目的 探究镀层重量对Al-10Si镀层冷成形钢板组织与性能的影响规律,阐明镀层防护作用与加工成形性能之间的平衡关系,为优化镀层工艺提供依据。方法 采用热镀锌模拟器制备单面镀层重量分别为30、40、50、75 g/m²的钢板;利用扫描电镜、显微硬度计、摩擦磨损试验机及激光共聚焦显微镜等分析镀层微观组织、硬度、摩擦磨损行为、划痕特性及冷弯性能。结果 随镀层重量增加,合金层厚度由1.67 μm增至2.35 μm,镀层硬度由55.7HV升至81.2HV;摩擦失效时间由248 s延长至大于300 s;磨损量由2.79×10⁶ μm³增至12.25×10⁶ μm³;冷弯后表面裂纹密度与缝隙增大,但镀层未剥落。结论 增加镀层重量可提升硬度与耐磨性,但过重会导致摩擦力波动加剧、划痕稳定性下降及冷弯裂纹扩展;合理控制镀层重量可在保证耐蚀性的同时避免加工开裂。

This study systematically investigates the effect of coating weights on the microstructure, mechanical properties, tribological behaviors, and cold formability of Al-10Si coated cold-formed steel sheets, aiming to clarify the trade-off between protective performance and formability. Four single-side coatings with weights of 30, 40, 50, and 75 g/m² are prepared with a hot-dip galvanizing simulator. The substrate is 1.0 mm thick DX51D steel, and the bath temperature is (650±2) ℃. A multi-scale characterization approach is employed. The cross-sectional microstructure is examined by field-emission scanning electron microscopy with EDS; The hardness is measured using a micro-Vickers tester under 0.02 kg for the coating and 5 kg for the substrate; Reciprocating ball-on-plate friction tests (0.5 N normal load, 5 mm/s sliding speed, 20 mm stroke, 440C stainless steel ball of 6 mm diameter) are conducted for 300 s; Scratch tests are performed using a diamond stylus with progressively increasing load from 0 to 20 N over 60 s; Wear tracks and volumes are analyzed by laser confocal microscopy; and cold bending tests (180° bend, mandrel diameter 1a) are carried out to evaluate cracking and adhesion.
Quantitative microstructural analysis reveals that as the coating weight increases from 30 to 75 g/m², the total coating thickness rises from 10.18 μm to 26.56 μm, and the underlying Fe-Al intermetallic alloy layer thickens from 1.67 μm to 2.35 μm. The morphology of the alloy layer evolves from a granular FeAl₃-dominated surface at a low coating weight to a smoother, finer-grained structure at higher weights. The Si-rich phase (plate-like) becomes more abundant and uniformly distributed with increasing coating weights, as confirmed by EDS mapping on a lightly etched 75 g/m² sample, where Si content in the coating rises markedly. The Vickers hardness of the coating increases from 55.7HV at 30 g/m² to 81.2HV at 75 g/m², while that of the substrate hardness remains unchanged. This hardening is attributed to the higher volume fraction of finely dispersed hard Si-rich particles, which act as obstacles to dislocation motion and also refine the coating matrix by providing heterogeneous nucleation sites.
In friction tests, the time to coating failure (when the friction coefficient rises sharply due to exposure of the steel substrate) extends from 248 s (30 g/m²) to 257 s (40 g/m²) and further to 287 s (50 g/m²); for 75 g/m², the coating remains intact after 300 s without being worn through. However, the increase in failure time is not proportional to the coating weight increment (33.3%, 66.7%, and 150% weight increases yield only 3.6%, 15.7%, and >21.0% longer failure time, respectively). The average friction coefficient before failure is 0.050-0.056 for all coatings, but for 75 g/m², the friction curve exhibits larger fluctuations due to the presence of abundant hard Si-rich particles that detach and roll between the ball and coating surface, transforming sliding friction into a mixed rolling-sliding mode. The wear scar width increases from 244 μm to 307 μm with increasing coating weights, and the calculated wear volume (from confocal profilometry) grows dramatically from 2.79×10⁶ μm³ (30 g/m²) to 12.25×10⁶ μm³ (75 g/m²). Notably, the wear depth (Z-axis range) does not increase monotonically; it peaks at 51 μm for 50 g/m² and then decreases to 37 μm for 75 g/m², suggesting that an excessive coating weight may promote the formation of lubricious debris that partially mitigates vertical wear despite increasing lateral wear volume.
Scratch tests using progressive loading show that the time to coating breakthrough increases from 5.6 s (30 g/m²) to 32.9 s (75 g/m²), indicating improved coating-substrate adhesion with heavier coatings. However, the lateral force (F_x) becomes larger and the scratch curve shows significantly increased oscillations at 75 g/m², implying unstable scratch resistance. The scratched volume also increases with the coating weight, consistent with the wear volume trend. Cold bending tests reveal that as the coating weight increases, the surface crack density and crack width on the bent outer radius rise progressively: at 30 g/m², only a few fine cracks appear; at 40-50 g/m², a network of microcracks with widths of 0.5-3 μm forms; at 75 g/m², crack widths widen to 1.5-5 μm, but importantly, no coating spallation or substrate exposure occurs. This indicates that although the coating becomes more brittle and less compatible with substrate deformation due to the thicker hard Si-rich phase and Fe-Al intermetallic layer, its adhesion remains sufficient to prevent delamination.
In conclusion, this work provides quantitative relationships between the coating weight and key performance indices: hardness, wear resistance, scratch adhesion, and cold bending crack resistance. The newly identified non-linear correlations (e.g., wear volume vs. weight, friction stability vs. weight) and the observation that excessive coating weights degrade friction stability and scratch smoothness without proportional gains in wear protection offer practical guidelines for optimizing Al-Si coating weights for cold-formed steel applications, balancing corrosion resistance, wear protection, and formability.