With the background of emission peaks and carbon neutrality, light weight has become an irreversible trend in the development of the automobile industry. It is an inevitable choice to use a large amount of ultra-high-strength steels to realize light weight and safety of automobiles. Ultra-high-strength martensitic steels can be divided into hot-formed steels and cold-formed steels according to the forming process. In recent years, ultra-high-strength martensitic steels have been rapidly developed in automotive battery pack frameworks, door guard beams, bumpers, A-pillars, etc., depending on their good plasticity and advanced forming technology. In this paper, the recent progress of ultra-high-strength martensitic steels for automobiles is systematically reviewed, the mechanisms of alloying, strengthening, and toughening are emphatically expounded, and the hydrogen embrittlement problems in application are summarized. Finally, the prospects of manufacture and application of ultra-high-strength martensitic steels for automobiles in the future are forecasted.
Zn–Al–Mg coating galvanized steel in resistance spot welded (RSW) in different configurations of DC51D was investigated to illustrate the nugget evolution process and mechanical properties of the joints. Results show that the microstructure of welded joints can be divided into nugget zone (FZ), heat-affected zone (HAZ), and base metal zone (BM). FZ was composed of lath martensite. The average hardness value of the weld joint was 110 HV0.2 while the FZ was up to 300 HV0.2 due to the formation of lath martensite. The failure modes can be divided into interface fracture (IF) and pull-out fracture occurred (PF) under different welding parameters, in which shear dimples showed had a typical plastic fracture morphology. The best range for welding parameters was found to be 12–18 cycles in which the nugget diameter reached 5.5 mm. The process of nugget evolution in HAZ and FZ was discussed.
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