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Outline
Capacitor Discharge Welding (CDW) was utilized to perform projection welding between double-layer high-strength hot-formed steel and nuts. An orthogonal experimental design was adopted to systematically investigate the influence of various process parameters on the performance of the projection welding joints, with particular emphasis on nugget size and torque strength. Based on the experimental results, optimal welding parameters were identified through range analysis and comprehensive weighted scoring. The optimal conditions were determined as follows: electrode pressure of 0.3 MPa, welding time of 1.1 s, welding voltage of 320 V, and cooling time of 0.5 s. Under these parameters, the heat-affected zone (HAZ) on the nut side is subdivided into coarse-grain and fine-grain regions, with a microstructure primarily composed of equiaxed ferrite. On the hot-formed steel side, the HAZ consists of a fully quenched zone, a partially quenched zone, and a tempered zone. The fully quenched zone exhibits a coarse lamellar martensitic microstructure, whereas the partially quenched zone features a mixed microstructure comprising martensite, ferrite, and bainite. The tempered zone is predominantly constituted by tempered martensite. Three-dimensional fracture morphology analysis reveals that the fracture mode of the projection welding joint between the upper nut and the hot-formed steel is characterized by a ductile-brittle mixed fracture, while the fracture mode in the lower-layer hot-formed steel joints is primarily brittle in nature.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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