一种钛合金螺栓头部镦锻裂纹的失效分析

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。

Failure analysis on upsetting crack for titanium alloy bolt head

A Ti6Al4V countersunk head bolt with Φ6 mm occurred perforations in the bolt head failure in the tensile strength testing, and its tensile strength decreased by 3%-5% on average.Therefore, macro and micro fracture qualities, microstructure and chemical composition of the failure parts were analyzed by SEM, EDS, OEM and other means, and the micro cracks were found inside the bolt head.The result shows that due to the large clearance of the raw material cutting machine, material incision occurs burr in the process of cutting, and then the burr is brought into the head end to form a micro cracks in the process of block upsetting so as to decrease the strength of bolt head finally.By adjusting the clearance of the raw material cutting machine, micro cracks at the bolt head can be significantly reduced or eliminated.In addition, the head forming height can be raised to meet the use requirements by turning processing to eliminate transverse crack eventually.