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某型6 mm航空用Ti6Al4V型沉头螺栓在测试抗拉强度时出现了大量螺栓头部穿孔断裂破坏的情况,螺栓抗拉强度平均下降了3%~5%。采用SEM、EDS、OEM等手段对穿孔破坏零件断裂部位的宏微观断口、金相组织及化学成分进行了分析,发现螺栓头部端面存在微裂纹。结果表明,由于原材料切断装置间隙过大,导致原材料在切断过程中切口出现毛刺,在镦锻过程中毛刺埋入头部端面而形成微裂纹,最终导致螺栓头部强度降低。通过调整原材料切断装置间隙,螺栓头部的微裂纹可以明显缩短或消除。此外,也可以适当提高头部成形高度,通过车削加工消除端面裂纹,最终达到使用要求。
The Ti6Al4V-type countersunk head bolts of a 6 mm aviation used a large number of bolt head piercing fracture failure conditions when testing the tensile strength, and the bolt tensile strength decreased by 3% ~ 5% on average. The macro-microscopic fracture, microstructure and chemical composition of the rupture parts of perforation failure parts were analyzed by means of SEM, EDS and OEM, and it was found that there were micro-cracks on the end face of bolt head. The results show that because of the gap between the raw material cutting device is too large, resulting in raw material in the cutting process burrs incision, upsetting burrs buried in the head end face and the formation of micro-cracks, and ultimately lead to reduced strength of the bolt head. By adjusting the gap between the material cutting device, the microcracks on the head of the bolt can be significantly shortened or eliminated. In addition, you can also properly increase the height of the head forming, end-face machining by turning to eliminate cracks, and ultimately meet the requirements.