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.

Cr⁶⁺ is widely applied in automotive metal coating and leather, Cr⁶⁺ test is an indispensable index for the test of prohibited substances on automobiles. In order to test Cr⁶⁺ content in the metal coating of automotive materials, a rapid semi-quantitative detection procedure was established by the test strip method. Compared with ultraviolet method and point test method in QC/T 942—2021 Test Methods of Hexavalent Chromium in Automotive Materials, results of the strip test method are basically consistent with traditional qualitative and quantitative test methods. The advantage of strip test method is that the test can be completed within 5 minutes, far less than that of the traditional method that takes 4 to 8 hours. Meanwhile, operation of the test is simple, which saves large amount of test consumables and reduces waste discharge.

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.

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.

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.

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.

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.

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%.