle and research progress of size optimization, topological optimization and shape optimization in automobile structure lightweight, performance characteristics of lightweight materials and high-strength materials in material lightweight and application in automobile, basic principle and existing problems of manufacturing processes including hydraulic molding, laser welding and thermal forming. In terms of the current development trend, structural integration, research and development of lightweight materials with better comprehensive performance and adoption of more advanced manufacturing processes are important approaches to achieve automobile lightweight.

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 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.

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.

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.

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%.

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.

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.